Masonry Paint: What to Buy, How to Apply It, and When to Paint

Paint the exterior of your extension with the wrong product, skip the prep, or pick a week in November, and you'll be scraping flaking paint off the walls within three years. The paint itself costs under £50 for a 5-litre tin. Repainting the whole thing because it failed costs ten times that in scaffolding and labour. Getting masonry paint right the first time is one of the cheapest ways to protect a building that cost you tens of thousands to construct.

What it is and what it's for

Masonry paint is a thick, weather-resistant coating formulated for exterior walls. It bonds to render, concrete, brick, pebbledash, and blockwork. Standard masonry paint is water-based acrylic, which means it cleans up with water and dries quickly, but the resins in the formula are designed to flex with thermal movement and resist UV degradation in a way that interior emulsion cannot.

You can't use interior paint outside. Interior emulsion lacks the flexibility to handle the expansion and contraction that exterior walls go through across UK seasons, and it has no resistance to driving rain. It'll peel within months.

Masonry paint does two things: it protects the render or substrate from water penetration, and it provides a uniform colour finish. On a new extension, the render is the structural weather barrier; the paint adds an extra layer of protection and makes the building look finished. On older properties, masonry paint may be the primary defence against moisture, particularly on solid-wall construction where there's no cavity.

There are no building regulations that specify masonry paint type or brand. This is an aesthetic and maintenance decision, not a compliance one.

Types, finishes, and specifications

Three finish types cover almost every domestic exterior job.

The coverage figures above are per coat. You need two coats minimum on any surface, and three on bare or new render.

Smooth or textured: how to decide

If your wall is pebbledash, use smooth. The wall already has texture built into the surface, so adding textured paint on top just eats through more product for no benefit. If your wall is plain smooth render with fine hairline cracks, textured paint fills those cracks better and hides surface irregularity. If you're repainting over existing smooth masonry paint that's in reasonable condition, stick with smooth.

Colour availability is wider in smooth finishes. If you want a specific colour (Cornish Cream is a popular one), check whether it's available in textured before committing. Many brands only offer textured in a handful of standard shades.

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What about silicone and pliolite?

Standard acrylic masonry paint is what most homeowners buy. Two specialist types exist, and you'll see them mentioned in trade catalogues.

Silicone masonry paint is waterproof but breathable. Standard acrylic can trap moisture behind the paint film, which then freezes in winter, expands, and lifts the coating. Silicone formulations let water vapour escape while repelling liquid water. Emperor Masonry Paint is the best-known UK brand (BBA certified, independently tested to 25 years). It costs roughly double standard acrylic. Worth considering on exposed or north-facing elevations where moisture is a persistent problem.

Pliolite masonry paint is solvent-based and can be applied in temperatures down to -5C (compared to 5-10C for water-based). Professional decorators use it when painting in late autumn or early spring. Tools can't be cleaned (they're disposable), recoat time is 16 hours instead of 3-4, and it smells. Unless you're painting in October and can't wait until spring, you don't need pliolite.

How to work with it

Surface preparation determines whether masonry paint lasts 5 years or 15. Every forum thread, every professional guide, every experienced decorator says the same thing: the paint you choose matters far less than the prep you do before opening the tin.

Preparation sequence

1. Fix the building first. Check all gutters, downpipes, and flashings. A leaking gutter dripping water down a freshly painted wall will cause failure within a year. Fix any cracks in the render wider than a hairline with exterior filler. Rake out and repoint any damaged mortar joints.

2. Clean the surface. Pressure wash the entire area and let it dry for at least 48 hours (longer if the weather is cool or humid). You're removing dirt, algae, lichen, and loose material. If you can see green or black growth, follow up with a fungicidal wash after pressure washing. Apply the fungicidal wash, leave it for the manufacturer's recommended time (usually 24 hours), then rinse.

3. Remove loose coatings. If you're repainting, scrape off all flaking or peeling paint with a wide scraper. Don't paint over it. The new paint will only bond as well as whatever's underneath it, and loose old paint peels off in sheets, taking the new coat with it.

4. Stabilise if needed. Run your hand across the bare render. If it leaves chalky dust on your palm, the surface is friable and needs stabilising solution (a diluted PVA-type primer that binds the loose surface). Apply one coat of stabiliser, let it dry, then paint. If the render feels solid with no chalking, skip this step. Don't use stabiliser routinely on large areas; it can reduce breathability.

5. Mask everything. Windows, sills, downpipes, doors. Masking tape and dust sheets. Masonry paint is thick and spatters. Getting it off uPVC window frames after it dries is unpleasant.

Application

Use a long-pile roller (19-25 mm nap) on a 9-inch or wider frame with an extension pole. The long pile gets paint into the texture of the render. A short-pile roller leaves gaps in every surface irregularity. Cut in around windows, doors, and edges with a 3-4 inch masonry brush.

Work from top to bottom, in sections roughly 1 metre wide. Keep a wet edge to avoid overlap marks. On hot days, this means working faster or choosing a day when the wall is in shade. Sandtex dries slower than Dulux Weathershield, which actually helps on warm days because it gives you more time to maintain that wet edge.

Two full coats is the minimum on any surface. Three coats on new render or bare masonry. Allow 3-5 hours between coats in dry weather. Most quality masonry paints are shower-resistant within 20-30 minutes, but don't push it if rain is forecast within 4 hours.

Painting new render

New render needs time to cure before painting. The practical minimum is 3 months. The ideal is 6-12 months. During curing, hairline cracks develop as the render shrinks (this is normal), and you can fill these before painting rather than discovering them under your new paint job.

How do you know the render is ready? It changes colour. Fresh render is dark grey. As it dries and cures, it lightens to a pale grey or near-white. If any section is still noticeably darker than the rest, it's still holding moisture. Wait.

When to paint

In the UK, paint exterior masonry between April and September. The ideal temperature range is 5-25C with low humidity and no rain forecast for at least 24 hours after application.

North-facing walls dry more slowly and are more prone to algae regrowth. Paint these in the warmest, driest part of summer. South-facing walls in full sun can get too hot in July and August; paint dries before you can spread it, leaving roller marks. Paint south-facing walls in morning shade or on an overcast day.

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How much do you need

Coverage depends on the surface. Smooth render absorbs less paint than pebbledash, which can use three times as much per square metre.

Measure the wall area in square metres (height x width, minus window and door openings). Then use these rates:

• Smooth render or brick: 8-10 m2 per litre per coat. A 5L tin covers 40-50 m2 per coat, or 20-25 m2 over two coats.
• Rough/textured render: 4-5 m2 per litre per coat. A 5L tin covers 20-25 m2 per coat, or 10-12 m2 over two coats.
• Pebbledash or roughcast: 2-3 m2 per litre per coat. A 5L tin covers 10-15 m2 per coat, or 5-7 m2 over two coats.

A single-storey rear extension with roughly 25-30 m2 of rendered external wall (after subtracting windows and doors) needs two to three 5L tins for two coats on smooth render. The same extension in pebbledash might need five to six tins.

Cost and where to buy

The guarantee claims require proper surface preparation and application. Nobody is getting 15 years from Dulux Weathershield applied over damp, algae-covered render in October. On a well-prepared, dry wall painted in June, 8-12 years before significant fade or deterioration is realistic for any of the mid-range brands. Budget paint (sub-£20 per 5L) typically needs attention within 3-5 years.

Coloured paint costs more than white or magnolia. Sandtex Trade 5L in Brilliant White is £28; the same tin in a custom colour is £39. Dulux Weathershield follows the same pattern. Factor this in if you're painting a large area in anything other than white.

Where to buy

All major UK merchants stock masonry paint: B&Q, Wickes, Screwfix, Toolstation, and Travis Perkins. For trade-grade products (Sandtex Trade, Dulux Trade Weathershield, Johnstone's Stormshield), try Trade Paint Direct or Paint Direct online, or open a trade account at a builders' merchant. Trade accounts are free to open and typically offer 10-15% off list prices.

Spring sales at B&Q and Screwfix regularly discount masonry paint by 20-30%. If your painting window is May or June, buy the paint in March during the sale.

Alternatives

If you're finishing an extension exterior, masonry paint isn't the only option.

Through-coloured render (such as K Rend or Weber) is applied as a coloured finish coat over the base render. It never needs painting because the colour is integral to the material. More expensive upfront (your renderer will charge a premium), but zero maintenance for 20-30 years. If you're still at the plastering stage, ask your renderer about this option before defaulting to painted render.

Masonry cream/clear sealant provides invisible water protection without changing the colour of the substrate. Useful if you have attractive facing brickwork that doesn't need paint but does need weather protection. Not a substitute for masonry paint on rendered walls.

Exterior render paint systems from specialist suppliers (Sto, Parex) are professional-grade coatings applied as part of an insulated render system. These are specified by the renderer, not chosen by the homeowner.

Common mistakes

Painting in the wrong weather. Below 5C, water-based masonry paint won't cure properly. Above 30C, it dries before you can spread it. Rain within 4 hours of application washes pigment out. Check a 5-day forecast before starting.

Skipping the prep. This is the single most common failure. Pressure washing alone isn't enough if there's algae, loose paint, or friable render underneath. Budget a full day for preparation on a typical extension. The painting itself is the easy part.

Not treating the source of damp. Paint peeling in one specific area usually means water is getting in from above: a leaking gutter, a cracked flashing, or a missing drip detail. Repainting over the peeling area without fixing the water source guarantees repeat failure.

Painting new render too soon. Three months minimum. Painting fresh render traps moisture and alkali salts behind the film, causing bubbling and white salt deposits (efflorescence) on the surface. Wait until the render has fully lightened in colour.

Using one coat. One coat of masonry paint looks acceptable for about six months. Then it fades unevenly, shows brush marks, and offers inadequate weather protection. Two coats is the minimum. Three on bare surfaces. The second coat is what provides the actual protection; the first is just the bonding layer.

Where you'll need this

• Decoration - exterior masonry paint for the rendered or bare blockwork walls of the extension
• Garden and External Works - painting rendered surfaces, boundary walls, or external features

These materials appear across any extension or renovation project that involves exterior rendered walls. The guidance above applies regardless of project type.