Staining an older CCA deck in Ottawa every year?

Health Canada recommends applying a sealant every year to older CCA-treated decks, using an oil-based or water-based stain. That same guidance says paints and other film-forming finishes are not recommended for this purpose.

The USDA Forest Products Laboratory supports the penetrating-finish approach for decks generally. The FPL says film-forming finishes, including paint and solid stain, are very difficult to maintain on decking and are rated low suitability for that surface. Penetrating finishes need to be refreshed every few years, and the FPL's US figures give some guidance on intervals: a water-repellent preservative lasts about 1 to 2 years, a tinted deck finish about 1 to 2 years on smooth-sawn boards and 2 to 3 years on weathered or saw-textured boards, and a semitransparent stain about 2 to 3 years on new boards and 3 to 6 years on weathered ones. These are US figures, and the FPL notes that expected life depends on climate and exposure.

A few things to keep in mind with an older CCA deck. Health Canada notes that residential decks built before 2004 are likely to have been made from CCA-treated lumber. Health Canada says CCA is no longer available for residential construction projects. Health Canada says never to burn CCA-treated wood, indoors or outdoors. When you sand or saw it, wear a dust mask, eye protection, gloves and long sleeves. For the annual stain application itself, the same precautions apply if you are doing any surface preparation that creates dust.

The FPL's main point about why wood decks get replaced is worth keeping in mind: the most common reason is checking and splitting, not decay. Keeping water beading on the surface, rather than soaking in, is the best way to slow that process. Health Canada's yearly sealant advice for CCA decks and the FPL's preference for penetrating finishes point the same way.

On the permit side, we found no City of Ottawa statement on whether refinishing or staining an existing deck requires a permit. If you are doing anything beyond the finish, such as replacing boards or making structural changes, ask the City's Building Code Services before starting.

If you are thinking of hiring someone for the preparation and staining work, the question worth settling before you agree to anything is what surface preparation they plan to do and which specific product they intend to apply, so you can confirm it is a penetrating oil or water-based stain rather than a film-forming finish.