Water soluble extractives are most troublesome because of the difficulty of keeping water out of wood that is in service.
Extractive stains can appear in several forms.
Diffused discoloration can result from rain or dew penetration through the finish whereas rundown discoloration typically results when water collects on an unfinished surface, such as the back of siding or unprimed ends of boards. Water-based finishes can dissolve extractives and cause discoloration as a result. Extractive discoloration Extractive bleeding resulting from ice-dams Several factors will affect the amount and type of extractive discoloration. The heartwood of certain wood species, such as Western Red Cedar and Redwood, may have high concentrations of water soluble extractives, whereas other species, like some pines and firs, may have higher concentrations of pitches and resins. The moisture content of the wood substrate also affects extractive staining.