Epoxy coating

I just read another slant by a bui;der that says that epoxy coating your plywood constructed boat is a bad idea. He says that the epoxy will eventually lose its bond or crack and allow water to enter the wood and then inspire rot to consume the plywood. I bought this fellow's book..."How to Build Glued-Lapstrake Wooden Boats" - John Brooks and Ruth Ann Hill. It's a great book with great ideas and procedures, wonderful photos and descriptions and much on how-to. But, I wonder about this epoxy advice.

Sounds like the authors may be experienced with polyester resin impregnated fiberglass, but not epoxy...? Epoxy doesn't just lay on the surface, it soaks in and blends with the fibers of wood, correct? 

We are at this epoxy coating stage and wish for experienced input here...


Bill C. 

8 replies:

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RE: Epoxy coating

Good quality marine epoxy, such as the stuff sold at CLC, will not debond if properly applied in the first place and protected with a UV absorbent layer.

A too-thin layer on a flexible surface may eventually develop micro-cracks through fatigue. Putting on sufficient epoxy or, better yet, a layer of 4-oz glass will keep that from happening.

So what do they want you to coat it with, if not epoxy? My currently oldest epoxy-covered boat is almost 6 years old and shows no sign of cracks or rot, while my painted & varnished boats in the 70's & 80's all had rot within 3 years.

When was that book written? 



RE: Epoxy coating

First printing in 2004. They say prime and paint or just varnish. We'll go with these recomendations by CLC to use the epoxy.

Bill C. 

RE: Epoxy coating

I have many years experience with varnished teak and painted wood in the marine environment. Without immediate attention to chips, scratches and dents, water will penetrate, the wood will get wet and the varnish will begin to fail. We ran a test on the teak bow sprit of a large yacht that we circumnavigated on 1998 - 2001. The deck of the sprit was epoxied then coated with one coat of the varnish we used for build up and one top coat. The sides of the sprit were not epoxied but finished with the same number of coats of varnish (7-9) as the adjacent teak cap rail. Obviously the sprit was subjected to almost four years of UV and countless submersions in the sea. The top of the sprit held up better than the varnished cap rail. This test proved the value of an epoxy base to me. That said, because the varnish on large yachts is often removed during yard periods I do not use epoxy on largely decorative surfaces but always would on a wood boat. Here is the process we use on exterior teak that works well over epoxy. On teak sanded with 80 grit paper we build up with Captains Varnish, enough coats (4-5 coats) to fill the grain of the teak. This is the stage you would be at when finishing an epoxy surface. We then use 70% Epifanes Clear Varnish and 30% Captains Varnish thinned with 333 and applied with a badger brush to finish. There are individual properties in these varnishes that have proven themselves over the years to be the best combination for UV and abrasion protection. We usually apply three finish coats. We sand each build up coat with 220 grit on a rubber sanding block, then on the last build up coat and between the finish coats we do a 400 grit wet sand. We only and always use denatured alcohol on cotton rags to wipe with. On Okoume plywood or the wood usually used to strip build a boat I would not consider applying varnish to any surface that would be exposed to UV or rough treatment without a first coat of epoxy. SEEYA Jack

RE: Epoxy coating

I would say the folks who recommend against the epoxy don't have much experience with it.  I'd also ask what they recommend instead.  How is paint and varnish better than epoxy with paint and varnish?  Seems like they may be just recommending this as a money "saving" effort for the builder, or possibly a money "making" effort if they happen to also offer boat building classes.

I built my boat in 2004 and still haven't bothered to varnish it at all.  The epoxy is still holding up quite well and keeping the water out.  No rot or any issues with damage to the wood. I even stored it outside for a year.



RE: Epoxy coating

I wouldn't say John Brooks lacks experience with epoxy.  He has built many glued lapstrake boats and designed a few as well.  Ditto for Iain Oughtred, a very prolific boat designer who also spurns epoxy coating.  Both are strong believers in epoxy for gluing a boat together, they just don't believe it's a magic bullet for protecting wood.

There appears to be two antithetical viewpoints on the use of epoxy on boats: keep it to a minimum versus encapsulate your boat with it.  Just search the WoodenBoat forums for the many epoxy flame-fests.

I don't have experience enough to have a viewpoint one way or the other.  But I'd be wary of completely disregarding the opinions of those that do have a great deal of experience, even if those opinions seem wrong.  I also will hazard a guess that the wood-fiberglass-epoxy "composite" construction that characterize stitch-and-glue and strip-built kayaks may not be optimal on other kinds of watercraft.  Kayaks typically are "dry sailed", even garaged, between uses.  Many other types of small boats are used as tenders that are left in water and full sunlight for extended periods.

I've completed just one boat so far.  I epoxy coated my Eastport Pram without trepidation.  The designer specified epoxy coating, so that's what I did. I'd like to build more boats, and not just stitch-and-glue boats.  I find glued lapstrake fascinating, especially given it's differences from stitch-and-glue. If the designer of a glued lapstrake boat says not to epoxy coat, I probably won't.

Just my 2 cents.


RE: Epoxy coating

Epoxy has replaced polyester resin for the most part and that IMO is a good thing. Polyester resin was used as a fix-all and some folks attempted to use it as a wood sealer, as epoxy is now. When a report of cracked and blistered 'fiberglass' coating is heard, polyester impregnated fiberglass is what first comes to mind. Polyester resin does not impregnate the wood grain as epoxy does, so remains a basic coating on the surface with little adhesion.

This question of epoxy coating was for opinions. These authors and designers are offering the same - opinions. Epoxy itself is a fantastic porduct as an adhesive, filler, coating, etc, & etc. The stuff is very prone to oxidation and the surface will degrade in direct sunlight - its only major drawback.

I have built boats of various sizes for many years commercially. I owned and worked a boatyard for 27 years with a 60 ton marine railway. We maintained and  repaired wooden boats in the early years. I've had experience with both resin systems and the misconceptions that many boat owners have with their appropriate uses.

SteveU, The traditional method of glued lapstrake construction is cumbersome in comparison to the stitch and glue method. The skill and preserverance required for glued lapstrake is the major drawback and this 'new' method has opened small boat construction up to many who could not make a start with traditional methods. The backbone to construct the boat is the precise portion and once built, many hulls can be constructed. I built  Ian Oughtred's 13 1/2' acorn a few years ago intending to build only one. I was heart broken to destroy all the work that went into the building framework. Good luck with your endeavor, it's a reward to complete one!

RE: Epoxy coating

Wow, that was a bunch of good info! Kudos especially to jacknlin for sharing the secrets of the trade. For the engineers among you, just this useless tidbit to add: Epoxy beat out polyester partly because it is stronger. Polyester develops "micro-cracks" because the boat flexes more and because the plastic is less strong. These micro-cracks further weaken the laminate (glass-to-plastic interface) and vessel structure, and also contribute to the moisture penetration and subsequent rot or delamination mentioned above.

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