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Douglas-fir and southern yellow pine are available saw-textured (Table 16�C1). Saw-textured plywood holds paint much better than does smooth plywood. If smooth plywood is to be painted, scuff-sand it with 50-grit sandpaper and use high-quality latex paint. Latex primer and top-coat generally perform better than oil-alkyd paint. Paint performs poorly on smooth plywood if used as siding but reasonably well on smooth plywood in protected areas such as soffits. Resin-treated paper bonded to plywood forms a medium-density overlay (MDO); MDO eliminates cracks caused by lathe checking and provides plywood with excellent paintability, composite frame windows suppliers in south africabut the edges are still vulnerable to water. Seal the edges with oilalkyd primer or an edge sealer formulated for this use. Paper over-laid products should not be finished with semitransparent stain or other penetrating finishes. Use film-forming finishes such as paints or solid-color stains and ensure sufficient film thickness (0.004�C0.005 in. (0.10�C0.13 mm), or 4�C5 mils). even if the paint adheres to the treated wood, the dark oils tend to discolor paint, especially light-colored paint.
Wood treated with a water-repellent preservative, by vacuum-pressure or dipping, is paintable. Fire-retardant- (FR-) treated wood is generally painted rather than left unfinished because the FR treatment may darken or discolor wood. FR treatment does not generally interfere with adhesion of finishes; however, you should contact the paint manufacturer, the FR manufacturer,high adaptability to climate lumber fascia boards and the treating company to ensure that the products are compatible. Some fire retardants may be hydroscopic and cause wood to have high MC. FRs for wood used outdoors are formulated to resist leaching. Weathering Weathering is the general term describing outdoor degradation of materials and manifests itself physically and chemically (for example, cracking and exfoliation of rock, corrosion of metals, and photodegradation of organic materials).
Ultraviolet (UV) radiation in sunlight catalyzes photodegradation of organic materials exacerbated by moisture, temperature change, freeze�Cthaw cycles, abrasion by windblown particles, and growth of microorganisms. Degradation occurs near the surface of wood, wood products, and finishes. Effect on Wood Weathering takes many forms depending on the material; wood and wood products initially show color change and slight checking. Leaching of water-soluble extractives, chemical changes, and discoloration of the surface by microorganisms cause color change. cost of composite prodcutsAs weathering continues, wood develops checks on lateral surfaces and checks and cracks near the ends of boards, and wood fibers slowly erode from the surface. Wood consists of three types of organic components: carbohydrates (cellulose and hemicelluloses), lignin, and extractives. Weathering affects each of these components differently, and physical and chemical changes affect paintability.
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