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.
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.