Understand pressure-treated lumber ratings, when you need ground-contact stock in Alberta, and how to fasten and cut it safely.
What pressure treatment does
Pressure treatment forces wood preservative deep into the lumber. That protection helps the wood resist rot, fungal decay and insect damage, which are the reasons outdoor wood fails.
In Canada, residential treated lumber uses copper-based preservatives such as ACQ or copper azole (CA). Look for the CSA O80 treatment mark on the tag or stamp.
Above-ground vs ground-contact
Treated lumber is sold with different levels of preservative retention. Above-ground stock suits deck boards, railings and other parts that stay clear of soil. Ground-contact stock carries a higher retention and is the right choice for posts, timbers and anything touching soil or sitting where water collects.
In Alberta, spring melt and frost heave keep the ground wet and moving, so use ground-contact stock for any post or timber that goes into or sits on the ground.
Use the right fasteners
Modern preservatives can corrode ordinary steel. Use hot-dip galvanized or stainless fasteners and connectors that are rated for treated lumber, and check the tag on the lumber and the fastener packaging.
Cutting and handling
- Wear gloves, eye protection and a dust mask when cutting or sanding.
- Brush a copper-based end-cut preservative on freshly cut ends.
- Do not burn treated wood, and follow local guidance for disposal of scraps.
Let it dry before staining
New treated lumber is often wet from treatment. Allow it to dry for several weeks, depending on weather, before applying stain or sealer so the finish can soak in. Alberta's dry air can speed drying, but sealing too early or too late both cause problems, so ask us if you are unsure.
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