Wood Finishes for Outdoor Projects

[ZendoDeb]

Fine Woodworking Magazine (May/June 09) has an article on various wood finishes for outdoor furniture. While a Tear isn't furniture, I thought the results would be useful. Especially since I was involved in several "discussions" about wood finishes. Here is a summary of their results.

They tested several finishes in several locations. Including New Mexico, Louisiana, Oregon and somewhere in upper New England - though I forget where exactly. They may have had a Midwestern locale as well, but that didn't make an impression. It also didn't matter as you will see.

They tested finishes for one year - exposed to weather. They tested mahogany (my guess is various species, since real Honduran mahogany is fairly expensive - but I don't have that level of detail in my notes) and white oak.

Here goes. Application was per instructions.

Watco Exterior Wood Finish. $14/qt. 2 coats. Deteriorated to shades of gray in all areas except New Mexico.

Zar Exterior Polyurethane. $22/qt. 3 coats. Deteriorated so that about 20% of wood had no finish - gray/weathered.

McCloskey Man O'War Spar Marine Varnish. $20/qt. 4 coats. OK on mahogany, deteriorated on white oak - except in New Mexico.

Epiphanes Clear Varnish. $45/qt. 7 coats. - They listed the result as "excellent" Finish looked *almost* as good as when first applied in all locations. (Thinned per directions which if memory serves is about 25% or more by volume for the 1st coat.)

CPES (Smithes) 3 coats followed by Epiphanes Clear Varnish 5 coats. (Didn't get their price for Smithes... but it is $57/qt at Jamestown Distributors.) Total of 8 coats. Listed result as "very good"

On a personal note - don't let the CPES/varnish fail. Maintenance is mandatory since CPES is really difficult to remove. Exposed to UV, most epoxy turns a milky translucent color. Not attractive on wood.

One of the discussions I got in on was on a finish left for 3 years. If you want a finish that requires no maintenance for 3 years, your only choice is paint.

I have no idea why some finishes lasted longer in New Mexico except that it probably has something to do with the relative humidity. The article didn't say.

[kennyrayandersen]

pretty interesting (I"m a big fan of the mag). My put is that if you are going to make a woody, you should have a good place to store it so that it's not out in the elements all of the time. That would probably be the single biggest contributor to long finish life that you could make.

[2morrows]

On the Manowar it says not to use on decks. My wife thinks that might be because people hang out on decks and in turn would be inhaling fumes coming off from the varnish. Extending that thought, she is unsure if we should finish our camper in it where we will be sleeping in it. I could find lots saying it's dangerous and to work in a well ventilated area but not anything on if it is harmful in the long run. Anyone know?

[asianflava]

Hmmm, I'm currently building a table to hold my Dutch oven table and my Big Green Egg. I used a Varthane Spar Urethane for outdoor projects. I put 4 coats on all the wood.

[48Rob]

Interesting study...but terribly flawed in my opinion.

Maybe I missed something in the explanation, if so, sorry.

To be accurate, each finish tested should use the same number of coats.

Two coats of product "Y" didn't hold up as well as seven coats of product "Z".

Hmmm wonder why?

2-3- even 4 coats of finish isn't enough for outdoor exposure.
With porous wood, it can take 6-8 coats to completely encapsulate the wood.

UV protection is very important, but means nothing if the finish isn't "waterproof" because the grain didn't get sealed with two or three skimpy coats...
Unsealed wood will turn gray very quickly from exposure to moisture...


Rob

[ZendoDeb]

If a manufacturer called for 2 coats - thats what they did. If it says 2 coats on the side of the can, how many coats are you going to apply. The varying number of coats in the application was due to the varying instructions provided by the manufacturers.

And I know the Ephiphanes says a MINIMUM of 7 coats. I know people who go for 15.

[ZendoDeb]

Usually varnish in the Marine environment contains a warning DO NOT USE ON DECKS. And Man O'War is marketed as a marine spar varnish.

This is because some newbie buys a boat with teak decks, and doesn't understand why they have been let turn gray. So he sands and varnishes them.

Weathered - or sanded if you have the time and money - teak decks are the best non-skid you can find. Varnished teak decks are like trying to walk on a bucking ice rink.

(If you want the sanded look, they need to be sanded regularly. Then they need to be replaced regularly.)

Most high-gloss varnish is not appropriate for flooring. Slippery when wet. VERY slippery when wet.

Varnish - real varnish, not polyurethane, not urethane - has been used on furniture - including beds - for centuries. Well that and shellac. I have been on boats where most of the interior has been varnished.

Once cured - full cure is usually 7 or 8 days on the stuff I use - there is no off-gassing. That is true of paint as well, full cure is usually a few days to a week - depending on latex vs alkyd vs linear poly.

There are high-gloss floor varnishes - well, the one I use on the interior of my boat is a single part urethane. (Not polyu - just regular u-.) But they are made to be non-slip. Falls are serious on land. They can be deadly at sea.

[48Rob]

Zendo,

My apologies.

I read, and interpreted the info you posted, I did not look up the article.

If the manufacturer made those recomendations, then it makes sense why the tests were performed the way they were.

Still seems like a pretty lopsided study, true to the "directions" but completely unrealistic for real world applications.

Shame on the company that would allow an unsuspecting do it yourselfer to create a nice wood project and then allow it to be ruined by "following the directions" on the can of sealant.

Rob

[doug hodder]

One of the discussions I got in on was on a finish left for 3 years. If you want a finish that requires no maintenance for 3 years, your only choice is paint.

Are you including clear coat in this "paint" category? I've had very good results with epoxy and clear coat over dyed mahogany, lots of depth to the finish. Gives a great finish and look to anything that you aren't going to be walking on and unlike a varnish, can go a long time without refinish work. Doug

[gdpipkorn]

Does clear coat "paint" Offer the same uv protection as spar varnish?

[doug hodder]

In the wooden boat world it's what's used on a lot of the new construction now and the tech guys at West Systems think it is much better, based on my conversations with them. I think spraying 2 coats of clear once beats X number of coats every other year. Lots less maintenance. I've gotten 9 years out of a boat finished with clear coat, but also I don't just leave it outside all the time. My woody tear has 3 years on it now and looks like new. You would be docked points on a judged show if your boat originally had a varnish finish on it and you did an auto clear, but then you get docked points if the wire isn't the right color also. Doug

[ZendoDeb]

Clear coat - usually 2 part linear poly, like the stuff used on cars - does have a lot of UV. It is used a lot, but mostly in New England.

There is some discussion among folks in Florida. It looks great, while it lasts. But you have to do a lot of preemptive maintenance.

If ever the epoxy starts to darken, it is really tough to get back to where you started. Penetrating epoxy does soak into the wood.

The consensus is that it lets new-boat manufacturers get a finish that looks like 7 or 11 coats of varnish with about a third the labor. The finish should last beyond the warranty period of a year or two, then it is the owner's problem.

Your mileage may vary.

[gdpipkorn]

Thanks for your advice. We have 3 coats spar applied now. We store inside and plan to do a fresh coat every 2-3 years. Is it possible to spray clear coat over spar if we would choose to switch?

[ZendoDeb]

Is it possible to spray clear coat over spar if we would choose to switch?

In general I would say no, given that all the clear-coat systems I know of are 2 part polyurethane. (I have seen this first hand)

You can't paint 2-part poly over one part paints. I am going to assume that this means 1-part varnish as well. The solvent used in the 2-part polyurethanes is so powerful, it will begin to strip the one-part undercoat before it has a chance to cure. Results in bubbles, sags and general degradation of the finish.

I only know this because the deck of my boat is painted with 1 part paint (a previous owner...) and so I can't use 2-part without striping all the finish off. There are new strippers that make this possible, but I looked long and hard for a primer that would let me move up to 2-part finishes with no luck.

You would have to strip the spar varnish down to bare wood and start again. Not hard to do. Real varnish strips very easily with a heat gun.

[gdpipkorn]

Thanks , You guys are terrific!