My deck is turning grey and has some green mildew spots — can I just stain over it?

No, you should never stain directly over grey, weathered, or mildew-covered wood. Applying stain over a compromised surface is one of the most common mistakes Vancouver homeowners make, and it leads to poor adhesion, uneven colour, and premature stain failure — often within a single rainy season.

The grey colour on your deck is caused by UV damage breaking down the wood's lignin, which is the natural binding agent in wood fibres. The green spots are mould or mildew thriving in Vancouver's damp, mild conditions. Both need to be addressed before any stain will bond properly.

Proper preparation involves several steps. First, the deck should be cleaned with a quality deck cleaner or a mild oxygen bleach solution to kill mould and remove surface grime. Next, power washing at an appropriate pressure — typically 1,500 to 2,000 PSI for cedar, higher for pressure-treated — removes the damaged grey layer and opens up the wood pores. After washing, a wood brightener is often applied to restore the wood's natural pH and colour. Finally, the deck must dry completely for at least 48 to 72 hours of dry weather before staining.

In Metro Vancouver, timing this process is crucial. The best window is typically mid-July through early September when you are most likely to get the consecutive dry days needed for washing, drying, staining, and curing. Attempting this during our shoulder seasons often results in moisture being trapped under the new stain.

The prep work is honestly the most important part of any staining project. Consider booking a professional deck restoration service in late spring so you are on the schedule for prime summer staining weather.

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