Most waterproof paint over epoxy?

[spirit]

What is the most waterproof paint to use over epoxy-encapsulated marine plywood?

[Mrleft8]

Epoxy.

[Kaa]

Epoxy is waterproof by itself, so the point of the paint over epoxy is not to keep water out. Its point is:

• To keep the epoxy out of UV which kills it;
• To provide a bit of protection against dings, scratches, scuffs, etc.;
• To look pretty.

Kaa

[JimD]

Two pack poly's will be the hardest if you don't mind the headache of using the stuff.

[spirit]

There are places on a boat (like a partially foam-filled, poorly ventilated, steamy plywood compartment in the sun) where it would be nice to have something more waterproof than three coats of epoxy. In an article on moisture exclusion effectiveness in Epoxyworks (#25, summer 2007), the Gougeons reported that wood treated with 3 coats of West System 105/205 still gained 8% weight in 100% humidity in 8 weeks. Vinyl ester was pretty good, two-part polyurethane worse, and high-solvent epoxy and resorcinol formaldehyde almost useless. Only paraffin wax was a better barrier than epoxy.

Does anyone have experience with the ability of a wax coating to increase the moisture exclusion properties of epoxy on marine plywood?

[esingleman]

Remember slowing down the moisture on the way in also slows down the moisture on the way out.

[wwaterman]

I just finished painting with the two-part linear polyurethane from System Three (W-LPU). I'm very happy with it. Although I haven't put the stuff to the test yet, it seems like its really able to take a beating.

I just posted pictures here:

http://www.woodenboat.com/forum/showthread.php?t=83312

[Steve Lansdowne]

I like the System 3 LPU also, though it is very thin. In 2001 or so I made a supplemental street sign painted with it and hung it on the fence. I used a roller / brush rather than sprayed it on. Sealed it with the clear LPU. It is in as good condition today as it was the day I hung it, Texas weather and all.

[paladin]

I used Imron on my boat and it did damn well for almost 20 years.....but then also I waxed and buffed it periodically...

[Peter Malcolm Jardine]

I did the Chris Craft in Imron and it has held up fantastically well. tough as nails. I would never do a bigger boat in anything but two part now...

[pipefitter]

Use an osmosis blocker such as interlux interprotect 2000e as a primer.

www.yachtpaint.com

"InterProtect® 2000E is a unique two-part epoxy designed to reduce the potential of water absorption by fiberglass hulls. InterProtect is unique among epoxies because it has Micro-Plates®, a protective barrier within its film to slow down water permeation. Technically, InterProtect Micro-Plates provide millions of overlapping microscopic plates that create a barrier similar to shingles on a roof. These overlapping Micro-Plates eliminate any direct path for water migration and also improve the sag resistance of the epoxy making application easier."

[David G]

There is no finish product that will totally solve your issue of a dampish compartment. How about ventilating the compartment in some way? A deck hatch that's only removed when the boats under cover is one example.


"It is so much easier to suggest solutions when you don't know too much about the problem" -- Malcolm Forbes

[kengrome]

There are places on a boat (like a partially foam-filled, poorly ventilated, steamy plywood compartment in the sun) where it would be nice to have something more waterproof than three coats of epoxy.

Why don't you treat the wood in these areas with Copper Naphthenate since you're never going to be able to waterproof it no natter what you do anyways?

Only paraffin wax was a better barrier than epoxy.

Well okay, I guess you could wax it if you want to, but that's bound to create other problems you may not know about until later. I've never heard of this being done but I can imagine the potential for trapping moisture inside the wood ...

[StevenBauer]

Epoxy coating the marine ply is the problem. Skip the epoxy and just use paint.


Steven

[Todd Bradshaw]

I really believe you are over-thinking this one and trying to create solutions to a problem that doesn't exist. There are thousands of boats out there with epoxy-sealed watertight compartments that are doing just fine and have been that way for as long as 30-40 years. Assuming that you do a good job of building and sealing the compartment, there is no reason to suspect that you will ever have a problem. If desired, you could add a barrier coat like the Interlprotect or Gougeon filler powder mixed into resin, but you probably don't need it. The plain text explanation for the Interlux advertising hype posted above, by the way, is that they add aluminum flake powder to the epoxy. In order for water to get through it, it has to zig-zag around all the tiny aluminum flakes. It works, but you generally need about ten mils of coating thickness for it to be effective - which may be as many as five or six rolled-on coats, depending on how thick or thin the resin mix happens to be. For a well-sealed closed compartment, it probably isn't needed.

Adding a watertight inspection port isn't a bad idea on any closed compartment and can allow you to vent it as needed and check it for moisture any time you want. It may also be a decent place to stow your car keys or camera at times.

The problem with the idea of just using paint as your sealer so that moisture can "escape" from the wood and the compartment easier is that moisture that penetrates plywood and then finds it's way out usually does at least some damage in the process. This is why even the best marine plywood manufacturers, like Bruynzeel, specifically state on the warranty sticker on every sheet that the warranty is only valid if the end grain on the sheet's edges has been properly sealed. Nothing on earth will completely resist water (the Grand Canyon being a good example) but given the choice of keeping it out of plywood with either paint or epoxy resin, I'll take plain old epoxy every time.