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Curing Colored Concret

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Question:

This integrally colored floor was cured with a non-breathable curing paper. What are the white marks on the surface, and how do we remove them?

 

Answer:

A non-breathable curing material will create a vacuum that sucks moisture from the concrete up to the surface. The moisture then has nowhere to go because it is trapped beneath the non-breathable covering. Anything carried to the surface along with all that moisture (such as natural salts in the concrete) will be left on the surface as the moisture evaporates once the covering is removed.

The white haze on the concrete surface seen in the picture is dried salt residue, or efflorescence, that was left behind when the cover was removed. Non-breathable curing membranes tend to create more efflorescence because of the dramatic vacuum they create when placed on wet concrete. A breathable covering is always preferred, especially on colored concrete.

In this case, using lots of water to remove the surface salts while they were still wet would have minimized the white haze. Now, however, multiple passes of a rotary scrubber with a scrubbing pad are needed to remove the deposits.