Efflorescence is the white, powdery deposit you sometimes see on brick or stone: salts carried out of the masonry by water and left behind as it evaporates. On its own it’s usually harmless, especially on newer walls. Spalling is when the face of a brick or stone flakes, crumbles or pops off. That’s real damage, and it almost always means the masonry is staying too wet — often because of hard cement pointing, impermeable paint, or a leak keeping one area saturated.
The two are connected: both are signs of water moving through a wall. Here’s how to read them and what to do.
What is efflorescence on brick?
All bricks, stone and mortar contain some soluble salts. When water soaks into a wall, it dissolves those salts. As the wall dries, the water evaporates at the surface and leaves the salts behind as a white, fluffy or crusty deposit.
Efflorescence on new brickwork is very common. A new house or extension is full of construction water, and as it dries out over its first year or so, salts come to the surface. NHBC’s guidance for new homeowners describes these deposits as natural salts from the wall materials that aren’t harmful and usually disappear over time.
On older walls, efflorescence is a pointer to where water is getting in or concentrating:
- below a leaking gutter, downpipe or overflow
- at the base of a wall where ground levels are high or rain splashes back
- under defective copings, sills or chimney flashings
- where pointing has failed and lets rain in
Is efflorescence a problem?
Usually not in itself. It’s worth investigating if:
- it keeps coming back in the same place years after construction
- it’s getting worse or spreading
- it appears inside the house, which can indicate a leak, penetrating damp or salts from rising damp
- it comes with spalling, crumbling mortar or staining
How do you get rid of efflorescence?
- Wait and brush. On new work, dry-brush the deposit off as it appears. It will generally reduce as the wall dries.
- Don’t wash it off with lots of water. That puts the salts back into solution and can draw them back into the wall.
- Fix the water source. On an older wall, efflorescence will keep coming back until the leak, overflow, splashback or failed pointing is dealt with.
- Be cautious with acid cleaners and sealers. Sealing a wall that still contains salt and moisture can push the problem further in, where it does more harm (see below).
What is spalling brick and stone?
Spalling is the breakdown of the outer face of a brick or stone. You’ll see faces flaking away in layers, crumbling to powder, or sometimes a whole face popping off in one piece. Spalling stone may also be described as delaminating or exfoliating.
It has two main causes, and they usually work together.
Frost damage
When saturated masonry freezes, the water expands and pushes the surface off. A brick or stone that stays dry rarely suffers frost damage; one that is wet when the frost arrives can lose its face in a single winter. Exposed walls, chimneys, parapets and garden walls — anywhere that stays wet and catches the cold — suffer most.
Salt crystallisation
When water evaporates inside the surface of the masonry rather than at it, salts crystallise in the pores. Crystal growth exerts pressure and pushes the surface off. This is why efflorescence and spalling are linked: they’re the same process happening in a slightly different place. Salts on the surface are cosmetic; salts just under the surface are destructive.
Why hard cement pointing and masonry paint cause spalling
Older brick and stone buildings were built with lime mortar, which is softer and more permeable than the bricks or stone around it. Water in the wall preferentially evaporates through the joints, and the mortar — not the masonry — takes the wear. Historic England and SPAB both make the point that lime mortar is designed to be the sacrificial part of the wall.
Hard cement pointing turns that around. Cement mortar is less permeable than many traditional bricks and sandstones, so water now leaves through the face of the brick or stone instead. That’s where salts crystallise and frost does its damage. SPAB describes how hard cement pointing makes the bricks and stones the most permeable part of the wall, so they suffer the greatest frost and salt action. The tell-tale sign is masonry eroding back while the cement pointing stands proud.
Impermeable masonry paint and water-repellent sealants do something similar. They stop the wall drying through the surface, so salts and moisture build up behind the coating. Conservation guidance describes how salts trapped behind relatively impermeable coatings such as acrylic paint or water-repellent sealants crystallise and push off the surface — spalling or exfoliation.
The Yorkshire angle: sandstone, gritstone and Pennine weather
Much of West Yorkshire and the Pennine fringe is built from local sandstone and gritstone — the hard, coarse millstone grit and the finer sandstones that make up so many terraces, mills and farmhouses. These stones are durable, but they’re still vulnerable when kept wet.
Things we commonly see on stone houses in the area:
- Cement repointing on stone terraces, with the stone arrises (edges) breaking down around the joints
- Masonry paint applied over stone to tidy up soot-blackened or patched elevations, later blistering and taking the stone face with it
- Spalling at low level where pavements, paths or garden soil have been raised against the wall
- Chimney stacks and gable tops losing their faces where they take the full force of driving rain and frost
The wet, windy Pennine climate means walls here spend a lot of time damp, so anything that slows drying matters more than it would in a drier part of the country.
How serious is spalling?
| What you see | Usually means |
|---|---|
| White powder on new brickwork | Normal drying out; brush off and wait |
| Recurring salts below a gutter or overflow | A local water source; fix the leak |
| Odd bricks with flaking faces | Frost or salt damage; replace the worst, fix the cause |
| Widespread spalling with cement pointing standing proud | Wall can’t dry through the joints; repointing in lime needed |
| Paint blistering with stone coming away | Trapped moisture; coating needs careful removal |
| Deep erosion, loose stones, bulging | Needs investigation — may affect the wall’s stability |
Most spalling is a maintenance and durability problem rather than a structural one. It gets serious when it’s deep, widespread, or affects load-bearing stones such as lintels, quoins or chimney stacks — and loose material falling from height is a safety risk in its own right.
How do you treat spalling brick and stone?
- Find and fix the water source — gutters, downpipes, overflows, copings, flashings, ground levels.
- Remove hard cement pointing carefully, without damaging the arrises of the brick or stone, and repoint in a suitable lime mortar. Historic England publishes detailed guidance on repointing brick and stone walls.
- Remove impermeable coatings where they’re trapping moisture, using a method suited to the masonry. If a finish is wanted, use a genuinely breathable one. Note that conservation guidance warns limewash shouldn’t be applied to sandstone that hasn’t previously been limewashed.
- Replace badly damaged units — cut out and replace bricks, or piece in matching stone. Some lightly spalled masonry can simply be left once the cause is dealt with.
- Avoid quick fixes like rendering over the damage or applying water-repellent creams to a wall that’s still wet and full of salts, unless a specialist has confirmed it suits that wall.
Costs depend on how much repointing is needed, access and scaffolding, whether coatings need removing, and how many units need replacing.
When to get a survey
If you’re buying an older brick or stone house with spalling, efflorescence or painted masonry, a survey will note the condition and the likely cause. Where damp is getting through to the inside, our guides to rising damp, condensation and penetrating damp and how to treat damp walls explain the next steps. Our damp checker can help you narrow down what you’re seeing.
Our damp and timber surveys are carried out by a PCA Qualified Technician in damp and timber, and we don’t sell treatments or repairs — so the advice is about fixing the cause, not selling a product. The fee is fixed and quoted for the property. Get in touch with the address and a few photos of the wall.
Sources and further reading
- Repointing brick and stone walls — Historic England
- Inappropriate cement pointing — SPAB
- Vapour permeable paint — The Building Conservation Directory
- Damp in historic buildings — Historic England
- Guide to your new home — NHBC