Renewing a weathered deck surface seems simple enough, but even experienced contractors make mistakes if it's not their everyday business, according to Jim Grant, a professional wood refinisher from San Diego. He offers four pieces of advice for getting a great finish.
1. Know when to strip. A deck that's merely dirty and faded will probably just need a cleaning before the stain goes on, but a severely deteriorated coating should be removed with a chemical stripper. Look for crazed or peeling surfaces, severe pet scratches, or a visibly worn footpath across the deck. Even if the damage is localized, strip the whole thing to ensure an even coating.
How to strip is a separate article. "You really need to know what you're doing," cautions Grant. Strippers contain sodium hydroxide—lye. Used wrong, you can end up with chemical skin burns and dead vegetation. This step is best left to a specialist. Make sure to always neutralize after stripping.
2. Use a real cleaner. If the deck just needs cleaning, a lot of guys use TSP or household bleach. Bad idea, says Grant: these can leave dirt in the wood grain that leads to a splotchy finish. Commercial deck cleaners are much stronger, and do a more thorough job.
Scrub the cleaner into the surface then rinse it off with water.
3. Always use brightener. After stripping or cleaning, apply an oxalic acid based wood brightener. Although some people skip this step, it makes for a better result. That's because cleaners and strippers can both darken the wood; the brightener will restore its natural color and will also lighten any tannin bleed. Let it dry, then lightly sand any splintered or damaged spots smooth.
4. Know your finishes. Transparent stains spread easier than semi-transparent or solid stains, and highlight the wood grain, but need to be renewed every year or two. Although solid colors can go three or four years between re-coats, they provide a completely different look. If the client asks you to cover a semi-transparent stain with a solid color, Grant recommends coating two sample boards first, so they can confirm that it's what the want.
Apply the stain with a sprayer, roller or brush on an extension pole. If using a water-based stain, it's important to maintain a wet edge to avoid lapping.
Let the stain dry at least 24 hours before walking on it. And don't forget to schedule future maintenance with the customer.