Retaining Wall Waterproofing: The System to Apply Before Backfilling
Retaining wall waterproofing is done on the soil side, and that face can only be reached before backfilling. The Armstrong system is: repair honeycombs and tie-rod holes, apply one coat of ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210 and two coats of RAINSEAL BMW 250, then protect the coating and backfill. ROOFEX 2K 711 is the alternate. A wall that is already backfilled is treated from the exposed face with RAPIDSTRONG GROUT PU injection and a ROOFEX COP crystalline coating.
By Armstrong Chemicals Pvt. Ltd. · ISO 9001:2015 certified · Protecting buildings, roofs and structures since 1982
Section 1 of 10: Start here
1
Check
Soil side, water, wall
2
Route
Match your wall
3
Repair
Joints, holes, honeycombs
4
Coat and protect
Then drain and backfill
Step 1
Retaining wall seepage: check these five things first
Damp patches on the face of a retaining wall, white salt streaks, water weeping from joints after rain, rust stains and paint or plaster that keeps falling off are the usual signs of retaining wall seepage. A retaining wall holds back soil, and soil holds water. After rain that water presses on the back of the wall for days or weeks. Retaining wall waterproofing keeps it out of the concrete. One fact comes before everything else: the soil side of the wall can only be coated before backfilling. Five checks decide the method.
Positive side and negative side on a retaining wall
Positive side: the soil side
Which face
The face the water touches, behind the wall in the soil.
When it can be done
Only while the soil is still open: a new wall before backfilling, or after digging the soil out.
How it works
A coating here is pressed onto the wall by the water, so it stops the water before it enters the concrete.
Negative side: the exposed face
Which face
The face you can see and reach, away from the soil.
When it is the only option
Once the soil is back, the soil side is buried and cannot be reached. The wall can only be treated from this face.
How it works
Leaks are injected, joints rebuilt and a crystalline coating seals the concrete from inside, because a thin film on this face is pushed off by the water behind it.
1
Is the soil side still open?
If the wall is new and not yet backfilled, coat the soil side now. Once the soil is back, that face is buried.
2
Is it damp, or is water running?
Damp and salt are seepage through the concrete. Water running from a crack or joint is a leak and is stopped first by injection.
3
Where does it come through?
Look at the horizontal joints between pours, the wall and base joint, tie-rod holes, honeycombed patches and cracks. Water rarely comes through sound concrete.
4
Does the wall drain?
Check for weep holes and whether they run after rain. A wall with blocked or missing drainage carries far more water pressure.
5
What is on the exposed side?
An open garden wall can tolerate some damp. A wall that forms the side of a basement, a parking floor or a room cannot. See basement waterproofing for basement walls.
Step 2
Find the right retaining wall waterproofing method
Match your wall to one route. Several Armstrong products suit most routes. An Armstrong expert helps pick the one that fits the site.
Route A · Positive side
New wall, soil side still open
Repair the soil side, apply one coat of ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210 and two coats of RAINSEAL BMW 250, protect the coating, then backfill. Same system whether the soil is dry or wet. Where water stands behind the wall, add the drain and free-draining fill.
Route B · Positive side
Coating done, ready to backfill
Protection, drainage and careful backfilling decide whether the coating survives.
Route C · Negative side
Existing wall, damp and salt on the face
The exposed face is stripped, the joints are repaired and a crystalline coating is applied in two coats.
Route D · Negative side
Existing wall, water running through
The running crack or joint is injected with a water-reactive grout, then the face is treated.
Route E · Negative side
Treated before and still leaking
Check drainage and re-inject first. Digging out the soil to coat the back of the wall is the last resort.
Not sure
Let the treatment finder suggest a route
Answer three questions and see a starting recommendation.
Coat the soil side before the soil goes back. It is the one step on a retaining wall that cannot be done later without digging.
Step 3
Retaining wall treatment finder
Answer three questions for a starting recommendation, including whether water is seeping or flowing, then confirm it with an Armstrong expert. Every product shown suits the wall described.
1
Is the soil side of the wall open?
2
What do you see on the wall?
3
How wet is the soil behind it?
Answer all three questions to see the recommended starting point.
Do the work
Positive side waterproofing for a retaining wall before backfilling: the soil side system
This is the Armstrong treatment procedure for the soil side of an RCC retaining wall. It is positive side waterproofing: the coating sits between the water and the wall. The wall is cast, cured and repaired first, then coated, then protected.
The soil side of a new retaining wall. The coating keeps water out of the concrete, the protection layer keeps the backfill off the coating, and the drain takes the water away.
1
Start with dense concrete
An integral waterproofing compound in the mix cuts the water the concrete absorbs: CONPROOF LW 200, CONPROOF 500, or CONPROOF RMC ADMIX 88 for ready-mix. Compact well and cure fully, with ROOFEXCURE WB on faces that are hard to keep wet. Doses and mixing are on the waterproof concrete page.Why: A dense wall absorbs less water to begin with, and every coating after it has less to hold back.
2
Clean the soil side
Remove laitance, dirt, shuttering release agent, curing compound and every loose particle, so the coating bonds to sound concrete.Why: A coating bonds only to clean concrete, and laitance and release oil leave a layer that peels.
3
Repair pot holes, honeycombs, tie-rod holes and pour joints
Cut back pot holes, honeycombs and voids to sound concrete, open tie-rod holes and pour joints to a clean groove, and fill them all with polymer repair mortar, ROOFCRETE AR over a bond coat of ROOFBOND SBR 401, placed while the bond coat is still tacky. Mixing is on the structural concrete repair page.Why: Voids and honeycombs are direct paths for water, and a coating over a void is unsupported.
4
Seal shutter joints and pipe entries
Pack them flush with a putty of ROOFBOND SBR 401, cement and graded sand mixed 1:1:1.Why: These joints and pipe entries are the commonest places for water to get through a wall.
5
First coat on the soil side: ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210
Both are flexible cementitious coatings, and Armstrong lists retaining walls among the uses of each. Mix as the data sheet says, and apply one continuous, even coat of either over the whole soil side, from the base to above the finished soil level.Why: The flexible cementitious coat is the waterproof layer next to the concrete, and it bridges fine cracks.
6
Top coats of RAINSEAL BMW 250 over the first coat
Thin RAINSEAL BMW 250 with 20% clean water and put on two coats, leaving 6 to 8 hours between them. It is water based and ready to use from the container, and Armstrong lists retaining walls among its uses. It cures to a black, rubbery film with 500% elongation.Why: The bituminous coats add a second membrane over the first and resist the salts in the soil.
7
Let it dry, then protect it
Each coat of RAINSEAL BMW 250 dries in 40 to 50 minutes, depending on the weather. Cover the finished coating with a protection layer before backfilling: mortar in thin coats, a bitumen protection board or a dimpled drainage board.Why: Each coat needs to dry before the next, or before the soil goes against it, so it does not smear or wash off.
Which coating for the soil side of a retaining wall
ROOFEX 2K 711 in two coats is the alternate specification in the Armstrong treatment procedure, in place of the coats above, as the site engineer specifies. It resists 10 to 12 bar and works on brick and stone as well as concrete.
Two coats
A flexible cementitious coating on its own
Either is also applied alone as a full coating in two coats, with the second coat crosswise to the first. Quantities are in the table below. An Armstrong expert confirms the build-up for the site.
Do the work
Retaining wall drainage and protection before backfilling
A sound coating can still be lost in a day if stones are tipped against it. And a wall with no drainage holds a full depth of water behind it after every storm. Protection and drainage are part of the waterproofing. The protection step is from the Armstrong treatment procedure.
Read it from the wall outward: coating, protection layer, gravel wrapped in filter fabric, then soil in thin lifts. The numbers match the steps below. Water that reaches the gravel drops to the pipe and leaves through the outlet and the weep holes.
1
Protect the coating
Cover the coating with a protection layer before any soil goes back. Choose one of three:
Mortar, in thin coats
The Armstrong procedure. Cement-sand mortar or plaster in thin coats, never a screed, which sags and hollows on a vertical face. Screed belongs on horizontal surfaces such as terraces, pool floors and base slabs. Over RAINSEAL BMW 250, sprinkle fine dry sand on the last coat while it is wet so the mortar bonds. The usual practice is about 20 mm of 1:3 cement mortar mixed with CONPROOF 500 at 500 ml per 50 kg bag, built in coats and cured for 7 days.
Bitumen protection board
A black board of polymer-modified bitumen, 3 to 6 mm thick, that takes the knocks from stones and site traffic. It is stuck to the coating with the board maker's adhesive or tape and its butt joints are taped. It protects but does not drain.
Dimpled drainage board with geotextile
A plastic sheet with dimples 8 to 20 mm high. Dimples face the wall, the geotextile faces the soil, sheets overlap by at least 100 mm and run down to the base drain. It protects and drains in one layer. Use taller dimples where machines compact the fill.
Why mortar and not a screed
Screed
Where it belongs
Floors, terraces and slopes to drain.
What it is
A thick (25 to 75 mm), stiff, rammed mix.
On a wall
Sags, bonds poorly, sounds hollow and shrinks. Nothing on a wall needs levelling or a fall.
Mortar or plaster
Where it belongs
Walls, columns and ceilings.
What it is
A workable mix, put on thin (about 12 to 20 mm) in coats.
On a wall
Bonds to the sanded coating and protects it.
Never backfill against a bare coating. A geotextile on its own is not enough protection. Keep sharp stone and anything larger than about 50 mm out of the fill.
Why: Backfilled soil and stones scrape and puncture a coating, so it is protected before the soil goes back.
2
Provide a drain at the base
A perforated pipe at the foot of the wall, laid to a slight fall and led to an outlet, carries water away before it builds up. Surround the pipe with 75 to 100 mm of clean stone or gravel, wrapped in filter fabric so it does not silt up.Why: A drain stops water building up against the wall, and water that is not pushing needs less waterproofing.
3
Place free-draining fill next to the wall
Clean gravel, crushed stone or coarse sand against the protection lets water drop to the drain. A filter fabric keeps soil out of it, so the drain does not clog. Keep heavy clay out of the fill: it holds water, swells when wet and pushes harder on the wall.Why: Clean gravel drains water down to the pipe, whereas clay held against the wall keeps it wet.
4
Keep the weep holes open
Where the design has weep holes, sleeve them through the wall and through the coating, seal around each sleeve, and keep them clear of mortar.Why: Weep holes relieve water pressure, and a blocked one lets the pressure build up.
5
Backfill in layers
Do not backfill until the wall has cured (at least 7 to 10 days after casting) and any props or top bracing are in place. Then backfill soon after the coating and protection are done, so they are not left in the sun. Place the soil in thin layers and compact each with light equipment near the wall. Keep rubble, sharp stone and site waste out of the fill.Why: A wall that has not cured, or soil dumped at once, can crack the wall or the coating.
6
Shed surface water at the top
Slope the finished ground away from the wall, at least 5% (about 150 mm of fall over the first 3 m), or collect it in a surface drain. Cap the top with a clay-rich, low-porosity soil so rain does not soak straight down into the gravel behind the wall.Why: Ground that slopes toward the wall sends rain to it, so the finished ground slopes away.
Why drainage matters. Each metre of water standing behind a wall adds about 0.1 bar of pressure at its base. Drained soil puts far less water against the coating and against the wall itself.
Do the work
Seeping concrete: grout through drilled holes before any lining goes on
When water leaks, seeps or sweats through porous, honeycombed or cracked concrete, it has to be stopped inside the concrete first. This is the standard negative-side method for tanks, pools, basements, lift pits and retaining walls. A lining laid over concrete that is still seeping is pushed off by the water behind it: it blisters, lifts and fails. Grouting through drilled holes fills the internal voids and capillaries along the path of the water, so the surface is dry and sound before the coating or membrane goes on. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.
1
Drill the injection points
Drill 12 to 14 mm holes with an electric drill into the leaking or honeycombed zone, to the depth the member needs (14 to 16 mm on thick retaining walls).Why: The holes intercept the pathways the water is travelling along, so the grout reaches the voids instead of just sitting on the surface.
2
Fix the nozzles
Fix a rubber injection nozzle in each hole with a quick-setting putty of cement mixed with the set accelerator RAPIDSTRONG QS 113. For active flow, the single-component plugging compound RAPIDSTRONG PLUG can be used to fix the nozzle instead.Why: The nozzle must be locked into the hole before pumping starts. If it is not, the pressure blows it out and the grout runs back out of the hole.On site: The datasheet gives RAPIDSTRONG QS 113 at 500 ml to 2 L per 50 kg of cement and asks for a site trial, so trial the dose on the job before fixing every nozzle.
3
Seeping or sweating concrete: cement slurry
Mix a cement slurry with a non-shrink grout additive and pump it into each nozzle with a grout pump at about 140 psi, until that point refuses to take any more. Any of three additives can be used: RAPIDSTRONG GROUT ADMIX at 250 g per 50 kg of cement, RAPIDSTRONG GROUT PB 66 (a polymer grout additive, dosed as on its datasheet) or ROOFEX GP (a crystalline grout compound, dosed at 250 g per 50 kg of cement).Why: The slurry fills the internal voids and capillaries. The additive keeps it from shrinking away from the concrete as it sets, which an ordinary cement slurry does, and the crystalline option also seals the capillaries.On site: Work from the lowest nozzle upward on a wall, so the slurry pushes the water and air out ahead of it.
4
Running or gushing water: polyurethane resin
Where water is flowing or gushing, cement slurry would simply wash away before it sets. First stop the surface flow with RAPIDSTRONG PLUG in a V-groove, then inject RAPIDSTRONG GROUT PU, the single-component polyurethane grout, with air-compressed injection equipment at about 500 g per grout point.Why: The polyurethane reacts with the water itself, expanding and stiffening to block the flow, so it works where cement cannot.On site: A hard-working point can take 0.3 to 0.75 kg. Polyurethane grouting alone only stops the flow; it is not a guaranteed waterproofing system, so follow it with the lining or coating the structure needs.
5
Remove the nozzles and seal
Once grouting is complete, remove the nozzles and patch every hole flush with a putty of ROOFCRETE AR and cement.Why: This leaves a smooth, sound, watertight surface ready for the final lining.
6
Check before lining
Look at the face again after the grout has set. Any point still wet gets another nozzle beside it before the coating, membrane or plaster goes on.Why: A single wet patch left behind becomes the first blister under the new lining.
Negative side waterproofing: retaining wall leakage solution for a wall that is already backfilled
When the soil is already in place, the soil side (the positive side) is buried and cannot be reached. The only option is the negative side: the wall is treated from the exposed face, with materials that work from inside the concrete. The damp patch is where the water arrives, not where it enters, so the first job is to trace the path. Seepage through a retaining wall is also driven by the soil behind it, so drainage is checked before anything is coated.
An existing wall treated from the exposed face. Running leaks are injected, joints are rebuilt, and the crystalline coating seals the pores from within.
1
Expose the bare concrete
Strip paint, putty, plaster and all loose, old and flaking material until the concrete and the leak paths can be seen. If the wall was plastered, the plaster must come off completely: a crystalline coating cannot soak into plaster or paint.Why: Treatment from the inside works on bare, sound concrete, and not on paint or plaster.
2
Trace the entry paths
Mark construction joints, cracks, honeycombs, tie-rod holes and pipe entries along the length of the wall. Water seen low on the face often enters higher up.Why: The water enters at a few points, and marking them along the length tells you where to work.
3
Check the drainage first
Rod out blocked weep holes and clear the outlet of the base drain. Divert roof water and surface water away from the top of the wall.Why: A blocked weep hole or drain keeps the pressure on the wall, and treating the wall while it is blocked fails.
4
Plug the holes and joints, then inject the leaks
Plug leaking pot holes, tie-rod holes and pour joints with RAPIDSTRONG PLUG 31 or WONDERSEAL PLUG XL, the fast-setting plugging compounds. Then grout the leaking joints and cracks with RAPIDSTRONG GROUT PU, the water-reactive grout. It foams up on contact with flowing or gushing water and sets in 36 to 48 seconds, so the flow does not have to be blocked first. Where there is no water at the point, water is injected first to start the reaction. RAPIDSTRONG GROUT PFC 79 is the alternative grout. The method is on the injection grouting page. Armstrong grouting is done with 12 to 14 mm holes (14 to 16 mm on thick retaining walls) fitted with pressure packers about 75 mm long, fixed with RAPIDSTRONG PLUG. The PU grout is injected with an air-compressed unit at about 500 g per grout point, and the holes are sealed with ROOFCRETE AR and cement after the packers are removed.Why: Running water washes any coating away, so it is stopped first by plugging and then injecting the leaks.
5
Repair pot holes, tie-rod holes and pour joints
Cut pot holes, honeycombs, tie-rod holes, cracks and pour joints to a clean groove and fill them with the ROOFCRETE AR system, over a bond coat of ROOFBOND SBR 401, worked in while the bond coat is tacky. Where the crew batches on site, ROOFCRETE AR 576, a polymer admixture mixed with cement and sand, does the same job. Moist-cure the repair for at least 7 days. Or inject RAPIDSTRONG GROUT VM 99 where the joint must be bonded.Why: Voids repaired with a bonded repair mortar give the coating a sound face.
6
Seal expansion joints with sealant
An expansion joint is not filled rigidly. It is sealed with ROOFEX-SEAL PS polysulphide sealant, after priming. See expansion joint sealing.Why: An expansion joint moves, so it is sealed with a flexible sealant and never filled rigidly.
7
Seal the concrete from inside
Dampen the face and apply ROOFEX COP, ROOFEX or ROOFEX 2K 711 in two coats, with the second coat within 48 hours, then mist 3 to 4 times a day for 2 to 3 days with no curing compound. Protect it from rain for 24 hours. A crystalline coating reacts with the cement and moisture to grow crystals in the pores and hairline cracks, so the concrete itself becomes waterproof. If water reaches it later, the unreacted chemicals can react again and seal new hairline cracks, which is the self-healing claim. It works on tiny cracks only. It needs bare, damp, sound concrete, cannot bridge wide or moving cracks, and is not a decorative finish. On brick or stone walls use ROOFEX 2K 711.Why: The crystalline coating works in the concrete against the water pressure, from the inside.
8
Check for seepage, then re-plaster
Watch the wall for seepage first. The crystals need time to form, so judge it after the coats have cured, not on the day. Full activation takes 2 to 4 weeks. Re-plaster only when it is 100% leak-proof. Use cement-sand mortar or plaster in thin coats, never a screed, which sags and hollows on a vertical face. Screed belongs on horizontal surfaces such as terraces, pool floors and base slabs. A protective plaster of ROOFCRETE AR, or a plaster modified with ROOFBOND SBR 401, restores the face and protects the coating.Why: The crystals take time to form, so the wall is judged after some days before it is plastered over.
How the crystalline coating works, and when to use a membrane instead
Water is let into the concrete face, the crystals grow in the pores, and the wall itself becomes waterproof. The wall is dampened first, because the reaction needs water. If water enters later, the chemicals left in the concrete can react again. That helps tiny cracks only.
Crystalline coating (ROOFEX COP, ROOFEX 2K 711)
How it works
Active chemicals soak into the concrete and grow crystals inside the pores and hairline cracks.
Water pressure from behind
Handles it, because it is not a skin that can peel off. This is why it suits the negative side.
Cracks
Seals hairline cracks only. It cannot bridge wider or moving cracks.
Surface and finish
Needs bare, damp, sound concrete. Breathable. Plain grey, not decorative.
Membrane coating (ROOFCOAT FLEXI 100, RAINSEAL BMW 250, PU)
How it works
A flexible film on the surface keeps water out as a skin.
Water pressure from behind
A thin film on the inside face can blister or be pushed off.
Cracks
Stretches over moving cracks.
Where it belongs on a retaining wall
On the soil side, where the water presses it onto the wall.
ROOFEX COP or ROOFEX 2K 711
ROOFEX COP
Type
Single-component, cement-based powder.
Coats
Two slurry coats at 0.75 to 1 kg/m² each. Dry shake at 1.6 kg/m² on fresh concrete and dry pack at 1.5 kg/m² for joints.
Cracks
Seals cracks up to 0.4 mm.
Packs
1, 5 and 25 kg.
ROOFEX 2K 711
Type
Two-component: 1 kg liquid and 2 kg powder, with about 20% water.
Coats
2 to 3 coats, 1.2 to 1.6 kg/m² in total (about 1 mm), by brush or spray. Pot life is 45 min to 1 hr at 30 °C, so mix small batches.
Pressure and flexibility
10 to 12 bar hydrostatic resistance and up to 16% elongation. Also for brick and stone.
Packs
15 and 30 kg.
Both go on dampened, sound concrete with the second coat within 48 hours, and are cured by mist only. Allow 48 hours before foot traffic. Both say to contact Armstrong for high hydrostatic pressure.. A live crack is not a job for the crystalline coat: use a flexible sealant or a membrane there.
Below ground, the same rule applies. Water pushes from the soil side, so a coating on the soil side holds and a thin film on the inside is pushed off. When only the exposed face can be reached, the leak paths are injected and the concrete is sealed with a crystalline coating. The full explanation, with the positive side and negative side options compared, is on the basement waterproofing page.
Do the work
When retaining wall seepage keeps coming back: drainage, re-injection and excavation
Treatment from the exposed face manages water that has already reached the wall. The soil and the water are still there. If seepage returns, work up the ladder one rung at a time. Digging out the backfill is the extreme case and comes last.
1. Clear the drainage again
Weep holes and the base drain block with silt over time. Rod them out again and check where the outlet runs.
2. Re-inject
Find the path that is still open and inject it again. A resin injection can be repeated. Re-coat that zone.
3. Relieve the pressure
Where the design allows, an engineer may add weep holes or drains to bring the water level behind the wall down.
4. Excavate and coat the soil side
Only where the first three have not held and the site allows it: dig out the fill, repair the wall and apply the soil side system as for a new wall.
Structure
Rust stains and concrete breaking away
Water that has run through a wall for years rusts the steel. The repair follows the steel repair sequence. See structural concrete repair.
Movement
Leaning, bulging or wide cracks
These are structural signs, not waterproofing ones. A structural engineer must see the wall before any coating or injection.
Masonry
Stone or brick retaining walls
A masonry wall is treated from the exposed face with ROOFEX 2K 711, which is compatible with brick and stone. Keep its weep holes open.
Reference
Retaining wall waterproofing coatings compared: soil side and exposed face
Every product here is a sound choice for the job it is made for. They differ in chemistry and in which face they go on.
Into running cracks and joints from the exposed face
ROOFCRETE AR or ROOFCRETE AR 576: which repair mortar
Pre-packed kit
ROOFCRETE AR
Two-part, fibre-reinforced polymer-modified repair mortar. Part 1 is the polymer liquid and Part 2 is the powder, in a fixed factory ratio, so there is no batching error. 25 kg pack, about 1.30 sq.m at 10 mm per pack, 6 to 100 mm per layer, shelf life 6 months. Choose it for large or critical repairs and for crews that do not batch on site.
Site-batched admixture
ROOFCRETE AR 576
A latex polymer admixture added to a site-batched cement and sand mortar, about 1:3, at 500 ml to 2 L per 50 kg of cement depending on repair depth. Liquid in 1, 5, 10, 20 and 210 L packs, 6 to 100 mm per layer, shelf life 24 months. Choose it for volume work and where local cement and sand are used.
The method is the same for both: cut back to sound concrete, saturate it to a saturated-surface-dry state, apply the bond coat (ROOFBOND SBR 401) and place the mortar into the tacky coat, compact, finish, then moist-cure for at least 7 days.
What changes with the face you can reach
When it can be done
Positive side (soil)
Only before backfilling, or after excavation
Negative side (exposed face)
Any time
What else is needed
Positive side (soil)
Protection layer, drainage, careful backfill
Negative side (exposed face)
Joint repair first, moist curing after
What the soil does
Positive side (soil)
Presses on the coating, so it needs protecting
Negative side (exposed face)
Presses water through the wall, so drainage is checked
First choice?
Positive side (soil)
Yes, wherever the soil side can be reached
Negative side (exposed face)
Where the soil side cannot be reached
Reference
Retaining wall waterproofing chemicals and products by stage
Work out the quantity for your own job. Enter your measurements and get the material needed.
How much waterproofing material for a retaining wall 50 ft long
Approximate quantities for a wall 50 ft long and 10 ft high, coated on one face: 500 sq.ft, or about 46 sq.m. Figures are worked out from each product's stated coverage on a smooth, prepared surface. Injection grout and repair mortar depend on the defects found and are measured at site. An Armstrong expert confirms the final quantity after seeing the site.
ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210, one coat under RAINSEAL BMW 250
Stated coverage
Taken as half of the two-coat quantity
For 500 sq.ft
ROOFCOAT FLEXI 100: 8.4 to 13 litres, plus 17 to 25 kg of cement. ROOFBOND RFX PLUS 210: 2 units
RAINSEAL BMW 250, two coats
Stated coverage
1 litre covers 30 sq.ft in two coats
For 500 sq.ft
About 17 litres
ROOFEX 2K 711
Stated coverage
1.2 to 1.6 kg per sq.m in total
For 500 sq.ft
56 to 75 kg
ROOFCOAT FLEXI 100, two coats
Stated coverage
20 to 30 sq.ft per litre for two coats
For 500 sq.ft
17 to 25 litres, plus 34 to 50 kg of cement
ROOFBOND RFX PLUS 210, two coats
Stated coverage
13 to 14 sq.m per 20.1 kg unit
For 500 sq.ft
4 units
ROOFEX COP, two coats (exposed face)
Stated coverage
0.75 to 1 sq.m per kg per coat
For 500 sq.ft
93 to 124 kg
ROOFEX, two coats (exposed face)
Stated coverage
0.75 kg per sq.m per coat
For 500 sq.ft
About 70 kg
Standards and tests behind retaining wall waterproofing products
The test standards behind the flexible coatings, crystalline coatings and injection grouts are listed on the basement waterproofing page, because the same products are used.
RAINSEAL BMW 250 states 500% elongation and resistance to dilute acids, dilute alkalis and salt solutions.
The structural design of a retaining wall, including its drainage and weep holes, is the structural engineer's. Waterproofing does not replace it.
Reference
Retaining wall waterproofing material calculator
Enter the length and height of the wall to see the coating needed for one face. Quantities only. Injection grout and repair mortar depend on the defects found and are measured at site.
1
Choose your units
2
Enter the measurements
3
Which system?
Enter the measurements to see the estimated quantity of material.
Reference
Seven mistakes that make a retaining wall leak
Backfilling before the soil side is coated. The face is buried for good. Every later repair has to be made from the wrong side.
Backfilling straight onto the coating. Stones puncture it during compaction. Protect it with a mortar layer or a protection board first.
Leaving tie-rod holes and shutter joints open. Water finds them first. Pack them before coating.
No drainage behind the wall. Water builds up to full height and presses on every weak point.
Painting over the damp patch. Paint traps the moisture and is pushed off again. Trace the path and treat that.
Coating over old plaster and loose material. Remove everything loose and old so the coating touches sound concrete.
Filling a moving joint with mortar. It cracks again. Moving joints take a sealant.
Retaining wall waterproofing questions and answers
Which chemical is used for retaining wall waterproofing?
After the wall is cast, cured and repaired, and before any soil is placed against it. That is the only time the soil side can be reached.
What if the retaining wall is already backfilled?
It is treated from the exposed face. Running leaks are injected, joints and honeycombs are rebuilt, and a crystalline coating is applied in two coats and kept moist for 2 to 3 days.
Can retaining wall leakage be fixed without excavation?
Yes, in most cases. Injection and crystalline treatment from the exposed face are made for this. Excavation to coat the soil side is kept as the last resort.
Why must the coating be protected before backfilling?
Because backfill contains stones, and compaction drives them into the wall. A protection layer of mortar, bitumen board or dimple board takes the damage so the coating does not.
Does drainage matter if the wall is waterproofed?
Yes. Drainage lowers the water level behind the wall, so there is less pressure on the coating and on the wall. Waterproofing and drainage work together.
Which coating resists chemicals and salts in the soil?
RAINSEAL BMW 250 resists dilute acids, dilute alkalis and salt solutions. ROOFCOAT FLEXI 100 resists dilute acids, alkalis and salts. ROOFBOND RFX PLUS 210 is a chloride and sulphate barrier that protects the steel in the concrete.
How do I stop water seeping through a retaining wall?
What is positive side waterproofing on a retaining wall?
Waterproofing on the face the water touches, which is the soil side. The water presses the coating onto the wall. It is the first choice wherever that face can be reached.
Should weep holes be sealed to stop the wall looking wet?
No. Weep holes are part of the drainage and are kept open. Blocking them lets water build up behind the wall.
How is the retaining wall of a basement waterproofed?
The same way on the soil side, before backfilling. Because the other face is a usable space, the standard of dryness is higher. See basement waterproofing.
Is a water tank wall treated the same way?
No. A tank is lined on the inside, which is the face the stored water touches, with a lining tested for drinking water. See water tank waterproofing.
Get the right waterproofing system for your retaining wall
Tell us the wall length and height, whether it is backfilled and what you see on the face. An Armstrong applicator or distributor will recommend a system. Toll free 1800 103 2034. Armstrong manufactures retaining wall waterproofing chemicals in Bengaluru and supplies them all across India, with South India as its major hub.
About this guide
Written by the technical team at Armstrong Chemicals Pvt. Ltd., an ISO 9001:2015 certified manufacturer of construction and waterproofing chemicals in Bengaluru, with more than 200 products. Armstrong has been protecting buildings, roofs and structures since 1982 and supplies all across India, with South India as its major hub.
The methods on this page are Armstrong's standard procedures. Doses, thicknesses and the number of coats are adjusted to the conditions on each site. Load-bearing repairs and strengthening are designed by a structural engineer.
Last updated · Questions on this method: toll free 1800 103 2034
Retaining Wall Waterproofing: The System to Apply Before Backfilling
Retaining wall waterproofing is done on the soil side, and that face can only be reached before backfilling. The Armstrong system is: repair honeycombs and tie-rod holes, apply one coat of ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210 and two coats of RAINSEAL BMW 250, then protect the coating and backfill. ROOFEX 2K 711 is the alternate. A wall that is already backfilled is treated from the exposed face with RAPIDSTRONG GROUT PU injection and a ROOFEX COP crystalline coating.
By Armstrong Chemicals Pvt. Ltd. · ISO 9001:2015 certified · Protecting buildings, roofs and structures since 1982
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1
Check
Soil side, water, wall
2
Route
Match your wall
3
Repair
Joints, holes, honeycombs
4
Coat and protect
Then drain and backfill
Step 1
Retaining wall seepage: check these five things first
Damp patches on the face of a retaining wall, white salt streaks, water weeping from joints after rain, rust stains and paint or plaster that keeps falling off are the usual signs of retaining wall seepage. A retaining wall holds back soil, and soil holds water. After rain that water presses on the back of the wall for days or weeks. Retaining wall waterproofing keeps it out of the concrete. One fact comes before everything else: the soil side of the wall can only be coated before backfilling. Five checks decide the method.
Positive side and negative side on a retaining wall
Positive side: the soil side
Which face
The face the water touches, behind the wall in the soil.
When it can be done
Only while the soil is still open: a new wall before backfilling, or after digging the soil out.
How it works
A coating here is pressed onto the wall by the water, so it stops the water before it enters the concrete.
Negative side: the exposed face
Which face
The face you can see and reach, away from the soil.
When it is the only option
Once the soil is back, the soil side is buried and cannot be reached. The wall can only be treated from this face.
How it works
Leaks are injected, joints rebuilt and a crystalline coating seals the concrete from inside, because a thin film on this face is pushed off by the water behind it.
1
Is the soil side still open?
If the wall is new and not yet backfilled, coat the soil side now. Once the soil is back, that face is buried.
2
Is it damp, or is water running?
Damp and salt are seepage through the concrete. Water running from a crack or joint is a leak and is stopped first by injection.
3
Where does it come through?
Look at the horizontal joints between pours, the wall and base joint, tie-rod holes, honeycombed patches and cracks. Water rarely comes through sound concrete.
4
Does the wall drain?
Check for weep holes and whether they run after rain. A wall with blocked or missing drainage carries far more water pressure.
5
What is on the exposed side?
An open garden wall can tolerate some damp. A wall that forms the side of a basement, a parking floor or a room cannot. See basement waterproofing for basement walls.
Step 2
Find the right retaining wall waterproofing method
Match your wall to one route. Several Armstrong products suit most routes. An Armstrong expert helps pick the one that fits the site.
Route A · Positive side
New wall, soil side still open
Repair the soil side, apply one coat of ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210 and two coats of RAINSEAL BMW 250, protect the coating, then backfill. Same system whether the soil is dry or wet. Where water stands behind the wall, add the drain and free-draining fill.
Route B · Positive side
Coating done, ready to backfill
Protection, drainage and careful backfilling decide whether the coating survives.
Route C · Negative side
Existing wall, damp and salt on the face
The exposed face is stripped, the joints are repaired and a crystalline coating is applied in two coats.
Route D · Negative side
Existing wall, water running through
The running crack or joint is injected with a water-reactive grout, then the face is treated.
Route E · Negative side
Treated before and still leaking
Check drainage and re-inject first. Digging out the soil to coat the back of the wall is the last resort.
Not sure
Let the treatment finder suggest a route
Answer three questions and see a starting recommendation.
Coat the soil side before the soil goes back. It is the one step on a retaining wall that cannot be done later without digging.
Step 3
Retaining wall treatment finder
Answer three questions for a starting recommendation, including whether water is seeping or flowing, then confirm it with an Armstrong expert. Every product shown suits the wall described.
1
Is the soil side of the wall open?
2
What do you see on the wall?
3
How wet is the soil behind it?
Answer all three questions to see the recommended starting point.
Recommended starting point
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Sequence of work
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Why this one
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Before any product goes on, remove all loose, old and flaking material back to sound concrete. This is a starting point, and an Armstrong expert confirms the final choice after seeing the site.
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Every product below suits this job. Pick the one that fits the site, or ask an Armstrong expert to choose with you.
Positive side waterproofing for a retaining wall before backfilling: the soil side system
This is the Armstrong treatment procedure for the soil side of an RCC retaining wall. It is positive side waterproofing: the coating sits between the water and the wall. The wall is cast, cured and repaired first, then coated, then protected.
The soil side of a new retaining wall. The coating keeps water out of the concrete, the protection layer keeps the backfill off the coating, and the drain takes the water away.
1
Start with dense concrete
An integral waterproofing compound in the mix cuts the water the concrete absorbs: CONPROOF LW 200, CONPROOF 500, or CONPROOF RMC ADMIX 88 for ready-mix. Compact well and cure fully, with ROOFEXCURE WB on faces that are hard to keep wet. Doses and mixing are on the waterproof concrete page.Why: A dense wall absorbs less water to begin with, and every coating after it has less to hold back.
2
Clean the soil side
Remove laitance, dirt, shuttering release agent, curing compound and every loose particle, so the coating bonds to sound concrete.Why: A coating bonds only to clean concrete, and laitance and release oil leave a layer that peels.
3
Repair pot holes, honeycombs, tie-rod holes and pour joints
Cut back pot holes, honeycombs and voids to sound concrete, open tie-rod holes and pour joints to a clean groove, and fill them all with polymer repair mortar, ROOFCRETE AR over a bond coat of ROOFBOND SBR 401, placed while the bond coat is still tacky. Mixing is on the structural concrete repair page.Why: Voids and honeycombs are direct paths for water, and a coating over a void is unsupported.
4
Seal shutter joints and pipe entries
Pack them flush with a putty of ROOFBOND SBR 401, cement and graded sand mixed 1:1:1.Why: These joints and pipe entries are the commonest places for water to get through a wall.
5
First coat on the soil side: ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210
Both are flexible cementitious coatings, and Armstrong lists retaining walls among the uses of each. Mix as the data sheet says, and apply one continuous, even coat of either over the whole soil side, from the base to above the finished soil level.Why: The flexible cementitious coat is the waterproof layer next to the concrete, and it bridges fine cracks.
6
Top coats of RAINSEAL BMW 250 over the first coat
Thin RAINSEAL BMW 250 with 20% clean water and put on two coats, leaving 6 to 8 hours between them. It is water based and ready to use from the container, and Armstrong lists retaining walls among its uses. It cures to a black, rubbery film with 500% elongation.Why: The bituminous coats add a second membrane over the first and resist the salts in the soil.
7
Let it dry, then protect it
Each coat of RAINSEAL BMW 250 dries in 40 to 50 minutes, depending on the weather. Cover the finished coating with a protection layer before backfilling: mortar in thin coats, a bitumen protection board or a dimpled drainage board.Why: Each coat needs to dry before the next, or before the soil goes against it, so it does not smear or wash off.
Which coating for the soil side of a retaining wall
ROOFEX 2K 711 in two coats is the alternate specification in the Armstrong treatment procedure, in place of the coats above, as the site engineer specifies. It resists 10 to 12 bar and works on brick and stone as well as concrete.
Two coats
A flexible cementitious coating on its own
Either is also applied alone as a full coating in two coats, with the second coat crosswise to the first. Quantities are in the table below. An Armstrong expert confirms the build-up for the site.
Do the work
Retaining wall drainage and protection before backfilling
A sound coating can still be lost in a day if stones are tipped against it. And a wall with no drainage holds a full depth of water behind it after every storm. Protection and drainage are part of the waterproofing. The protection step is from the Armstrong treatment procedure.
Read it from the wall outward: coating, protection layer, gravel wrapped in filter fabric, then soil in thin lifts. The numbers match the steps below. Water that reaches the gravel drops to the pipe and leaves through the outlet and the weep holes.
1
Protect the coating
Cover the coating with a protection layer before any soil goes back. Choose one of three:
Mortar, in thin coats
The Armstrong procedure. Cement-sand mortar or plaster in thin coats, never a screed, which sags and hollows on a vertical face. Screed belongs on horizontal surfaces such as terraces, pool floors and base slabs. Over RAINSEAL BMW 250, sprinkle fine dry sand on the last coat while it is wet so the mortar bonds. The usual practice is about 20 mm of 1:3 cement mortar mixed with CONPROOF 500 at 500 ml per 50 kg bag, built in coats and cured for 7 days.
Bitumen protection board
A black board of polymer-modified bitumen, 3 to 6 mm thick, that takes the knocks from stones and site traffic. It is stuck to the coating with the board maker's adhesive or tape and its butt joints are taped. It protects but does not drain.
Dimpled drainage board with geotextile
A plastic sheet with dimples 8 to 20 mm high. Dimples face the wall, the geotextile faces the soil, sheets overlap by at least 100 mm and run down to the base drain. It protects and drains in one layer. Use taller dimples where machines compact the fill.
Why mortar and not a screed
Screed
Where it belongs
Floors, terraces and slopes to drain.
What it is
A thick (25 to 75 mm), stiff, rammed mix.
On a wall
Sags, bonds poorly, sounds hollow and shrinks. Nothing on a wall needs levelling or a fall.
Mortar or plaster
Where it belongs
Walls, columns and ceilings.
What it is
A workable mix, put on thin (about 12 to 20 mm) in coats.
On a wall
Bonds to the sanded coating and protects it.
Never backfill against a bare coating. A geotextile on its own is not enough protection. Keep sharp stone and anything larger than about 50 mm out of the fill.
Why: Backfilled soil and stones scrape and puncture a coating, so it is protected before the soil goes back.
2
Provide a drain at the base
A perforated pipe at the foot of the wall, laid to a slight fall and led to an outlet, carries water away before it builds up. Surround the pipe with 75 to 100 mm of clean stone or gravel, wrapped in filter fabric so it does not silt up.Why: A drain stops water building up against the wall, and water that is not pushing needs less waterproofing.
3
Place free-draining fill next to the wall
Clean gravel, crushed stone or coarse sand against the protection lets water drop to the drain. A filter fabric keeps soil out of it, so the drain does not clog. Keep heavy clay out of the fill: it holds water, swells when wet and pushes harder on the wall.Why: Clean gravel drains water down to the pipe, whereas clay held against the wall keeps it wet.
4
Keep the weep holes open
Where the design has weep holes, sleeve them through the wall and through the coating, seal around each sleeve, and keep them clear of mortar.Why: Weep holes relieve water pressure, and a blocked one lets the pressure build up.
5
Backfill in layers
Do not backfill until the wall has cured (at least 7 to 10 days after casting) and any props or top bracing are in place. Then backfill soon after the coating and protection are done, so they are not left in the sun. Place the soil in thin layers and compact each with light equipment near the wall. Keep rubble, sharp stone and site waste out of the fill.Why: A wall that has not cured, or soil dumped at once, can crack the wall or the coating.
6
Shed surface water at the top
Slope the finished ground away from the wall, at least 5% (about 150 mm of fall over the first 3 m), or collect it in a surface drain. Cap the top with a clay-rich, low-porosity soil so rain does not soak straight down into the gravel behind the wall.Why: Ground that slopes toward the wall sends rain to it, so the finished ground slopes away.
Why drainage matters. Each metre of water standing behind a wall adds about 0.1 bar of pressure at its base. Drained soil puts far less water against the coating and against the wall itself.
Do the work
Seeping concrete: grout through drilled holes before any lining goes on
When water leaks, seeps or sweats through porous, honeycombed or cracked concrete, it has to be stopped inside the concrete first. This is the standard negative-side method for tanks, pools, basements, lift pits and retaining walls. A lining laid over concrete that is still seeping is pushed off by the water behind it: it blisters, lifts and fails. Grouting through drilled holes fills the internal voids and capillaries along the path of the water, so the surface is dry and sound before the coating or membrane goes on. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.
1
Drill the injection points
Drill 12 to 14 mm holes with an electric drill into the leaking or honeycombed zone, to the depth the member needs (14 to 16 mm on thick retaining walls).Why: The holes intercept the pathways the water is travelling along, so the grout reaches the voids instead of just sitting on the surface.
2
Fix the nozzles
Fix a rubber injection nozzle in each hole with a quick-setting putty of cement mixed with the set accelerator RAPIDSTRONG QS 113. For active flow, the single-component plugging compound RAPIDSTRONG PLUG can be used to fix the nozzle instead.Why: The nozzle must be locked into the hole before pumping starts. If it is not, the pressure blows it out and the grout runs back out of the hole.On site: The datasheet gives RAPIDSTRONG QS 113 at 500 ml to 2 L per 50 kg of cement and asks for a site trial, so trial the dose on the job before fixing every nozzle.
3
Seeping or sweating concrete: cement slurry
Mix a cement slurry with a non-shrink grout additive and pump it into each nozzle with a grout pump at about 140 psi, until that point refuses to take any more. Any of three additives can be used: RAPIDSTRONG GROUT ADMIX at 250 g per 50 kg of cement, RAPIDSTRONG GROUT PB 66 (a polymer grout additive, dosed as on its datasheet) or ROOFEX GP (a crystalline grout compound, dosed at 250 g per 50 kg of cement).Why: The slurry fills the internal voids and capillaries. The additive keeps it from shrinking away from the concrete as it sets, which an ordinary cement slurry does, and the crystalline option also seals the capillaries.On site: Work from the lowest nozzle upward on a wall, so the slurry pushes the water and air out ahead of it.
4
Running or gushing water: polyurethane resin
Where water is flowing or gushing, cement slurry would simply wash away before it sets. First stop the surface flow with RAPIDSTRONG PLUG in a V-groove, then inject RAPIDSTRONG GROUT PU, the single-component polyurethane grout, with air-compressed injection equipment at about 500 g per grout point.Why: The polyurethane reacts with the water itself, expanding and stiffening to block the flow, so it works where cement cannot.On site: A hard-working point can take 0.3 to 0.75 kg. Polyurethane grouting alone only stops the flow; it is not a guaranteed waterproofing system, so follow it with the lining or coating the structure needs.
5
Remove the nozzles and seal
Once grouting is complete, remove the nozzles and patch every hole flush with a putty of ROOFCRETE AR and cement.Why: This leaves a smooth, sound, watertight surface ready for the final lining.
6
Check before lining
Look at the face again after the grout has set. Any point still wet gets another nozzle beside it before the coating, membrane or plaster goes on.Why: A single wet patch left behind becomes the first blister under the new lining.
Negative side waterproofing: retaining wall leakage solution for a wall that is already backfilled
When the soil is already in place, the soil side (the positive side) is buried and cannot be reached. The only option is the negative side: the wall is treated from the exposed face, with materials that work from inside the concrete. The damp patch is where the water arrives, not where it enters, so the first job is to trace the path. Seepage through a retaining wall is also driven by the soil behind it, so drainage is checked before anything is coated.
An existing wall treated from the exposed face. Running leaks are injected, joints are rebuilt, and the crystalline coating seals the pores from within.
1
Expose the bare concrete
Strip paint, putty, plaster and all loose, old and flaking material until the concrete and the leak paths can be seen. If the wall was plastered, the plaster must come off completely: a crystalline coating cannot soak into plaster or paint.Why: Treatment from the inside works on bare, sound concrete, and not on paint or plaster.
2
Trace the entry paths
Mark construction joints, cracks, honeycombs, tie-rod holes and pipe entries along the length of the wall. Water seen low on the face often enters higher up.Why: The water enters at a few points, and marking them along the length tells you where to work.
3
Check the drainage first
Rod out blocked weep holes and clear the outlet of the base drain. Divert roof water and surface water away from the top of the wall.Why: A blocked weep hole or drain keeps the pressure on the wall, and treating the wall while it is blocked fails.
4
Plug the holes and joints, then inject the leaks
Plug leaking pot holes, tie-rod holes and pour joints with RAPIDSTRONG PLUG 31 or WONDERSEAL PLUG XL, the fast-setting plugging compounds. Then grout the leaking joints and cracks with RAPIDSTRONG GROUT PU, the water-reactive grout. It foams up on contact with flowing or gushing water and sets in 36 to 48 seconds, so the flow does not have to be blocked first. Where there is no water at the point, water is injected first to start the reaction. RAPIDSTRONG GROUT PFC 79 is the alternative grout. The method is on the injection grouting page. Armstrong grouting is done with 12 to 14 mm holes (14 to 16 mm on thick retaining walls) fitted with pressure packers about 75 mm long, fixed with RAPIDSTRONG PLUG. The PU grout is injected with an air-compressed unit at about 500 g per grout point, and the holes are sealed with ROOFCRETE AR and cement after the packers are removed.Why: Running water washes any coating away, so it is stopped first by plugging and then injecting the leaks.
5
Repair pot holes, tie-rod holes and pour joints
Cut pot holes, honeycombs, tie-rod holes, cracks and pour joints to a clean groove and fill them with the ROOFCRETE AR system, over a bond coat of ROOFBOND SBR 401, worked in while the bond coat is tacky. Where the crew batches on site, ROOFCRETE AR 576, a polymer admixture mixed with cement and sand, does the same job. Moist-cure the repair for at least 7 days. Or inject RAPIDSTRONG GROUT VM 99 where the joint must be bonded.Why: Voids repaired with a bonded repair mortar give the coating a sound face.
6
Seal expansion joints with sealant
An expansion joint is not filled rigidly. It is sealed with ROOFEX-SEAL PS polysulphide sealant, after priming. See expansion joint sealing.Why: An expansion joint moves, so it is sealed with a flexible sealant and never filled rigidly.
7
Seal the concrete from inside
Dampen the face and apply ROOFEX COP, ROOFEX or ROOFEX 2K 711 in two coats, with the second coat within 48 hours, then mist 3 to 4 times a day for 2 to 3 days with no curing compound. Protect it from rain for 24 hours. A crystalline coating reacts with the cement and moisture to grow crystals in the pores and hairline cracks, so the concrete itself becomes waterproof. If water reaches it later, the unreacted chemicals can react again and seal new hairline cracks, which is the self-healing claim. It works on tiny cracks only. It needs bare, damp, sound concrete, cannot bridge wide or moving cracks, and is not a decorative finish. On brick or stone walls use ROOFEX 2K 711.Why: The crystalline coating works in the concrete against the water pressure, from the inside.
8
Check for seepage, then re-plaster
Watch the wall for seepage first. The crystals need time to form, so judge it after the coats have cured, not on the day. Full activation takes 2 to 4 weeks. Re-plaster only when it is 100% leak-proof. Use cement-sand mortar or plaster in thin coats, never a screed, which sags and hollows on a vertical face. Screed belongs on horizontal surfaces such as terraces, pool floors and base slabs. A protective plaster of ROOFCRETE AR, or a plaster modified with ROOFBOND SBR 401, restores the face and protects the coating.Why: The crystals take time to form, so the wall is judged after some days before it is plastered over.
How the crystalline coating works, and when to use a membrane instead
Water is let into the concrete face, the crystals grow in the pores, and the wall itself becomes waterproof. The wall is dampened first, because the reaction needs water. If water enters later, the chemicals left in the concrete can react again. That helps tiny cracks only.
Crystalline coating (ROOFEX COP, ROOFEX 2K 711)
How it works
Active chemicals soak into the concrete and grow crystals inside the pores and hairline cracks.
Water pressure from behind
Handles it, because it is not a skin that can peel off. This is why it suits the negative side.
Cracks
Seals hairline cracks only. It cannot bridge wider or moving cracks.
Surface and finish
Needs bare, damp, sound concrete. Breathable. Plain grey, not decorative.
Membrane coating (ROOFCOAT FLEXI 100, RAINSEAL BMW 250, PU)
How it works
A flexible film on the surface keeps water out as a skin.
Water pressure from behind
A thin film on the inside face can blister or be pushed off.
Cracks
Stretches over moving cracks.
Where it belongs on a retaining wall
On the soil side, where the water presses it onto the wall.
ROOFEX COP or ROOFEX 2K 711
ROOFEX COP
Type
Single-component, cement-based powder.
Coats
Two slurry coats at 0.75 to 1 kg/m² each. Dry shake at 1.6 kg/m² on fresh concrete and dry pack at 1.5 kg/m² for joints.
Cracks
Seals cracks up to 0.4 mm.
Packs
1, 5 and 25 kg.
ROOFEX 2K 711
Type
Two-component: 1 kg liquid and 2 kg powder, with about 20% water.
Coats
2 to 3 coats, 1.2 to 1.6 kg/m² in total (about 1 mm), by brush or spray. Pot life is 45 min to 1 hr at 30 °C, so mix small batches.
Pressure and flexibility
10 to 12 bar hydrostatic resistance and up to 16% elongation. Also for brick and stone.
Packs
15 and 30 kg.
Both go on dampened, sound concrete with the second coat within 48 hours, and are cured by mist only. Allow 48 hours before foot traffic. Both say to contact Armstrong for high hydrostatic pressure.. A live crack is not a job for the crystalline coat: use a flexible sealant or a membrane there.
Below ground, the same rule applies. Water pushes from the soil side, so a coating on the soil side holds and a thin film on the inside is pushed off. When only the exposed face can be reached, the leak paths are injected and the concrete is sealed with a crystalline coating. The full explanation, with the positive side and negative side options compared, is on the basement waterproofing page.
Do the work
When retaining wall seepage keeps coming back: drainage, re-injection and excavation
Treatment from the exposed face manages water that has already reached the wall. The soil and the water are still there. If seepage returns, work up the ladder one rung at a time. Digging out the backfill is the extreme case and comes last.
1. Clear the drainage again
Weep holes and the base drain block with silt over time. Rod them out again and check where the outlet runs.
2. Re-inject
Find the path that is still open and inject it again. A resin injection can be repeated. Re-coat that zone.
3. Relieve the pressure
Where the design allows, an engineer may add weep holes or drains to bring the water level behind the wall down.
4. Excavate and coat the soil side
Only where the first three have not held and the site allows it: dig out the fill, repair the wall and apply the soil side system as for a new wall.
Structure
Rust stains and concrete breaking away
Water that has run through a wall for years rusts the steel. The repair follows the steel repair sequence. See structural concrete repair.
Movement
Leaning, bulging or wide cracks
These are structural signs, not waterproofing ones. A structural engineer must see the wall before any coating or injection.
Masonry
Stone or brick retaining walls
A masonry wall is treated from the exposed face with ROOFEX 2K 711, which is compatible with brick and stone. Keep its weep holes open.
Reference
Retaining wall waterproofing coatings compared: soil side and exposed face
Every product here is a sound choice for the job it is made for. They differ in chemistry and in which face they go on.
Into running cracks and joints from the exposed face
ROOFCRETE AR or ROOFCRETE AR 576: which repair mortar
Pre-packed kit
ROOFCRETE AR
Two-part, fibre-reinforced polymer-modified repair mortar. Part 1 is the polymer liquid and Part 2 is the powder, in a fixed factory ratio, so there is no batching error. 25 kg pack, about 1.30 sq.m at 10 mm per pack, 6 to 100 mm per layer, shelf life 6 months. Choose it for large or critical repairs and for crews that do not batch on site.
Site-batched admixture
ROOFCRETE AR 576
A latex polymer admixture added to a site-batched cement and sand mortar, about 1:3, at 500 ml to 2 L per 50 kg of cement depending on repair depth. Liquid in 1, 5, 10, 20 and 210 L packs, 6 to 100 mm per layer, shelf life 24 months. Choose it for volume work and where local cement and sand are used.
The method is the same for both: cut back to sound concrete, saturate it to a saturated-surface-dry state, apply the bond coat (ROOFBOND SBR 401) and place the mortar into the tacky coat, compact, finish, then moist-cure for at least 7 days.
What changes with the face you can reach
When it can be done
Positive side (soil)
Only before backfilling, or after excavation
Negative side (exposed face)
Any time
What else is needed
Positive side (soil)
Protection layer, drainage, careful backfill
Negative side (exposed face)
Joint repair first, moist curing after
What the soil does
Positive side (soil)
Presses on the coating, so it needs protecting
Negative side (exposed face)
Presses water through the wall, so drainage is checked
First choice?
Positive side (soil)
Yes, wherever the soil side can be reached
Negative side (exposed face)
Where the soil side cannot be reached
Reference
Retaining wall waterproofing chemicals and products by stage
Work out the quantity for your own job. Enter your measurements and get the material needed.
How much waterproofing material for a retaining wall 50 ft long
Approximate quantities for a wall 50 ft long and 10 ft high, coated on one face: 500 sq.ft, or about 46 sq.m. Figures are worked out from each product's stated coverage on a smooth, prepared surface. Injection grout and repair mortar depend on the defects found and are measured at site. An Armstrong expert confirms the final quantity after seeing the site.
ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210, one coat under RAINSEAL BMW 250
Stated coverage
Taken as half of the two-coat quantity
For 500 sq.ft
ROOFCOAT FLEXI 100: 8.4 to 13 litres, plus 17 to 25 kg of cement. ROOFBOND RFX PLUS 210: 2 units
RAINSEAL BMW 250, two coats
Stated coverage
1 litre covers 30 sq.ft in two coats
For 500 sq.ft
About 17 litres
ROOFEX 2K 711
Stated coverage
1.2 to 1.6 kg per sq.m in total
For 500 sq.ft
56 to 75 kg
ROOFCOAT FLEXI 100, two coats
Stated coverage
20 to 30 sq.ft per litre for two coats
For 500 sq.ft
17 to 25 litres, plus 34 to 50 kg of cement
ROOFBOND RFX PLUS 210, two coats
Stated coverage
13 to 14 sq.m per 20.1 kg unit
For 500 sq.ft
4 units
ROOFEX COP, two coats (exposed face)
Stated coverage
0.75 to 1 sq.m per kg per coat
For 500 sq.ft
93 to 124 kg
ROOFEX, two coats (exposed face)
Stated coverage
0.75 kg per sq.m per coat
For 500 sq.ft
About 70 kg
Standards and tests behind retaining wall waterproofing products
The test standards behind the flexible coatings, crystalline coatings and injection grouts are listed on the basement waterproofing page, because the same products are used.
RAINSEAL BMW 250 states 500% elongation and resistance to dilute acids, dilute alkalis and salt solutions.
The structural design of a retaining wall, including its drainage and weep holes, is the structural engineer's. Waterproofing does not replace it.
Reference
Retaining wall waterproofing material calculator
Enter the length and height of the wall to see the coating needed for one face. Quantities only. Injection grout and repair mortar depend on the defects found and are measured at site.
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Enter the measurements
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Which system?
Enter the measurements to see the estimated quantity of material.
Estimated quantity
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This is an estimate of material only, worked out from each product's stated coverage on a smooth, prepared surface. Rough or porous surfaces use more, so allow about 10% extra. Crack sealing, patch repair, plaster, coving and tiling materials are not included. An Armstrong expert confirms the final quantity after seeing the site.
After the wall is cast, cured and repaired, and before any soil is placed against it. That is the only time the soil side can be reached.
What if the retaining wall is already backfilled?
It is treated from the exposed face. Running leaks are injected, joints and honeycombs are rebuilt, and a crystalline coating is applied in two coats and kept moist for 2 to 3 days.
Can retaining wall leakage be fixed without excavation?
Yes, in most cases. Injection and crystalline treatment from the exposed face are made for this. Excavation to coat the soil side is kept as the last resort.
Why must the coating be protected before backfilling?
Because backfill contains stones, and compaction drives them into the wall. A protection layer of mortar, bitumen board or dimple board takes the damage so the coating does not.
Does drainage matter if the wall is waterproofed?
Yes. Drainage lowers the water level behind the wall, so there is less pressure on the coating and on the wall. Waterproofing and drainage work together.
Which coating resists chemicals and salts in the soil?
RAINSEAL BMW 250 resists dilute acids, dilute alkalis and salt solutions. ROOFCOAT FLEXI 100 resists dilute acids, alkalis and salts. ROOFBOND RFX PLUS 210 is a chloride and sulphate barrier that protects the steel in the concrete.
How do I stop water seeping through a retaining wall?
What is positive side waterproofing on a retaining wall?
Waterproofing on the face the water touches, which is the soil side. The water presses the coating onto the wall. It is the first choice wherever that face can be reached.
Should weep holes be sealed to stop the wall looking wet?
No. Weep holes are part of the drainage and are kept open. Blocking them lets water build up behind the wall.
How is the retaining wall of a basement waterproofed?
The same way on the soil side, before backfilling. Because the other face is a usable space, the standard of dryness is higher. See basement waterproofing.
Is a water tank wall treated the same way?
No. A tank is lined on the inside, which is the face the stored water touches, with a lining tested for drinking water. See water tank waterproofing.
Get the right waterproofing system for your retaining wall
Tell us the wall length and height, whether it is backfilled and what you see on the face. An Armstrong applicator or distributor will recommend a system. Toll free 1800 103 2034. Armstrong manufactures retaining wall waterproofing chemicals in Bengaluru and supplies them all across India, with South India as its major hub.
About this guide
Written by the technical team at Armstrong Chemicals Pvt. Ltd., an ISO 9001:2015 certified manufacturer of construction and waterproofing chemicals in Bengaluru, with more than 200 products. Armstrong has been protecting buildings, roofs and structures since 1982 and supplies all across India, with South India as its major hub.
The methods on this page are Armstrong's standard procedures. Doses, thicknesses and the number of coats are adjusted to the conditions on each site. Load-bearing repairs and strengthening are designed by a structural engineer.
Last updated · Questions on this method: toll free 1800 103 2034
