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Treated Wood Wood used in structures fully exposed to the weather, such as in decks and fences (particularly those portions of the structure in ground contact), needs preservative treatment to protect it from decay (rot) and termites. Wood used in marine exposure also requires preservative treatment to protect it from decay and marine borers. For some uses, building codes may require treatment of wood with either preservative or fire-retardant, or both. Wood is pressure-impregnated with three types of preservatives: (a) preservative oils (such as coal-tar creosote), (b) organic solvent solution (such as pentachlorophenol), and 16�C10 General Technical Report FPL�CGTR�C190 Figure 16�C11.wpc outdoor decking Absorption of water causes differential dimensional change of surface flakes to give an uneven surface (telegraphing). (c) waterborne salts (such as copper quaternary ammonium complexes, copper azole, and chromated copper arsenate (CCA)) (Chap. 15).
Note: Except for the all-wood foundation, CCA-treated wood is not used in residential construction. Components for doors and windows are usually dip-treated with a water-repellent preservative (WRP). The American Wood Protection Association sets standards for pressureimpregnated and dip-preservative treatment of wood (AWPA 2008). Wood treated with waterborne preservatives, such as copper-based systems, can be painted or stained if the wood is clean and dry. Bleed of preservative through finishes, particularly latex-based paints and solid-color stains, can occur if wood is still wet from the preservative treatment. Allow wood to dry before painting; 1 week should be sufficient. decking cost calculator uk Wood treated with coal-tar creosote or other dark oily preservatives is not paintable, except with specially formulated finishes such as two-component epoxy paints; 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, 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, wpc floor for sale 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.
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