I am debating whether to epoxy barrier coat my mahogany plywood planked hull (no cloth) or to skip this step and apply finishes, would like your comments.
Also, is there any advantage in using a bottom paint, i.e., Interlux VC Performance Epoxy (no antifouling properties) instead of topside paint on a trailered boat?
Senior Member
Hi Russ,
I epoxy coated all of my mahogony brightwork with thinned epoxy then varnished. Everything in the boat is epoxy coated (outside of the hull has 6 oz glass) in an effort to protect the boat for as long as possible. I keep the boat on a trailer in the garage, so I should be able to give it to my grandkids in 50 years!!!
I used VC epoxy on the bottom for two reasons: 1) It provides a very hard finish for beaching the boat and dragging onto the trailer, and 2) the few times when I will keep the boat in the water for up to a weeks time I have been told that regular topsides paint on the bottom wouldn't last. I am pleased with the results.
Jeff
Senior Member
My boat was epoxy built, so there was no question about having to re-do her with E. Water underneath the epoxy is not a good thing; so most people advise that if you're going to do the outside, the inside should be done as well.
You've got a big question. After gaining experience with the epoxy, I'm a believer in it. In fact, I'm constantly on the prowl around the house looking to make a "permanent" fix... The one downside, and it must be compensated for, is that the boat will loose all flexability. She has got to be dry when you start.
This is a good thread, and I'm interested in what the other folks will have to say.
Yes, there is an advantage to the epoxy-barrier-coat. I'm familiar with the Interlux 2000 product. It has a density that retards permiability (more waterproof to microscopic water molecules with its plate sytem). It slows, if not ends, water migration through osmosis. However, you will need to use an "etching primer" such as the Petit brand "no sand primer" to get anytype of adhesion from any bottom paint.
[ 07-29-2004, 11:32 PM: Message edited by: Elco's ]
The answer to this question seems to depend on what generation of Forum Members is giving the advise. The books differ as well.
I suspect WEST and System Three would object to their epoxy being diluted. If I needed less viscosity I'd use heat or a different formulation. MAS is thinner than either of the above and System Three makes one with viscosity that is like water.
Whether I'd coat true mahogany with epoxy prior to painting would depend on my mood on the fateful day. Probably not. Fir I would definately coat. Okoume (African manogany to some) probably.
Wary eye on yardarm
For my own process, I follow in Norm's footsteps regarding what to epoxy and what not to epoxy. Don't you think that the mahogany with varnish to be adequate? Why clear coat with epoxy and (you'll have to if it sees sunlight) then varnish it? You will need UV blockers to protect the epoxy. As for thinning the epoxy (as divulged in another thread), I do it for, presumably, sinking the epoxy into oily species of wood (not mahogany)--but I do it only for laminating.
Senior Member
I had the same question recently with building the Pooduck. I am happy I decided to coat inside and out with epoxy. Because it was still quite cool here when I did it I thinned the mixed epoxy with about 15% acetone.(takes a lot of stirring to get it mixed) I found it was easily applied with a 4"foam roller and the finish was pretty smooth. I cleaned up the few ineveitable drips and runs with a sharp paint scraper. It helps if you have the time to plan on an hour or two while the epoxy is setting up to keep a look out for drips and clean them up then. I sanded with 220 then 320 before finishing with paint / varnish. I did try to use full strength on all the end grain.
If it were above 20C (70F) I would probably go with unthinned epoxy with a foam roller. Even though it's quite thick it should soak in well.
Good Luck
Senior Member
For me, Kirby paint went over West System epoxy sanded with 220 without the use of any primer. The epoxy feels a lot smoother than it is; so sand, wipe & sand again. The 320 is probably a good idea. After reading up on thinning West System epoxy, I don't think I'd thin it for barrier coating. They claim that the thinner will eventually evaporate, and since the epoxy is in a hardened state, you end up with something approaching swiss cheese (holes in it).
Unless you're in a big hurry to varnish, or your boat is partially epoxied, and you need a barrier coat, I didn't notice any great improvement using the epoxy as a base coat. If your in a hurry, getting the first three or four coats of epoxy on in a single day is great, but you've still got to put 3 or 4 coats of varnish over that. That beats nine coats of varnish, which takes time, but I'm finding that everything is taking a loooong time; so, I can find time to varnish.
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Having just restored a non epoxy coated plywood rotted and checked dinghy I can respond both professionally and on a personal level.
I would coat all weather exposed plywood (maybe regular wood too) with a solvent thinned or flexible epoxy. The solvents will aid pentration and mess up the epoxy to the point of giving it some flex. Flex is a good thing and perhaps required as wood expands and contracts with moisture content, while epoxies expand with temp. Plus, thin plywood has lots of give an flex. The epoxy 'skin' needs to be able to handle that too.
Also epoxies make a great primer under just about any kind of paint thus making the final paint (or varnish) job potentially last much longer.
paul oman
progressive epoxy polymers
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