To coat or not to coat...

[Idon84]

...that is the question.

I'm working on my cover-boards which are curved 12' x 3/4" lengths of Ediman Mahogany that are thru bolted over the hull deck joint with 1/4" flat head machine screws.
Ignore reference to sampson posts

The old parts...

Side profile of hull/deck joint and area where cover boards fit.


Here are my questions:
1. Should I coat the areas that are against the hull with a couple of coats of neat epoxy before beding or is that overkill? These parts, which I hope to NEVER remove again, are to be painted when finished, not varnished like before.
2. Is their some kind of special beding compound should I use for wood? Sika 291 LOT is what I plan on using...

Thanks all,

[Hirilondë]

I am not sure what question 1 means. Sikaflex 291-LOT is a great choice for this application.

[Idon84]

Sorry for the confusion...

Coating the mahogany with epoxy prior to installation.

[Tim]

I don't think there's a need to coat all wood with epoxy, but if you do decide to epoxy coat, be sure to coat all surfaces of all pieces, and ensure that there are no bare spots or "edges" to the coating to allow water in beneath.

If it were me, I'd bed it properly and paint it well and not coat with epoxy.

[Hirilondë]

I wouldn't epoxy the wood either. I would consider priming it first though, or varnishing if you were going that route. When you bed bare wood, then paint or varnish it after, you get a mechanical seem where the paint meets the bedding. When this seem fails you get moisture behind the paint or varnish. By priming first you get an overlap instead.

[Quetzalsailor]

Coating out w/epoxy can't hurt. As Tim said, you would want the entire piece 'encapsulated'. And encapsulated wood should hold paint very nicely, that is, until the watertight surface is damaged.

Coating out w/epoxy under finish is great deal of trouble; it takes two coats each sanded out to ensure no pinholes, etc.; care to keep the coating thickness fairly uniform and the prefitted places still fitting with the thickness; even with care and determination, epoxy tends to go on lumpy and then run (easier on large flattish areas using a roller), and it does not sand out as easily as thinner applications of paint. Subseqent damage repair is made more complicated by having to repair the epoxy under the paint (or varnish). (I've done this coating out under varnish and paint for house floors, countertops, shower door, sill and frame, and am doing it on an old FD.)

What's Ediman Mahogany? If it has similar rot resistance to the original material, it would do as well as the original. That boat looked pretty nice under varnish for 29 years. Not bad longevity.

Certainly priming (if not encapsulating) is important with porous wood (as compared to Teak), when bedding. Primers have to be compatible to the bedding compound. As true in the good old days of linseed oil and oil-based bedding compounds as today.

[Rachel]

Coating out w/epoxy can't hurt.

In my opinion, I wouldn't go so far as to say that. I'm not anti-epoxy, and I'm not saying that it will hurt to coat the board, but I would say that it is possible for it to cause a problem. In my mind, anytime a "living," (natural) product is encapsulated, there is the chance of having a problem -- say, if or when the coating develops a small break. Enough to let moisture in, but not to let it back out easily.

I have coated things in epoxy myself, at times (and I don't just mean my hair and clothes), so it's not like I would never choose it, but I just wouldn't be so casual about the decision. It does seem that there is a general tendency to believe that all wood needs to be epoxied, when it lasted just fine for centuries without it.

I guess I'm just saying that it's something that should be carefully considered (as Idon is doing). I probably wouldn't coat in this case, because I have this nagging feeling that epoxy doesn't fail gracefully. Of course you hope not to have to deal with the covering boards again, but...

Rachel

PS: I hope this doesn't seem too ranty.

[Idon84]

Thanks for the input.

Priming sounds like the route I'll be taking. I'll be using System # WR-155 primer so I'll test it out with the Sika 291 LOT to test for compatability.

Edinam (Tiama) is an African mahogany(technically not a "true" mahogany). It has similar rot resistance characteristics as other mahoganies. I choose it because I could get 12"x144" boards in vertical grain. The tree grows much taller than other African mahoganies which allows for vertical grain in such long/wide boards at a reasonable price.

Thanks for the advice & opinions... moving forward.

Bryon

[Quetzalsailor]

Rachel, you're exactly right.

The encapsulation needs to be perfect and needs to be maintained. Failure of the encapsulation puts the adacent finish at risk, mostly since the wood changes size as it takes up water. I have a failure on one of my kitchen countertops, caused by a chronically leaky coffee maker that I did not catch for a month or so. The hot water expanded the coating and cracked it, then the water got into the wood below which happened to be the pith of the tree. (The pith is not as stable as the rest of the antique heart pine.) As a matter of curiosity and sloth, I have not repaired that top; it's been over 10 years and the lifted finish extends no farther than the original 1/8" x 6-8" or so despite damp sponge wipedowns and spills.

Epoxy joints and repairs that I have less confidence in are large joints where the rest of the wood is not coated (with something at least!). In these cases, I think that the joint is unwilling to move but the adjacent wood is free to. The wood will eventually tear alongside the joint if the change in size is great enough. Given all the glued structures with great long joints that serve well, I suppose my lack of confidence is not supported. But think of all those masts with split joints.

[Idon84]

Sometimes it is hard to determine what is true and what is BS, maybe because I read too much. For instance I've read the section from Larry Pardey on reason's not to use Epoxy for most situations. I have to take what he says with a grain of salt and not treat it like gospel. Then there are others that use it for EVERYTHING and stand behind it 100%. Epoxy is great stuff when used correctly, the trick seems to be knowing when that is. If it's out in the open (direct sunlight) and not painted I don't use epoxy, furthermore I don't like the idea of epoxy coating prior to varnishing. Just my thoughts so far.

My hatches were epoxied and although still together you can visibly see where the epoxy has broken down because of lack of maintenance on the varnish and it's exposure to direct sunlight. I will probably rebuild the hatches out of epoxy with much varnish just to see what happens over time. But things like bowsprits, bulwarks, sampson posts etc. I'm staying away from epoxy and going to use Resorcinol. Who knows... that may be bad over time too but my research has not found anything to suggest that, yet.

When I bought the boat the owner quickly made a bowsprit out of knotty pine glued together with epoxy then encapsulated with epoxy. It wasn't even 1 season before the wood had started to break the joints and currently sits on the scaffolding next to the boat almost completely de-laminated. I'll bet it was from the encapsulation. I guess it all boils down to getting as many opinions as possible and then making the best informed decision based on that.

Thanks again,

[Tim]

Sometimes it is hard to determine what is true and what is BS

You've just succinctly pinpointed what this forum is all about.

It's a jungle out there; one needs a good machete.

[Quetzalsailor]

We had a window salesman in for a presentation today who spoke to the problem with encapsulation by describing a demonstration he'd used in the past. Take two sponges; dip them in shellac?) so that one is coated on all 6 sides and the other only on 5 sides. After they're dry, dip them both in water. The first sponge's coating will survive and the second sponges' coating will be split by expanding.

This fellow was touting Norwood Windows, made in Canada and sold there and at least in the eastern US. Pretty good looking stuff, particularly if good quality and historic appearance is important. They encapsulate every stick of wood in their coated windows and guarantee the finish (for appearance) for 15 years. The encapsulation integrity apparently will go lots longer.

Clearly damaged parts of those windows would have the same problem that we all have been speaking to (I did not discuss that with him).

I've been thinking about the particular problem for this boat which is that the covering boards are fairly wide and I think I see that they are bedded into a recess; an edge and a face are bedded (what? maybe 5" wide overall and 7/8" thick? This is a pretty wide board to be sealed/bedded, isn't it? Would not the wood have a tendency to curl and lift away from the bedding, particularly if the rings are cupped down? Don't rings tend to flatten? (I'd have to look at a dock to remind myself.) Even vertical grain wood will misbehave if you give it a chance, which is one reason that deck boards and house flooring are narrow.