Bathroom Waterproofing Chemicals and Systems, Before Tiling or After a Leak

Bathroom leakage: find where the water is escaping

Bathroom leakage and seepage show up somewhere else: a damp patch on the ceiling of the flat below, peeling paint on the bedroom wall, a wet floor outside the door. Bathroom waterproofing works when it deals with the points where water actually gets in, which are the pipe sleeves, the joints, the wall and floor junction and the floor itself. The same applies to a toilet or washroom. Five checks tell you which treatment you need.

Find the right bathroom waterproofing method

Match what you found to one route. The right repair is the smallest one that reaches the real source.

Diagnose first, repair second. A leaking pipe and a leaking floor look the same from below and need different repairs. Be wary of any promise that every bathroom leak can be fixed without breaking tiles.

Bathroom waterproofing finder

Armstrong makes flexible cementitious, polyurethane-cement and crystalline waterproofing coatings for bathrooms, along with the grouts, sealants, repair mortars and tile adhesives that go with them. Every one is a sound choice. They differ in chemistry and finish, so the pick depends on the bathroom and the leak. Answer three questions for a starting recommendation, then confirm it with an Armstrong expert.

Bathroom: waterproof, then plaster and screed

In a bathroom, the waterproofing goes on the slab and the plaster and screed go over it, so the membrane is protected and the floor still falls to the trap. This is the order for a floor that will be tiled. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Prepare the surface

   Clean the surface of dirt, dust and old coatings. Where loose mortar or cement lumps are present, chip them off with an electric chipping machine, remove the debris and wire-brush the surface.Why: The membrane bonds to sound, clean concrete, not to dust.
2. 2
   Two coats of membrane

   Apply two coats of ROOFCOAT FLEXI 100 mixed with cement.Why: Two coats close the pinholes a single coat leaves.
3. 3
   Bond coat and impervious plaster

   Apply ROOFBOND PB 210 mixed with cement as a bond coat. On the wet bond coat lay a 1:4 cement-sand plaster about 20 mm thick, mixed with CONPROOF 500 at 500 ml per 50 kg of cement.Why: The bond coat ties the plaster to the membrane, and the integral compound makes the plaster itself resist water.
4. 4
   Fix the traps

   Fix the floor trap and P-trap and seal every joint with an acrylic putty of ROOFCOAT FLEXI 100, cement and sand.Why: The trap is where water leaves the floor, so a poor joint here leaks into the ceiling below.
5. 5
   Screed to falls

   Lay a 1:2:4 screed with 12 mm aggregate and CONPROOF 500 at 500 ml per 50 kg of cement, about 40 mm thick, so the floor falls to the trap. For a heavier build-up, apply ROOFBOND SBR 401 mixed with cement as a bond coat at about 300 g per sq.m and lay a polymer screed with 12 mm aggregate and ROOFCRETE AR, about 75 mm thick on average.Why: The fall carries water to the trap instead of letting it stand on the tiles, and a standing film of water is what finds any weak joint.

Pipe and floor-joint bore packing

Water seeps into a slab around pipes and along floor joints, where the original concrete never bonded to the pipe or the next pour. Packing the bore closes that path. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Open a groove

   Chip a groove 6 to 10 mm wide around each pipe or along each floor joint, and clean out dust and dirt.Why: The compound needs a clean, defined groove to lock into. A hairline gap cannot hold it.
2. 2
   Pack it

   Seal the groove with the instant plugging compound WONDERSEAL PLUG XL, finishing level with the surface all round the pipe.Why: It sets fast, so it stops water that is still moving and does not shrink out of the groove.
3. 3
   Seal trap and pipe joints

   Seal the joints of traps and pipes with an acrylic putty of ROOFCOAT FLEXI 100, cement and sand.Why: This flexible putty absorbs the small movement of the pipe, which a rigid mortar does not.

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.

Bathroom, toilet and utility waterproofing: the standard sequence

This is the standard sequence for this area, in the order it is carried out. Each step prepares the surface for the next, so a step skipped or done out of order shows up later as a leak, a blister or a hollow tile. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Prepare the surface

   Clean the surface of dirt, dust and old coatings. Chip off loose mortar and cement lumps with an electric chipping machine, remove the debris and wire-brush the surface.Why: Every membrane in this sequence is only as good as its grip. It bonds to clean, sound material, not to dust or loose screed.
2. 2
   Groove and seal cracks and joints

   Open every crack and joint to a V-groove about 6 mm wide and deep, clean it out, and fill it with ROOFEXSEAL PU 212, the single-component polyurethane sealant.Why: A hairline crack moves with temperature. A rigid coating over it cracks along the same line, but a flexible sealant in the groove moves with it.
3. 3
   Stop the leaks

   Where water comes through, grout it through drilled holes as in the section above: 12 to 14 mm holes, rubber nozzles fixed with cement and RAPIDSTRONG QS 113, cement slurry made with RAPIDSTRONG GROUT ADMIX (250 g per 50 kg of cement), RAPIDSTRONG GROUT PB 66 or ROOFEX GP pumped at about 140 psi until refusal, then seal the holes with ROOFCRETE AR and cement.Why: The membrane goes on a dry, stable surface. Water pushing from behind lifts any coating laid over it.
4. 4
   Two coats of the cementitious membrane

   Apply two coats of ROOFBOND RFX PLUS 210 as a slurry, about 1.5 kg per sq.m in total, over the slab and up the vertical surfaces to 300 mm above finished floor level. Put the second coat on once the first has set enough to take it.Why: Two coats close the pinholes a single coat leaves, and the 300 mm upturn means water on the floor cannot run behind the membrane at the wall.
5. 5
   Pond to test

   Pond water on the floor for 7 days and check the ceiling below for any damp patch before anything is laid over the membrane. Some specifications call for a ponding test without fixing a period, so the test period is set by the job.Why: This is the only moment a leak can be fixed easily. Once the screed and tiles are on, finding and repairing the same leak means breaking all of it out.
6. 6
   Protective plaster over the membrane

   Lay a protective plaster about 20 mm thick on the floor and on the walls up to 300 mm, in 1:3 cement mortar mixed with CONPROOF 500 at 500 ml per 50 kg bag. Form a cove at the floor-wall junction, finish with a broom texture to take the next layer, and cure for 7 days.Why: Tiles and screed bond to a plaster, not to a membrane. The plaster also stops the membrane being scraped when tiles are laid.On site: Tiles go on this plaster or screed, not directly on the membrane.
7. 7
   Form the cove at the wall junction

   Chip off loose material and clean the junction. Apply ROOFBOND SBR 401 mixed with cement as a bond coat, then form a cove at the 90 degree junction up to 6 inches (150 mm) in 1:4 cement-sand mortar mixed with CONPROOF LW 200 at 200 ml per 50 kg of cement, finished neatly.Why: A sharp 90 degree corner is where coatings tear and crack first. A cove lets the membrane run round the corner as one continuous skin.
8. 8
   Seal around every pipe

   Seal the periphery of each pipe with polymer concrete made with ROOFCRETE AR 576. Fix a socket around the pipe, grout the socket with the same polymer concrete, and prove it with a ponding test.Why: A pipe passing through a slab leaves a gap that ordinary mortar shrinks away from. This is one of the commonest places for a leak to come back.

Bathroom waterproofing before tiling: the Armstrong sequence

Bathroom and toilet waterproofing in a new building is done on the bare slab, before tiling closes everything up. It is a sequence of treatments, not one coat at the end. Pipe sleeves, joints, the wall and floor junction and the floor itself each fail differently, so each gets its own step.

1. 1
   Clean the slab and walls

   Remove all loose material, dust and mortar droppings from the slab and the lower walls.Why: The membrane bonds to clean concrete, and mortar droppings and dust stop it.
2. 2
   Seal the pipe sleeves and bore holes

   These are the most common leak points in a new bathroom. Drill to the required width and depth, fix nozzles with RAPIDSTRONG QS 113 rapid-hardening putty, then grout under pressure with cement slurry dosed with RAPIDSTRONG GROUT ADMIX, RAPIDSTRONG GROUT PB 66 or ROOFEX GP, all free-flow, non-shrink additives. Ordinary cement slurry shrinks as it cures and leaves a gap around the pipe.Why: These are the commonest leak points in a bathroom, and the packing closes the gap through the slab.
3. 3
   Treat construction joints and cracks

   Cut a V-groove of at least 6 mm width and depth along every construction joint and crack, clean it and fill it with ROOFEXSEAL PU 212, a single-component polyurethane sealant.Why: A joint or crack moves, so a flexible sealant in a groove takes the movement.
4. 4
   Form the coving

   Chip off loose material at the wall and floor junction and clean it. Apply a bond coat of ROOFBOND SBR 401 mixed with cement, then lay a coved cement plaster fillet, up to 6 inches, in a 1:4 mix dosed with CONPROOF LW 200. The rounded profile removes the sharp corner where cracking starts.Why: A rounded fillet lets the membrane run round the corner as one skin.
5. 5
   Apply the waterproof coating in two coats

   Apply two coats over the floor and up the walls: 2,000 mm above finished floor level on the shower walls, 1,000 mm on the walls behind the basin, taps and bathing area, and at least 300 mm on every other wall. ROOFCOAT FLEXI 100 and ROOFBOND RFX PLUS 210 are flexible polymer cementitious coatings made to stretch with the slab. ROOFCOAT FLEXI 100 is mixed 1 litre to 2 kg of cement and 200 ml of water. ROOFBOND RFX PLUS 210 is a two-part pack of liquid and powder.Why: Two coats close the pinholes in the first, and the stated heights stop water running behind the coating at the walls.
6. 6
   Ponding test for 7 days

   Flood the coated floor and hold the water for 7 days. A coating can look finished and still leak. Ponding is the only test that tells the two apart, and it must happen before tiling.Why: A coating can look finished and still leak, and a 7-day flood test finds it before the tiles cover it.
7. 7
   Waterproof base plaster

   Over the coating, the floor and lower walls take a protective plaster about 20 mm thick, in a 1:3 cement and sand mix dosed with CONPROOF 500, broom finished, and cured for a minimum of 7 days.Why: The plaster protects the membrane from the tile work, and the tiles bond to it.
8. 8
   Seal pipes through the walls

   Where pipes pass through walls, fix the socket and grout around it with polymer concrete made with ROOFCRETE AR 576.Why: The socket and polymer concrete close the gap round each pipe, where water follows it down.
9. 9
   Tile and grout

   Fix the tiles with TILEX 351 PLUS or TILEX 350, and grout the wet zones with TILEX EPOXY STAIN FREE 100.Why: A wet-area adhesive and grout stay bonded and keep water out of the joints.

The companion article bathroom waterproofing: why the sequence matters explains each stage.

Bathroom leakage repair without breaking tiles

Bathroom leakage can be fixed without breaking tiles when the leak is through the tile joints, around the floor drain or around fittings, the tiles are firm, and the pipes have been ruled out. It cannot fix a leaking concealed pipe or failed waterproofing under loose tiles.

1. 1
   Dry the bathroom

   Stop using it for two to three days so the joints dry out. Grout and sealant do not bond in wet joints.Why: Grout and sealant do not bond to wet joints, so the bathroom is taken out of use to dry.
2. 2
   Rake out and clean the joints

   Remove the old grout from the floor joints and the lower wall joints, and clean out all loose material. TILEXKLEEN AC / DA / LC removes cement haze, grease and oil from tiles. Do not use an acid cleaner on the joints just before epoxy grouting.Why: New grout bonds to clean, firm joint sides, and old grout is porous.
3. 3
   Regrout with epoxy grout

   TILEX EPOXY STAIN FREE 100 is a three-part, 100% epoxy grout that is stain-free and resists chemicals. Mix all three parts together and add nothing else. Clean the tile surface within 30 to 40 minutes. Where a cement grout is preferred, use TILEX TG U 1600 for narrow joints or TILEX TG S 1500 for joints of 3 mm and above, mixed with TILEX URP ADMIX 73, the latex additive listed for wet area grouting.Why: Epoxy grout is non-absorbent and does not let water through the joints.
4. 4
   Seal around the drain, pipes and fixtures

   Clean the gap around the floor trap and every pipe that passes through a tile. Seal with ROOFEXSEAL PU 212, a polyurethane sealant that takes ±25% joint movement. Seal the wall and floor corner the same way.Why: The gap round the drain and pipes is where water goes down, and a flexible sealant takes the movement.
5. 5
   Cure, then test

   Let the grout and sealant cure. Cement grouts need 24 to 48 hours before they see water. Then flood the floor for a few hours and check the ceiling below.Why: Grout and sealant need to cure before they see water, and the test shows whether the repair has worked.

Sunken slab waterproofing: open the bathroom floor and rebuild

This is the full repair for a leaking bathroom. A sunken bathroom is a slab dropped below floor level and filled, with the trap and pipes buried inside. Once water gets into that filling it sits there and finds the weakest point in the slab. The rebuild removes everything down to the slab, fixes what is found, and builds the floor back in the right order.

1. 1
   Strip to the slab

   Remove the tiles, the bedding and any filling in the sunken floor. Clean the slab and the lower walls and remove all loose material. Repair any leaking pipe now and test it under pressure before going further.Why: The waterproofing goes on the slab itself, so the bedding and filling above it have to come off.
2. 2
   Seal the pipe sleeves and repair the slab

   Pack the gap around every pipe through the slab with a non-shrink grout made with RAPIDSTRONG GROUT ADMIX, dosed at 250 g per 50 kg of cement. Where water is still coming through, stop it first with RAPIDSTRONG PLUG 31. Rebuild damaged concrete with ROOFCRETE AR.Why: The gap round each pipe through the slab is a leak path and is closed with non-shrink grout.
3. 3
   Seal the joints and cracks

   Cut a V-groove of at least 6 mm along every construction joint and crack, clean it and fill it with ROOFEXSEAL PU 212.Why: Joints and cracks move, so they get a groove and a flexible sealant.
4. 4
   Form the cove

   Apply a bond coat of ROOFBOND SBR 401 and form a cove at the wall and floor junction in plaster dosed with CONPROOF LW 200.Why: A rounded fillet lets the membrane turn the corner without tearing.
5. 5
   Apply the waterproofing in two coats

   Coat the floor and take it up the walls. ROOFCOAT PU 2K is a polyurethane-cement membrane for under-tile wet areas, with nil water penetration at 5 bar. It covers 6 to 8 sq.ft per kg in two coats, with 3 to 4 hours between coats. ROOFCOAT FLEXI 100 and ROOFBOND RFX PLUS 210 are flexible polymer cementitious coatings used on sunken slabs, bathrooms, toilets and wet areas, in two coats.Why: Two coats close the pinholes, and the membrane is taken up the walls.
6. 6
   Test with water

   Let the membrane cure. ROOFCOAT PU 2K needs at least 3 to 5 days of air curing. Then block the drain, flood the floor and leave it. Check the ceiling below. Do not cover the membrane until it has passed.Why: A flood test finds any leak before the screed and tiles are laid over it.
7. 7
   Lay the screed

   Lay the screed to slope towards the drain, with CONPROOF LW 200 in the mix at 200 ml per 50 kg bag of cement, over a bond coat of ROOFBOND SBR 401. Any filling in a sunken floor should be clean, light material, not debris.Why: The screed protects the membrane, and falls to the drain.
8. 8
   Tile and grout

   Fix the tiles with TILEX 351 PLUS, a C2 TE adhesive listed for bathrooms, kitchens and wet areas, or TILEX 350. Grout with TILEX EPOXY STAIN FREE 100 and seal around the drain and fittings with ROOFEXSEAL PU 212.Why: A wet-area adhesive and grout complete the system and keep water out of the joints.

Water leaking from the bathroom to the flat below: stop it today

When water is coming through now, stop using the bathroom, find the source and stop the water first. These products are made to set against running water. A plug stops the water you can see. It does not replace the waterproofing.

Why a bathroom leak cannot wait

Repairing damp walls and ceilings after the bathroom leak

• Damp walls next to the bathroom. CONPROOF EP is a water-thinnable epoxy coating listed for toilet and kitchen walls and damp interior walls.
• Salt deposits. Treat with RAPIDSTRONG SALT FLUSHER before repainting.
• Repainting. SHINESHIELD Interior Emulsion is anti-fungal and is listed for high-humidity rooms.
• Concrete falling from the ceiling below. This is a structural repair. Follow the concrete crack repair guide.

Best waterproofing for a bathroom floor: choosing the coating under the tiles

The coating under the tiles is the main barrier in bathroom waterproofing. It goes on the slab, over the cove, and up the walls. Armstrong makes several, and each is a sound choice. They differ in chemistry and finish, and an Armstrong expert helps you pick.

How high up the bathroom walls

Standing water and splash do not stay on the floor, so the coating goes up the walls over the cove. The height depends on how much water each wall sees. All heights are measured from finished floor level.

Where the whole bathroom is small and the shower wets every wall, take all walls to 2,000 mm. Carry the coating across the door threshold as well, so water cannot pass under the frame. The cove at the wall and floor junction is formed first, and IS 3067 gives a 75 mm radius for that fillet.

Bathroom waterproofing chemicals and products by stage of work

How much waterproofing material for a 5 ft by 8 ft bathroom

Approximate quantities for the coating only. The floor is 40 sq.ft and a 300 mm upturn on all four walls adds about 26 sq.ft, so about 66 sq.ft in all. Taking one 5 ft shower wall up to 2,000 mm adds about 28 sq.ft more, so allow in proportion. Figures are worked out from each product's stated coverage. An Armstrong expert confirms the final quantity after seeing the site.

Standards and tests for bathroom waterproofing

• The ponding test: the coated floor is flooded and held, 7 days in Armstrong's sequence, before any tile is laid.
• IS 13182:1991 calls for impervious bathroom walls to at least 1 m, 2 m where a shower is provided, and at least 300 mm in water closets.
• IS 3067:1988 gives a 75 mm radius fillet at wall and floor junctions.
• CONPROOF LW 200 and CONPROOF 500 conform to IS 2645:2003 for integral waterproofing compounds.
• TILEX 351 PLUS is a C2 TE grade tile adhesive.
• ROOFCOAT PU 2K: nil water penetration at 5 bar.

Bathroom waterproofing material calculator

Enter the size of your bathroom and choose a coating to see how much waterproofing material it needs. The wall heights follow the table in Choosing the coating: 2,000 mm in the shower, 1,000 mm behind the basin and taps, 300 mm elsewhere. The calculator gives quantities only. Use the button at the end to talk to an Armstrong expert about your quantity.

Eight mistakes that make a bathroom leak again

1. Repairing before diagnosing. A new floor does not fix a leaking pipe.
2. Treating waterproofing as one coat at the end. Sleeves, joints and the cove each need their own step first.
3. Leaving pipe sleeves ungrouted. Ordinary cement slurry shrinks and leaves a gap around the pipe.
4. Stopping the coating at the floor. It has to turn up the walls over a cove.
5. Skipping the ponding test. Test the coating before the screed and tiles hide it.
6. Filling a sunken floor with debris. It holds water like a sponge.
7. Regrouting wet joints. The grout does not bond and the leak returns.
8. Repainting the ceiling below first. Paint over an active leak lasts a few weeks.

Bathroom waterproofing questions and answers