You grew tired of looking at it. So you finally decided one weekend to fix that dismal deck surface that looked as if thousands of feet had rubbed it raw. And it seemed like a simple do-it-yourself task. But when you applied the stain, it bubbled, dried and looked amateurish. Weather-resistant deck stain is not like ordinary stains; it doesn't penetrate much but instead lies on the surface to protect the wood.
Avoid Weather Extremes
Bubbles can occur when the outside temperature is too hot or too cold. The surface of the stain hardens before bubbles can escape, and they become trapped under a thin layer. Avoid this problem by applying the stain per manufacturer's recommendations, typically at a temperature no lower that 50 degrees Fahrenheit and no higher than about 80 degrees Fahrenheit. Do some tests on a scrap piece of similar wood if the temperature is borderline. If you see bubbles, stain the deck another day.
Moisture can also cause deck stain to bubble. If you've recently washed the deck or it's been raining, it's not a good idea to apply the stain right away. When deck stains dry, they also emit a certain amount of moisture. Combined with the moisture in the wood, the gel hardens just enough to create a bubble. If your deck has a questionable amount of moisture in it, don't apply the stain until it's dried for at least 72 hours. Wait a week if possible, and if it continues to rain, wait longer.
Despite preventative efforts, you may find that your stain continues to bubble. A certain amount of bubbling can be fixed simply by brushing the bubbles lightly with a soft brush when everything's still wet. Brush over them with strokes parallel with the grain to smooth them out. Don't use excessive force or move too fast, or you will create new bubbles. Just wipe them out with a couple of smooth strokes. Watch your progress and continue. If you're painting in haste, slow down if you continue to get bubbles.
Spirits in the Sky
If all else fails and you just can't seem to get a bubble-free finish on your deck, it's sometimes possible to thin the stain to allow bubbles to escape. Check the manufacturer's directions; if it doesn't say not to thin the stain, add a few ounces of mineral spirits, or follow the directions using the suggested thinner. Mix it in a clean can, a few ounces at a time and try some test pieces on scrap wood. Don't thin too much, just enough to prevent bubbling. Thinning stain prevents air or water from getting trapped.
If you notice blisters or bubbles after you've finished, you've still got options. Remove dried bubbles by allowing them to dry completely first and scrape them off with a paint scraper. If bubbles peel back and seem rubbery, the stain is still too wet. After removing dried bubbles, sand the surface lightly with 100-grit sandpaper, clean up the debris and apply more stain. If at any point you see larger bubbles or blisters while the stain is still wet, pop them with a sharp object and smooth everything out with a brush if needed.