Waterproofing Chemicals: Which Type for Terrace, Bathroom, Basement and Water Tank

Which waterproofing chemical suits which part of the house?

Start with this table. It gives the chemical family that fits each location and the reason it fits. The sections below explain each row.

Table 1: Waterproofing chemical by location

The pattern is simple. Where the surface moves and sees sun, you need stretch. Where it is covered and wet, you need adhesion and a dense film. Where water pushes from behind, you need a treatment that can take pressure.

What are the types of waterproofing chemicals?

Shop counters in India sell six broad families. The names on the tins vary, but almost every product falls into one of these.

Integral waterproofing compounds are liquids or powders mixed into concrete, plaster or mortar while it is being made. They do not form a coat. They make the concrete itself less permeable, which means water passes through it more slowly. The Indian Standard for them, IS 2645, requires a test cylinder made with the compound to let through less than half the water of the same mix without it, and caps the dose at 3 per cent of the cement’s weight. They belong to the admixture family, covered in our guide to concrete admixture types.

Cementitious coatings are two-part products: a liquid polymer and a cement-based powder, mixed on site into a slurry and brushed on in two coats. Sika’s India data sheet for SikaTop-107 Seal IN, a typical example, gives about 1.5 kg per square metre per coat and a finished thickness of about 1.2 to 1.5 mm in two coats. They bond well to damp concrete. They do not stretch much. The same sheet lists elongation at break (how far the film stretches before it tears) of about 10 per cent, so they bridge only hairline cracks.

Acrylic elastomeric coatings are ready-to-use liquids that dry into a rubbery film. Dr Fixit lists its Roofseal range at 300 per cent elongation with crack bridging of up to 2 mm, which is why this family is sold for exposed terraces. A light colour also reflects sunlight; the maker claims a roof surface up to 10°C cooler.

Polyurethane (PU) coatings are liquid membranes that cure into a tough, very flexible film. They suit terraces with movement and foot traffic, but many PU products need a UV-stable top coat when left exposed to the sun. Read the data sheet before leaving one bare.

Bituminous products are the oldest family: hot or cold applied bitumen coatings, and bitumen felts laid in layers. India has codes for them, including IS 1346 for waterproofing roofs with bitumen felts. Bitumen softens in strong sun, so on houses it now earns its place mostly below ground, on the outer face of basement and foundation walls.

Crystalline treatments are cement-based slurries whose chemicals react with water and free lime inside the concrete to grow crystals in its pores and fine cracks. Because they work inside the concrete, they can be applied from the dry side of a wall, which makes them useful on basements and sumps where the outside face cannot be reached.

Which waterproofing chemical is best for a terrace or roof?

For an open terrace that will stay bare, an elastomeric acrylic or a PU coating is the right family. The roof slab expands in the afternoon and shrinks at night, and every crack opens and closes with it. A coat that stretches 150 to 300 per cent rides that movement. A rigid cement coat at 10 per cent does not, so it cracks along the same lines as the slab.

If the terrace will get tiles, a screed or a brick-bat layer on top, the coat is protected from the sun and a flexible cementitious coating is the usual choice. Dr Fixit’s own note on its Pidifin 2K coating says the membrane must not take regular foot traffic and needs protection, which is exactly what tiles give it.

The chemical is only half the job. IS 3067, the Bureau of Indian Standards code for preparing buildings for waterproofing, sets out the roof details that decide whether any product works:

• Clear cracks wider than a hairline are cut to a V, cleaned and filled flush before any coat goes on.
• Moss, fungus and dust are removed by wire brushing.
• A rounded fillet of 75 mm radius is built where the roof meets the parapet, so the coat turns the corner without a sharp fold.
• On parapets taller than 450 mm, the treatment is tucked into a groove at least 150 mm above roof level, 75 mm wide and 65 mm deep. On lower parapets it is carried right over the top.
• Drain mouths are widened to two and a half times the pipe diameter and rounded, so water does not sit around the outlet.

The parapet junction, the drain mouth and the pipe through the slab get most of the code’s attention for a reason: they are where a coat has to fold, stop or seal around something. A perfect coat on the flat area cannot make up for a bare corner.

Figure 1: Layers of a tiled terrace, top to bottom

On a terrace left bare, the top two layers are dropped and the waterproofing coat itself becomes the finished surface, so it must be a UV-resistant elastomeric or PU product.

Which waterproofing is used in a bathroom?

Bathrooms use a flexible cementitious or acrylic-cement coating, applied to the floor and carried up the walls, then covered with tiles. The tiles and grout are not the waterproofing. Water gets through grout lines every day; the coat underneath is what stops it reaching the slab and the ceiling of the room below.

Dr Fixit, for example, sells three products for this job: Bathseal (single-component cementitious), Fastflex (two-component, fast-setting) and Pidifin 2K (two-component acrylic-cement). Its Bathseal Select is a ready-to-use liquid membrane listed at over 250 per cent elongation with crack bridging up to 3 mm.

Three points decide whether a bathroom stays dry:

• The sunken slab. Many Indian bathrooms have a lowered slab filled with brick bats or concrete to hide the pipes. The coat goes on the bottom and sides of that sunken slab before the filling, not only on the final floor.
• Pipes and the floor trap. Every pipe that passes through the slab or wall needs a collar or a filled joint first, as IS 3067 sets out for pipes through roofs. The coat is then taken over it.
• Cure before tiling. SikaTop-107’s data sheet asks for about 3 days before plaster or screed goes over the coat. Tiling the next morning traps a coat that has not finished curing.

How do you waterproof a basement?

A basement is the hardest case, because groundwater pushes against the wall rather than just running over it. The best time and place to treat it is from the outside, while the building is going up. IS 3067 calls this external tanking and says it should be the method for all new structures.

The code is specific about the site work:

• Do it in the dry season, when the water table is at its lowest, and keep pumping groundwater out until the treatment is done.
• Leave a working space of at least 600 mm all round the basement for applying the treatment.
• Lay a lean concrete base slab that projects at least 250 mm beyond the outer face of the structural walls, and turn the treatment up the walls over a 75 mm radius fillet.
• Avoid construction joints in basement walls as far as possible.

That 600 mm working space is dug by machine on almost every job. A backhoe loader such as the JCB 3DX handles the excavation for a house basement; compare other backhoe loader models for the size of your dig. Budget the extra width at the start. A basement dug tight to the wall line leaves no room to apply anything from outside.

On the outer face, bituminous coatings and membranes are common. For an existing building, where the outside cannot be reached, IS 3067 allows internal tanking: the walls are hacked rough, a fillet is built at every corner, and the treatment goes on the inside of the walls and floor. Cementitious and crystalline products are the usual choice here, because they bond to damp concrete and resist water pressure from behind. Pidifin 2K, for instance, is listed as holding 10 m of water pressure without leaking.

The code also allows gunite, mortar sprayed at high speed onto the wall, for damp-proofing. Joints in masonry are raked 12 mm deep first so the sprayed layer grips. The process is explained in our guide to shotcrete and guniting.

Which waterproofing is safe for a drinking-water tank?

Only a product the maker certifies for potable water contact. Ask to see the certificate. SikaTop-107 Seal IN, for example, lists a CFTRI (Central Food Technological Research Institute, Mysuru) certificate for repeated contact with water and food under the US FDA rule 175.300, and an SGS certificate showing freedom from acute lethal toxicity under IS 6582. Dr Fixit states that Pidifin 2K is CFTRI approved for water tanks. A product without such a certificate stays off the inside of a tank you drink from, however well it works on a roof.

The tank itself matters more than the coat. IS 3370 (Part 1), the Indian code for concrete structures that store liquids, sets M30 as the minimum grade for reinforced concrete tanks, with M25 allowed for tanks up to 50 cubic metres where M30 is hard to make, except in coastal areas. Dense, well-compacted concrete is the first waterproofing layer.

IS 3370 also gives the test every new tank should pass before it is coated or put into use:

Table 2: Water-tightness tests in IS 3370 (Part 1)

If the level is still falling but more slowly each day, the code allows the test to run another 7 days. Once the coat is on, respect its cure time before filling. Sika’s sheet asks for about 7 days before water immersion.

Can waterproofing chemical be mixed with cement?

Yes, but only the integral type, and it is not a replacement for a coat. An integral compound goes into the concrete or plaster mix at the maker’s dose. Dr Fixit, for example, prints 200 ml of its Pidiproof LW+ per 50 kg bag of cement. It reduces how much water passes through the concrete. It does nothing for a crack that opens later, because a crack is a gap, not a pore.

So the two work together. The compound makes the slab and plaster less porous; the surface coat bridges the cracks and seals the joints. On a roof slab or a tank wall, use both.

Neither works on poor concrete. Too much water in the mix, poor compaction and short curing leave a porous slab that no chemical fully seals. A self-loading concrete mixer such as the AJAX ARGO 4500 carries on-board weighing with a load cell, so every batch going into a roof pour is measured the same way and the water content stays steady. After the pour, keep the concrete moist for the full period; where water curing is hard, a curing compound holds the moisture in. Choosing the right cement for the slab is covered in our guide to the best cement for each job.

Why does waterproofing fail?

When a new coat leaks within a year or two, look for these causes first:

1. Corners and joints left bare. No fillet at the parapet, no collar at the pipe, an untreated drain mouth. Water finds the one gap.
2. Coat too thin. A cementitious coat sold at about 1.5 kg per square metre per coat, spread at half that to make the pack go further, gives half the film. Count the packs used against the area.
3. Wrong family for the place. A rigid coat on a bare roof, or a coat not rated for traffic left as a walking surface.
4. Dirty or loose surface. Coats bond to sound concrete, not to dust, laitance (the weak powdery skin on fresh concrete) or old flaking paint.
5. Covered or filled too soon. Tiles laid, or a tank filled, before the coat has cured.

A simple check after any terrace job is the same flood test IS 3370 sets for tank roofs: block the drains, hold about 25 mm of water on the roof for 24 hours, and look at the ceiling below. Damp patches mean a gap to find before the monsoon does.

Planning the pour, the dig and the coat together

Waterproofing is cheapest while the building is going up, because the slab, the basement walls and the tank are all open. Plan the integral compound into the concrete, the working space into the basement dig and the cure time into the tiling schedule.

Planning a slab or a tank? Compare concrete mixer models and prices and connect with a dealer near you. For the companies that make these chemicals, see our list of construction chemical companies in India, and for the rest of what goes into a building, the building materials guides. The roof and basement details quoted on this page are published as IS 3067:1988, Code of Practice for General Design Details and Preparatory Work for Damp-Proofing and Water-Proofing of Buildings, and the tank tests as IS 3370 (Part 1):2009, Concrete Structures for Storage of Liquids.

Prices, specifications and features are indicative, vary by variant, location and date, and should always be confirmed with the official OEM or authorised dealer before any purchase decision. DesiMachines is not liable for decisions taken on the basis of information that may have changed after publication. Product properties quoted on this page are as published by the makers named, read in October 2026; always follow the data sheet supplied with the pack you buy.