Wood that is chemically treated with preservatives, such as chromated copper arsenate or CCA (an arsenic-based chemical) or alkaline copper quaternary or ACQ (a water-based chemical), under extreme pressures become pressure-treated wood. This is typically done to protect the lumber from insects and extend its longevity. With the right preparation, pressure-treated wood can be painted or stained, but the wood requires at least three to four months of weathering to allow the chemicals in the lumber to ooze and evaporate before preparation can begin.
Using soapy water and a stiff bristled brush, scrub all surfaces to be painted, removing any chemical residue that may be left. Rinse well with clean water and dry completely. Pressure-washing the wood is not advisable, because doing so creates nicks and chips in the wood, leaving it vulnerable to insects. Drying the wood may take several days or weeks, depending on the temperature and humidity in the area. It's important to allow the wood to dry thoroughly before attempting to paint; otherwise, the paint or stain will not adhere to the wood properly.
Selecting the proper paint or stain is important when deciding to cover pressure-treated wood. A water-based stain is recommended for proper absorption into the wood. Paints need to be acrylic-based latex exterior use for CCA-treated wood, exterior or interior use for ACQ treated wood. An acrylic-based latex primer is also recommended for painting pressure-treated wood. The primer provides a set surface for painting, eliminating the need for multiple coats of paint color.
CCA-treated woods are "no longer being produced for use in most residential settings," according to the Environmental Protection Agency; this includes exterior decks and playsets, and it is not ad. However, existing structures may contain the substance. ACQ-treated woods can be used inside the home for moldings and trims; however, they should never be used for eating surfaces, such as tables, cutting boards, or countertops. Regardless of the type of wood being prepared or painted, follow general safety guidelines when doing any home construction or decorating project, and wear proper eye protection and gloves.