About Pressure-Treated Plywood

Written by peggy deland
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Pressure-treated plywood is normal plywood that has been specially treated to be more resistant to insect and weather damage. It is typically a greenish colour due to the chemicals used in the pressure-treating process. Pressure-treated plywood is soaked in a combination of preservatives under high pressure, which forces the chemicals deep within the wood. The plywood is then removed from the solution and placed flat in special racks to dry.


Pressure-treated plywood is far more resistant to insect and weather damage than normal plywood. The preservatives used in the process prevent the growth of mould and make the plywood unpalatable to termites and other insects. Pressure-treated plywood can be used in outdoor or hostile environments where normal plywood would be expected to fail. Pressure-treated plywood is relatively water resistant because the chemicals used in the pressure-treating process are not water soluble and reduce water absorption.


Pressure-treated plywood is easily identified by its unusual greenish tint, which can vary from light green to very dark green. It is heavier than untreated plywood due to the chemical load contained in the pores of the wood. Pressure-treated plywood is typically marked as such on the face of the board and may also have a yellow tag to identify it.


Pressure-treated plywood is manufactured almost exclusively as 4-foot-by-8-foot sheets, although retailers may re-saw it into other sizes depending on demand or customer request. Thicknesses range from approximately 3/8 inch to 1 inch. For boat flooring, individual sheets are glued together to achieve greater thicknesses, occasionally in excess of 2 inches.


Special galvanised, painted, stainless steel, or aluminium fasteners are usually used when installing pressure-treated plywood. There are two reasons for this. First, the chemicals used in the pressure-treating process can be quite corrosive to standard fasteners. Second, the environments that typically require pressure-treated plywood are almost always hostile to standard iron nails and screws.


Some pressure-treated plywood may contain arsenic and other toxic chemicals. Most pressure-treated lumber is not suitable for indoor use. Pets, children and adults may be exposed to toxic levels of these chemical. Pressure-treated plywood should not be used in or on the ground, as these chemicals can leech into the soil, contaminating groundwater. Sawdust from cutting pressure-treated plywood should be collected and disposed of properly. Some newer pressure-treated plywood does not contain these toxic chemicals, and this type should be selected whenever possible.

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