Q&A / 

Dealing With Efflorescence

DEAR TIM: There are white deposits on my chimney, on the face of a retaining wall and on my paver patio. I sometimes see these white crystals near cracks in my basement walls. I've tried washing them off and it looks good for a few hours. But the next day the deposits start growing again. What are they, are they hurting my home and most importantly, how do I get rid of them permanently? Tom B., Bethel, OH

DEAR TOM: The white deposits are almost certainly efflorescence. They're just salt crystals that are left behind when water evaporates from the masonry surfaces around your house

The problem starts inside your chimney, retaining and foundation walls, and your patio paving stones. The source of the problem can also be what's behind these materials.

These salt crystals appeared when water evaporated from a puddle on my concrete floor. Photo Credit: Tim Carter

These salt crystals appeared when water evaporated from a puddle on my concrete floor. Photo Credit: Tim Carter

Soil, brick, mortar, concrete block, concrete, etc. can all contain water soluble salts. There are many different types of salts with sodium chloride being one of the most common. Most salts readily dissolve in water as is evidenced by ocean water and any other body of water that's salty.

If you take saltwater and allow it to evaporate, the water turns into a gas (water vapor) leaving behind the dissolved salts. You can conduct this simple experiment yourself. Put a teaspoon of table salt into a cup of warm water and stir until it dissolves. Pour this solution into a shallow jelly roll baking pan. Once the water evaporates in a day, you'll see all the salt you dumped into the water.

When rain water enters your chimney, it dissolves the salts that may be in the mortar mix, the brick or even the sand used in the mortar. The same can be said about all the other masonry surfaces where you see the deposits. The salt can be in the soil and ground water is transporting the salt into the masonry surfaces.

The water in all of your masonry wants to evaporate. That's true of all water, unless the relative humidity of the air above the water or masonry surface happens to be 100 percent. But that's very rare.

This means that you have a constant invisible conveyor belt system delivering the unattractive salts to the surface of your masonry all the time.

These salts are not harming your home, but I do agree that they're unsightly. To stop the efflorescence from occurring, you need to do one of several things.

Stop the water from entering the masonry or soil that's dissolving the salts. This is much easier said than done. If you have a proper chimney crown with a great flashing under it that will help. You can also apply clear water repellents to the sides of the chimney to stop water from entering the masonry.

The backside of your retaining wall could have been treated with an asphalt spray to block water from soaking into the masonry. To solve the problem now, you can excavate all the fill material out from behind the wall and install a perforated drain pipe along the base of the wall. Backfill the wall with clean washed gravel so any water flowing through the soil towards the wall falls down through the gravel never making it to the wall.

You can try to do the same thing with your foundation wall, but that could be a massive undertaking.

Trying to clean off the salt deposits with water or any other chemical or liquid is a mistake. The water you're using dissolves the salt and transports it immediately back into the masonry. While you're rolling up your hose and putting away your scrub brush, the invisible conveyor belt system starts up and brings the salt back to the surface as the water evaporates once more.

The best way to deal with efflorescence, if you can't afford to do the waterproofing remedies, is to just brush off the salt from the surface. Depending on the amount of salt, it can sometimes be done with an old paint brush or it may require a stiff scrub brush.

The salts in chimneys will eventually deplete themselves and the problem will go away on it's own. But it can take years depending upon where you live and the amount of salt in the masonry materials.

You can watch an informative video about efflorescence at AsktheBuilder.com. Simply click on "efflorescence video". You'll not believe your eyes.

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One Response to Dealing With Efflorescence

  1. The inside of our then 70-year old house in the late 1970s had a bad case of the concrete being loose on the surface and efflourescence. If I would drag the back of my fingernails across the wall. There were many surfaces that had a hollow sound, and I had to attack those areas with a welder's chipping hammer or a putty knife, and then do a vigorous application of a wire brush to get all the loose material and salt off. I took bags and bags of rotted concrete out of the basement in the weeks and months I did all this. What a mess. I read that as water passes through the concrete from the ground, it picks up salts in the wall and carries them toward the inside surface where the water would evaporate and the dissolved salt begin to come out of solution and crystallize. The concrete at the surface where the crystallizing happened was pushed-away from the bulk concrete either by expansion from the crystals forming or by some chemical weakening of the bond between surface and bulk. I don't remember for sure, but it seems to me that after all this work I painted all the cleaned surfaces with a concrete adhesive, then I built stud walls, applied plastic sheeting and fiberglass insulation, and then sheetrock. The old walls in some places had cracks that ran at an angle from top to floor. A civil engineer I know said the concrete was probably mixed by hand on the site, and the cracks might have been where the workers took a lunch break and the morning concrete hardened before the next batch was shoveled in. I could see wood grain and knots images in the surface of the good concrete. The basement has about 7-feet of head room, and it appears it was dug out after the house was finished, then a wall formed inside the old foundation. I really don't know how deep the foundation goes, but the house was cheaply constructed in 1913. The ceiling joists and rafters are 2X4s. Blah, blah blah. Had to get it all off my chest!

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