Which masonry paint should I use on my house?

Vapour permeability is the property that matters and the one nobody reads. How to choose a masonry coating by what the wall behind it needs to do.

Difficulty: intermediate
Time: 20 min
Read: 4 min
Safety: caution

Short answer

Ask what the wall is first. Modern cavity-walled render takes a standard or smooth acrylic masonry paint. An older solid wall, lime render or anything showing damp needs a genuinely breathable mineral, silicate or breathable acrylic system. Textured masonry paint hides a rough surface but is very difficult to remove later.

Masonry paint is chosen on colour and on whether it is smooth or textured, and those are the two least important properties. The property that decides whether the coating and the wall survive together is vapour permeability: whether moisture inside the wall can pass out through the film. A wall that can only dry through its face, coated with something moisture cannot cross, will push the coating off and stay wet.

Safety

The wrong masonry coating on a solid wall traps moisture and does structural damage over years, not cosmetic damage. On any pre-1920s solid wall, on lime render, or on any wall already showing damp internally, get advice before coating it at all — and never apply a waterproofing sealer to a wall whose only route out for moisture is through its face.

Why an impermeable coating blows off a wall that needs to dry outwards

Step by step

Establish what kind of wall you have.A cavity wall built from roughly the 1930s onwards, with a damp-proof course and a ventilated cavity, has other ways to manage water. A solid wall of brick or stone, particularly a pre-1920s one, and anything rendered in lime, relies on being able to absorb water and give it back through its face. These need opposite things from a coating.
Find out what is already on it.This decides as much as the wall does. Existing plastic or impermeable masonry paint means a breathable coating on top achieves nothing, because the old film is still the barrier. Cut a small test area back and see how many layers there are and whether they are sound.
Choose the system, not the tin.For a modern rendered cavity wall: a good acrylic masonry paint, smooth or fine-textured, over a masonry stabilising solution if the surface is chalky. For a solid or lime-rendered wall: a mineral, silicate or specifically breathable acrylic system, applied with the manufacturer's own primer, because these systems only work as a matched set.
Treat 'weatherproof' and 'waterproof' claims with suspicion.A coating that stops liquid water entering while letting vapour out is a legitimate and useful thing. A coating sold as waterproofing or sealing is usually the opposite and will trap moisture. Look for a stated vapour permeability or diffusion figure rather than an adjective.
Decide smooth or textured on maintenance, not looks.Textured masonry paint has sand or fibre in it, fills hairline crazing and hides a rough render well. It is also much harder to clean, much harder to remove, and takes far more paint per square metre. Smooth is easier to maintain and easier to reverse.
Prepare for the surface you have, not the one you want.Kill and remove algae and moss with a suitable treatment and let it work, brush off all loose and chalking material, repair cracks and hollow render before coating, and use a stabilising solution on any surface that still dusts when brushed.
Do the whole elevation and respect the weather window.Masonry work has to go on within the temperature and humidity range on the tin, with time to dry before rain or overnight cold. Stop at a corner, a downpipe or a natural break rather than in the middle of a wall face, because a join in the middle of an elevation shows.

Tips

The honest option on an unpainted solid brick wall is very often to leave it unpainted. Once painted, it must be repainted forever, and stripping it is expensive and can damage the face of the brick.
A limewash or mineral system on an old wall looks right as well as performing right — the eroded, chalky appearance is the finish working, not failing.
Buy from a range that includes its own primer and stabilising solution and use them. Mixing a breathable topcoat with an impermeable primer wastes the topcoat entirely.

Common mistakes

Coating an old solid wall with a plastic masonry paint — It blocks the only route moisture has out. The film blisters and sheets off, frost shears the render face away with it, and the wall stays wet, which shows internally as damp and mould.
Painting over a wall that is already showing internal damp — The paint hides the symptom and delays the diagnosis. Establish where the water is coming from first — a coating never fixes a damp cause.

Questions people ask

What is the difference between breathable and standard masonry paint?

Vapour permeability: how easily water vapour passes through the cured film. Mineral and silicate paints are highly permeable and bond chemically to a mineral surface; standard acrylic masonry paints are far less so. On a cavity wall it rarely matters; on a solid wall it decides everything.

Can I put breathable paint over old plastic masonry paint?

You can apply it, but you gain nothing. The old impermeable layer is still the barrier. To make an old wall breathable again the existing coating has to come off, which is a substantial job.

How often does masonry paint need redoing?

Depends entirely on exposure, the system used and the wall. A sheltered elevation may go far longer than a driven-rain-facing one. Judge by the coating — chalking, hairline crazing and colour loss on the exposed elevations tell you before failure does.