Cypress finishing question

[David Tiell]

Making a couple large boxes out of cypress. They will be used outdoors. Looking for suggestions on finishing it. I did a search, and not really sure I found my answer, so I will ask it directly.

Which is better for finishing cypress for outdoor use? BLO with some sort of sealer, or a poly finish like Minwax Spar Varnish, or what?

TIA,

Dave

[Jeff Clow]

I made an outdoor table top from 3/4 cypress, and used a Thompsons Waterseal clone (don't remember brand) as a sealer. The table stays outside, exposed to all the elements. I expecte to put the table away for the winter & re-seal in the spring. Within a couple of months the sealer looks like it has disappeared, the top started to mold, and the slats of the top warp & bow like you wouldn't believe! The wood absorbes moisture and expands like a sponge. If your boxes will be exposed to much moisture, I would consider something that would seal the wood from the moisture, like poly or epoxy.
This was the first time I used cypress, and I don't think it was the correct wood for my application (or I should have sealed it better). I will be replacing the table top, possibly with redwood, or ipe.

[Steve Schoene]

Or what. BLO is a particularly bad choice if there is any chance that mildew could be a problem. Molds like to feed on it.

Consumer grade spar varnishes are a waste of time and money. Polyurethane in single part finishes is particularly liable to be damaged by UV so the claim that UV absorbers have been added just brings them back to so-so for exterior use.

The best finish for cypress outdoors is no finish at all, beyond soaking the ground contact surfaces with epoxy. Cypress is naturally rot resistant and will weather to an attractive grey that only needs an occasion washing to keep looking nice.

Second best is opaque stain or even paint in a light color.

Finally, if you must have a clear finish you must understand you are deciding for regular and continuing maintenance.

There are only three varnishes worth considering. Epifanes High Gloss Clear Varnish, Interlux Schooner, or Pettit Captain's. These will cost a lot more initially that the things labeled spar varnishes that you can find in local paint stores or the bor, but are cheaper in the long run. You may have to obtain it on line. www.defender.com is a good low price source.

You must apply 6 coats, lightly sanded between each with 320 grit, and with only the first one thinned according to directions, and only modest thinning of the rest. (Epifanes will require 10% or so.) Then, if the furniture is in full sun expect to sand and apply a renewal coat each year. After half a dozen years or so, or when you see any "yellow patches" which indicate the varnish is lifting from the wood, you must strip back to bare wood and start all over. All dings, and cypress is soft enough that you may expect them, must be patched promptly.

Again, best choice is no finish at all.

[David Tiell]

OK, thanks, for the responses guys! I think I will opt to leave unfinished.