Finishing outdoor cedar bench

[Bob Timms]

I'm replacing the armrest and slats on an old outdoor bench with cedar from the BORG. The boards are smooth on one side and rough on the other. I'm wiping a spar varnish on the smooth side (armrest finish built up more than slats for liquid protection from beverages). Is it OK to leave the rough side "as is" or should it be sealed also? My original thinking was cedar is good to go outside so I'll leave the backsides unfinished but I'm not sure of effects of outdoor weather on wood finished on one side only.

Comments and suggestions appreciated.

Bob

[Steve Schoene]

Finishing one side of outside wood is inviting warpage.

If you must varnish the cedar, then varnish all sides, and use a good spar varnish from a marine store, not a paint store or the borg. (Interlux Schooner, Pettit Captains, or Epifanes) And use enough coats. After the first coat, it needs to be brushed on diluted only enough to brush well. And it will take 6 coats. If you wipe on a heavily diluted varnish it will take 18 or more coats to come close to a protectively thick film.

Cedar is best left unfinished to turn a nice mellow grey. Or painted.

[Bob Timms]

Thanks Steve,

I started this project as an experiment - some time and a few $. My plan was to finish the armrest to protect from watermarks from drinks, etc. and just enough finish on the slats to give them the same color as the armrests. The armrests have maybe 4 - 6 coats of rustoleum marine spar on them at this point. Does it make sense at this point to switch to one of the marine varinishes you mentioned? Also, maybe it would make better sense just to let the slats remain natural and replace the armrest with natural ones. Its easy for me to do any of the above. Any additional input appreciated.

Bob

[Steve Schoene]

Well, since you have started with the spar, I would shift to the higher grade spar. Practical Sailor magazine (the boating equivalent of Consumer Reports) tests spar varnish every few years, and the top of the line spars outlast the lower grade spars dramatically.

No need to remove the Rustoleum. Just give it a good sanding with 320 grit and continue to add the higher grade spar. Three full coats over the armrests should do it. Be sure to coat both sides.

It is the thickness that provides the protection from UV. Otherwise, the UV absorbers get used up quickly and the varnish fails from the inside out, first turning "yellow" as it lifts from the wood, with the wood then darkening and turning grey.

If you really don't want the full film, glossy look of spar varnish, you could follow your plan of just one or two coats on the bench as long as you understand that to keep this from lifting and the wood turning grey you would have to sand it all off every year back to the bare wood, and reapply. Even with the full coatings expect to add a new coat about every year if in full sun, or every other year if it gets some shade, but you should only have to scuff coat if you don't let it get away from you. Patch any dings promptly.

Another suggestion is to to make a Sunbrella cloth cover for the bench so that it is out of the sun when not being used. This can add years to the life of the finish. Sun is the enemy, much more than water, though I would seal the end grain that sits on the ground with several coats of epoxy resin.

[Bob Timms]

I should have me mentioned earlier that the bench is under a canopy affair and does not receive any direct sunlight - in fact its mostly in shaded. It also only gets wet when we have a really hard rain. So maybe I'll get a little more milage out of it. Thanks - I'm off to find some of the marine varnish you recommended - will probably have to order it online.

Bob