Is efflorescence the same as chalking?

No. Chalking is the paint itself breaking down in the sun and comes off on your fingers in the color of the paint. Efflorescence is white or grayish mineral salt that comes from inside the masonry, often in a crust or a fuzzy bloom, usually lower on the wall or near where water gets in.

Can I just paint over efflorescence?

Not if you want the paint to stay. As long as water keeps moving through the wall, it keeps carrying salts to the surface, and they build up behind the new paint until it blisters and flakes. The source of the water has to be dealt with before the wall is cleaned, dried and primed.

Will efflorescence go away on its own?

On new stucco or a new block wall, a light bloom after the first wet season can fade once the wall has dried out and stopped releasing salts. If it keeps returning year after year in the same place, water is still getting into the wall and the cause needs to be found.

Do you waterproof the back of a retaining wall?

Waterproofing the soil side of a retaining wall means excavating behind it, and that belongs to another trade. Ebenezer will tell you plainly when that is what the wall needs. What he can do is prepare and coat the exposed face properly once the moisture problem is understood.

White Powder on Stucco and Block Walls

The white, crusty powder on a stucco or block wall is usually efflorescence: mineral salts carried out of the masonry by water and left behind when it dries. Painting over it fails, because the salts keep arriving and push the coating off. The water source is found and stopped first, then the salts are removed and the wall is dried and primed for masonry.

It shows up as a white crust along the bottom of a garden wall, a fuzzy bloom on the stucco under a planter, or pale streaks running down a block retaining wall after the first rain of the season. Homeowners often take it for old paint, mildew or something the sprinklers left behind. Usually it is none of those. It is efflorescence, and it is a message about water.

What is efflorescence?

Efflorescence is a deposit of mineral salts on the surface of stucco, concrete block, brick or concrete. Cement-based materials contain soluble salts. When water soaks into the wall, it dissolves them, travels to the surface, and evaporates, leaving the salts behind as a white or grayish powder or crust. No water moving through the wall, no efflorescence.

That last sentence is the whole diagnosis. The salt is a symptom. The cause is water getting into the masonry from somewhere it should not.

How do I tell it apart from chalking or mildew?

Three things look similar from a distance and need different treatment.

What you see	Most likely	How to check
Fine powder in the color of the paint, mostly on sunny walls	Chalking	Rub with a dark cloth; it comes off evenly in the paint color
Gray, green or black spotting on shaded walls	Mildew	A drop of diluted household bleach lightens it within a minute or two
White crust or fuzzy bloom, often low on the wall or below a planter	Efflorescence	Stiff and crystalline; dissolves in water, then comes back as the wall dries

If you are not sure, take a photo before you scrub anything and ask. The cleaning method depends on which one it is.

Where does the water come from in San Diego?

San Diego is dry most of the year, which surprises people when they see a wall full of salt. But the water usually is not rain. It tends to be one of these:

Sprinklers that hit the wall every morning, sometimes for years.
Planters built against the house without a waterproof lining, so the stucco behind them sits in damp soil.
Soil or mulch piled up over the weep screed, the metal strip at the base of the stucco that is meant to let moisture out and sit clear of the ground.
Retaining walls on hillside lots, which hold back wet soil on one side and dry out through the face on the other. Bonita and Spring Valley have a lot of them.
Downspouts that empty against the base of a wall.
Cracks and failed caulk at the top of a wall or around a window, letting water in above.
Marine air near the coast, in places like Imperial Beach, where walls that are damp most mornings move more moisture than walls a few miles inland.

The short winter rainy season makes the problem visible. Efflorescence often appears in a burst after the first heavy rains, because that is when a wall that has been dry all summer takes on water for the first time.

Why painting over it fails

Paint is a film on the surface. Efflorescence comes from behind the surface. If the water is still moving, it carries more salt out every time the wall wets and dries, and that salt now collects between the masonry and the paint. It crystallises, expands and pushes. The result is blistering, then flaking, usually in a band along the base of the wall or in a patch below the source. It can happen in a single wet season.

A coating that seals the face hard can make it worse on a wall that is wet from behind, because the moisture has nowhere to go except through the paint. On a retaining wall in particular, the choice of coating matters as much as the prep.

The order of the repair

Each step only works if the one before it was done.

Find the water and stop it. Redirect the sprinkler heads, pull soil back below the weep screed, extend the downspout, line or move the planter. Some of this you can do yourself before the painter arrives.
Let the wall dry. Masonry that has been wet for years does not dry overnight. In the dry months it may take a few weeks of no new water.
Remove the salts. Dry brushing with a stiff brush first, so the salt is not just dissolved and soaked back in. Then washing, and where needed a masonry cleaner used as its label directs, with thorough rinsing.
Repair what the salt damaged. Efflorescence that has been there a long time can loosen the surface of the stucco or the face of the block. Loose material is removed and patched.
Check that the wall is dry and sound. If the bloom returns within days of cleaning, the water has not been stopped.
Prime with a primer made for masonry. New patches and cement surfaces are alkaline, and a masonry primer is designed to tolerate that. Sherwin-Williams Loxon Concrete and Masonry Primer and Dunn-Edwards Eff-Stop are examples of the category.
Then paint, with a finish chosen for the wall: breathable where moisture still needs a way out, more elastic where hairline cracking is the bigger concern.

What this looks like on an estimate

During the repair check that follows the power wash, Ebenezer looks at where the salt is and what is above, behind and beside it. He will tell you what he thinks is feeding it, what you can change before the job, what the prep will involve, and whether the wall needs work that belongs to another trade, such as drainage or digging out behind a retaining wall to reach its soil side.

Repair and preparation of this kind are part of his stucco, drywall and wood repair work, and he waterproofs the exposed face of the wall as well. He holds a C-33 Painting and Decorating license, number 1120008, issued to Lemoon’s Painting Inc. If you are on a hillside lot in Bonita or Spring Valley, the city pages explain what else that terrain does to exterior paint.

If a wall keeps turning white no matter how often it is scrubbed, it is worth having someone look at where the water is coming from before another coat goes on. Ask for a free estimate and Ebenezer will walk the wall with you and explain what he sees.