SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/wood-blue-stain-blotchy

What can cause stain to soak into a board unevenly and look blotchy?

Fungal infection such as blue stain before drying.

Start playing free

  1. Applying stain with a natural bristle brush
  2. Blue-stain fungi that made the wood porous ✔
  3. Sanding with too fine a grit

Why: Blue-stain fungi or bacteria can make wood very porous, so it soaks up thin liquids like stain unevenly. The problem may not show a color change and cannot be fixed once the stain is applied.

Huh, didn't know that: You can test lumber before finishing by applying denatured alcohol or stain to a scrap to find infected areas.

The dad joke
What's blue and smells like red paint? Blue paint.
Like this card?
Play the game

References

Answer: Blue-stain fungi that made the wood porous. Blue-stain fungi or bacteria can make wood very porous, so it soaks up thin liquids like stain unevenly. The problem may not show a color change and cannot be fixed once the stain is applied.

  1. Wood Handbook: Wood as an Engineering Material, FPL-GTR-282 (USDA Forest Products Laboratory, 2021) research.fs.usda.gov/treesearch/62200
    These infections can make the wood very porous, allowing it to soak up large quantities of thin liquids such as stain.
    Checked 2026-10-10.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

Trades & ShopWhat does a pre-stain wood conditioner help prevent on woods like pine?Trades & ShopOSHA says a hand-fed circular ripsaw must be guarded by what?Trades & ShopOSHA requires hand-fed circular ripsaws to have which part to help stop wood being thrown back?

That's stuff everyone should know.