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Shrinkage Cracking on Stamped Concrete

Question:

I have a recently poured stamped concrete pool deck that shows hairline cracks all over the surface when it becomes wet. When the surface dries, though, it has a nice finish. The contractor sealed the surface a couple of days after concrete placement with a solvent-based product. Is this a sign of a poorly sealed surface? Since it's a pool deck, is premature failing a concern if it gets wet too often? Will applying an extra coat of sealer correct the problem?

Answer:

This issue has nothing to do with sealer. Those cracks you see are shrinkage cracks. They are caused when the surface of the concrete shrinks rapidly during the initial curing phase. When the concrete surface dries, or cures, too rapidly, the surface contracts (shrinks) and you end up with these small hairline cracks. (For more information, read Why Concrete Cracks.) Typically, shrinkage cracking is only an aesthetic issue and does not affect the structural integrity of the concrete. As you noted, you don't see the cracks unless the surface is wet.

Do not apply additional sealer. The sealer you have down now appears to be doing its job, so I suggest you reseal only when the original sealer has worn off. Overapplication of sealer will only lead to other issues, and will do nothing to eliminate the cracks.

Water highlights the shrinkage cracks on this
colored concrete surface.

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