Finishing Redwood slab tables for Arizona Climate

[Peter Clark]

I Have a project that is a couple 12' long by 4' wide by 3" thick or so Redwood Slabs tables. They will be going to Yuma Arizona. I have to build and deliver them next month. The Slabs will be coming from the North Coast of California and I will be building them in my unheated and moist shop. As you can imagine, I'm really worried about cracking in the tops after I deliver them. Yuma is hot and dry even on a high humidity day!

I'm hoping the slabs I find will have been properly seasoned but they will be wet with rain water. I'm thinking most of that moisture will dry out while I'm building the tables. Still the moisture level will be quite high for Yuma standards.

I'm wondering what would be a good way to slow down the evaporation once the tables get to Arizona. I will be using a Linseed Oil finish because these table will be outside.... But in the shade. This morning I was thinking about using penetrating epoxy as the base finish.

TIA for any thought or ideas-

[Bill Davis]

Yuma being in the southwest corner of Arizona is, as you say, rather dry with a average Jan RH of around 50% and for July it's about 20%. Those translate to an EMC of roughly 4 to 9%. You didn't say where your "unheated and moist shop" is but your RH and the MC of the wood as obtained is quite pertinent to what will happen and what you can do about it. Also the thickness of the 'slabs' and the length of time in your working environment definitely come into play. You say "I'm hoping the slabs I find will have been properly seasoned". I hope so. But on the other hand the shrinkage values for redwood put it in a category of 'quite stable' so that is to your advantage.

On a finish - your suggestion of using Linseed Oil (boiled I presume) is one of the least protective of finishes. It is soft and thin so is virtually no protection against scratching and it is easily penetrated by water and water vapor. Flexner says "Water vapor will pass through linseed oil finish almost as it it weren't there." In short, though it does have it's strong points, it is not the finish of choice for protection.

I'd say that to be successful you need to protect the wood from too much uncontrolled moisture change during the building phase and be sure its moisture content upon delivery to Yuma is the less than 10% range or... prepare your customer for the inevitable possibility of warping and cracking. Then if it doesn't they'll be extra happy.

[Scott Holmes]

Peter,

As mentioned BLO is not really a finish it a way to enhance grain and color.

Epoxy would seal the wood very well BUT and this is a big but, Epoxy will not expand nor contract and as the wood moves it will end up splitting away from the wood. And as a finish it will crack and craze and it also doesn't do very well in the sun. I have a son is AZ and I hear they have their fare share of sun.

This table will need to be recoated evry few years, as most boaters will tell you nothin' holds up to the UV rays very well.

I suggest a marine varnish that you get from a boat supply house or a marina. One of the best is Epifanes. Don't let the price change your mind it is worth every penny. You don't want any over the counter poly or spar poly. Poly is Highly susceptible to UV damage. So why put it outside?

[Peter Clark]

Thanks for the replies!
The Penetrating Epoxy is called Restore-It. I have used it as an underpayment (primer) for many projects from outdoor wooden gates to turned salad bowls. I have never used it in conjunction with Linseed Oil. Yes, the boiled type
After re-reading the Restore-It literature, it seems like putting a coat of varnish over the epoxy is what they recommend. Could have something to do with UV protection. I didn't want to use Varnish because of the build up and how it could potentially fail in the Arizona climate. Linseed Oil is soft and will move with the wood surface....

Thoughts?

Oh- My shop is located in the now soggy Sierra Foothills

[Chris Fournier]

I think that the key to your project at this point has far less to do with your finish choice and everything to do with the slabs moisture content. Do you know if the slabs are quartered, rift or flatsawn? There's no point in flattening these slabs until all the movement from drying has occured. You will not be getting a call back about finish if the slabs have twisted, checked or cracked!

I really don't think that your delivery timeline is realistic, even if you were able to kiln dry the slabs down to 6% MC, the drying process would gobble up a month. You have big wet slabs going to a notoriuosly dry climate where they will likely see some direct sunlight - this is indeed cause for worry. Take the time to get the MC down to Arizona levels.

I would agree that spar varnish is the finish of choice for this project - I wouldn't consider epoxy for a moment - if epoxy fails, and on slabs of this magnitude it certainly will, you'll have to start from scratch. Keep the finish film as thin as is possible. I've worked with large slabs from the Pacific Northwest so I am speaking from experience.

Whatever finish you decide to go with do some testing before you committ to the project proper. And don't use plain steel fasteners as they will react with the redwood and create black stains.

Here's a link that will give you some info about redwood: http://www.fs.fed.us/psw/publication...095_piirto.pdf

It is a priviledge working with wood like this, I hope that you really enjoy the project!

[Don Selke]

Peter:

As Scott said, a good UV varnish is a must and it will have to be recoated often. The Sun has no mercy here in the Southwest.
When I first moved here from Illinois, I used BLO on my new yard gate and it lasted about 2 months. I shut down my shop in June due to the heat and put the car in the garage. Try getting into a car that has been sitting in the sun for only a half hour and you can burn your buns off. Three things we really respect here is the sun, airconditioning and shade during the summer months.

[Peter Clark]

First off, anytime I get to work with special and unique materials is a privilege and I am honored when I get the opportunity. Some 20 years ago I had the opportunity to work with a 50 year old Elephant Ivory Tusk. The piece made with it ended up on the back cover of Fine Woodworking! I believe that as a craftsmen and an artist, all I do is bring out the best in the materials. Understanding how to best do that is the challenge.

You are right, My biggest concern is about moisture content. There is no way that I can get the material to a suitable MC for Arizona for the amount of $ the client is willing to spend. Therefore, I have to look at other alternatives. Have any of you ever worked with a penetrating epoxy? I'm not talking West Systems and the like. I am talking about an epoxy that will penetrate 1/4" into sound softwood and further in wood that has become more porous due to beginning stages of rot. My feeling is that I need to be able to slow down the moisture transfer as much as I can. Kinda like coating the tables with Anchor Seal, but on the inside. One good thing, I'm delivering the tables during the winter. I am going to call the manufacturer of the epoxy to see what they say. If anyone is interested, I will post results...

[Chris Fournier]

If you seal in significant amounts of water with the epoxy that you're suggesting I would be concerned about the effects of that water on the epoxy - especiually when the slab gets heat and sun come the warm weather. Epoxy tends to turn cloudy when it is exposed to moisture over a period of time.

I did use an epoxy system to "restore" some semi-decayed wooden components a long time ago and it was a messy experience. It has held up over the years.

I'd like to hear how this project progresses.

[Prashun Patel]

They finished some house shingles with BLO a few decades back around here and they turned black with mold. I guess BLO lets the water in, but does a poor job of letting it breathe out.

I'd use some other kind of Timber oil or clear deck sealer and just reapply it every year; or let it just turn that beautiful silvery grey it wants to turn. I wouldn't put a film finish on it. I've had bad luck with them; Too much maintenance.

IMHO, the best 'wood seasoner' is wax. It allows moisture to slowly and evenly evaporate.

[Barry Richardson]

Not to be a pessimist, but there is nothing that will keep the wood from cracking and warping with the climate change your talking about. Arizona is hot and dry...Yuma is about the hottest and driest place in AZ. The road to success here is to bring the wood down rough, let it acclimatize for a year or so, then dimension and finish it. I would advise your client that it is unrealistic to expect otherwise. As far as finishes go, if the piece is located in the sun, no finish will survive, especially a membrane finish. The best bet for patio furniture that is exposed to sun is BLO or Danish Oil, applied annually. Membrane finishes like Poly, even Spar Varnish, will bubble, peel, and scale off rather quickly. The bottom line is wood furniture does not do well outside in the AZ desert, so I have to wonder what your client is thinking... I do a lot of custom work for clients, and sometime you just have to tell them that what they're asking just cant be done...

[Howard Acheson]

First, let me say that linseed oil will provide no protection from changes in the wood moisture content. Water and water vapor goes right through BLO.

I think you are going to have a real problem with building in the NW and then shipping thick slabs to western Arizona.

First thing I would check on is the moisture content of the redwood. Has it been kiln dried? If so, when? What is the current equilibrium moisture content (EMC) of the wood?

There is going to a large shrinkage factor due to the change in moisture.

[Peter Clark]

Project update-
I'm still letting the slabs dry out a bit more. I have talked to the people at Restore-It. They say my application will work and I will get the results I'm looking for. I will need to coat the tables with an oil based UV inhibiting finish such as spar varnish.
Now I wait for mother nature to do her work....

[Peter Clark]

Well it took 2 years of sitting before I felt comfortable proceeding with this job. Here are a couple pictures of the finished tables. I ended up using system 3 epoxy to fill cracks that happened during the drying process and then I used system 3 spar varnish for the top coat. I hope they hold up!
DSC03252.jpg

[Eric Stear]

Peter, how have the tables held up so far? How does the finish look a year and a half later?

[Howard Acheson]

>>>> coat of varnish over the epoxy is what they recommend.

Yes, but don't use poly varnish. UV also attacks polyurethane. Use a marine exterior non-poly varnish. Don't use any big box "marine spar varnish". Go to a real marine supply store and look for brands like Interlux or Epifanes.