Is waterproofing a must for a house in Kerala?

Concrete is full of tiny pores that water creeps through, and it cracks. Fine cracks open as fresh concrete dries and shrinks, and again as a slab heats in the sun and cools in the rain. Water finds these cracks, the joints where one pour meets the next, and every gap around a pipe.

You may have heard that good concrete hardly absorbs water, and a well-made slab does absorb little. But leaks rarely come through the middle of a good slab. They come through the cracks, joints and corners, and every slab has those.

The corner where a terrace floor meets its parapet wall is the most common place a leak starts. Drain outlets and pipe openings come next.

What follows is slow. A damp patch on a ceiling. Paint that bubbles and peels, and white, salty marks on a wall.

Over the years, water that reaches the steel bars inside the slab makes them rust, and rust swells and cracks the concrete around it.

It always starts small.

Kerala gets rain from two monsoons. The south-west monsoon runs from June to September, and the north-east monsoon follows in October and November. Add the storms of April and May, and a roof in Trivandrum sees rain for months at a stretch, often heavy and driven by wind.

The air rarely dries out between showers, so damp has time to travel. Heat plays its part too.

A slab that bakes on an April afternoon and then cools fast in an evening shower stretches and squeezes every day. That daily movement is what opens fine cracks.

Every surface that meets water, whether from above, from inside or from the ground. In a typical Kerala home, that means eight places. The Bureau of Indian Standards names bathrooms, kitchens, toilets, balconies, verandahs and sunshades as the wet areas most open to leaks (IS 13182).

1. Terrace and roof slabIt takes the full force of the rain, and water stands on it if the slope is poor. Most leaks start here.
2. SunshadesRain lands on top, and water sits where the sunshade meets the wall.
3. Balconies and open sit-outsOpen to the weather, with a door into the house right at floor level.
4. BathroomsWater every day, under tiles. Tiles and grout are not waterproof on their own.
5. Kitchen and utility areaWet floors around the sink and the washing area.
6. Water tanks and sumpsWater presses on the walls all day, every day.
7. The plinthDamp can rise from the ground into the walls unless it is stopped where the walls meet the ground.
8. Slabs under sloped tile roofsCovered does not mean dry. Tiles can shift or crack in a storm. Wind drives rain under them. And the slab sits open to the weather for weeks while the roof goes up.

There is no single best method. The right one depends on where it goes and what it will face: sun, standing water, daily use or pressure from a tank. Here is what each does.

Good waterproofing is mostly about the edges and the order of work. Take this checklist on your next site visit.

1. The floor slopes to the drain.No coating survives water that stands for weeks.
2. The coat turns up the wall.About 30 cm on terraces and in bathrooms, 15 cm on sunshades.
3. Corners and pipes come first.Corners get a rounded fillet and pipes get a sealed collar before the main coat.
4. The surface is clean, dry and primed.Coating over dust or damp wastes the coating.
5. Two coats, not one.Each coat is left to cure before the next.
6. A protective layer goes on top.A screed, tiles or a cool-roof finish shields the coat from sun and feet.
7. A ponding test before tiling.Block the drains, fill about 5 cm of water, wait 48 hours and check every ceiling below.
8. It all happens before tiles and flooring.Never after.

48 hours of standing water. If the ceiling below stays dry, the tiles can go down.

Now, by a wide margin. During construction, waterproofing goes onto a bare, clean surface in a few days.

After a leak, the tiles, screed and plaster above it have to come off first. Then someone has to find where the water is really getting in, and every layer has to be redone.

There is also the cost nobody bills you for: a stained ceiling in the bedroom, and a monsoon spent putting buckets under it.

A terrace you can use, not one you worry about. Trivandrum.

We list every waterproofed area in writing, with the method and how far the coat turns up the wall. You know exactly what is protected before the first monsoon. Rzianz has delivered more than 300 homes, with over 25 years of experience in Kerala.

Terraces, sunshades and exposed slabs get a chemical waterproofing coat turned up the walls, then a protective screed or tiled finish on top.

Bathrooms are waterproofed under the screed and tiles, 30 cm up the walls, before the Jaquar, Grohe or Kohler fittings go in. We use Dr. Fixit, Fosroc and Berger systems on our homes in Trivandrum.

1. Tell us about your home.Send us your plot, your plans or your builder’s estimate on WhatsApp.
2. See every area, in writing.We show you how each part of your home will be waterproofed, and with what.
3. We build it that way.The same team that drew your home builds it, to what was written down.

For other ways a build can go wrong, read our guide to the most common building mistakes in Kerala. Holding a builder’s estimate already? Our free BOQ audit shows whether waterproofing is in it at all.