BLISTERING

Blistering is the formation of bubbles resulting from localized loss of adhesion and lifting of the paint film from the underlying surface.

• painting in direct sunlight or on a surface that is too warm, especially when applying a dark-colored solvent-based coating.
• applying an oil-based or alkyd paint over a damp or wet surface.
• excess humidity or other moisture escaping from inside through the exterior walls (less likely with latex paints, which allow water vapor to escape without affecting the paint film).
• exposure of a latex paint film to excessive moisture in the form of dew, high humidity or rain shortly after the paint has dried, especially if there was inadequate surface preparation and/or a lower quality paint was applied.

First, determine whether or not the blisters go all the way down to the substrate.

If they go down to the substrate, the problem may be due to moisture coming from inside. Take steps to remove the source of moisture, if possible. Repair loose caulk and consider installing vents or exhaust fans. If the building has wood siding, install siding vents in areas where blistering has occurred. Remove blisters by scraping and sanding, prime any areas where bare wood shows, and repaint.

If the blisters do not go all the way to the substrate, the problem is probably not related to moisture coming from behind. Rather, the blisters are likely from painting a warm surface in direct sunlight or exposing the paint film to excessive moisture. In any case, sand, scrape and then prime any exposed bare wood. Coat with a top quality acrylic latex exterior paint.

Primer: Spot prime with ACRI-SHIELD Acrylic Bonding Primer No. 515
Finish: One or more coats of ACRI-SHIELD Acrylic Finish No. 519 Flat, 739 Satin or 619 Gloss
Or
One or more coats of ACRI-PRO 100 Acrylic Finish No. 929 Flat, 3729 Satin, or 6029 Semi-Gloss

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