How-To Guide · Bathrooms
Bathroom Leakage Repair Guide: Find the Leak, Then Fix It Once
A leaking bathroom shows up somewhere else: a damp patch on the ceiling below, peeling paint on the bedroom wall, a stain near the door. This guide shows how to find where the water is escaping, when it can be fixed without breaking the tiles, and when the floor has to be opened and waterproofed again. The same steps apply to a toilet or washroom. Every Armstrong product for bathroom repair is listed at the end.
Six places a bathroom leaks
Water in a bathroom has many ways out. Most leaks come from one of these six.
- Tile joints. Cement grout cracks and wears. Water passes through the joints and sits under the tiles.
- The floor drain (nahani trap). The gap around the floor trap is the lowest point of the floor, so any water under the tiles collects there.
- A pipe or fitting inside the wall. A weeping joint behind the tiles wets the wall from within.
- The wall and floor junction. The corner moves and cracks, and water running down the wall enters there.
- The waste pipe through the slab. The hole around the pipe was never sealed properly, or the pipe joint below has opened.
- The door threshold. Water escapes under the door frame into the next room.
Find your leak
Spend a day on diagnosis before spending anything on repair. What you see and when you see it point to the source.
| What you see | Likely source | How to check |
|---|---|---|
| A damp patch on the ceiling below that grows after baths | The floor: tile joints, the drain or failed waterproofing | Dry the floor. Block the drain and flood the floor with a little water for a few hours. If the patch grows, the floor is leaking. |
| Dripping below even when nobody has used the bathroom | A water supply pipe under pressure | Close every tap in the house and watch the meter, or have a plumber pressure-test the line. |
| Dripping below only when the basin, shower or WC is used | A waste pipe, trap or its joint | Run one fixture at a time and watch from below. |
| Damp or peeling paint on the other side of the shower wall | Wall tile joints or a fitting inside the wall | Keep the shower off that wall for a few days. If it dries, the joints are leaking. If not, suspect the pipe. |
| Wet floor or skirting outside the bathroom door | The threshold or a floor that slopes the wrong way | Pour water near the door and watch where it runs. |
| Hollow sound when you tap floor tiles | Water trapped under loose tiles | Tap across the floor with a coin. Mark the hollow areas. |
For leaks elsewhere in the house, see the full water leakage, dampness and efflorescence guide.
Why a bathroom leak cannot wait
A bathroom is used every day, so the leak is fed every day. The slab under it never dries. That makes a bathroom leak faster and more damaging than a roof leak that only runs in the monsoon.
In a flat, the damage is also in someone else's home. Fixing the leak early means repairing one home, not two.
Two levels of repair
The right repair is the smallest one that reaches the real source. Start at level 1 only if the diagnosis supports it.
Level 1
Regrout and seal
No tiles broken. For leaks through joints, around the drain and around fittings, where the tiles are firm.
Works when tiles are sound, the damp follows bathroom use, and pipes have been ruled out.
Level 2
Open the floor and rebuild
Tiles and filling removed. The slab is repaired, waterproofed, tested with water and tiled again.
Needed when tiles are loose or hollow, a concealed pipe leaks, or an earlier repair has failed.
Be wary of any promise that every bathroom leak can be fixed without breaking tiles. Regrouting cannot repair a leaking pipe or a membrane that has failed under the floor.
Level 1: repair without breaking tiles
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.
Rake out and clean the joints
Remove the old grout from the floor joints and the lower wall joints. 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.
Regrout with epoxy
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 30–40 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.
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.
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.
Level 2: open the floor and rebuild
This is the full repair. It removes everything down to the slab, fixes what is found, and builds the floor back in the right order. The order matters as much as the products.
- 5 Tiles with epoxy grout
- 4 Tile adhesive
- 3 Screed with integral waterproofing compound, laid to slope
- 2 Waterproof membrane, turned up the walls over a cove
- 1 Repaired slab with sealed pipe sleeves and a bond coat
Figure 2. A rebuilt bathroom floor, shown top to bottom.
Strip to the slab
Remove the tiles, the bedding and any filling in a sunken floor. Clean the slab and the lower walls. Repair any leaking pipe now and test it under pressure before going further.
Seal the pipe sleeves and repair cracks
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.
Form the cove and apply the membrane
Form a cove at the wall and floor junction. Then apply the membrane in two coats 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 6–8 sq.ft per kg in two coats, with 2–6 hours between coats. ROOFBOND RFX PLUS 210 is listed for sunken slabs, ROOFCOAT FLEXI 100 for bathrooms and wet areas, and ROOFEX 2K 711 for wet areas and balconies. The coving and two-coat coating steps are explained in the new-building article.
Test with water
Let the membrane cure. ROOFCOAT PU 2K needs at least 3–5 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.
Lay the screed
Lay the screed to slope towards the drain, with an integral compound in the mix: CONPROOF LW 200 at 125–200 ml per 50 kg bag of cement. Use ROOFBOND SBR 401 as the bond coat.
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.
The companion article bathroom waterproofing: why the sequence matters covers each of these stages in detail.
Stopping an active leak today
When water is coming through now, stop it first and plan the proper repair after. These products are made to set against running water.
| Product | What it is | How it is used |
|---|---|---|
| RAPIDSTRONG PLUG 31 | Rapid plugging compound that sets in 30 seconds | Mixed to a dough, pressed into the leak point and held for 30 seconds. |
| WONDERSEAL PLUG XL | Hydraulic plugging compound that sets in the presence of water and expands as it sets | Pressed in as a stiff putty and held for 30–60 seconds, or forced in as dry powder. |
| RAPIDSTRONG QS 113 | Quick setting and waterproofing compound | Added to cement at 500 ml to 2 litres per 50 kg bag to make a fast-setting plugging mortar. |
| RAPIDSTRONG GROUT PU | Water-reactive polyurethane injection grout that gels in 36–48 seconds | Injected by an applicator through packers into a leaking crack or joint. |
A plug stops the water you can see. It does not replace the waterproofing. Follow it with the repair that matches the source.
Repairing the damage outside the bathroom
Once the leak is fixed and the structure has dried, the stained ceiling and walls can be put right.
- 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 anti-algae, and is listed for high-humidity rooms.
- Concrete falling from the ceiling below. This is a structural repair. Follow the concrete crack repair guide.
The waterproof paint guide covers the full wall build-up.
Seven common mistakes
- Repairing before diagnosing. A new floor does not fix a leaking pipe.
- Regrouting wet joints. The grout does not bond and the leak returns.
- Ignoring the drain. The gap around the floor trap is the lowest point of the floor and is easy to miss.
- Stopping the membrane at the floor. It has to turn up the walls.
- Skipping the water test. Test the membrane before the screed and tiles hide it.
- Using the bathroom too soon. Membranes, adhesives and grouts each need their curing time.
- Repainting the ceiling below first. Paint over an active leak lasts a few weeks.
Why Armstrong for bathrooms
A bathroom repair uses more kinds of product than any other job in a home: a plug, a grout, a sealant, a membrane, a screed admixture, a tile adhesive and a paint. Armstrong makes all of them, so every layer is from one manufacturer and made to work with the next.
- A repair for every level. From a tube of sealant to a full strip and rebuild, the products are in the range.
- Membranes made to go under tiles. Polyurethane-cement, polymer cementitious and crystalline, with stated figures such as nil water penetration at 5 bar.
- Joints that do not leak again. A 100% epoxy grout and a polyurethane sealant that takes ±25% movement.
- Quality you can check. Armstrong Chemicals is an ISO 9001:2015 certified company, and each product page gives its tested figures.
All Armstrong bathroom repair products
Every Armstrong product used in bathroom leak repair, grouped by the job it does. Select a product for its full data, coverage and application steps.
Stop an active leak Sets against running water
- RAPIDSTRONG PLUG 31Rapid plugging compound. Sets in 30 seconds.
- WONDERSEAL PLUG XLHydraulic plugging compound that sets in the presence of water.
- RAPIDSTRONG QS 113Quick setting and waterproofing compound for fast-setting plugging mortar.
- RAPIDSTRONG GROUT PUWater-reactive polyurethane injection grout. Gels in 36–48 seconds.
- RAPIDSTRONG GROUT PFC 79Water-reactive polyurethane injection resin for active seepage zones.
Grouts, sealants and cleaners For repair without breaking tiles
- TILEX EPOXY STAIN FREE 100Three-part 100% epoxy tile grout. Stain-free.
- TILEX TG U 1600Unsanded polymer cement grout for narrow joints in bathrooms and kitchens.
- TILEX TG S 1500Sanded polymer cement grout for joints of 3 mm and above.
- TILEX URP ADMIX 73Latex additive for wet area tile grouting.
- TILEX SUPERLATEX 333Latex admixture for cement grout. 200–250 ml per 50 kg bag of cement.
- ROOFEXSEAL PU 212Polyurethane sealant for pipes, fixtures and corners. ±25% movement.
- TILEXKLEEN AC / DA / LCCleaners for cement haze, grease and oil on tiles.
Waterproof membranes The layer under the tiles
- ROOFCOAT PU 2KPolyurethane-cement membrane for under-tile wet areas. Nil water penetration at 5 bar.
- ROOFCOAT FLEXI 100Acrylic polymer cementitious coating for bathrooms and wet areas.
- ROOFBOND RFX PLUS 210Reinforced flexible coating listed for sunken slabs.
- ROOFEX 2K 711Two-component crystalline coating for wet areas.
- RAINSEAL BMW 250Acrylic-bituminous coating listed for bathrooms and toilets. 500% elongation.
- ROOFCRETE URPSBR latex for waterproofing toilets and bathrooms.
Slab repair, bonding and screed Under the membrane and over it
- RAPIDSTRONG GROUT ADMIXNon-shrink grout admixture. 250 g per 50 kg of cement.
- ROOFCRETE ARPre-packed polymer repair mortar for slab repairs.
- ROOFBOND SBR 401SBR latex bond coat and waterproofing slurry.
- CONPROOF LW 200Integral waterproofing admixture. 125–200 ml per 50 kg bag of cement.
- CONPROOF 500Integral compound for plaster and screeds. 500 ml per 50 kg bag.
- CONPROOF No. 1Integral compound listed for bathrooms and toilets. 100 ml per 50 kg bag.
Tile adhesives To fix the new tiles
- TILEX 351 PLUSC2 TE adhesive for bathrooms, kitchens and wet areas.
- TILEX 350Thin-set adhesive for ceramic and vitrified tiles in bathrooms and kitchens.
- TILEX 353Elastic polymer adhesive for natural stone and large format tiles.
- TILEX 521Two-component flexible adhesive for tile-on-tile work.
- TILEX 512Polyurethane hybrid adhesive for drywall, gypsum boards and plywood.
Walls and ceilings after the leak Once the structure is dry
- CONPROOF EPWater-thinnable epoxy coating for toilet, kitchen and damp interior walls.
- RAPIDSTRONG SALT FLUSHERAnti-efflorescence primer for salt-affected walls.
- SHINESHIELD Interior EmulsionAnti-fungal interior emulsion for high-humidity rooms.