Epoxy On One Side Only?

[andrewmct]

I have read a lot about epoxying strip canoes, etc and one thing always comes up - you must glass the inside and outside to encapsulate the stripping. I talked to a canoe builder and he said that if water gets in, the wood will swell and delaminate the epoxy/glass. I understand that for a canoe the glass encapsulation is structural so this is a must. I am going to build a dory for beach camping and, from what I can see, many builders only glass the outside. If the inside is just painted, will the swelling of the plywood and frames delaminate the glassed outside? Do you really need to encapsulate the entire boat with glass and epoxy?

[JimD]

A beach camping dory is likely to get hard use both inside and out. Others may tell you different but if it were me I would not only epoxy inside and out, I would glass inside and out. Light cloth on the inside and side panels, heavy cloth on the bottom. Paint alone, or even epoxy and paint without glass will not stand up to hard use inside or water sitting in the bottom. It will crack, peel, chip, and let water in.

[MiddleAgesMan]

No. Glass on the exterior and paint on the interior will be just fine on a plywood hull. You could even skip the exterior glass but some glass tape at the chines would go a long way in preventing leaks and strengthening the joints.

[SaltyD from BC]

I'll go with the classic answer; it depends.

I had a 15 ft Diablo stich and blue (Bolger dory skiff) that I guy I worked with built. He glassed the outside, and painted the inside. It worked well like that for a couple of years living outside on a trailer even. Then one winter 3 feet of snow crushed my crude tarp tent and filled the boat up with snow, which melted and refroze.

This compromised the paint, the fir ply swelled up and I had to sand the interior right down to wood and let it dry out. Minor spots of rot even set which I had to repair. After which I glassed the inside bottom and flared side panels, but not the upper panels which stand almost vertical. This treatment was done 15 years ago and the skiff is still stored outside with no issues. (Well other than my buddy who now owns it has smashed one side up but that's another story). ..

[Candyfloss]

You are not comparing apples with apples here mate. A strip-built boat is essentially solid wood & solid wood expands & contracts much more than ply, & specially when it is cedar which most canoes are. Also, cedar is very soft, easily damaged, & glass helps protect the bottom. Canoe paddlers habitually drive their boats up on the beach, then get out, 'cos getting out while the boat is still floating is fraught with difficulty. So the conventional wisdom is, since you must glass the outside, you had best glass the inside, or at least "seal" it with epoxy. What that may consist of is a subject of much debate.

Your ply dory on the other hand is a totally different beast. Or will be when it is built. You say it is for beach camping? Lakes I take it. Dories were designed to be easily-built, industrial quality, knockabout boats. On this philosophy, build it cheap, paint it with porch paint, chuck it in the water & go camping. If you must gild the lilly, glass the chines for strength & to protect the ply endgrains, glass the bottom to protect that, & seal the interior with two coats of straight epoxy resin. Paint it with marine quality paints, chuck it in the water & go camping.

Good luck, have fun.

[JimD]

On a boat like this typically the inside will see just as much water and wear as the outside. Maybe more. Why treat them differently? At least glass the bottom of the inside. I'll go away now. Good luck.

[Thorne]

Candyfloss -

Don't get confused by the vagueness of "strip built" or "strip" -- these terms are used for two very different styles of building and the large gray area in between.

Strip built can mean anything from small boats and canoes made from tiny, very thin strips of solid wood (or other materials) glued together and covered with epoxy and fiberglass -- to the other extreme of big boats made from large, often square-dimensioned strips of solid wood nailed together, sometimes glassed and other times just painted.

Most strip-built canoes MUST be glassed to survive, as the cedar (or other wood) merely serves as a core (like balsa in some production fiberglass boats). It is too delicate and thin to provide much strength. It doesn't swell or shrink because it isn't directly exposed to water -- and the general consensus is that if the coating/glass is penetrated and not fixed, the boat will be eventually lost.

To answer the initial question, it all depends on the builder to decide. Glassing inside and out will provide better protection but increase the weight and costs of the boat.

f marine fir ply was used this is probably the best option, but if higher-quality occume or meranti marine ply was used, it is often just glassed in areas of high abrasion and on the seams.

[Richard Jones]

Built a 14' garvey type boat about 12 years ago with marine luan type ply. Glassed the outside, epoxy sealed the inside and painted inside and out with house paint. I've used it pretty roughly all these years and it's holding up just fine.