A white bloom or powdery deposit of crystalline material that sometimes appears on the surface of concrete or masonry is called efflorescence. It consists of crystalline salts brought from the interior of the concrete by water, and deposited on the surface by the evaporation of the water. When water moves through cracks and porosity in the concrete, it brings to the surface the soluble calcium hydroxide that result from the reaction between cement and water. After evaporation of the water, the calcium hydroxide remaining on the surface reacts with carbon dioxide in the air, forming calcium carbonate, the familiar white crystalline deposit. Efflorescence can be removed by washing the concrete with water and vinegar in most cases.
Southern California water has a high mineral content. When this water is deposited on to sealed concrete surfaces, ie; pool water splashed out, irrigation water from sprinklers, ect… it will evaporate leaving a white residue. Similar to water spotting left on a car after washing with out proper drying. This residue is easily wiped away with a Lime-away solution, but the only permanent solution is a water softener or the removal of the water source onto the treated surface.
One common cause of sealer problems is moisture retention in the surfaces to be sealed. In porous materials, such as common brick, Mexican tiles, concrete, ect… There is room for tremendous quantities of water, in many cases; this moisture cannot be seen on the surface. Causes of moisture problems will vary: a high water table, hydrostatic pressure from underground water sources, run off from heavy landscape watering in adjacent areas. We recommend that landscape irrigation water be controlled to prevent water from standing and drying on sealed surfaces and over watering of landscaped areas. Over watered soils can cause problems with efflorescence, thus breaking down sealer prematurely.