What is that white stuff on your concrete or masonry block wall? It can be just a white powder on your concrete, salt-like crystals, white fuzzy stuff, or what looks like white stalactites growing on your concrete wall. These white deposits happen when water is drawn out of a cementious material: it is called efflorescence.
It is a scientific reaction. You will commonly see primary efflorescence initially during the curing process. When concrete cures the water is naturally being drawn out of it and a sort of salt is left behind. Different admixtures can prevent this from happening but efflorescence at this stage is usually not a problem. After the concrete is cured, secondary efflorescence can happen if there is a water problem present. This happens after the concrete is established. This is when efflorescence is usually more than a white powder. Most people confuse secondary efflorescence with mold because it looks like a white, dusty mold growing on your concrete. It is not mold; however, it is a sign of a water problem. And where there is water there is mold and potential structural damage.
You can remove efflorescence with phosphoric acid but that won’t prevent that water problem. If you see efflorescence it means that water is getting trapped inside your block or concrete wall. If water is being trapped inside the foundation then spalling, scaling or cracking can happen in the future. Spalling is when the concrete begins to crumble and break apart. Spalling will weaken the concrete wall and ultimately the total structure. This is why waterproofers don’t use water repellants on both sides of the wall. They don’t want to trap moisture inside the wall.
Efflorescence happens with more porous materials like brick. It is common to see a brick wall almost turn all white from efflorescence. Basically water runs through the cement block or brick and pulls out the salt deposits or alkalies of salt from the Portland cement.
Some of the same waterproofing techniques and water diversion systems work to prevent efflorescence. Because when you prevent water intrusion you prevent efflorescence. Efflorescence is just a symptom of the real problem. You don’t want to just treat the symptom; treat the real problem and waterproof your foundation walls. Install a complete basement waterproofing system. Maintain your gutters and downspouts. Have the proper drainage in your yard and around the perimeter of your house. If you have water trapped in your wall, efflorescence is the least of your worries. Take care of the water problem before it causes serious structural problems.