Injection Grouting: Which Grout for Which Leak or Crack

Water leakage through concrete cracks: check before injection grouting

Water dripping through a basement wall, a damp line along a construction joint, a lift pit that fills up overnight, a crack in a column or a slab that leaks at the same place every monsoon: these are the jobs injection grouting is used for. In injection grouting, also called pressure grouting or crack injection, a grout is pumped through nozzles into the crack, joint or void, so that it fills the defect inside the concrete and not only at the surface. The work itself is routine. The choice of grout is what decides the result. Armstrong makes PU injection grouts, two-component injection resins, an epoxy injection grout, and crystalline and cementitious grouts, and each one is made for a different condition. Six checks tell you which.

Find the right injection grouting method for your leak or crack

Match what you found to one route. Each route names the Armstrong grouts made for it and takes you to its section. Where two or three grouts suit the job, all of them are listed, and an Armstrong expert helps you pick.

Stop the water first, restore the strength second, protect the surface last. Loose plaster, old coatings and flaking material are removed before any of it, so that every crack and joint can be seen and the packers sit in sound concrete.

Injection grout finder: PU, resin, epoxy or cement

Armstrong makes water-reactive PU grouts, two-component injection resins, an epoxy injection grout and crystalline and cementitious grouts. Every one is a sound choice for its condition. Answer three questions for a starting recommendation, then confirm it with an Armstrong expert.

Injection grouting procedure: how crack injection is done, step by step

The sequence is the same for PU, resin, epoxy and cement grouts. What changes is the grout, the pump and whether the crack is kept wet or dry. The work is done by an Armstrong applicator with an injection pump. The steps below show what a proper job looks like, so you know what to expect on site.

1. 1
   Clean and map

   Remove all loose, hollow and flaking plaster, old coatings and dirt from the area. Mark every crack, joint, honeycombed patch and wet spot, and mark both ends of any crack that is still growing.Why: Grout reaches the crack through the holes drilled into sound concrete, and marking every crack means none is missed.
2. 2
   Stop gushing points

   Where water is pouring from a hole or a single point, press in RAPIDSTRONG PLUG 31, which sets in about 30 seconds, or WONDERSEAL PLUG XL, which expands as it sets. This lets the rest of the work go on.Why: Flowing water carries injected grout away, so the worst points are plugged first.
3. 3
   Drill the holes

   Drill along the crack at about 45 degrees, so each hole crosses the crack near the middle of the wall or slab. Stagger the holes on either side of the crack. For RAPIDSTRONG GROUT PCR 89, Armstrong states holes of 12 to 14 mm on alternating sides of the crack.Why: Holes drilled at an angle cross the crack inside the concrete, so the grout reaches its full depth.
4. 4
   Fix the packers

   Set a packer or injection nozzle in each hole and tighten it. Where nozzles are surface-fixed, bed them in a quick-setting putty made with RAPIDSTRONG QS 113 and cement, and seal the crack surface between the nozzles so the grout cannot escape.Why: The packer seals the hole and takes the injection pressure, and a loose one blows out.
5. 5
   Wet it or dry it

   A water-reactive PU grout needs water to react. If the crack is dry, water is injected first. An epoxy grout needs the opposite, a dry crack.Why: A water-reactive grout needs water to react, so a dry crack is wetted first, while epoxy needs a dry one.
6. 6
   Inject from the bottom up

   Start at the lowest packer on a wall, or at the widest part of the crack on a floor. Pump with slow, steady pressure until grout appears at the next packer, close the first one and move up. RAPIDSTRONG GROUT VM 99 is stated for injection at about 40 psi and up to 200 psi. Cement grout made with RAPIDSTRONG GROUT ADMIX is stated for injection at 140 psi until refusal.Why: Grout pushes air and water up ahead of it, so it fills the whole crack with no pockets.
7. 7
   Re-inject where needed

   Any packer that took a large volume is injected again after the first pass has set. RAPIDSTRONG GROUT VM 99 and RAPIDSTRONG GROUT PCR 89 are re-injectable.Why: A packer that took a lot may not be full, and a second pass fills what the first left.
8. 8
   Remove the packers and make good

   Once the grout has cured, cut or remove the packers and patch the holes flush. Use RAPIDSTRONG PLUG 31 where the hole is still damp, or ROOFCRETE AR over a bond coat of ROOFBOND SBR 401.Why: The holes are patched flush, so the surface is sound and ready for the coating.
9. 9
   Watch it through a wet spell

   Check the injected line after the next heavy rain, or after the tank, pit or basement has seen water again, before the surface is finished.Why: The next heavy rain shows any line that still leaks, before the work is accepted.

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. 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. 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. 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. 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. 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. 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.

PU grout points: plug, pack, inject and seal

Polyurethane grouting stops water that is actually moving through a crack, joint or hole. The resin reacts with the water, expands and stiffens, so it works where cement and sealants wash away. The work is done point by point along the leak. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Plug active flow

   Where water is flowing from a crack, cut a V-groove and fill it with RAPIDSTRONG PLUG, the single-component instant-setting plugging compound.Why: Stopping the flow at the surface gives the resin a quiet point to build pressure behind.
2. 2
   Drill

   Drill 12 to 14 mm holes with an electric drill to the required depth, spaced along the crack so that each hole crosses it.Why: The hole must cross the crack to feed the resin into it.
3. 3
   Fix the packers

   Fix pressure-retaining packers (rubber-gripped aluminium or steel, about 75 mm long) in the holes with RAPIDSTRONG PLUG.Why: The packer holds the resin in and locks against the injection pressure.
4. 4
   Inject the PU

   Inject RAPIDSTRONG GROUT PU, the single-component aliphatic polyurethane grout, with air-compressed injection equipment. Allow about 500 g of grout for each grout point; a hard-working point can take 0.3 to 0.75 kg.Why: The grout expands as it meets the water and seals the crack along its length.
5. 5
   Remove the packers and seal

   Remove the packers and seal each hole with a polymer putty of ROOFCRETE AR and cement.Why: This restores a smooth surface for the coating that follows.
6. 6
   Know what it does

   Polyurethane grouting stops the flow of water through the crack. It is not guaranteed on its own, so follow it with the waterproof coating or the repair the structure needs.Why: Grouting is the first step of a repair, not the whole repair.

PU injection grouting for running water leakage

PU injection grouting is the method for active leaks: water running or dripping through a crack, a joint or a pipe entry in a basement, retaining wall, lift pit, sump or tunnel. A polyurethane grout reacts with the water it meets. It expands into the crack, the pores and the narrow gaps around it and sets, so the leak does not have to be dried or blocked first. This is the answer to the common question of whether injection works while water is flowing. It does, and the water is what makes it work.

How to stop water leakage from a crack with PU injection

1. 1
   Plug the worst points

   Stop gushing holes with a plugging compound so the crack line can be worked on.Why: The worst flows are stopped so that the crack line can be worked on.
2. 2
   Drill and fix packers

   Drill at an angle to cross the crack inside the concrete and fix the packers, as in the procedure section.Why: The holes cross the crack inside the concrete, and the packers hold the pressure.
3. 3
   Inject the PU grout

   Both PU grouts are pumped as a single component, normally with a low-pressure hand-operated pump. Armstrong states that high-pressure pumps with special packers or nipples are used in specific conditions.Why: The grout is pumped at low pressure, so it travels the crack without blowing out the packers.
4. 4
   Add water if the crack is not wet enough

   Where water is not naturally present in sufficient quantity, water is injected as well to start the reaction.Why: A water-reactive grout does not expand without water, so it is wetted first.
5. 5
   Watch the reaction

   The reaction is quick, so the result shows at the crack almost at once. Move to the next packer when foam or grout shows there.Why: The grout reacts quickly, so the result shows at the crack at once, and the next point can be worked on.
6. 6
   Follow up

   Once the flow has stopped, remove the packers and patch the holes. If the member is structural, the crack is then bonded with a resin. If the wall or pit is damp across its face, it is coated from inside.Why: Once the flow has stopped the holes are patched, and a structural crack needs its own repair.

PU injection stops the water at that crack. It does not make porous concrete watertight, and water that is blocked at one point can show up at the next weak point. That is why injection in a basement or pit is normally followed by a crystalline or high-pressure coating on the inside face. See basement waterproofing and lift pit waterproofing.

Epoxy and resin crack injection for wet and dry structural cracks

When a crack has to be bonded as well as sealed, a foam is not enough. Structural crack repair in concrete uses a low-viscosity resin that travels deep into the crack and cures to a solid that holds the two faces together. Which resin depends on whether the crack is dry or carries water. Any crack in a beam, column or load-bearing slab is assessed by a structural engineer before it is injected.

How to seal a crack in wet concrete with injection resin

1. 1
   Stop any flow first

   If water is running, inject a PU grout first and return when the flow has stopped. A damp or wet crack with no flow can be injected directly with RAPIDSTRONG GROUT VM 99 or RAPIDSTRONG GROUT PCR 89.Why: Running water washes out resin before it cures, so a flow is stopped first.
2. 2
   Drill and fix the nozzles

   For RAPIDSTRONG GROUT PCR 89, drill 12 to 14 mm holes on alternating sides of the crack and fix the nozzles with a quick-setting compound such as RAPIDSTRONG QS 113 mixed with cement.Why: Holes on alternate sides of the crack let the resin reach both faces.
3. 3
   Mix only what can be injected

   Stir each part separately, then mix Part A and Part B at 1:1 for RAPIDSTRONG GROUT VM 99. Its working time is only 25 to 30 seconds, so it is pumped with a two-component injection pump and never mixed in bulk. Where the ingress is heavy, an accelerator is added as Part C at 0.2%.Why: The resin sets in its pot life, and a mix that sets in the pump is lost.
4. 4
   Inject with slow, steady pressure

   Start at the lowest port on a wall or the widest part of the crack on a floor. Keep the ports open and move on when resin flows freely from the next port. Protect the resin from direct sun and heat.Why: Slow pressure lets the resin follow the crack to its full depth, where fast pressure blows out and leaves voids.
5. 5
   Re-inject if the crack is not full

   Both resins can be injected a second time through the same ports.Why: A second injection through the same ports fills what the first left.
6. 6
   Seal the holes

   After full cure, close the holes with a polymer cement mortar such as ROOFCRETE AR.Why: The holes are closed with a polymer mortar once the resin has cured.

Epoxy injection of a beam crack

A structural crack in a beam is not sealed from the surface. It is injected with low-viscosity epoxy under pressure so the resin travels into the crack and bonds the two faces together again. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Groove and fill

   Clear the crack groove with an air blower and fill it with ROOFCRETE EP, the three-component epoxy putty, levelling it to the surface.Why: The putty seals the surface of the crack so that the injected resin stays in.
2. 2
   Drill

   Drill 12 mm holes 75 mm deep into the crack at about 300 mm centres, blow them clean, and fix non-return nozzles with a fixing compound.Why: The nozzles are the entry points for the resin, and the non-return type keeps it from running back.
3. 3
   Inject

   Inject RAPIDSTRONG GROUT EP 403, the low-viscosity epoxy grout, through the nozzles one by one with an electric grout pump rated at 7,000 psi, until each nozzle refuses. The two parts are mixed 1 : 0.5, base to hardener by weight. Site orders allow about 0.5 kg of mixed grout per nozzle, and the nozzles are sealed afterwards with a plugging compound at about 0.2 kg per nozzle.Why: Epoxy this thin travels deep into hairline cracks and cures into a bond as strong as the concrete.
4. 4
   Patch

   Plaster any honeycombed area with polymer-modified mortar and level it to the adjoining surface.Why: This restores the section and gives a uniform surface.

Epoxy injection grouting for a dry structural crack

Epoxy injection glues a dormant crack back into one solid member. RAPIDSTRONG GROUT EP 403 used as resin and hardener alone, at 100:50, is fluid enough to enter gaps from 0.1 mm by capillary action and is non-shrink, so it stays in full contact with both faces. It is injected only after the crack has been shown to be dormant and the engineer has agreed the repair.

1. 1
   Confirm the crack is dormant and dry

   Use the tell-tale check from the start section. A crack that is still moving is not injected with epoxy.Why: Epoxy bonds a crack rigidly, so a crack that is still moving will crack again beside the repair.
2. 2
   Prepare the surface

   Contact surfaces must be free of dust, oil, grease and loose material, and the concrete must be sound.Why: Epoxy bonds to clean, sound concrete, and dust and oil stop it.
3. 3
   Mix

   Add 500 g of Part 2 slowly to 1 kg of Part 1 and mix with a slow-speed stirrer for 2 to 5 minutes, until the colour is uniform.Why: The epoxy cures fully only in the stated proportion and when fully mixed.
4. 4
   Inject without stopping

   Continuous flow matters, so enough grout is mixed and ready before pumping starts. Pot life for this mix is about 65 minutes at 20°C and 40 minutes at 30°C. The minimum hardening temperature is 10°C.Why: A break in the injection leaves a cold joint in the repair.
5. 5
   Make good

   Remove the packers and patch the holes once the grout has hardened.Why: The holes are patched once the grout has hardened, and the surface is made sound.

Where the crack comes with rust stains or spalled concrete, the steel is the real problem and injection alone does not fix it. See structural concrete repair.

Construction joint leakage and honeycombed concrete: cement and crystalline grouting

Not every leak is a crack. A construction joint, also called a cold joint or shuttering joint, is the line where one pour of concrete stopped and the next began: the wall to raft joint in a basement, the joint between two lifts of a retaining wall, the kicker at the base of a lift pit. The two pours never bond fully, so water finds the joint first. Honeycombed concrete is the other common case: poorly compacted concrete with voids, usually low on a wall or around congested steel. Both are filled, not just sealed.

How to make non-shrink grout at site and pressure grout honeycombed concrete

1. 1
   Open up and clean

   Cut back loose and honeycombed material to sound concrete. Along a joint, cut a V-groove for the full length and clean it out. Shutter joints are opened to a groove about 10 mm wide and deep.Why: The grout fills a sound, open crack, and loose material blocks it.
2. 2
   Fix the nozzles

   Fix nozzles along the joint, and on a grid over porous areas, with a putty of RAPIDSTRONG QS 113 and cement. Seal the surface between them.Why: The nozzles are the entry points for the grout, and they are fixed along a joint or on a grid over porous areas.
3. 3
   Mix the grout

   Add RAPIDSTRONG GROUT ADMIX to the mixing water first, then the cement, at 250 g per 50 kg of cement. A neat mix at a water to cement ratio of 0.40 to 0.44 gives about 36 litres of grout per 50 kg of cement. It suits Ordinary Portland and sulphate-resistant cement and is not used with high alumina cement. For a crystalline grout, ROOFEX GP is dosed at 250 g per 50 kg bag of cement. ROOFBOND SBR 401 is also listed as an injection grout additive that lowers viscosity and bleed in micro-crack grouting.Why: The admixture goes into the water first, so it spreads through the batch, giving a grout that does not shrink.
4. 4
   Use it in time

   Use the grout within 30 minutes of mixing and do not add water to revive it.Why: The grout begins to set, and water added to revive it weakens it.
5. 5
   Pump until refusal

   Inject from the lowest nozzle upward, at about 140 psi, until the concrete takes no more and grout shows at the next nozzle.Why: Starting low and pumping until the concrete takes no more fills the voids from the bottom up.
6. 6
   Cut off, patch and cure

   Remove the nozzles, fill the groove and the holes with ROOFCRETE AR over a wet bond coat of ROOFBOND SBR 401, and cure the patch.Why: The patch restores a sound surface, and curing gives the repair its strength.

Through cracks in an RCC slab: inject from both faces

A crack that shows on the top of a slab and on its soffit runs through the full depth. Injecting from the top alone leaves the lower half of the crack open, and the repair then fails from below even when the top looks finished.

• Fix packers on both faces, the top and the soffit.
• On each face, stagger the packers in a zig-zag across the crack and not in one straight row, so the grout spreads through the thickness.
• Inject from the top face first, then repeat the sequence from the soffit.
• Apply the crystalline coat or sealer on the soffit as well as on the top.
• Where the crack is fed by gravity from the top, the RAPIDSTRONG GROUT VM 99 data sheet says to seal the underside of the slab first and pour the resin into a V-notched crack until it is full.

Construction joints in new concrete: treat them before they leak

In new construction, joints and honeycombs are dealt with while access is easy. This is a small job at that stage and a large one after the basement is finished or the tank is filled.

1. 1
   Make the concrete watertight

   Use an integral waterproofing compound such as CONPROOF LW 200 in the mix and compact it well. See waterproof concrete.Why: A dense concrete with a compound in it has fewer leaks to repair afterwards.
2. 2
   Check after the shuttering is struck

   Mark every construction joint, tie-rod hole and honeycombed patch before plaster or backfill hides it.Why: Joints, holes and honeycombs are marked while the wall is open, before any coating hides them.
3. 3
   Pack honeycombs and seal tie-rod holes

   The Armstrong procedure for new RCC walls is to pack honeycombs, voids and pop-outs with polymer repair putty, and to seal tie-rod holes, shutter joints and pipe penetrations flush with a putty of ROOFBOND SBR 401, cement and graded sand at 1:1:1. Honeycombs that run deep into the member are injected with non-shrink grout made with RAPIDSTRONG GROUT ADMIX.Why: Honeycombs and tie-rod holes are paths straight through the wall.
4. 4
   Inject suspect joints

   Joints that show damp are injected with RAPIDSTRONG GROUT VM 99 or a crystalline grout made with ROOFEX GP before the waterproofing goes on.Why: Joints that show damp are injected, since a joint that has already leaked will leak again.
5. 5
   Then waterproof

   The coating or lining goes over a sound structure. See new construction waterproofing.Why: The coating or lining goes over a sound structure, and not over one that is still leaking.

When injection grouting is not the answer, and the extreme case

Injection grouting is a repair for a defect inside sound reinforced concrete. It is the wrong tool for some cracks, and for badly damaged concrete it is only the first of several steps. Repair comes first on every route. Breaking out and recasting is the last resort.

Will the crack come back after injection grouting?

A dormant crack that is fully filled does not reopen. Leaks return for three reasons: the crack was still moving, the grout did not match the condition, or the water moved to the next weak point in porous concrete. The first is settled by the tell-tale check, the second by the choice of grout, and the third by treating the surface after injection.

After injection, the concrete around the crack is often still porous. On the inside face of basements, sumps, lift pits and water-retaining structures, ROOFEX COP is applied as a two-coat slurry on dampened concrete. It grows crystals in the pores and seals hairline cracks up to 0.4 mm, and it works with water pressure from either side. It is rigid, so it comes after injection and never in place of it. Its stated coverage is 0.75 to 1 sq.m per kg per coat. On terraces and other exposed slabs, a flexible coating such as ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210 goes over the repaired crack. See terrace waterproofing.

PU vs epoxy injection grouting: compare Armstrong injection grouts

Every grout below is a sound choice for the condition it is made for. They differ in chemistry, in what they do to the crack and in the pump they need. Figures are from Armstrong data sheets and brochures.

Where pressure grouting for leakage is used

Injection grouting chemicals and products by stage

How much grout is needed for injection grouting

Resin quantity cannot be worked out from the length of a crack alone, because it depends on the width and depth of the crack and the voids behind it. Armstrong does not publish a consumption per metre, and a trial injection sets the figure for each job. What can be worked out is the number of injection points and the cement grout. The example below is a 6 metre run of leaking joint and two bags of cement mixed into grout for the honeycombed area beside it.

Standards and checks for crack injection work

• IS 456:2000, clause 35.3.2, gives the surface crack widths reinforced concrete is designed around: 0.3 mm in general, 0.2 mm for members exposed to moisture or in contact with soil or groundwater, and 0.1 mm for severe exposure.
• RAPIDSTRONG GROUT EP 403 conforms to ASTM C-881-78, and its strength is tested to BS 6319 Part 2.
• RAPIDSTRONG GROUT VM 99 strengths are tested to DIN EN 196 T1.
• RAPIDSTRONG GROUT ADMIX is stated to give 1 to 4% expansion to ASTM C827, with nil chloride to BS 5075. It complies with BS 1881 Part 116:1983.
• RAPIDSTRONG GROUT PB 66 complies with BS 1881 Part 116:1983.
• ROOFEX COP complies with BS 1881 Part 116:1983 and ASTM C1107.
• Site check: grout showing at the next packer, no fresh seepage after the next wet spell, and for tanks and pits a fill test before the surface is finished.

Injection grouting quantity calculator

Enter the length of crack or joint, the face it is in and the cement you plan to mix into grout. The calculator gives the number of injection points, the grout additive and the crystalline coat. Quantities only.

Seven mistakes that make injection grouting fail

1. Epoxy in a wet or running crack. Epoxy does not cure against running water. Stop the water with a PU grout first.
2. PU foam in a structural crack and nothing else. A water-reactive PU grout stops water. It does not restore strength to a beam or column.
3. Rigid resin in a moving crack. The grout holds and a new crack opens beside it. Check for movement first.
4. Injecting plaster. A plaster crack has no depth for a grout to travel through. Groove it and fill it.
5. Packers too far apart, or in one straight row. The grout then misses parts of the crack. Stagger the packers and wait for grout at the next one before moving on.
6. Treating one face of a through crack. The lower half stays open. Inject from the top and from the soffit.
7. Stopping at the injection. Porous concrete lets water move to the next weak point. Coat or line the face after the leak is stopped.

Injection grouting questions and answers