Terraces rarely leak in the middle of the slab. They leak at the edges — the parapet junction, the drain mouth, the tile line. That is because a terrace is a roof that people use: walked on, washed, furnished, tiled. Waterproofing one is therefore an edges-first job, and the middle is the easy part.
How a terrace differs from a plain roof
- Foot traffic: the finished surface must survive walking, dragging and washing — coatings are chosen and protected accordingly.
- Drainage in use: water must actually reach the outlets. A terrace that ponds is a terrace that will leak, whatever is coated on it.
- The parapet junction: the right-angle where floor meets wall moves with temperature and is the single most common leak line.
- Tiles: water under debonded tiles travels freely and exits far from where it entered.
(A bare, unused slab is a simpler problem — that sequence is in the roof guide.)
The sequence
1. Test the drainage before anything else
Pour water and watch. If it stands in corners or flows away from the outlets, the falls need correcting first — screed repair is waterproofing, even though no chemical is involved yet.
2. Deal with what is on the surface
Hollow and lifting tiles come up; sound surfaces are cleaned back hard. An old failed coating is removed, not coated over.
3. Repair cracks and open joints
Cracks are cut open and filled. The junction where the floor meets the parapet gets special attention — a coved fillet is formed so the waterproofing turns the corner in a curve, because coatings crack on sharp right angles.
4. Detail the drains and penetrations
Each drain mouth is sealed where the outlet pipe meets the slab, and every pipe or railing post through the surface is collared. These ten-minute details are where five-year leaks are prevented.
5. Coat — floor and parapet together
The waterproof coating covers the floor and continues up the parapet walls well above splash height. Stopping at the floor line leaves the junction — the most likely failure — half-protected.
6. Protect the coating for the life it will lead
A terrace in daily use needs its coating protected — with a wearing layer or tiling laid per the system's specification — so feet and furniture meet the protection, not the membrane.
The habits that keep it watertight
- Keep drain mouths clear — a blocked outlet turns a terrace into a pond every monsoon
- Do not let heavy planters sit in standing water against the parapet
- Recheck the junction line each year before the rains
- Treat new cracks when they are hairlines, not after they map
Frequently asked questions
Can I waterproof over existing tiles?
Only if every tile is sound and bonded — and even then the junctions and grout lines govern. Hollow tiles must come up; there is no coating that fixes a debonded layer beneath itself.
The leak shows in the room below, but the terrace looks fine. How?
Water travels between layers. A hairline at the parapet can exit metres away. This is why diagnosis starts at the edges and drains, not above the stain — and why photographs of the corners and outlets tell us more than pictures of the stain.
When should it be done?
Dry season, finished well before the monsoon, with cure time in hand. Emergency monsoon patching exists, but it is triage, not treatment.