Term: tannin staining

Tannin staining refers to a type of discoloration that occurs when natural tannins—organic compounds found in certain woods, especially hardwoods like cedar, redwood, and oak—bleed through paint or coatings and appear as brown or yellowish stains on the surface.

This typically happens when:

• The wood is exposed to moisture, which activates the tannins.
• Inadequate priming or sealing is done before painting.
• Water-based (acrylic) paints are used without proper stain-blocking primers.

Common scenarios where tannin staining occurs:

• Painting over bare or inadequately primed timber.
• Painting exterior timber surfaces exposed to rain or humidity.
• Using low-quality or incorrect primers.

Prevention and treatment:

• Use a high-quality, stain-blocking primer (such as an oil-based or shellac-based primer) before applying topcoats.
• Ensure the timber is dry and clean before painting.
• Apply multiple coats of primer if necessary, especially on high-tannin woods.

In the Australian painting industry, managing tannin staining is crucial for achieving a professional, long-lasting finish—particularly on exterior timber cladding, fascia boards, and decking balustrades.