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What Is Efflorescence?

What Is Efflorescence?

Exterior renovationsWhat Is Efflorescence?

Have you noticed white spots on your brick cladding or basement walls? If so, it's probably efflorescence. Never heard of it? Check out the following to find out what’s causing it and how to fix it.

What You Need to Know About Efflorescence


Efflorescence is a white, crystalline deposit that develops on lime-, masonry cement-, or cement-based building materials. It frequently develops on brick claddings, concrete slabs, or on the inner side of foundation walls.

Although it's often mistaken for mould, it's very different because it doesn't grow on organic substances. Moreover, it can only be white in colour, unlike mould, which can vary in colour (black or yellowish) and tends to dissolve in water.

Development of Efflorescence

Stone and concrete, both of which contain the previously mentioned components, also have trace minerals in them. When water enters the substance, it dissolves the salts. Eventually, the water that dampened the materials evaporates, causing the dissolved salts to rise to the surface. Thus, these salts (calcium hydroxide) are the very basis of the crystalline deposits that can develop on the surface of a given material.

Besides the presence of salts in the previously mentioned substances, some elements can heighten the development of those deposits, like:

  • The presence of micro fissures, which increase the absorption of water around the main fissure;

  • Adding too much water to the base material;

  • Exposure to mineral-rich soil;

  • Inadequate water drainage methods;

  • A topcoat too thin to serve as a protective layer for the base coat;

  • The lack or malfunction of a French drain;

  • Too much moisture rising from the ground.

Although it's important to remove any traces of efflorescence on the material or to have the material in question replaced, if necessary, it's also crucial to have a functional French drain, to limit the amount of moisture near and around the foundation.

Do you want to know more about the costs related to a French drain installation? Check out our article (French only).


When Does Efflorescence Begin to Develop?

Efflorescence_Everything to Know About Efflorescence

This phenomenon occurs mostly during periods of high humidity, often during the late fall and early spring. During these times, evaporation rates are lower due to a combination of high humidity and cold temperatures.

As a matter of fact, calcium hydroxide dissolves much more readily under these circumstances. But why not in summer? Quite simply because the temperature is so warm that the salts found in the materials don't have sufficient time to dissolve. 

It's important to note that the presence of these minerals doesn't carry any health risk for those exposed, so there's no need to worry about it.

How to Remove Efflorescence


1) If caused by moisture found in construction material

If it is caused by water mixed in with a material in question (such as cement), the problem can easily be fixed. Once the water has completely evaporated, simply clean the surface with a water-based cleaner, which is sold in stores.

Also, you can make a mixture of two equal parts water and vinegar to remove stains. Note that a water-based cleaner should only be used during dry, warm weather. If it's used in cold or wet weather, it could make the efflorescence problem worse, and that's definitely not the intended outcome!

If the above-mentioned solutions don't work (which is rarely the case), you can opt for a stronger hydrochloric or muriatic acid cleaner. However, when using an acid-based product, use a hard bristle brush to scrub the efflorescence, and make sure to use protective gloves and goggles, as well as a respirator mask.

Finally, if you wish to use an acid to treat the problem, it's best to leave this task in the capable hands of a professional, as there are risks involved in using this type of product. In fact, improper use of this product can have adverse effects on the material and even cause its deterioration. Also, note that this method should be used as a last resort.

2) If caused by excess moisture in a dry material

On the other hand, efflorescence can be caused by water infiltrating a dry material, such as water seeping under or around a building. If this is the case, the problem will persist as long as the underlying damage isn't repaired, or the foundation isn't properly sealed.

Note that if it occurs as a result of a dry environment, it'll lead to a very specific problem: water will evaporate prior to reaching the last layer of the material. As a result, the salt build-up below the surface of the material will eventually lead to deterioration. As you might expect, removing the material is the key to fixing it.

Prevent the Development of Efflorescence

traces of efflorescence_Everything to Know About Efflorescence

To lessen the likelihood of the development, several measures can be put into practice, such as:

  • Ensuring that the construction components are made in such a way that water rising up cannot reach the masonry elements;

  • Selecting materials that have, ideally, low levels of salts, and aren’t porous;

  • Properly storing masonry materials to avoid contamination by water found in the soil;

  • Putting together features to protect masonry elements from moisture ;

  • Ensuring the functionality of the French drain at all times.


Avoid doing…

Because efflorescence is likely to limit the structural soundness of materials or products adhered to its surface, avoid assuming that it can simply be concealed. In any case, it's important to note that the following actions aren't recommended:

  • Sticking an insulation panel to a vapour barrier or air barrier showing signs of efflorescence;

  • Applying layers of paint or topcoat to surfaces;

  • Installing insulation over affected material.

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Last modified 2023-11-07

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