Efflorescence happens naturally as concrete cures.
“I built a retaining wall out of stackable blocks last year, and they are turning white and chalky-looking. When I wet them down, the blocks look great, but when they dry out they look white again. I don’t like what I’m seeing – can you help?”
-Steve
Those powdery white stains on your blocks are likely caused by efflorescence. As concrete cures, the moisture slowly migrates to the surface of the block where it evaporates into the air. Like a candle wick, the water brings dissolved salts and minerals from within the concrete mixture. As the water evaporates, those minerals are left on the surface of your block, giving it a whitish, hazy or streaky stain.
In most cases, this problem is temporary – eventually the salts will all be removed from the concrete, and the efflorescence will stop. How long this takes depends on the ingredients with which the concrete was made, and how long it takes for the concrete to cure and dry out completely.
However, with landscape retaining walls, your blocks are constantly being exposed to ground water and hydrostatic pressure, which can force moisture (and more salts from the soil) into the blocks to later show up as efflorescence.
Efflorescence on wall at joints in the underground drainage channel.
Here are some tips for dealing with efflorescence:
Efflorescence is ugly, but it does not affect the strength or functioning of the block.
Normal efflorescence should stop once the concrete is completely cured. Ongoing streaky stains or cakey buildup, particularly at joints and cracks, may indicate a problem with water infiltration and drainage.
It’s important to reduce the amount of moisture that is getting into your wall. Mortared walls should be treated on both sides with a waterproofing sealer. Non-mortared, stackable retaining walls should be backfilled with gravel, with water drainage directed off to the sides. This prevents water pressure from building up in the soil behind the wall (and forcing itself into the concrete blocks).
Avoid pressure-washing or overly wetting your blocks. This makes them look nice at the time, but it forces water into the concrete, inviting more efflorescence.
Clean off light stains with a dry, stiff brush, then remove the dust with a damp sponge. If you have heavy stains, try scrubbing with white vinegar. Stubborn stains can be removed with a masonry cleaning solution.
Cleaning solutions are often specialized to address particular mineral stains. Understanding Efflorescence (EaCo Chem, PDF 8.43mb) has an illustrated guide to different types of efflorescence, as well as recommended products to address each problem.
dear danny lipford, i have a problem on a garage floor. dont know if it is a white fungus or what. its coming out of the cracks. i bought this house in richardson texas in october. did not have the problem then. we have had a lot of rain, my son believes water is under the foundation of the garage. please help. im 78 and my husband is not living to help with the problem . do you have any idea what to do. my daughter and i have put bleach, boric acid but it seems to be back. help please. virginia smith
How do I treat the Mineral Efflorescence from the old plaster wall.
Steven, check out the tips above for cleaning efflorescence stains. You can start with vinegar, but if that doesn’t work, there are cleaning products you can buy.
Hi Danny,
Can the same solution (to of page) be used to clean white stains from a painted besser block wall without effecting the paint? I think the white stain is lime? the wall was core filled?
Cheers
Mark
I just built a concrete block retaining wall & am now ready to install stone veneer, but i also have the efflorescence problem. Will the white powder effect the mortar being applied? I don’t want it coming loose & the stones falling off. And if I clean it off and then install the stone, can the white powder come back afterwards behind the mortar and cause a problem? Thanks for your help..Mark
I’m being requested by my HOA to paint over the White Efflorescence Stains on my cinder block Retaining Wall. We have had a wet winter here in AZ, and the ground behind the wall is very wet. I’m worried that if I paint the area, the paint will adhere in some spots, and not in others due to the dampness of the block, causing more of an eye sore than the efflorescence. What do you suggest I do? Paint or scrub or something else?
I had a contractor install the retaining wall a few years ago and this happens every year after the snow melts away. the contractors wants nothing to do to correct the situation so he had the supplier handle it which they have stopped by to clean it up every year. Last year it just needed the cleaning once and the years back were multiple times. I’m thinking of taking the contractor to small claims for poor quality work. But on the other hand the supplier thinks it may have been a bad batch of bricks so they want to handle the cleaning themselves at no cost to me. Sounds like a hassle every spring.
To all in Az. with Efflorescence pblms. I too had the same problem with my block walls and my foundation. Eventually the foundation started chipping away abit. The home was still under warranty. I called and told builders main office that it was a problem. They came out dug all around walls and foundation. Sand blasted walls and foundation treated it all with some type of coating and filled it all with sand and gravel. I no longer have any problems. Now my neighbor says his side of the wall has it. I found out my neighbor was draining his pool next to block wall so that’s why I had so much trouble. Good luck ..call a home builder .
dear dan,
i have a big problem. my block wall which connects to a neighbor was never sealed. therefore the wall leaks on to my side.the other side of the wall is higher so it goes onto my side. i have spoken to my neighbor many times and they will do nothing. i took them to court and the court will do nothing. the wall is in the backyard and the water company will do nothing. my question to you is, will this damage the strength of the wall and what ideas do you have to cover it up or hide it. the wall is about 12ft. high and 15 ft. long.
thanks for your help.
herb
i have a house built on a steep hill, the garden is landscaped on 4 levels, block walls about 4 or 5 feet tall, 20ft long. the walls were backfilled with rocks unearthed when the ground was excavated for the house and water tank (no water supply here, cisterns only). the walls were never rendered, just painted with white exterior emulsion, as are the concrete steps joining the levels to each other. after 8 years the steps and walls are losing their paint, there is green slime underneath it. There’s some efflorescence, but the cement in the steps looks waterlogged and is crumbling. i scrub the walls and steps with bleach solution before painting, but this is becoming necessary 2 or 3 times a year because black mould, green slime stain the concrete, some of it is like damp sugar. Is there a quick fix for this, I don’t want to rebuild the walls?
HOA hit us with green belt side of block wall lit up with efflorescence to take care of. I looked on my side of the wall and there is not much on the home side of it. Should the more pronounced residue be on the side water is hitting or the other side? Hoping someone knows. I want to first make sure I am responsible before i go crazy with effort or hiring someone to take care of it.
We have efflorescence appearing on 4 of our rendered garden walls. We have a sloping block in Queensland Au and all walls have also been painted on top of the render. We noticed it appearing after about a year of gardens being completed and have scraped back the render in those areas and coated the areas waterproofing which is applied with a brush. My question is will this be enough to stop the efflorescence comming back. We cannot afford to dig behind all of these walls to waterproof the back side. Any help information would be greatly appreciated . Thankyou.
I have a problem with efflorescence in my basement cinder block walls that were painted about 10 years ago. First coat about 35 years ago. I had new air condition installed about 7 years ago that draws air from outside, Could this be making basement cooler to make this happen. Can solution you recommend be applied over the painted walls and then touch up with the waterproofing paint? Who do you get to fix this kind of problem. I can’t afford to dig up outside this 30 ft wall. Please help.
Hi, Haenrietta,
We recommend submitting questions involving unique situations like yours to the Today’s Homeowner Radio Show.
Please use this form to contact Danny Lipford, America’s Home Expert, directly: https://www.todayshomeowner.com/radio/ask-questions/
Take care!