Bubble effect in concrete sealer

Q. I had a concrete pad and porch sealed with Butterfield color lot # 57948. The weather was warm and dry and the sealer was not put on until approx 16 hrs after the pad was poured. The porch was poured in Oct 2010.

My question is why did it dry without soaking into the concrete. It dried on top and left a bubble effect over both the pad and porch. Also, what is the best way to correct this problem?

A. Butterfield's Sealers are topical, film forming sealers that dry on top of the concrete and leave a protective coating. They are not penetrating sealers that absorb into the concrete and leave no trace on the surface.

I have also used these sealers and had blistering or bubbles form after it has dried. These sealers are very sensitive to temperature, you cannot apply them in the heat of the day because:

1. If the sealer is applied too thick, the top of the sealer will dry too fast, not allowing the solvent in the sealer to evaporate and escape thus forming bubbles.

2. Newly poured concrete has a lot of moisture in it that needs to escape in the form of moisture vapor. Applying a topical sealer in the morning or in the heat of the day as the slab is heating up by the sun will not give the sealer enough time to fully cure or strengthen to handle the amount of moisture vapor that is evaporating out of the slab causing blisters of bubbles.

3. Never apply concrete sealer if moisture is visible on the surface of the concrete (from rain, dew, or washing the concrete).

The best time to seal a newly poured concrete slab is early evening as the slab is cooling down. Apply the sealer in very thin coats, two coats 24 hrs apart is recommended. This gives the sealer enough time to cure and be able to withstand the pressure of moisture vapor escaping.

You can pop the bubbles by hand or with a stiff bristle broom, vacuum the surface and roll or spray on some xylene. This will re-wet the sealer and make it look like new again.

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