The Annapolis Wherry manual wants the builder to encapsulate all wood in epoxy. I have built boats with this method,but now I'm leaning against this approach because: 1) Health issues with more fumes and sanding dust, 2) More cost, 3) more weight, and 4) a WHOLE lot more work. I'm just not sure the end result justifies these points. I will, however, epoxy the ends and edges of the plywood. Your thoughts?
Don't worry about trying to keep the epoxy out of the stitch holes when pre-coating. It's quick and easy to drill out any that get epoxy in them. In fact, I find drilling out filled holes a lot easier than keeping the epoxy out of the holes in t he first place.
Just be sure not to wait too long between pre-coating and stitching. After a few days the epoxy starts stiffening the wood panels as it cures and extreme curves become difficult.
Laszlo
Thank you for your response. You have convinced me to barrier coat everything. I plan to pre-coat all panels on the workbench careful not to cover the stitching holes.
A comment to jimgr. If I understand your note, you recommend sanding the first coat of epoxy before proceeding. On page 37 of the WEST system manual, on applying second and subsequest coats, they recommend to apply all coats when previous coats have cured to a tacky stage to avoid sanding and to ensure a chemical bond (primary bond, page 30).
Regarding the re-coating recommendation by West Systems, variously referred to as "wet-on-wet" or "hot coating": it works and can be a real time-saver, allowing as many as 3 coats in a day. The window for doing that is when the epoxy feels tacky to the touch but will no longer transfer to your finger.
just some notes on efficient pre-coating...
a foam roller is the easiest way to get a good, thin precoat. i use the ones from clc https://clcboats.com/shop/products/boat-building-supplies-epoxy-fiberglass-plywood/foam-roller-covers.html
they are 8 inches and i cut them in half to fit nicely on a 4 inch roller. my technique
prior to the first coat, confirm stable or decreasing temperature over the next 8 hours of the intended start time:
1) roll on a thin coat and tip it out with a foam brush - let it cure
2) light sanding with 180 or 220 sandpaper - emphasis on light - your objective is to knock down any bubbles or little wood fibres that may have stuck through...
3) roll on a second thin coat and tip it our with a foam brush - let it cure.
once it has cured, you will, in my experience, not notice any significant change in stiffness. i have built an annapolis wherry, it does not have any severe bends...so while i don't disagree with laszlo's comments, i don't think the concern would come into play on a wherry. so if you are taking some time between steps....i am pretty confident you can barrier coat one weekend....and do your stitching a weekend or more later with no problems.
h
That epoxy you're skipping is the waterproofing for the boat. Without it you're depending on the varnish or paint to protect the boat from water damage or rot. Raw wood is a mobile substrate which will cause the paint and varnish to flex. Varnish that flexes will develop fatigue microcracks which will allow water into the wood, causing it to swell which in turn will cause the varnish to flex which will open up more cracks and let in more water.
Epoxy coated wood is sealed against water. It forms a stable substrate so the varnish maintians its integrity. Look at tradisional boats. They need to be refinished every year. Epoxy encapsulated boats can go many years between refinishes.
Finally, okoume is not the most rot-resistant wood. It needs epoxy to work properly.
So skip the epoxy if you want, it's your boat. Just be aware that all the work you save will have to be done over and over again unless you just want to give up on your boat and trash it. It's a false savings.
Laszlo
Hi Bob,
i agree with laszlo but let me try to explain it differntly.
buidling with plywood is simply not like building old style wooden boats with timbers/complete cuts of wood.
while the glue used in maring grade plywood is waterproof, the plywood itself is simply not engineered for consistent submersion or being wet the way an old style wooden boat is conceived. the whole approach and experience in the industry for stitch and glue (and cold molded hulls as well) is that the okoume plywood needs to be epoxy encapsulated.
in addition to the paint issues described above, the boat will gain plenty of weight in water if its not encapsulated. so don't think about this as a way to save weight.
that said, when we say encapsulated, we are not talking about a bug in a piece of amber kind of encapsulation....we are just talking about a couple mills of thickness and basically, what amounts in the industry as a 'barrier coat' on all exposed surfaces to keep the wood dry....and create a nice stable substrate for your finish. when the encapsulation is handled like a barrier coat (thin, complete, consistent application, like a layer of waterproofing paint), the weight added is minimal.
a little focus on technique for coating will also minimize fumes and dust.
i hope that helps.
h
adding just one thing to the above: when a piece of wood is processed( cut sanded) wood fibers are pushed doen into the cell lumens. When it is wetted with water, paint, varnish or resin the fibers stand out and is why the first coat is rough. These fibers need to be sanded off not just to make it smooth but to remove the fibers from sticking through the resin, varnish or paint and removing an avenue for water to migrate through the encapsulation ( resin, paint). The second coat then is able to form a complete isolation of the wood from the water. And as such no swelling to crack the resin or varnish.