In New Jersey and probably most other states white stains, spots or lines are often noticed on freshly sealed parking lots. These stains were probably there before the sealcoating was done but did not stand out on the oxidized pavement (Oxidized pavement is gray in color). Now the contrast between the jet black newly sealed asphalt and the white stains make them really stand out.
The problem was not caused by the sealcoating contractor but was there before the sealer was applied. The problem is being caused by the natural elements in our environment. These elements are mineral salts or calcium carbonite (part of lime stone). These culprits are in the water, soil and gravel under or along the side of the pavement. Believe it or not salt is present year round. Water usually is how these elements get on the pavement by either water run off or pumping up through the asphalt.
The white stains can show up anywhere on the parking lot or driveway, but where there are crack or puddles they will be more prevalent. The mineral, salt and calcium carbonate can be easy pumped up through cracks of any size, or accumulate in a low area or puddle. When the surface dry’s off the white residue is left behind. Thus causing the ugly white stains. Often times in the shape of white dots or squiggly lines.
There really is nothing you can do. If you immediately reseal the area the unsightly white stains will most probably just reappear. Time is the real solution. Eventually in most cases the rain will just wash them away.
Examples of the white stains: