Could you give me some advice on putting a finish on some garage doors I had made out of Brazilian mahogany, please? – Bill Reilly
Michael Dresdner: As a wood, Brazilian mahogany poses no special finishing problems, so I’d choose a clear finish that looks elegant and holds up well on a garage door.
Any wood left outdoors will be subject to wide swings in humidity. That means the wood will absorb and release lots of moisture vapor, causing it to expand and contract much more than wood kept indoors. Thus, you want a finish that is both durable enough to withstand the elements and flexible enough so that it won’t crack as the wood moves.
My first choice would be a true exterior long oil varnish, such as spar varnish. Though it’s less common now, you can still find it at marine supply outlets and even some hardware and paint stores. My second choice would be an exterior polyurethane varnish, either oil-based or water-based.
You probably don’t want to stain such an attractive wood, but if you do, choose a 100 percent pigment stain. Dyes may fade in sunlight; pigments won’t. Use a furniture stain, not an exterior siding or deck stain, as they may contain wax and can cause problems under varnish.
Chris Marshall: One downside to varnish, however, is that it could crack or peel eventually. When the time comes to refinish those doors, you’d have to strip them first – and that’s a lot of work. So, an all-in-one stain and wood preservative, such as the ubiquitous “deck” stain, might be a reasonable alternative here. A semitransparent version fortified with UV inhibitors could be used all by itself, and you’d have a range of color choices that wouldn’t obscure the attractive grain pattern of your doors. Sure, it will eventually fade, but at that point you could clean and re-stain the doors without needing to remove an old layer of varnish.