Efflorescence is a white, powdery substance that appears on the surface of concrete, masonry, and stucco products. It's a very common occurrence and, although it's usually harmless, efflorescence can be a real eyesore. It goes unnoticeable on plain, gray concrete and block but becomes very visible on colored concrete and brick. Normally, the problem doesn't show up until weeks or months after installation and often becomes a dispute between angry customers and contractors.

Efflorescence is caused by water moving through concrete and masonry products. As it travels through in a process called capillary action, the water dissolves salts contained in the material. When the water reaches the outside, it evaporates and leaves the salts on the surface. Overtime the buildup of the salty deposits can become quite significant. Lower temperatures, humidity, rain, or anything that will keep the material wet such as sprinklers facilitates this process.

Despite efforts of manufacturers and contractors to limit efflorescence in their products, they are using raw earth materials that contain salt and will vary in salt content from batch to batch and from one location to another.

Removing Efflorescence

Most efflorescence can be removed by pressure washing with water or scrubbing with water and a brush. The water will dissolve most of the salts but must be rinsed away completely. Tougher deposits can be removed with special cleaning products. Acid washing with diluted muriatic acid should only be used as a last resort because it will etch away some of the cementitious material on the surface. Muriatic acid should be diluted to1 part acid and 12 parts water. The surface then needs to be neutralized with a solution of baking soda or diluted household ammonia. This will stop the acid from attacking the material any further.

Preventing Efflorescence

When it comes to concrete, there are a few steps that can be taken to limit or prevent efflorescence. Proper drainage away from a slab will help reduce moisture moving up from the subgrade. This also includes eliminating any unnecessary sources of water such as downspouts that dump water underneath a slab.

Concrete sealers can also prevent efflorescence from reoccurring. Although regular film forming sealers will stop water from seeping down into the pores, they still allow moisture from the sub-grade to pass through. This can create and trap efflorescence between the sealer and the concrete. Penetrating sealers are the best defense against efflorescence. These silicone-based sealers work by penetrating the surface and reacting with free lime to form calcium silicate. It's like filling the capillaries and pores with cement to block the migration of water. If the water can't get to the surface, then salts can't be left behind.