Here’s another reader question from a reader and my answer:
“I have a follow up question to your response to a question regarding varnished wooden doors that appeared in the June 2018 (#239) issue of Popular Woodworking. I live in the Texas Hill Country and have a northeast facing alder door that has good overhang protection against water, but it does receive direct morning sun for several hours. The door is about 4 years old and I know for a fact that it was originally finished with Minwax Helmsman spar varnish, which according to you provides little in the way of UV protection.
The finish is beginning to develop a blue-grayish chalking/oxidation, which is rough to the touch. If I wet the surface with mineral spirits, the topcoat returns to clear and transparent while wet. I’d like to know what is the best course of action at this stage? Can I lightly sand and re-coat using a true marine-grade spar varnish with good UV protection, or will I need to do something more drastic?”
Here’s my answer:
I actually restored a front door, recently, with sun deterioration similar to yours but worse. It was in Los Angeles at my son’s house where the door receives direct sunlight in the mornings. Unfortunately, stupid me, I didn’t think of taking pictures.
The finish on the lower part of the door was very rough and also bluish/gray like yours. First, I sanded the roughness smooth. Then I tested for color, like you did with the mineral spirits, and saw that the color wasn’t restored. So I wiped on and wiped off an oil-based walnut stain. This restored the color. Then I brushed on several coats of a marine varnish, Interlux, which I bought at a marina in Los Angeles. It’s been about five years now and the door is still in pretty good shape, though I can see that I’ll need to do this again in several more years.
Your challenge, living in the Texas Hill Country, is that it’s unlikely you’ll find one of these UV-resistant varnishes locally. You may have to order something online. Common brands are Z Spar, Pettit, Epifanes and Interlux. I don’t know the difference in UV resistance among these, but they are all effective.
Two possibilities of marinas you can order from are jamestowndistributors.com and westmarine.com. I think West Marine has stores in Houston and the Dallas area. You can also order from Amazon.
Every situation is a little different, but I think this is enough information for you to proceed successfully.