Rehash on Epoxying Seams

[wallacethegreenmonster]

I have done a lot of searching but not quite found the answer or enough opinions in regards to this. I am finishing up building a 16 foot plywood flatbottomed clamming skiff with PL premium as the main adhesive. There are four bottom pieces made of plywood so there are three transverse seams where the plywood pieces meet. I have heard negative reviews on epoxying the whole bottom to "try to get a seal and protect it" and that this is a surefire way to ruin a plywood boat and accelerate rot. What about running thin strips of glass over the seams with epoxy? Will this be as detrimental, and more importantly will it be beneficial? And will this also accelerate rot? I am just not sure how watertight my PL seams are and really like the idea of another layer of something there on the outside. Should I just use 5200 and put it on the seams on the outside even though there is really no gap to put it in? Thanks for any thoughts.

[Lewisboats]

FWIW there are thousands of plywood boats with glassed bottoms out there...my own included. I watched my skiff slide on it's bottom at about 60 on the hwy...and the bottom remained nicely intact thank you very much. The seams have tape on them and the bottom is glassed over the tape. The corners have up to 4 layers of glass on them from overlapping the tape and the bottom glass. There are two schools of thought...let the wood breath and encapsulate (Gougeon bros). Looking at the first...only the first layer of veneer would be able to breath due to the glue line. If you penetrate the glue line the water is going to migrate out from there and be trapped by the glue...regardless if the outside layer has glass on it or not. Why not put something tougher than that thin outside veneer of wood on the outside and try to prevent that penetration and migration to begin with. Your biggest concern should be getting that endgrain as protected as possible as this is where the most likely point of entry would be to the inner plys. PL Premium has a nasty habit of foaming up which introduces voids in the glue...microscopic tho they may be. I makes for great gap filling but at the expense of having sponge toffee for water resistance in that spot. If you don't want to glass the bottom...don't. But at least tape the seams to seal them properly...outside and IN 'cause I bet you might get some water in bottom eventually, even if it is just rain.

I never understand why people who love varnished wood and hate epoxy covered wood can't see the irony of one plastic or another...especially if one is used under the other and the combo protects the wood 10 times better.

[Thorne]

Almost any boatbuilding book that covers stitch & glue or ply & epoxy will clearly show how to fill and tape a seam - buy one. Our hosts have a great selection, BTW.

http://www.woodenboatbooks.com/images/325111.jpg (http://www.woodenboatstore.com/Prodinfo.asp?number=325-111&item=1) http://www.woodenboatbooks.com/images/325075.jpg (http://www.woodenboatstore.com/Prodinfo.asp?number=325-075&item=1) http://www.woodenboatbooks.com/images/325120.jpg (http://www.woodenboatstore.com/Prodinfo.asp?number=325-120&item=1)
http://www.woodenboatbooks.com/images/325116.jpg (http://www.woodenboatstore.com/Prodinfo.asp?number=325-116&item=1)


Personally I think it is a good idea, and as Steve says above, it will help protect the seam strength-wise as well as moisture-wise.

[Cuyahoga Chuck]

Plywood boats last as long as boats of any other construction if they are TOTALLY encapsulated in epoxy. As long as the wood offers no habitat for wood eating microbes the structure is safe. The microbes need food, air and water. Cut off any one and they die.
Epoxy is permiable but much less so than conventional coatings. It, also gets a bodacious grip on the wood it covers. Much stonger than paint.
If a panel is epoxied on the outside but has a less substancial coating on the inside the danger from rot could be greater. If the microbe filled water gets trapped under a tight epoxy coating the moisture can't be dried up quickly and the microbes love it.
If you had thrown your lot in with an all epoxy-glued boat it wold be better and more straightforward to guarantee the boat was completely sealed. The spots that need a guaranteed seal the most are the edges of the plywood. Water wicks into endgrain like a freight train. In my judgement, sealing end grain is job number one. But, the taped seam should be supported by coating the adjacent plywood fields with epoxy to get the best results.
Only you can judge whether any of this can be applied to your boat.

[RodB]

I'm amazed at how much disinformation there is out there on epoxy encapsulated craft...usually disseminated by those who do not build with epoxy.

I wonder how many on this forum would go along with the detailed studies and data compiled by and published by the Gougeon brothers? I wonder how may epoxy detractors have read the in depth studies published by the Gougeon brothers in "Epoxyworks" on how numerous epoxy built boats have lasted many years in great shape. BTW, Epoxyworks also has a few articles on a fairly broad study on what were the "failure points" of many epoxy built boats after numerous years. They examined scores of boats and showed statistically what were the most common problem areas, and also specified which woods seem to be the best for the long term. The Geogeon brothers have been and continue to be the single most scientific researchers in boatbuilding with epoxy and constantly modify methods to improve building technology...and constantly strive to improve modern epoxy composite boatbuilding methologies. There are may others whom have years of experience, like the designer of my boat, who has personally built over 60 boats with these modern methods and had the opportunity to see how many of these boats have withstood the test of time. . . all this has gone into this opinion on how to properly build a epoxy composite boat to be "bullet proof"... almost as maintenance free as a fiberglass boat.

The previous poster makes a good point, don't try to build using a hybrid methodology of both epoxy composiite and traditional...choose one type of building philosophy and stick to it.

Evaluate the type of craft you want to build, how much maintenance you want to deal with, consider your budget for materials and what life expectancy you desire for this craft.

If its a throw away practice boat, go ceap and easy on everything, and use it till it falls apart. If its a toy you want to use for many years, consider better materials and methods that will insure a very long life expectancy.

If I wanted to build a sweet, long lasting plywood craft...I would have built the entire boat with epoxy and glassed all exterior surfaces with 6oz cloth. Joints would have been double taped with fiberglass and well coated with epoxy. She would have been completely encapsulated in epoxy and lasted for many many years...cause if I was going to spent the time to build something, I would want to do a good job both in finish and methodology.

RB