Staining. Timber

Wood is painted in order to preserve from decay, to minimize changes in moisture content that lead to distortion, and for decoration. It is a waste of time and effort to apply expensive paints or stains to exterior wood not previously treated with preservative. Preservatives are designed to penetrate the timber to protect against microorganisms and insect attack. Modern preservatives can be over-coated with paint without problems. 

Bleeding. Discoloration caused by migration of components from the underlying film. Substrates that can cause problems are those coated with tar- or bitumen-based materials, paints made on certain red and yellow organic pigments (which are partially soluble in solvent), some wallpapers, and timber stains that contain soluble dyes. The remedy is to use a specially formulated sealer or an aluminum paint. 

The presence of polyphenols and tannins in woods such as oaks, western red cedar, eucalypts and Nothofagus sp. leads to blue-black tannin stains during sawing of moist timber, or in the grain around metallic wood fastenings when the wood remains moist. 

Species sueh as oak and beech check quite readily, and to avoid this problem the humidity is kept high early in the kiln schedule. Also the temperature is kept low in order to maintain the timber s strength. Only as the lumber dries and becomes stronger can the humidity be lowered and the temperature raised to provide more rapid drying eonditions. Surfaee ehecks forming early in the kiln schedule may close up later when the surfaee fibres go into compression and the core into tension, although the failure plane remains in the tissue. Such checks can be revealed subsequently as hairline streaks if the wood is stained. 

As a rule, wood should be dried to its fiber saturation point or below before preservative treatment. Kiln-drying is eommon for dimension lumber, but the method of drying varies with elimate and eapital resourees. For large timbers and railroad ties air-drying is used, despite the inereased time required. However, in some elimates it is diffieult to air-dry material before it begins to suffer attaek by stain fimgi or even deeay fungi, and alternative approaehes must be eonsidered. 

Nitrogen-substituted 4-aminophenols have long been known as antipyretics and analgesics, and the production of these derivatives represents significant use of this compound. 4-Aminophenol is also used as a wood stain, imparting a roselike color to timber (156), and as a dyeing agent for fiir and feathers. 

Products and Uses Frequently used on telephone poles, pilings, fences, railroad ties, landscape timbers, playground equipment, outdoor wood products, outdoor furniture, in wood varnish, stain, and sealant. Also added to laundry spray starch. 

Aspen Populus tremuloides) is the most widely distributed tree species in North America. In Canada aspen represents more than 50% of the merchantable hardwood timber. Its previously neglected utilization has increased substantially in recent years. A serious limitation to its use in the pulping process, however, is the pronounced susceptibility to blue stain caused by fungi (77). 

For sapstain treatment (protection of freshly cut and sawn timber against staining fungi and superficial moulds) borax is used in mixture with other fungicides, in particular with sodium pentachlorophenate (Section 5.6.3), but with sodium phenylphenolate (Section 5.4.1) or with quaternary ammonium compounds (Section 16.1) too. 

European Standard EN 152-1, 1988. Laboratory method for determining the protective effectiveness of a preservative treatment of converted timber against blue stain in service (brushing procedure). 

Blue stain in service. Bluestain in service can be evaluated either in the laboratory or as part of a field evaluation using coated timber samples such as L-joints (EN 330, 1993). In the laboratory, accelerated results can be obtained although treated samples are often pre-conditioned by external weathering or by a period of exposure to UV in the laboratory (EN 152, 1988). Performance is evaluated by determining the degree of visual defacement. 

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