How we supply it: Waterproofing is arranged through a partner applicator who quotes, supplies, applies and bills it and pays us a referral commission. If the terrace needs a slope-correcting screed first, the M-Sand and 6 mm chips come from us so the applicator starts on a properly falling surface.
In one line: Waterproofing is a continuous layer of coating, membrane or admixture that stops water passing through a roof slab, wet-area floor or below-ground wall.
Which system for which surface
| Situation | Usually chosen | Why |
|---|---|---|
| Exposed terrace, no tiles | Acrylic or PU liquid membrane | Takes sun and foot traffic, easy to recoat |
| Terrace that will get tiles or screed | Polymer cementitious coat under the finish | Bonds to screed and tile adhesive |
| Bathroom and balcony floors | Polymer cementitious coat, up the walls | Thin, bonds well, sits under tiles |
| Large flat roof | APP or SBS bitumen sheet with protection | Thick, continuous, lapped membrane |
| Sump and new below-ground concrete | Crystalline admixture or coating | Seals pores inside the concrete |
What waterproofing has to do
Waterproofing is a continuous layer of coating, membrane or admixture that stops water passing through a roof slab, wet-area floor or below-ground wall. The word that matters is continuous: one gap at a pipe or corner defeats the rest.
A traditional weathering course of brick-bat concrete and clay tiles adds slope and insulation, but it is not a waterproofing layer by itself.
The five common systems
| System | How it goes on | Watch out for |
|---|---|---|
| Polymer cementitious (two-part) | Brushed in two coats | Needs a finish on top if walked on or exposed |
| Acrylic liquid membrane | Rolled, with fibre mesh at cracks | Recoat every few years; ponding shortens life |
| Polyurethane (PU) membrane | Rolled or sprayed | Needs a dry, well-prepared surface and UV top coat |
| APP or SBS bitumen sheet | Torch-applied, lapped sheets | Hot work; needs a protection layer |
| Crystalline | Admixture in concrete or brushed slurry | Will not bridge cracks wider than hairline |
Application steps that prevent leaks
- Repair cracks, honeycombing and pipe sleeves first; open cracks into a V and fill with polymer mortar.
- Form a sand-cement cove fillet where floor meets wall so the coating does not bridge a sharp corner.
- Prepare the surface as the system requires: damp for cementitious coats, dry for most liquid membranes.
- Apply the coats at the stated coverage, embedding fibre mesh at cracks, corners and outlets, and take the layer 150–300 mm up the walls.
- Seal around every pipe and drain with the system's collar or sealant detail.
- Flood test: block the outlets, pond 25–50 mm of water for 24–72 hours and inspect the ceiling below.
- Protect with screed or tiles where the system needs a cover.
Checks before tiles go down
- Get the data sheet's coverage per m² per coat and check the material delivered matches area × coverage × coats.
- Check product dates, and that both parts of two-component packs come from matching lots.
- Ask for a contrasting colour on the second coat so you can see coverage.
- Inspect upturns, outlets and pipe penetrations closely.
- Insist on the flood test and look at the ceiling below before any tiling.
Storing waterproofing materials
- Keep containers in shade; heat shortens pot life and can spoil liquid membranes.
- Keep the two parts of each kit together and mix whole kits in the supplied ratio.
- Store fibre mesh and bitumen rolls dry and flat, away from the welding area.
Mistakes that bring leaks back
- Coating a terrace that has no slope, so water ponds and attacks the membrane.
- Stopping the layer at floor level instead of turning it up the wall.
- Drilling through finished waterproofing to fix railings or pipes.
- Calling a painted cementitious coat on an exposed terrace a finished system.
- Skipping the flood test to save a day.