Wood Preservation Canada - Frequently Asked Questions

Frequently Asked Questions

What is pressure treatment?

Pressure treatment is a process that forces chemical preservatives into the wood. Wood is placed inside a closed cylinder, then vacuum and pressure are applied to force the preservatives into the wood. The preservatives help protect the wood from attack by termites and fungal decay.

How do wood preservatives work?

A wood preservative must have the ability to do three things: (1) penetrate the wood, (2) neutralize the food supply within wood in which decay fungi and wood destroying insects live, and (3) be present in sufficient quantities in a non-leachable form so that its protection outlasts the useful life of the wood product. Effective preservatives will also kill existing decay, fungi and insects, which might already exist in the wood. A true wood preservative is a toxic material, to be used with care. It will penetrate wood fibers and stop the organic enemies of wood.

What projects can I use Alkaline Copper Quaternary (ACQ) or Copper Azole (CA) preserved wood on?

ACQ and CA preserved wood are registered for use in Canada by the Pest Management Regulatory Agency (PMRA) for the following uses: decks, patios, landscaping timbers, gazebos, residential fencing, walkways and boardwalks and freshwater docks.

Is CCA preserved wood still used?

CCA is registered for use in permanent wood foundations, agricultural applications such as farm fencing and posts, and industrial applications such as marine pilings, utility poles, bridge timbers and guard rail posts.

How much preservative is in treated wood decking?

Wood preservatives used at the commercial treating plant are concentrated liquids, but treated wood contains only a small amount of wood preservatives. For example, ACQ pressure treated wood generally contains only 0.75% to 1.2% of wood preservative; the rest of the lumber is just wood. Concentrations in pressure treated wood for uses such as preserved wood foundations, marine pilings or utility poles vary and will be higher than that in wood used for residential applications.

I’m building a deck, what do I need to know about handling preserved wood?

Whenever you use preserved wood there are some tips you need to follow:

Wear a dust mask and goggles when cutting or sanding wood.
Wear gloves when working with wood.
Some preservative may migrate from the treated wood into soil/water or may dislodge from the treated wood surface upon contact with skin. Wash exposed skin areas.
Wash thoroughly after use with soap and water and before eating or smoking.
Wash work clothes separately from other household clothing before reuse.

Is there a preferred way to store preserved wood while working on my projects?

There are a few simple precautions you should take to store your preserved wood:

Unload lumber in a dry place
Elevate lumber on stringers to prevent absorption of ground moisture and to allow air circulation. Do not store lumber in direct contact with the ground.
Cover lumber stored in an open area with a material that will give protection from the elements, but be porous enough to allow moisture to escape. Polyethylene or similar non-porous covers may trap moisture.

How do I make my deck last?

To protect your investment, a regular maintenance program is important. A good maintenance program begins during construction and continues throughout the life of a project. Here are some important construction tips:

Use an end-cut preservative (copper naphthenate in ground contact or zinc naphthenate above ground) on all cuts and holes that expose untreated wood.
Use a fastening system that provides maximum holding power and corrosion resistance, and follow the manufacturer’s recommendation for all metal products.
Use screws to add extra holding power for decking and all applications where appearance is important.
Drill pilot holes, especially when working near the edge of the board. This will minimize splitting.
Apply a weather resistant finish. Any exposed wood, pressure treated or not, should be protected from the weather. Application of a quality clear water repellent or semi-transparent stain which contains a water repellent will help minimize the cycles of moisture take-up and loss the wood goes through outdoors. For maximum protection, a water repellent should be applied as soon as the deck or other project construction is completed.

Why do I need to drill pilot holes?

Drill pilot holes to minimize splitting, especially when nailing or screwing near the edge or end of a board.

For what projects should I not use preserved wood?

Do not use preserved wood for the following:

Preserved wood should not be used where it may come into direct or indirect contact with drinking water, except for uses involving incidental contact such as fresh water docks and bridges.
Do not use preserved wood under circumstances where the preservative may become a component of food, animal feed or beehives.
Do not use preserved wood as mulch.

Why do I need to use an end-cut preservative?

When building your outdoor project with preserved wood, it is important to protect the cut ends of boards from fungal decay. All cuts and holes that expose untreated wood should be liberally brush-coated with two applications of an end-cut preservative (copper naphthenate in ground contact or zinc naphthenate above ground) before the wood is installed. Always follow the manufacturer’s recommendations.

What kind of fasteners do I need to use for my preserved wood deck?

Use corrosion-resistant fasteners; preserved wood is designed for long-term performance in outdoor applications and, therefore, require high quality, corrosion-resistant nails, screws, other fasteners, hardware and any metal product.

Warning – Certain metal products (including fasteners, hardware and flashing) may corrode when in direct contact with preserved wood. To prevent premature corrosion and failure it is important to follow the recommendations of the manufacturers for all metal products.

Is there any material that I can’t use with preserved wood?

Do not use preserved wood in direct contact with aluminum; when using preserved wood in close proximity to aluminum products, such as aluminum siding, flashing, and door and window frames, a 1/4" minimum space must be allowed for between the preserved wood and the aluminum products. Polyethylene or nylon spacers can be used to maintain the 1/4" spacing. Another option is to use a polyethylene barrier, with a minimum thickness of 10 mils, between the preserved wood and the aluminum product to prevent direct contact of the wood and the aluminum.

Can I apply a finish to my deck or fence?

If you desire to apply a paint, stain, clear water repellent or other finish to preserved wood, we recommend following the manufacturer's instructions and label of the finishing product. Before you start, we recommend you apply the finishing product to a small exposed test area before finishing the entire project to ensure it provides the intended result before proceeding.

I’ve finished building my deck, what do I do with the leftover wood?

Here are some tips for when you’ve finished working with preserved wood:

Do not burn preserved wood.
All sawdust and construction debris should be cleaned up and disposed of after construction.
Preserved wood may be disposed of in landfills or burned in commercial or industrial incinerators or boilers in accordance with federal, provincial and local regulations.

Why can I not burn treated lumber?

Preserved wood must not be burned because combustion breaks the unique bond formed between the preservative solution and the wood. When this bond is destroyed, the components of the preservative can be released in the form of ash and particulates, which can be harmful if inhaled. It is completely proper and legal to send treated wood to a landfill.

Will the colour of my preserved wood deck change with time?

The green color of preserved wood is the result of the treatment process. Over a period of time, this color will diminish and change to a pleasing light brown, if left unstained.

How do I clean mold from my deck?

Remove mold with soap and water. Mold growth can and does occur on the surface of many products, including untreated and treated wood, during prolonged surface exposure to excessive moisture conditions. To remove mold from the treated wood surface, wood should be allowed to dry. Typically, mild soap and water can be used to remove remaining surface mold.

Where can I get more information about preserved wood?

For more information visit www.ptw-safetyinfo.ca.