thompson's wood sealer...is that possible?!

[oceangboy2000]

alright guys and girls, hope everyones new years was great. Ive got a quick question for everyone. In a stitch and glue plywood construction project (luan...i know, i know!) i have some people who are stopping by to see the progress are convinced that a coat of epoxy on the interior is not nessicary, only a coat of deck water proofing. Im not to sure about that one! any thoughts? thanks!~dan

[wdnboatbuilder]

DON"T BELIEVE IT thats ******** if you just seal tone side of a sheet of plywood and you leave the other side un-sealed do you not think the moisture won't get in? Of course it will so you just seal the top,bottom,and sides this seal in the 8% or so moisture content and every thing else out (rot,which is alot of moisture and then drying out and the cells of the wood breaking down over time). I worked for a builder, if thats what you want to call him, anyway he sealed just the inside of the boat and stained and varnishes the outside. This boat come back 6 years later and we had to replace one side of the chine, two planks up the topside and 3 down the bottom, the "builder" makes a comment I can't understand I sealed the inside with three coats!?. Duhhhh,,, I did not last long thereafter.

Never use Thompson's on a boat

[oceangboy2000]

haha thanks, i was pretty sure that it was a big no go but i figured i better give it a chance on the forum! one more quick one since we're on the subject. Polyester resin for sealing purposes? just on the inside? just throwing ideas out there to get feedback on. thanks everyone~dan

[PAR]

Moisture will get into wood, no matter what reasonable actions a builder may take, it's just a matter of time. Some building methods rely on moisture to swell joints closed, others rely on coatings to keep the joints as dry as possible. The construction choices that ask for much adhesive, to hold the boat together, are very susceptible to moisture and must be well sealed.

Since you're using lauan, a very good coating system should be strongly considered. If the boat is a stitch and glue or a tape and seam build, you've pretty much opened the can on epoxy. Once you enter the epoxy envelope, you must go all the way or you're really only using expensive plastized paint. In other words, the end grain should receive special attention (CPES or other penetrating epoxy) all holes, cutouts, notches, all sides of every piece (likely to see even mild splashing) to be installed (before it's installed) should be coated with some form of epoxy. This is the epoxy spiral (as I call it) once started, it can add a great deal to the effort, materials and cost of a build. Some build methods require this, but others don't. If using less then recommend materials, you'd be best served trying to protect them as well as you can.

Poly doesn't stick as well to wood as epoxy. There are lots of delaminated transoms, stringers and other such things in the used production boat world to bear this out. Moisture also effects poly differently then epoxy and can lead to it becoming unstuck. The home building craze in the early 70's, where a catamaran was growing in every other backyard, had the vast majority coated and 'glassed sheathed using poly. The sheets of 'glass hanging from their flanks, a few years later should be warning enough.

[wdnboatbuilder]

Here's the problem, Thompson's and polyester are a pourous material they both will allow moisture through, once you have allowed moisture in wil will have more than the 8% what product you allow will lift. Of course on slower than the other. Not sure what kinda epoxy your using but there are better epoxies than WEST!!!!!!

[oceangboy2000]

Hey guys thanks for all the information. Im pretty well into the "epoxy spiral" now, but all your input is awesome. I wish they taught this stuff in school! its a little embarassing to be a few months from graduating with a naval arch degree and still not be sure about the little details for wooden construction. As far as which epoxy im useing...i live only a few miles form clark craft so i use thier "epoxy plus" system http://www.clarkcraft.com/cgi-suppli...98754b80d37cba . so far so good! im almost ready to start working on my foils and stuff! thanks again guys~dan