Materials & comparisons
Cementitious vs PU vs Torch-On Waterproofing: Which System for Which Surface
Waterproofing is not one product. Matching the system to the surface — and to whether it will be tiled, walked on or exposed to sun — is what decides how long it lasts.
Written by Renovix Home Services · Published
The short answer
Which waterproofing system should I use — cementitious, PU or torch-on?
Use cementitious waterproofing under tiles in wet areas such as bathrooms, because it bonds to the screed and tile adhesive sticks to it. Use a PU or acrylic liquid membrane on exposed surfaces that flex and sit in the sun, such as balconies and some flat roofs, because it stays elastic. Use torch-on bituminous membrane on larger flat roofs that need a thick, robust, fully sealed sheet. PU injection is not a membrane at all — it is a targeted repair that seals a specific crack or ingress point from within the concrete. Our rates for each are below.
Key points
- Cementitious systems are the standard under tiles — they bond to the substrate and are tileable.
- PU and acrylic liquid membranes stay flexible, so they handle sun-exposed surfaces that move.
- Torch-on membrane is a thick sheet system best suited to larger flat roof areas.
- PU injection fixes a specific leak path; it does not waterproof a whole surface.
- Preparation and detailing — falls, upstands, corners, floor traps — matter more than the brand of product.
The systems compared
| System | How it works | Where it belongs | Honest limits |
|---|---|---|---|
| Cementitious | Cement-based slurry brushed or trowelled onto the screed, bonding to it | Bathrooms, wet kitchens, yards, anywhere that will be tiled over | Rigid — it does not bridge a moving crack, and it is not designed to sit exposed to sunlight |
| PU / acrylic liquid membrane | Liquid coating that cures into a continuous elastic film | Balconies, exposed slabs, some flat roofs, planter boxes | Needs a clean, dry, properly prepared base; UV performance depends on the product and on being applied at the right thickness |
| Torch-on bituminous membrane | Rolled bituminous sheet melted onto the substrate with a torch | Larger flat roofs and areas needing a thick, robust sheet | Requires open-flame work and skilled lapping; not suited to small, intricate internal areas |
| PU injection | Resin injected into a crack, expanding to seal the water path | A specific, identified leak point — a slab crack, a construction joint, a ceiling ingress | Repairs one path only; it is not a substitute for waterproofing a surface |
| External wall coating | Elastomeric coating applied to a prepared external wall | Wall seepage and rain-driven damp on the outside face | Only works if the source is the wall face — not if water is arriving from a leaking pipe or roof |
Choosing by surface
- Bathroom floor and wet walls: cementitious membrane over a properly falled screed, flood tested, then tiled. This is the standard for a reason — the tile adhesive needs something to bond to.
- Balcony: a flexible liquid membrane where the surface is exposed and moves with the heat, or a cementitious system if it will be tiled over. The critical detail is the upstand at the door threshold.
- Flat roof: torch-on for larger areas needing a robust sheet; liquid membrane where the geometry is complicated with many upstands and penetrations.
- External wall with seepage: an elastomeric coating after the cracks are treated — but only once you are sure the water is coming through the wall face and not from a pipe or the roof above.
- A single identified crack leaking into a ceiling: PU injection, which seals the path without opening the whole slab.
Our waterproofing rates
These are the published starting rates for the waterproofing scopes we carry out. Which one applies depends on the surface and on whether existing finishes have to come off first.
| Bathroom Waterproofing with Tile Hack & RelayFull bathroom re-waterproofing: hack existing tiles, apply cementitious or PU membrane, flood test, screed and relay new tiles. | RM1500per bathroom |
|---|---|
| Flat Roof WaterproofingWaterproofing for flat roof, roof terrace or car porch using torch-on membrane or PU liquid membrane. | RM8per sqft |
| Balcony & Yard WaterproofingWaterproofing for tiled balcony or yard, including tile hack, membrane and re-tile or screed. | RM800per job |
| Wall Seepage & External Wall CoatingWater-repellent coating for external wall showing damp, efflorescence or seepage. | RM6per sqft |
| PU Injection for Ceiling LeakPU injection grouting to seal active leak at ceiling or wall crack. Flat rate per bathroom ceiling where applicable. | RM350per job |
Rates below come from our published price list and are starting prices — the final quotation depends on the actual site condition and scope.
Prices start from the stated amount. Final quotation depends on actual site condition, scope, materials, accessibility and installation requirements.
How a proper waterproofing job runs
Find out where the water is actually coming from
Coating the wrong surface is the most expensive mistake in this trade. A stain on a ceiling can come from the bathroom above, a roof, a façade or a pipe, and each has a different answer.
Prepare the substrate
Loose material is removed, cracks are treated and the surface is cleaned. No membrane bonds to dust, laitance or a damp, contaminated base.
Correct the falls
Water has to run to the outlet. Where the screed falls the wrong way or ponds, that is corrected before waterproofing, not compensated for afterwards.
Apply the system to the right thickness
Coats are applied in the specified number and direction, with corners, upstands and pipe penetrations detailed properly — these are where leaks start.
Flood test
The area is filled and left to stand, and the space below is checked. A membrane that has not been tested is an assumption, not a result.
Protect and finish
Tiles, screed or a protective layer go over the membrane where the surface will be used. An unprotected membrane in a trafficked area wears through.
How long waterproofing lasts
Any honest answer here is a range, not a number. A tiled bathroom membrane that was properly detailed and is protected by the tile above it lasts a long time; an exposed coating on a balcony that bakes in the sun and is never recoated has a much shorter life. What shortens all of them is the same short list: poor preparation, insufficient thickness, missing upstands, unsealed penetrations, and standing water that never drains. We do not publish a lifespan figure for any system because the substrate and the detailing decide it, not the tin.
- Keep floor traps and roof outlets clear — standing water is the enemy of every system.
- Check the silicone at the shower corners and floor-to-wall junction once a year and replace it when it lifts or discolours.
- On an exposed balcony or flat roof, inspect the coating after each rainy season for cracking, blistering or thin spots.
- Fix a small crack in a coating early. Water that gets under a membrane spreads sideways and lifts far more than the crack itself.
Tell us which surface is leaking, what is above and below it, and whether the problem follows rain or follows water use inside the home. That is what determines the system — and we would rather diagnose it correctly than sell you the wrong membrane.
FAQs
Questions people ask about this
Can I apply PU coating over my bathroom tiles instead of hacking?+
It is not the right solution for a bathroom floor. The membrane belongs under the tiles, bonded to the screed, so a coating over the finished tile surface is walked on, worn through and interrupted by every grout line and the floor trap. Where hacking is not possible, the honest alternative is to identify the specific leak path and treat that instead.
Is torch-on better than a liquid membrane?+
Neither is better in general — they suit different surfaces. Torch-on gives a thick, robust sheet that works well over larger flat roof areas. Liquid membranes are seamless and easier to detail around many upstands, pipes and awkward corners.
What is a flood test and why does it matter?+
The waterproofed area is sealed, filled with water and left to stand while the space below is monitored. It is the only way to prove the membrane works before it is covered with tiles. Skipping it means the first test is your neighbour's ceiling.
Do I need to waterproof a balcony that is already tiled?+
Only if it is leaking or the detailing has failed. If water is reaching the room below or the ceiling under it, the membrane beneath those tiles is either absent or breached, and a surface coating over old tiles is at best a temporary measure.
Will waterproofing fix my damp wall?+
It depends on why the wall is damp. If rain is driving through the external face, an external coating after crack treatment is the right answer. If a pipe is leaking inside the wall, or water is tracking down from a roof or balcony above, coating the wall changes nothing — the source has to be found first.