how best to protect woodwork outdoors?

May 14, 2022 1:06 PM

We have a slab of eucalyptus currently being engraved with text, to be used as a marker outside tilted with the lettering upward, and fully exposed to the weather: rain, sun, whatever. (This is in California, so frost is rare and it has never snowed here yet). What is the best protective clear coating to use, if any? Suggestions have been to leave it as plain wood, covering with clear epoxy, and painting with marine spar varnish, but I've seen instances of each of the latter peeling, so I'm hoping someone can recommend what will last longest.
posted by anadem to Home & Garden (7 answers total)

Any kind of finish that sits on the surface will eventually flake due to UV exposure (varnish quite soon, epoxy a little later). Then you have to remove the old finish before you can re-apply, which is a huge pain. Don't go down this road! The alternative is to use an oil finish which penetrates the wood and can be re-applied as needed without needing to remove anything. Boiled linseed oil is the simplest option, but there are lots of options on the market (danish oil, tung oil, etc).

Fortunately, eucalyptus is a rot-resistant wood, so an oil finish is going to be plenty to keep this looking good for decades.
posted by ssg at 1:19 PM on May 14, 2022

On my slab pine countertops, I applied 5 or so coats of Waterlox and after 10 years, they look great.
posted by theora55 at 2:20 PM on May 14, 2022

I once made some trinkets out of eucalpytus wood slices: basically ovals that had some holes drilled into them. They looked and worked great at first, but 6 months later they had all cracked and broken or split around the holes. I think what happened is they dried out, shrank, and split. This was in a dry place in California.

If you are using "a slab" that would probably last longer, but still, I might want to figure out a way to keep it moist and seal that moisture in somehow?
posted by soylent00FF00 at 2:53 PM on May 14, 2022

ssg has it, but one variation is to do unboiled/raw linseed oil before tung or boiled linseed. It will sink in more. Also try to get pure oils imo, some stuff sold as 'tung oil' has a lot of additives and from my reading they likely make the product worse on average.
posted by SaltySalticid at 2:56 PM on May 14, 2022

This is a pretty good tutorial on how to use tung oil. I would thin the first coat with mineral spirits so it soaks in better.

***SAFETY WARNING***
Don't wad up the tung oil rags, they may catch fire by spontaneous combustion. Spread them out until they are thoroughly dry.
posted by H21 at 3:14 PM on May 14, 2022

Yeah, just watched an episode of This Old House this morning refinishing a mahogany deck railing with an oil based finished. Should last 2-3 years before reapplication. They sanded off the old finish, applied the oil with a brush, waited a while and wiped off the excess with rags. Rags were put into an empty paint can with water to be disposed of at a local hazardous waste center. Oily rags can just go poof into a fire all by themselves. The less transparent option (some sort of varnish) would last 3-4 years, the final option was something more paint like that showed none of the underlying grain 4-5 years.

I'd go for oil and fixing it up every couple of years for an outdoor thing.

Oh, and try not to touch it for a few days. Once the excess is rubbed off with a cloth, let it sit for a couple of days before putting it in place if you can.
posted by zengargoyle at 3:39 PM on May 14, 2022

Many thanks all! Oil it is, and I've got tung oil (used on my skin-on-frame canoe) just didn't think of it.
posted by anadem at 4:59 PM on May 14, 2022