Wood products that have been preserved by pressure treatment in Canada use preservatives registered for this purpose by PMRA/Health Canada. Treated products are produced according to the requirements of a series of treatment and commodity use standards contained in CSA O80 Wood Preservation, or to the requirements of the purchaser.

Wood treated with these preservatives is protected against biological decay, insect and marine borer attack because the treatment process forces the preservative deep into the wood cell structure. The effective long term resistance to biological degradation makes pressure treated wood a suitable building material for a wide range of uses.

General Use and Handling Practices

• Avoid direct skin contact when handling or working with pressure treated wood. Wear gloves.
• Avoid frequent or prolonged inhalation of sawdust from wood, treated or untreated. When sawing or machining wood, especially in confined areas, wear a dust mask. Whenever possible, these operations should be performed outdoors.
• When power-sawing and machining, wear goggles to protect your eyes from flying particles.
• Wash exposed area thoroughly after skin contact, and wash hands before eating, drinking or use of tobacco products.
• If preservatives or sawdust accumulates on clothes, launder before reuse, but wash clothes separately from other household clothing.
• Dispose of treated wood by ordinary trash collection or burial. Do not burn treated wood. Hazardous chemicals may be produced as either part of the smoke and/or ashes.

General Use Site Considerations

The recommendations contained in CSA O80 Wood Preservation standards are based solely on the efficacy of the preservative for specific applications. Preservatives and their uses are regulated by government authorities. It is the responsibility of the user to ensure that the end use of treated wood does not conflict with current laws and regulations.

• Treated wood should not be used where it may come in direct or indirect contact with public drinking water, except for uses involving incidental contact such as docks and bridges.
• Do not use pressure treated wood where it may become a component of food or animal feed. For example, treated wood should not be in direct contact with silage.
• Do not use pressure treated wood for cutting boards or countertops.
• Do not use pressure treated wood for construction of those portions of beehives which may come in contact with the honey.
• CCA treated wood used for patios, decks and walkways should be free of surface preservative residues.
• Do not use creosote or pentachlorophenol treated wood for farrowing or brooding facilities.
• Wood treated with creosote or pentachlorophenol should not be used where it will be in frequent or prolonged contact with bare skin (i.e.: chairs and other outdoor furniture).
• Creosote treated wood should not be used in residential interiors.
• Creosote treated wood in interiors of industrial buildings should only be used for wood-block flooring and industrial building components which are in ground contact and are subject to decay or insect infestation.
• Wood treated with creosote should not be used in the interiors of farm buildings where it may be in frequent direct contact with domestic animals or livestock which may bite or lick the wood.
• Pentachlorophenol treated wood should not be used in residential, industrial or commercial interiors except for laminated beams or for building components which are in ground contact and are subject to decay or insect infestation.
• Wood treated with pentachlorophenol should not be used in the interiors of farm buildings where it may be in direct contact with domestic animals or livestock. In farm buildings, pentachlorophenol treated wood may be used only where the wood is in ground contact (i.e.: posts, support poles, foundation support and the bottom six inches of stall skirts boards).

Field Treatment

Pressure treatment substantially extends the service life of wood and enhances its durability. Through the pressure treatment process the outer section of a piece of wood accepts preservatives and forms a protective shell which acts as a barrier from wood-destroying fungi, insects and bacteria. In order to be effective, this protective barrier must be continuous or free of any openings which would allow decay-causing organisms access to the untreated section of the wood member. To prevent damaging the protective barrier, it is strongly recommended that all machining of the wood such as adzing, boring, chamfering, framing, gaining, incising surfacing or trimming be done prior to treatment.

Where this is not possible, field treatment is necessary to ensure the integrity of this protective barrier. When fabricating on the job-site is a necessity, all cuts, holes and injuries of the surface of treated material must be field protected in order to restore the continuity of the protective shell. Field protection can be afforded by brushing, dipping, soaking or coating. Whatever application method is used, care should be taken to assure that the affected surfaces are thoroughly saturated with the field treating solution. When brushing or dipping a minimum of two generous coats should be applied. The second coat should only be applied after the first has been absorbed by the wood. Horizontal holes may be filled by pouring the preservative into them with a bent funnel. Care should be taken to keep preservatives off the ground.

Whenever possible, cuts, holes and injuries of wood surfaces should be field treated using the same preservative with which it was originally pressure treated. Of course, the field preservative has to be compatible with the original preservative and the end use intended. Other preservatives specified in CSA O80 for the individual product may also be used. Acceptable field treatment preservatives include creosote and creosote mixtures, copper naphthenate solutions containing a minimum of 2% copper.

When applying a field preservative, use precautions as stipulated on the preservative label.

Whenever possible the cut ends of posts etc. should be installed above the ground and field treatment applied. This is because the decay risk is higher at or below ground level.