Ask the Staff

Question: I have built a set of Adirondack chairs out of oak as a housewarming gift for my daughter. What is the best finish to apply so the furniture will hold up outdoors? The chairs are for her deck and will get almost full exposure to the sun and elements.

Answer: The best way to protect wood outdoors is to paint it, since an opaque pigmented coating repels water and blocks UV rays very effectively. The problem with pigment, of course, is that it will also hide the wood. If you want the wood to show, a clear exterior finish that also contains UV absorbers will provide the most protection. UV absorbers are chemicals added to clear finishes that work like sunscreen and absorb UV radiation, dissipating it as heat and thus preventing wood deterioration under the finish.

The most effective UV-resistant coatings are marine-type finishes, such as McCloskey Spar Marine Varnish and Waterlox Original Marine Finish . Marine finishes tend to have more UV absorbers and can better withstand direct sun than traditional spar varnishes. Lower-end home center "UV-resistant" finishes very often don't contain sufficient UV absorbers to be effective. Also, many oil finishes, regardless of the amount of UV absorbers they may contain, are applied too thinly to provide any real protection. These finishes don't build on the wood, so there isn't adequate thickness for the UV absorbers to be of much use. For best results, a thick film must be built on the wood.

As with sunscreen, UV absorbers wear out over time, so the protection is only temporary. For continued protection, proper maintenance is imperative for exterior finishes. With varnish, this entails sanding off the top coat every year or so (or more often in full-sun applications) or when the finish dulls, and reapplying a couple of coats. Once varnish starts to crack, however, it must be stripped before a new varnish coating can be applied. Recoating cracked or peeled varnish is not recommended, so it’s a good idea to refinish long before the finish show signs of deteriorating to avoid having to sand off the existing finish.

Waterlox Marine Finish is a tung oil-based finish that is more expensive than spar varnish, but easier to maintain. When the gloss level of the film begins to fade, you’ll know it’s time to re-coat the surface. However, sanding is not necessary - simply clean the surface and reapply more Waterlox and allow to dry.

With a little maintenance every couple of years or so, you should have good results with either finish and get many years of enjoyment from your chairs. You might consider giving your daughter a gallon of Waterlox Marine Finish along with the chairs and suggesting she wipe on a fresh coat every summer. It may save Dear Ol' Dad some trouble in the long run!

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