What the climate does to a slab here
Heat is the part people forget. A concrete terrace in Vijayawada or Guntur can sit in the sun above 45°C in May, then cool through the night. It expands and contracts every day, and over a few seasons that opens hairline cracks, especially along the parapet where the slab meets the wall at a right angle. When the rain comes, those cracks are the way in.
Then there is standing water. Very few terraces have enough slope to the outlet, so water collects in low spots and sits for hours or days. A coating that would survive a passing shower has to hold back ponded water for weeks in a heavy season. Along the coast, from Machilipatnam up to Visakhapatnam, cyclonic rain driven by wind adds pressure at parapets, outlets and joints.
The common methods, compared
Each of these has a place. None of them works if it is laid on a weak, cracked or dirty surface.
- Polymer-modified cementitious coatings: brushed on in two coats across each other, they bond well to concrete, tolerate a damp substrate better than most, and can be walked on once cured. This is what we use on most house terraces, finished with a protective top coat.
- Liquid-applied elastomeric coatings: more flexible, useful where a slab moves a lot, but they need a properly dry, sound surface and a protective layer where there is foot traffic.
- Bituminous and sheet membranes: common on large commercial roofs. They work when the laps and edges are done well; the edges, outlets and parapet upstands are where they usually fail.
- Terrace tiles or brick bat coba: these protect a waterproofing layer and help with heat, but tiles on their own are not waterproofing. Water gets through the joints and sits underneath. See open terrace tile waterproofing if your terrace is tiled.
Why preparation decides the result
Most failed terraces we see did not fail because the product was wrong. They failed because the coating was put over loose, flaking material, over an old coat that was already lifting, or over cracks that were never opened and filled. In the next monsoon the new coat comes away with whatever it was stuck to.
That is why our method spends most of its effort before any coating goes on: grinding the surface to strong concrete, pressure grouting cracks that go through the slab, chipping out and repacking hollow patches, V-grooving and sealing surface cracks, and packing a rounded cove at every parapet joint. The two coats and the top coat come last.
Details that matter in heavy rain
- Outlets: the coating has to be taken down into the rainwater outlet, and the outlet kept clear of leaves and debris.
- Parapet coving and upstands: the coating should run up the parapet, not stop at the floor line.
- Pipe and cable entries: anything passing through the slab needs to be sealed separately.
- Water tanks and solar frames: their bases and fixings are common leak points and need treating around, not just near.
- Slope: where water ponds badly, correcting the slope is sometimes worth doing before coating.
When to do the work
Coats need dry weather to cure, so the safest window across most of Andhra Pradesh is January to May. Inspect the terrace in the first months of the year, book the work early, and avoid leaving it until the first rains of June when every crew is busy and the weather is unreliable. Crack grouting and urgent repairs can be done at other times; we plan coating only for clear days.
If you are building new, the cheapest time to waterproof is before the floor finishes go on. See new building waterproofing. For an existing house, start with terrace waterproofing.