Ask the Staff
This question first appeared in our October 2007 issue of Wood News Online.
Question:
I had a mahogany front door installed on my house about 8 months ago, and the finish is already peeling off. The installer said they used an exterior finish purchased at a home center. Why didn't the finish last longer, and how should I go about fixing it?
Answer:
I can think of several possible reasons why the finish failed on your door. In general clear finishes don't hold up as well as opaque finishes. A properly prepared surface coated with an oil-based primer and several coats of high quality modified acrylic paint will usually last years longer than clear or stained finishes. The farther south you live and the type of sun exposure you get can also affect the longevity of a door's finish. Most contractors do a good job of hanging doors, but don't have as much knowledge about finishing materials or how to use them. This is especially true with exterior finishes. As a result they will purchase finishing products from home centers that are of poorer quality than those available at specialty shops.
If you choose to refinish your front door, the most durable option is painting. As for staining and clear coating, the process is more involved and time consuming. Here are some basic instructions.
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Remove the door from the hinges and remove all hardware. Lay it flat on some saw horses or a sturdy table. You'll need to cover the opening with plywood or hang a temporary door.
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Remove all the old finish with a good chemical stripper. Most strippers have wax in them, so you'll have to wash the door down with paint thinner once you're done stripping. If you don't remove the leftover wax, the new finish won't stick.
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Sand to 180-220 grit.
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If you choose to color the door, use a high quality pigment stain like Varathane or Bartley's. Most stains sold at home centers have dye colors added to them and they won't hold up in sunlight.
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Once the stain is dry, start applying a true longlasting oil spar varnish. Here's a hint. If you paid under $50 a gallon for it, then it won't hold up. The best go for $90 a gallon. Professional quality marine/spar varnishes like Waterlox Marine are made from tung oil to give them elasticity so they can expand and contract during seasonal movements. Cheaper varnishes cure hard and tend to peel once the weather changes. Also, good spars are loaded with ultraviolet light-refracting minerals, which keep the sun from breaking down the finish.
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You should thin the first two coats of varnish 1:1 with paint thinner, and apply it with a natural hair brush. Pay particular attention to the top and bottom edges of the door where the end grain of the door's stiles are. Moisture exchange happens more rapidly there, so you need to load these areas up with extra varnish.
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Lightly sand between coats of varnish with 220 grit sterated paper. Sterated paper (Norton 3X) won't clog and scratch your finish like conventional paper.
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Apply at least 3 more full strength coats of varnish.
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Since high quality spar varnish deteriorates from the outside, you'll need to inspect the outer coat each year. Typically you'll lightly sand the surface and wipe on a thinned coat of new varnish as needed.
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One last note. Always use high gloss spar varnish for all outdoor projects. Satin sheen finishes have flattening agents added to them, which weaken the cured film. If you want a lower sheen, you can use high gloss for all but the last coat and apply satin on the final pass. Another solution is to wait 5 days after the final coat is dry, and rub down the sheen with some 0000 steel wool lubricated with paint thinner.
Thanks for your question,
Chris Black
Highland Woodworking
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