When applying US SPEC sealers it is pertinent to make sure all the moisture has dissipated from the concrete you are sealing. The white blushing and dark lines are caused by excess moisture in the concrete. Moisture content can be tested several different ways:  taping a plastic sheet over an area and waiting to see if visible condensation occurs or using a moisture meter. You are looking for a moisture content as close to 0% as possible.

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