An expert's guide to efflorescence in brickwork

At some time or another, you may have seen a white, salt-like substance coming out of brickwork and wondered what it is.

Well, the technical name for that chalky-looking powder is 'efflorescence', and it’s actually very common, affecting well over 50% of buildings in the UK. It’s more commonly associated with new-build properties for reasons we’ll explain further down, but older buildings are susceptible to it, too.

Efflorescence is a recognised industry phenomenon that can sometimes occur in brickwork, as a brick manufacturer we are often asked how easy it is to remove it and how to stop it from coming out in the first place. So, we’ve pulled together this handy guide that covers everything you need to know.

What is the salt that comes out of bricks?

The chalky substance coming out of bricks isn’t just one thing but rather a collection of water-soluble salts that consist of sulphates and carbonates. 

The clay contains minerals such as potassium, magnesium, sodium and calcium that stem from the raw material used to make the bricks in the first place.

What causes it?

The first thing you need to know here is that the sulphates and carbonates naturally present in bricks dissolve in water. So, as you can imagine, bricks can pick up moisture from anywhere, whether it’s rain or general humidity.

Although it’s what happens after the bricks have absorbed the moisture that’s more interesting. Bricks are porous by their nature, meaning they can absorb quite a bit of water, and as we know already, the elements inside dissolve because of the moisture. 

As the brick wall begins to dry out, the water containing those dissolved salts gradually migrates to the surface, where it eventually evaporates, leaving behind that layer of crystallised white powder that’s so common.

The important thing to remember here is that efflorescence is a perfectly natural phenomenon, and it doesn’t mean there’s anything wrong with the bricks themselves.

Is it harmful?

You’ll be glad to know that efflorescence is harmless from a health perspective, but it can be a bit of an eyesore. 

The only thing to keep an eye on is the condition of the brickwork and if it returns after it’s been removed. Although it’s not totally uncommon for efflorescence to reappear, if it persistently comes back in the same spot while the rest of the wall is fine, then there may be signs of water ingress from somewhere, which will need further investigation. 

It's important to note that efflorescense is purely a cosmetic occurence bought about from normal wetting and drying cycles, whereas subflorescense can be a consequence of persistent water ingress due to an inherent flaw in the design or construction detail.

Is it definitely coming from the bricks?

Across the construction industry, it’s a widely recognised assumption that the white deposits you’re seeing are coming from the bricks, when in practice they can also stem from the mortar as part of a phenomenon called ‘lime bloom’.

Lime bloom happens when free lime inside wet cement makes its way to the surface and hardens into limestone when it dries out. Compared to efflorescence, which is water-soluble and can be brushed away, lime bloom is a hard, crusty layer of limestone that requires a mild acid cleaner to remove it.

If you’re unsure whether you’re dealing with efflorescence or lime bloom, then apply some water to the affected area of the wall. If it’s efflorescence, then the salts will dissolve in the water and disappear. If it’s lime bloom, the layer of limestone will remain visible even when it’s wet.

How do you remove efflorescence from walls?

Since efflorescence stems from water-soluble elements, it typically washes away on its own thanks to the rain and wind, so we’d always recommend leaving it for a while to see if it disappears naturally over time.

If that doesn’t fix the appearance, or you’d simply prefer to get rid of it sooner as opposed to later, then use a soft brush to speed up the process, don’t be tempted to use something harsher, like sandpaper or a wire brush, since these will likely damage the appearance of the brick.

You may see advice elsewhere saying to wet the wall first before brushing, but we’d recommend avoiding that since the brick will draw the moisture in, and the problem will come back once it’s dried out.

Chemical brick cleaners and solutions are available for really stubborn stains, but make sure you follow the instructions carefully since they’re usually quite acidic and can damage the wall if used incorrectly. We’d suggest avoiding these if you can, due to the potential for damage if you get it wrong.

How do you stop it from coming out in the first place?

To prevent efflorescence from appearing in the first place, you need to get a handle on the brickwork absorbing moisture.

Tackling this can be done during the construction phase by doing things such as the following:

• Keeping bricks covered during the construction phase, where possible.
• Ensuring bricks are being stored on ground that has adequate drainage and are not left in standing water.
• Ensuring drip details, such as window sills, are effective and are not directing water back to the masonry and causing excessive water ingress.
• Covering cavities, which will help prevent water ingress until the building is fully enclosed.
• Fitting rainwater goods (i.e. guttering and downpipes) as early as possible.
• Make all efforts to prevent bricks becoming saturated.

To further combat this issue from potentially arising, our range of bricks are S2-rated, meaning they have low active soluble salt content. As a result, the chances of experiencing efflorescence are noticeably lower than with non-S2-rated bricks.