Waterproof Paint Guide: What Works on Your Walls, and What to Do Before You Paint

What "waterproof paint" really means

People use the words "waterproof paint" for four different things. They look similar in the tin and do very different jobs on the wall.

A lasting result on an exposed wall usually uses three of the four: a barrier primer, an elastomeric coating, and an emulsion on top for colour.

Where the water comes from

Before you choose a paint, work out how water is getting into the wall. There are three paths, and paint can stop only one of them.

1. Rain on the outside face. Water soaks through cracks, joints and porous plaster. A waterproof coating on the outside stops it. This is the job waterproof paint is made for.
2. Damp rising from the ground. Moisture climbs up through the base of the wall and brings salts with it. You see a tide mark, white powder and peeling paint in a band near the floor. Paint on the surface does not stop it. The wall needs a salt and damp treatment, and the source needs attention.
3. A leak from the other side. A bathroom, a concealed pipe, a water tank or the terrace above. Until that leak is fixed, any paint on the dry side will blister and fall off.

If you are not sure which path you have, use the symptom-by-symptom diagnosis in our guide to water leakage, dampness and efflorescence. For the terrace above, see the roof waterproofing guide.

Why it pays to treat damp early

A damp patch looks like a paint problem. It is a wall problem. Left alone, moisture breaks down the plaster, feeds fungus, and in concrete walls reaches the steel inside. Each stage costs more than the one before.

Repainting the same wall every year is the most expensive way to deal with damp, because the money buys a finish and never a fix. Doing the layers under the paint once is what makes the paint last.

Find your wall

Match your wall to one of these and start there.

The wall build-up, layer by layer

A painted wall that stays dry is a system. The paint you see is the last and thinnest layer. What is under it decides how long it lasts.

1. Masonry or concrete. The wall itself.
2. Plaster with an integral compound. CONPROOF 500 or CONPROOF No. 1 in the mix makes the plaster denser and less absorbent.
3. Crack, joint and salt treatment. RAPIDSTRONG CRACK SEALER 85 or RAPIDSTRONG CRACK SEALER 75 for cracks, WONDERSEAL XL around frames, RAPIDSTRONG SALT FLUSHER where salts appear.
4. Putty. RAINCARE WALL PUTTY fills small imperfections and gives a smooth, water-resistant base.
5. Primer. RAINCARE CP Primer indoors and on new plaster. RAINCARE WP Exterior Primer outdoors.
6. Waterproof coating. On exposed walls, RAINSEAL 200 or another elastomeric coating. This is the layer that keeps the rain out.
7. Finish paint. A SHINESHIELD emulsion for the colour and finish you want.

A sheltered interior wall in good condition needs only putty, primer and paint. An exterior wall that takes driving rain needs every layer.

Exterior walls: waterproof coatings and paints

On an outside wall you are choosing two things: the waterproof layer and the visible finish. Some coatings do both.

Waterproof coatings for external walls

For a west or south wall that heats the rooms behind it, a solar reflective coating waterproofs the wall and reflects the sun's heat.

Exterior emulsions for colour and finish

Exposed concrete has one more enemy besides rain: carbonation, which lets the steel inside rust. ALSTRONG AC is listed for anti-carbonation protection of exterior and internal concrete.

Interior walls

Inside the house, the finish matters as much as the protection. The rule is the same: a dry, treated wall first, then paint.

• Damp walls. CONPROOF EP is a water-thinnable epoxy coating listed for damp interior walls and for toilet and kitchen walls. It is non-toxic and non-flammable.
• Salt-prone walls. RAPIDSTRONG SALT FLUSHER goes on as a pre-treatment before painting.
• Levelling. RAINCARE WALL PUTTY in two coats of 1–2 mm each.
• Priming. RAINCARE CP Primer covers 80–100 sq.ft per litre and is ready for the topcoat in 4 hours.

Bathrooms, kitchens and other humid rooms are where anti-fungal paint earns its place. If the damp is coming from the bathroom on the other side of the wall, the fix is in the bathroom. See bathroom waterproofing: why the sequence matters.

Clear finishes for stone, brick and tile

Some walls should not be painted. Natural stone, exposed brick, cladding and heritage surfaces need protection you cannot see.

A repellent soaks in and leaves no film, so the surface looks unchanged. A clear coating forms a film on the surface and gives more protection, with some gloss.

Step-by-step: how to waterproof and paint a wall

1. Find and stop the source

   Decide which of the three water paths you have. Repair the leaking pipe, the bathroom or the terrace first. A coating cannot hold against water coming from behind.

2. Strip and clean

   Remove loose and flaking paint, damaged plaster, dust, oil, fungus and algae. Wire brush the wall and wash it down. Let it dry fully.

3. Repair cracks, joints and plaster

   Fill fine cracks with RAPIDSTRONG CRACK SEALER 85 and wider ones with RAPIDSTRONG CRACK SEALER 75. Seal the gaps around window and door frames with WONDERSEAL XL, a flexible sealant that can be painted over once it has skinned. Where plaster is loose, hack it off and replaster with RAPIDSTRONG CP over a bond coat of ROOFBOND PB 210 mixed 1:1 with cement. Cure new plaster with water for at least 7 days.

4. Treat salts

   Where there are salt deposits, brush on RAPIDSTRONG SALT FLUSHER in two coats, the second at right angles to the first after at least 4 hours. Leave it 24 hours before the next layer.

5. Putty

   Apply RAINCARE WALL PUTTY in two coats of 1–2 mm. Let the first coat dry for 12–24 hours and sand lightly between coats and before priming.

6. Prime

   Indoors and on new plaster, apply RAINCARE CP Primer and allow 4 hours. Outdoors, apply RAINCARE WP Exterior Primer diluted with 20% water and allow at least 4–6 hours. Very porous walls may need two coats of primer.

7. Coat and finish

   On exterior walls, apply the waterproof coating first: two coats of RAINSEAL 200, 3–4 hours apart. Then apply the exterior emulsion, with 4–6 hours between coats. Dark colours may need a third coat. Indoors, thin the first coat of emulsion 1:1 with water and the topcoat with 500–600 ml of water per litre.

How much you need for 1,000 sq.ft of wall

These quantities are worked out from each product's stated coverage. Rough or porous walls use more.

Armstrong does not publish prices. For a quantity and quote matched to your walls, request a quote.

Seven common mistakes

1. Painting over a damp wall. The paint traps the moisture and blisters within months.
2. Painting over salts. Salt crystals grow under the film and push it off.
3. Skipping the primer on new plaster. Fresh plaster is alkaline and attacks the paint.
4. Filling a moving crack with a rigid filler. It cracks again. Use a flexible sealant.
5. Using emulsion alone on a wall that takes driving rain. A thin paint film cannot bridge cracks. Put an elastomeric coating under it.
6. Painting before the plaster or putty has dried. Each layer needs its drying time.
7. Treating the wall and not the source. A leak from a bathroom or terrace has to be fixed there.

Why Armstrong for walls

Most paint brands sell the top coat. A wall that stays dry needs the layers under it too. Armstrong makes every layer, from the compound in the plaster to the colour on the surface, so the whole wall is one system from one manufacturer.

• The waterproofing is in the system, not only in the paint. Integral compounds, crack fillers, salt treatment, putty, primers, elastomeric coatings and emulsions are all in the range.
• A coating for every wall. Eight waterproof coatings for external walls, six emulsions, and four clear treatments for stone and brick.
• Made in India for Indian walls. Armstrong formulates and manufactures in Bengaluru for strong sun, heavy monsoon rain, humidity and salts. The coatings state the figures that matter here: 2000 hours of UV resistance, no algae or fungus growth, and elongation up to 700%.
• Quality you can check. Armstrong Chemicals is an ISO 9001:2015 certified company, and each product page gives its tested figures.

All Armstrong wall waterproofing and paint products

Every Armstrong product used on walls, grouped by the stage of work. Select a product for its full data, coverage and application steps.

Questions and answers