How to apply masonry paint

Video by Ronseal. This guide draws on "How To Paint Masonry | DIY Tips from Ronseal" from the official Ronseal UK channel. Ronseal have been making exterior coatings for decades and their how-to content reflects that — straightforward, practical, and useful before you buy anything. Worth a watch for the brush technique on rough render especially.

1. Check the wall surface first

Have a close look at what you are painting. Render, pebbledash, brick, and blockwork all take masonry paint differently. Tap the wall with your knuckles — a hollow sound suggests the render has blown and may need patching before painting. Paint over hollow render and it will fall away, taking your new coat with it.

Look for cracks, staining, green algae, or efflorescence (the white salty bloom you sometimes see on old brickwork). All of these need treating before you open a tin of paint.

2. Clean the surface thoroughly

Masonry paint will not bond properly to a dirty or dusty wall. Brush off any loose material with a stiff brush, then wash the wall down. A pressure washer speeds this up considerably, but keep the pressure moderate — too much force on old render will do more damage than good.

If there is green algae or black mould, treat the wall with a fungicidal wash and leave it for the time recommended on the label. Paint over live mould and it will carry on growing underneath.

3. Fill cracks and repair any damage

Small hairline cracks in render can be filled with exterior flexible filler or a masonry sealant. Apply it with a filling knife, smooth off, and let it dry fully. Larger cracks — anything over about 2 mm wide — may indicate movement and are worth investigating before you fill and paint over them.

For blown render, hack it back to solid material, dampen the area, and apply a sand-and-cement patch or ready-mixed exterior render. Give it time to cure before painting. Rushing this step is false economy.

4. Apply stabilising primer if needed

Chalky, powdery, or very porous surfaces should have a coat of stabilising primer before the paint goes on. It binds the surface and gives the masonry paint something solid to grip. On a wall in good condition you can often skip this step, but on anything older or patchy it is worth doing.

Dilute the primer slightly with water if the surface is very absorbent, so it soaks in rather than sitting on top. Let it dry completely before moving on.

5. Apply the first coat of masonry paint

Use a large masonry brush or a thick-pile roller designed for rough surfaces. Work from the top of the wall downward, so any drips land on unpainted masonry rather than on a coat you have already laid. On pebbledash or rough render, a brush is more forgiving than a roller — it pushes paint into all the texture.

Do not try to cover everything with the first coat. Masonry paint is designed to go on in two coats, and pushing for full opacity in one pass usually leads to runs or uneven coverage.

6. Apply the second coat

Let the first coat dry thoroughly — usually a minimum of four hours, but check the tin. The second coat is applied the same way: top to bottom, working methodically. This coat should bring you to full, even colour with no bare patches showing through.

Work in dry, mild weather if at all possible. Frost or rain within 24 hours of application will ruin the finish. In Kent, late spring and early autumn are often the best windows — warm enough but not baking, which can dry the paint too fast before it has time to bond properly.

When to call a handyman

Call Richard if the wall needs scaffolding or a tall tower to reach, if there is significant render failure that needs a proper repair, or if you are not sure whether the existing paint is a specialist coating that needs a specific primer. Getting the preparation wrong on exterior walls is an expensive mistake to put right.