water proofing your wood

[steepski]

Hi all, thanks for all the advice in this awesome forum. I'm starting my foamie build. (I'll start a build post soon) I've got the trailer frame built, and the floor plywood all cut out, but haven't painted it with "the mix", and haven't started gluing anything to it. I live in a very wet area (PNW), and will be towing the trailer through lots of rain and wet snow, so I want the plywood floor to be super waterproof. The current floor is 5 sections that I plan on joining together with lap joints.

Here's what will be glued to the plywood floor: I will be gluing the lap joints on the plywood together with TB2, then gluing ( with TB2) and screwing wood rails to the top of the floor (to hold the bottom of the foam walls), Then gluing the foam walls to the plywood with Gorilla glue, and finally gluing the bottom edge of the outer canvas skin to the bottom of the plywood floor (when it wraps around from the foam wall) Also, some of the interior furniture might be secured to the floor with glue and screws.

I would like to waterproof the plywood before doing all that, as it seams much easier to get it completely sealed before it is all assembled, and I don't want water getting in anywhere. However, I'm concerned that the glue won't stick to the polyurethane surface on the plywood. I've looked through the forums (including this post), but couldn't get a clear answer. Any advice?

Thanks!

[tony.latham]

I think you're spot on. It's a heck of a lot easier to poly the parts before hand.

Here's a 5' wide ceiling that's been finished and almost ready to install. Just tape off the surfaces that will be glued.



Tony

[rruff]

I think you're spot on. It's a heck of a lot easier to poly the parts before hand.

What plywood do you use? There was speculation that some plywood glues may not tolerate solvent: viewtopic.php?f=2&t=49207&start=15

[tony.latham]

I think you're spot on. It's a heck of a lot easier to poly the parts before hand.

What plywood do you use? There was speculation that some plywood glues may not tolerate solvent: viewtopic.php?f=2&t=49207&start=15

I use 1/8" & 1/2" Baltic birch, ACX and 1/4" underlayment. I've never had an issue with plywood and and any of the glues that I use–-TB2, PLP, GG or epoxy.

I'm convinced that the problem Mike had with his roof was water getting into his non-exterior plywood. Luan is made for cabinets and doors inside homes. You can put scraps of those plywoods and put them in a bucket of water for a week and they won't delaminate.

TL

[rruff]

I'm convinced that the problem Mike had with his roof was water getting into his non-exterior plywood.

Mike used Rot Doctor epoxy sealer. He also said the luan supposedly had water resistant glue. The problem is that it wasn't solvent resistant.

[steepski]

Yeah, perhaps taping the edges of the plywood is the way to go. I'd be a little worried about water getting in under the foam and canvas somehow and getting into the wood. I guess if it's all glued down and painted that probably won't happen though.

[ghcoe]

Yeah, perhaps taping the edges of the plywood is the way to go. I'd be a little worried about water getting in under the foam and canvas somehow and getting into the wood. I guess if it's all glued down and painted that probably won't happen though.

Remember that the TBII is also water resistant. Just make sure you coat the non-treated areas with a good coat of glue when you attach the walls.

[tony.latham]

I'm convinced that the problem Mike had with his roof was water getting into his non-exterior plywood.

Mike used Rot Doctor epoxy sealer. He also said the luan supposedly had water resistant glue. The problem is that it wasn't solvent resistant.

I have not used Rot Doctor products but I think they are an epoxy cut with xylene. Straight epoxy doesn't have solvents and will not cause plywood to come apart.

T

[rruff]

Straight epoxy doesn't have solvents and will not cause plywood to come apart.

"The mix" is 25% oil based poly and 75% mineral spirits, per this thread.

[tony.latham]

Straight epoxy doesn't have solvents and will not cause plywood to come apart.

"The mix" is 25% oil based poly and 75% mineral spirits, per this thread.

I'm not sure what that has to do with my post?

I use "the mix" and have never thinned it that far. I'll thin it down to 70% poly and 40% spirits. If I really want to waterproof something, I'll seal it with Raka epoxy.

T

[rruff]

I'm not sure what that has to do with my post? I use "the mix" and have never thinned it that far. I'll thin it down to 70% poly and 40% spirits. If I really want to waterproof something, I'll seal it with Raka epoxy.

"The mix" is the main subject of this thread, and appears to be the most advocated method on this forum.

You may seal with straight epoxy, but commercial wood sealers and most home brews contain a solvent for far greater penetration.

[tony.latham]

"The mix" is the main subject of this thread, and appears to be the most advocated method on this forum.

Delving beyond the title of this post, you're correct.

The Mix is pushed on this forum as a cheaper waterproofing over epoxy. But the Mix leaves voids as the solvents evaporate where epoxy doesn't. There are places on my builds where I'll used the Mix but on any exposed wood––under the sheathing and the floor of the galley––I've coated all of mine with epoxy and that's where the rubber meets the road. You can save a few bucks by using the Mix instead of epoxy but not a lot.

For some reason, there are a few folks here that seem to be afraid of epoxy. It's different but you won't find the wooden boat guys shying from it.

Tony

[QueticoBill]

For some reason, there are a few folks here that seem to be afraid of epoxy. It's different but you won't find the wooden boat guys shying from it.

Tony

I suspect that its more aversion to the cost rather than "afraid" of epoxy. It is more expensive at every step - materials, tools, clean-up.

[tony.latham]

For some reason, there are a few folks here that seem to be afraid of epoxy. It's different but you won't find the wooden boat guys shying from it.

Tony

I suspect that its more aversion to the cost rather than "afraid" of epoxy. It is more expensive at every step - materials, tools, clean-up.

I think you're right about the perceived cost of epoxy. A gallon of Miniwax is about $40 and two gallons of thinner will bring the bill to $70. Raka's Six-Quart kit is $100 so it's a rough savings of $30. (Their three-quart kit is $60 and that'll do one teardrop but I like to have extra in my shop.) It costs me about $4500 to build a teardrop and three ten-dollar bills is cheap insurance for something that takes three months of my labor (yeah, there's a nap or two in there somewhere).

I suspect it's more of figuring out where you're going to order it from and looking at a price of three figures vs. swinging by Ace Hardware and picking up three cans and running a credit card.



Tony

p.s. By the way, when's this Idaho winter gonna leave so I can go camping?

[rruff]

Raka's Six-Quart kit is $100

US Composites is even cheaper. If you buy 6.6 gal you can get it down to $44/gal + shipping. http://www.shopmaninc.com/epoxy.html