Wood finish cracking or crazing

Likely causes

The causes the most sources give come first.

1. Too thick a film: heavy coats, or layer on layer of old finish.

   Two sources: Mohawk (RPM) and USDA Forest Products Laboratory , sources [1, 2]

2. The Wood Handbook says wood swelling and shrinking under the film as it gains and loses moisture cracks a film that is too thin or not flexible enough.

   One source: USDA Forest Products Laboratory, the federal reference on wood and how it takes a finish , sources [2]

3. The Wood Handbook says raised grain cracks a film from below, and that finishes with no water in them are the most prone, because they never raise the grain before they set.

   One source: USDA Forest Products Laboratory, the federal reference on wood and how it takes a finish , sources [2]

How to tell which

1. The Wood Handbook says cracks along the grain often follow the dense latewood bands, while cracks across the grain point to the wood moving under the finish or a thick build of old finish.

   One source: USDA Forest Products Laboratory, the federal reference on wood and how it takes a finish , sources [2]

The fix

1. The Wood Handbook says that if the cracking is not severe, sand it and add one or two coats; where the old finish has cracked badly, take it off and finish the bare wood again.

   One source: USDA Forest Products Laboratory, the federal reference on wood and how it takes a finish , sources [2]

Next time

1. Build the film in thin coats and keep the total within the maker’s limit: Mohawk gives 4 mils dry, General Finishes up to 5 mils for Arm-R-Seal.

   Two sources: Mohawk (RPM) and General Finishes , sources [1, 3]

2. Raise the grain and sand it before the first coat.

   Two sources: USDA Forest Products Laboratory and General Finishes , sources [2, 4]

Often comes with

• Raised grain
• Cloudy or white finish (blushing)

The finishes it applies to: oil-based polyurethane, spar urethane, lacquer. Every other problem: the finish troubleshooter.