New learning at LS

[Clinton B Chase]

As I go through the cold molding/cruising boat building course at The Landing School, I visit the small boat shop all the time to get some tips on my own small boat project(s)...like my Nutshell for this winter. I learned that it is good to epoxy barrier coat the planks before they are cut that is epoxy paint the scarfed plywood sheets, This makes the plywood behave when cutting it (no ripps, etc) sands better b/c the epoxy makes the material more homogeneous and therefore predictable under grit, and the epoxy barrier coat will be a moisture barrier. The last one is my only lingering question, however. IF, IF water gets into the wood, and the wood is encapsulated in epoxy, how will the water ever get back out...no drying out possible. Any way thought I'd add this to the list...food for thought.

Cheers,
Clint

[Thad Van Gilder]

That's why epoxy encapsulated boats don't last as long as traditionally planked boats!!!

-Thad

[Stephen Hutchins]

Heat will cause the water to evaporate.

[Bruce Hooke]

A few thoughts:

1. The water can get back out the same way it got in.

2. Epoxy is not a perfect barrier to water, so given time, water will makes its way back and forth through the epoxy barrier. Which direction it goes depends on which side of the barrier is wetter (the wood or the air or water next to it). This clearly means that below the waterline water will very slowly find its way into the wood, but on the inside of the boat and above the waterline any water in the wood will slowly find its way out to the air.

3. What we are generally worried about when the subject of water & wood comes up is rot. As I understand it, even if water does get into the wood and stay there, the epoxy greatly slows down the flow of oxygen, which the rot spores need in order to grow and spread, so even a damaged epoxy coating does a lot to protect the wood.

4. Epoxy coated boats need to be maintained like any other boat. Part of this maintenance should be touching up places where the epoxy coating has been breached, just as you would touch up spots where the paint coating has been breached, but of course it takes a lot more to breach the epoxy coating than it would a coating of paint.

5. Plenty of wood & epoxy boats have lasted for quite a long time so the "system" clearly works. Trying to decide whether traditional wood boats will last longer than epoxy coated boats or vise versa strikes me as a fairly futile exercise, because both can last pretty much forever if they are properly maintained. Of coures over time this will mean that almost every element of the structure will get replaced at some point...

[Steve Lansdowne]

This is a question which has been debated back and forth for some time. Some folks are against epoxy coating wood, while others think it is a good idea. There seem to be strong opinions on both sides.

[Clinton B Chase]

[QUOTE]Originally posted by Bruce Hooke:
[QB]A few thoughts:

1. The water can get back out the same way it got in.

Bruce,

What is your reasoning here? Mine is that a crack or small puncture introduces to the wood amazing amounts of water through capillary action. The wood is happy to absorb and retain it in the same vessels that transported water up and down the tree. It might not start to rot right away but will slowly. And a wet plank will make the hull soft and flexi. If water could just get back out than why are wood cored decks in old fiberglass boats absolutely soaked? The water is very happy to stay in the wood unless exposed to dry air and/or some heat for a while.

I would prefer to not coat the wood with epoxy for barrier coating purposes, but the plywood behaves SO much better in cutting and sanding with epoxy primer on there that I may do it anyway.

This is a long standing debate. John Brooks is against it (see his book) and he knows what he's talking about!

Cheers,
Clint

[Bob Cleek]

Epoxy encapsulation is a fool's errand. Epoxy "breathes" and moisture will transfer through it, albeit more slowly. I can imagine that "playwood" might cut more cleanly with a barrier coat on it, but wouldn't it simply be easier to use a fine toothed plywood saw blade to reduce splintering on the edges? (Why use plywood at all, but that's another discussion altogether.) I would think the expense of putting a barrier coat on plywood would not be jusifiable.

CPES will slow the absorption and drying cycles, but is relatively "breathable." I wouldn't use any other epoxy in a futile attempt to try to prevent moisture from permeating the wood. As mentioned above, the problem with "barrier" epoxies, which are close to impermiable, is that the moisture will find the path of least resistance and "soak" those areas. Healthy wood "breathes." Encapsulation was a fad that has had its day. We have found it does not work as once they thought it might.

[JimConlin]

To extend the concept of pre-coating plywood with epoxy, which can save a lot of work later, i've wondered whether for lightly loaded things like joinery it would be OK to pre-coat plywood sheets with an epoxy-based primer like Interlux 404/414. I've certainly found that the errant dribble of epoxy adheres well to it, but i've wondered whether anyone has characterized the material's mechanical properties. The Interlux tech support people were only able to read the can to me.

[ 10-01-2005, 04:52 PM: Message edited by: JimConlin ]

[pipefitter]

The reason most wood cored fibreglass boats wood cores rot is because of neglect and waterlogged foam.People that own fiberglass boats dont generally think about the wood but just the polyester.The figure that water isnt visibly leaking in while they are using it so it must be waterproof,right?Meanwhile,drain holes get plugged up while sitting outside uncovered on the trailer and rainwater fills it to the deck and beyond and eventually saturates the foam which is tight to the wood cored deck.Then there is things like haystacks calhoun jumping in from the dock causing hairline cracks around hatches,etc.
On transoms with rotten wood cores there is almost always cracks on the top and corners of the outboard mount area that just are open to the rain and it begins swelling the wood,delaminating the glass hence making room for yet more water in between the skins. Again,it's always going to be about maintenence.A coverd glass boat with wood cores will last for a very long time. I've seen guys put in those pie eyes in decks,squirt some 52 around the flange and leave raw plywood under the fitting not even thinking that the bilge is going to have water in it at some point up to that level.
If any boat is maintained as it needs it,you shouldn't have to do anything to it other than maybe have it painted because you waxed and buffed the gel coat away.
Foam core or any of the new wood free core materials are designed to be sold to the the hose it and forget it vinyl siding crowd with one exception that I am aware of.The Boston Whaler with their "whaleboard" cores is some extremely tough stuff.It will ring the heads off of 1/4" SS lags if it isn't predrilled properly and I dont even care for their boats.

[ 10-01-2005, 05:23 PM: Message edited by: pipefitter ]