Blue stain in service

Other names:

Often confused with 'sap stain' or 'blue stain' of freshly felled logs or fresh sawn timber. These fungi are mostly from different genera, although they cause a blue colour which is still detectable in service.

Habitat:

Lives in the sapwood cells of moist wood, but mainly ray cells. It cannot grow in waterlogged wood, or below about 20% moisture content. Fungal hyphae penetrate the cell walls and feed on cell contents, but not on the substance of the wood.

Damage characteristics:

Shows up as disfigurement of the wood, and especially of clear finishes. Early failure of surface coatings is caused by rupture of the fruit-bodies.

Discolouration is caused by sap stain which has occurred in the log but may still be detectable after drying and use of the timber. This will only affect the aesthetic value of the wood. Damage to coatings will only occur through the growth of blue stain in service.

Identifying features:

Black or blue-black streaks and patches in wood or coating. Sometimes dark hyphae and fruit-bodies are present (tiny nodular structures erupting through the coating and producing numerous dark spores). Staining penetrates deeply and often cannot be removed by surface planing.