Concrete sealer blisters and bubbles

by Jeff
(Iowa)

Q. We had stamped concrete put in around our pool area last summer. We live in Iowa. It was sealed 2 days after being poured and the sealer bubbled and turned a white chalky color.

This summer someone came back and applied a product called xylene and told us it would reactivate the old sealer. He applied it yesterday afternoon and last evening there were some bubbles but didn't look bad. This a.m. he came back and applied another coat to get rid of the bubbles. He applied it before the sun was on it. I came home at noon and there were hundreds of bubbles all over the concrete and two spots were white again.

What can I do? I am severely frustrated and am running out of money to keep having the same problems. Please help with any suggestion. Thanks!!

A. Concrete sealer blisters and bubbles as well as concrete sealer whitening are caused by moisture. When concrete is freshly poured it has a high water content (mixing water).

After the concrete hardens this water escapes the concrete as a gas (water vapor). Most decorative concrete sealers are quite sensitive to moisture. They form a film or skin on the surface of the concrete and don't allow this gas to escape. This moisture vapor is what is causing the blisters and whitening of the concrete.

When concrete is a year old or older it absorbs moisture from the air (humidity and dew) and from rain. As the sun comes up and heats up the concrete this moisture also leaves the concrete as a gas. If the concrete is sealed in the morning or during the heat of the day, blisters and bubbles will form because the sealer hasn't cured or hardened enough to resist the pressure from the moisture escaping the concrete.

Xylene is commonly used to re-wet the sealer and lay the bubbles back down. The bubbles and blisters should be broke open for this to work best. In most cases xylene should fix the whitening also. If it doesn't these areas will have to be stripped of the sealer and re-sealed.

The best time to seal new decorative stamped concrete is 28 days after it is poured. It can be wet cured or curing paper can be used to cure the concrete in the first week.

The best time of day to seal new or old decorative concrete (or use xylene) is late afternoon or early evening when the concrete is cooling down and the sun is setting. By now most all the moisture has escaped the concrete from the day and night before.

The temperature should be 50 - 70 degrees. This will give the sealer all night to harden and best resist any moisture escaping the next day. Once the sealer is fully cured, blisters and bubbles will not be a problem.