Does encapsulating Honduran Mahog cause dryrot?

[TomRCCL]

Greetings:

I'm building a shellback dinghy and want to encapsulate the quarter knees, breast hooks, etc. in epoxy for protection. Does anyone know if this could cause dry rot by trapping mossture in the mahogony?
I've heard advice both ways. 1] By all means, cover it in epoxy and 2] the exact opposite advice. Any thoughts on this. I'm leaning strongly towards encaspulating them in epoxy but would love to hear from others who may have been down this road already.

Cheers,


Tom

[jonboy]

Dry rot ,no it's a fungal infection, so unless the wood is contaminated already it will be fine and to be on the safe side disinfect it first with pure bleach, thymol, general household anti-fungals, anti- bathroom mould products.
But encapsulating green, or unseasoned or wet wood you might get good old rot, but it won't be 'dry rot'.

There's been no genuine Honduras mahogany since about 1880, so is your wood salvaged from a piece of old furniture or somesuch?? If it is, a dose of phenyl-phenol woodworm killer wouldn't be a bad idea and it will whack any mould too... Most 'Cuban' 'Honduran' mahogs are african hardwoods... even Brazilian stuff is hard to get these days and almost certainly isn't Swietenia Mahagoni, really the only true south american Meliacae wood
Bit irrelevant I know, but if the wood is well dry, and well encapsulated it should be ok . I'd go for a good varnish and watch for damage to the varnish skin , because removing epoxy if you compromise the surface and rot does get in is a prize pain in the wosname.

[paladin]

There's plenty of original Honduras Mahogany....I have a few dozen trees still standing and cut one about three years ago and If I was to build another boat I'd cut one and ship it to Washington state to be cut........It is tightly controlled as to how many are cut.
That said....NO! if you encapsulate it won't cause rot. Nothing, absolutely NOTHING lives in a styrene atmosphere. Clean it well, wipe with acetone, let it dry 48 hours or so and paint on the epoxy. After the epoxy sets, varnish it with a good UV varnish, at least 4 coats.

[Thorne]

As above you can do that, but the question at hand is "Why?"

Solid wood that doesn't sit in a wet location shouldn't rot, and most small open boats with either ply or solid wood hulls do not have their breasthooks, quater knees, gunwales, etc coated in epoxy.

Wood attached to the bottom planks like transom braces or the stem might be a better candidate for this process. But if the wood shrinks or swells it will crack the epoxy and probably the varnish as well, allowing moisture and potential rot that way. And solid wood will shrink/swell in ways that plywood won't -- which is why it is often coated with fiberglass as well as epoxy.

Remember that you'll have to varnish these anyway to protect the epoxy against UV damage, but any deep nicks/dents/scrapes will have to be sanded through the epoxy back to wood. Will you then try to wood the entire part and recoat with epoxy, or leave the epoxy with an incomplete barrier?

I personally wouldn't bother using epoxy on those parts, but have used CPES with a hotcoat of varnish to get the very best bond between wood and varnish -- as the wood/coating layer is where most paint/varnish failure will occur. The CPES will give a bit of protection to the wood and creates a layer that looks like 2 thin coats of varnish.

Here's my dory skiff with the obligatory swimsuit model (really!!) - none of the spars, breast hook, quarter knees, thwarts, partners, pinrails, etc are epoxied, and all are from white oak or doug fir.

http://forum.woodenboat.com/showthre...ighlight=china

This boat is a highly-modified catspaw dinghy built from fully 'glassed doorskins (!!) for the hull, but again none of the spars, trim, thwarts, etc were epoxied -

[Todd Bradshaw]

Personally. I love epoxy resin, but I think most epoxy-coated trim looks very "plastic". I remember being at a fancy antique powerboat show a few years ago where there was a mix of restored classics and new replicas - all with superb workmanship and thick gloss varnish. You could walk down the docks and pick out the epoxy-coated replicas in a heartbeat. There was just something different about the look of the real varnished wood and the epoxy-coated and then varnished wood - which tended to look a bit fake by comparison. You also need to understand that epoxy doesn't go on like varnish does. If you want to epoxy-coat your trim and then get it ready for a smooth, quality finish under the final varnish, you will have a lot of sanding to do to get the resin smooth, and probably mostly by hand, sanding out lumps and drips in very hard epoxy resin.

Chuck - there ain't no styrene in epoxy resin. That would be polyester resin.

[paladin]

I know, Todd....but youse gets the same effect with the acetone and the epoxy....it's just the old saying from the trimaran days.......back when we didn't have epoxy......

[Bob Smalser]

I've heard advice both ways. 1] By all means, cover it in epoxy and 2] the exact opposite advice. Any thoughts on this?

People confuse their resins in their sea stories.

Epoxy resin allows moisture transmission in and out and accordingly, doesn't rot the wood. Older polyester resins don't breathe as well, and some are also hygroscopic and can quickly rot wood encapsulated in them. Automotive Bondo is one of the more famous offenders.

So why don't plywood-cored fiberglass-polyester resin boats fall apart? The plywood was installed dry and completely sealed. Wood can't rot unless it reaches 20% moisture content or higher. But let moisture in by abrading or drilling through the fiberglass layers, and that plywood core quickly turns to a black, smelly ooze.

[Todd Bradshaw]

Huh? Sorry, but that just isn't true. Epoxy is slightly moisture permeable over extended periods of time (as is damned near every other substance known to man - water ALWAYS wins) but polyester is even more porous due to the fact that it isn't 100% solids (unlike most epoxy) and because polyester contains evaporating solvent (styrene monomer) that flashes off during cure (causing shrinkage). Boat graveyards are full of boats with rotted plywood cores (decks, transoms and floors) "sealed" with polyester resin. Granted, in many cases, this can be blamed, at least to an extent, on poorly bedded hardware (motor brackets, stantions, assorted screws. etc.) but much of it is because polyester resin is a pretty poor wood sealer which also doesn't adhere very well to most wood, often resulting in delamination. It's used in production fiberglass boatbuilding because it's a hell of a lot cheaper, faster to lay up and get out of the mold so that you can start the next one, and because it's easier to use - more tolerant of mixing variations and the cure time can be adjusted as needed by varying hardner amounts to match the working conditions.

You can sit around and wait for your epoxy resin to "breathe" if you want, but you're going to be there an awfully long time (like decades). Surprisingly, the next best sealer to epoxy resin is tar. Polyester resin is way down the list.

[Thorne]

Well I'll stay out of THAT Battle of the Titans, but I have heard that CPES will let a certain amount of moisture pass -- supposedly making it a good choice for some applications below paint or varnish which do likewise.

[wizbang 13]

Epoxy will not rot the mahogany ,but I would do as TB said (for the reason he stated)and just varnish it. That being said I might epoxify everything ELCE on the boat that is painted!

[Todd Bradshaw]

CPES will absolutely let a certain amount of moisture pass - because it has a huge concentration of evaporating solvents and they tend to leave tiny holes in the coverage as the stuff hardens and they evaporate away. There are plenty of woodworking products known as "sealers" - oil-based sealers, vinyl sealers, etc. Many of them seem to do little more than raise the grain and stick it that way so that you can sand it smooth. When you get right down to brass tacks, most of them really don't even come close to "sealing" the wood in a boatbuilding sense. I would never put CPES on a boat expecting it to seal moisture in or out. But...I certainly might use it like a really tenacious primer to get down deeper into the wood and form sort of a graduated wood/resin matrix and then to get a similarly good grip on my paint or varnish top coats. I think that's the true value of CPES - that it has the ability to make subsequent finishes stick better and stay stuck (last) better (with the exception of epoxy resin, which should already exceed the grain strength of the wood, which is all the bond you can get). As just a sealer, and with all that solvent in there, I wouldn't expect CPES to actually seal any better than laquer, thinned varnish or anything else containing a lot of solvent. They all leave holes and all holes pass moisture - just like Gore-Tex does, but I do think CPES may have a more important role to play and probably should really be called "Clear Penetrating Epoxy Primer".

The other thing that you have to keep in mind is that even the best epoxy coating job is limited in terms of how much wood thickness it can stabilize. If you take a big, thick hunk of wood and resin coat it, you may retard the penetration of moisture into that wood, but if it decides to move (expand, contract, etc.) the resin isn't going to stop it. Unless you load it up with fibers, it just doesn't have enough brute force to do so. This is one reason that taking an old carvel-planked timber yacht and slathering it with epoxy resin isn't a good idea. The most durable wood/epoxy boats are built from thin layers of wood, connected and stabilized by thin layers of epoxy.

[floatingkiwi]

There's plenty of original Honduras Mahogany....I have a few dozen trees still standing and cut one about three years ago and If I was to build another boat I'd cut one and ship it to Washington state to be cut........It is tightly controlled as to how many are cut.
That said....NO! if you encapsulate it won't cause rot. Nothing, absolutely NOTHING lives in a styrene atmosphere. Clean it well, wipe with acetone, let it dry 48 hours or so and paint on the epoxy. After the epoxy sets, varnish it with a good UV varnish, at least 4 coats.

You say you have trees standing? Where> Are they growing on land You own and live on or are they elsewhere and earmarked for your use only?

[paladin]

They stand on land that I own......I can cut for my own use after filing an "intent" but if for commercial purposes (sale) I am allowed to cut a limited number of trees based on the hectares of land that I own, that are also in the "forest", and then in proportion to other land/tree owners. I own slightly less than 100 hectares, and about 60-70% is under tree cultivation....so I don't stand much of a chance against the commercial growers.....if they are allowed to cut one tree per 150 hectares.....I can cut a half a tree a year...or some ridiculous reasoning.......I haven't cut anything in 8 years or so, so I can cut a couple almost anytime....sorta saving them in case the transplant works.
The company I own is in San Pedro Sula, Honduras. It's an electronics assembly house. I do the design/engineering here, ship the stuff there for build.

[Eric D]

Chuck, you never cease to amaze me....truly, that is a compliment. Thanks for your participation on this forum. Best of health.

[villtur]

Post no 3: "I have a few dozen trees still standing and cut one about three years ago and..."
Post no 13 (by same person):".......I haven't cut anything in 8 years or so, so I can cut a couple almost anytime...."
Strange. We in the north no understand??

[paladin]

Perhaps I should have said that I have cut a tree for my own use but have not cut a tree "Commercially" in 8 years.
I can cut a tree or two for my own use, but to do so commercially and export the wood or tree I have to file the appropriate paperwork with the "state". If I cut a tree and have it exported to the U.S., even for my own use, I have to go through the same procedures as for a "commercial" sale......if for use inside the country, just a filing that I am doing so and the mill that is handling the processing is all that is required.

The tree that was cut was used for my own use in that the building that I own in San Pedro Sula needed to be finished inside as the upper floor was bare cinder block walls with no insulation. It cost me virtually nothing to have one tree cut, made into paneling and enough wood was obtained to finish the top floor of the building, and the balance to the sawmill for doing the processing.

I have not sold anything from the property or exported any product from the forest.

Does that help your comprehension of the language?

[villtur]

Me mucho feel better. It seems though that I comprehended the language but I realize now that I should be able to read thoughts; which my vife tells me all the time. Terrible shortcoming of us northern males.

[floatingkiwi]

The transplant will work if you believe it will.
Best wishes mate.