Fiberglass over solid wood vs ply

[imported_Dutch]

i done several projects where i have glassed over old plywood to add strength and water titeness to a tired hull, believing that the more stable plywood would not break the epoxy-fiberglass bond as it goes through wet dry cycling. so far ive had no failures on my projects. i have never done it over a solid wood, such as mahogany, believing that the shrink swell cycle of solid lumber would quickly break the bond. am i wrong or right?

[Keith Wilson]

The conventional wisdom is, "Don't do it" for precisely the reasons you described. OTOH, there are some limited circumstances where it works. The thinner the boards and the less they move, the more likely it is to be OK. Around here it's fairly common to glass over the outside of an old wooden racing scow. The planks are thin, the boat is sailed off a trailer, the wood doesn't move much, and it works just fine. The antique powerboat people, the 1941 Chris-Craft with 38 coats of mirror-like varnish folks, often sheath the bottoms of their boats with glass and epoxy. Again, relatively thin stable planking, and the boats live on their trailers - it's a vast improvement over bailing frantically every time you launch. No less a wooden boat authority than Bill Garden had his new 12' cedar-planked catboat sheathed in glass and epoxy.

So under the right circumstances, it works. Slapping a layer of 6 oz. glass and epoxy on a decrepit working lobsterboat or a 1950s Tahiti ketch would not be a good idea, however.

[ 02-10-2005, 02:32 PM: Message edited by: Keith Wilson ]

[Frank Wentzel]

I would like to add that, most often, when an epoxy/glass laminate fails on a solid wood hull it is not on the plank itself that the "zipper" occurs but at the joint area. Hoever, the fact that it doesn't fail on the plank itself doesn't make it any more viable as a repair/restoration technique.

/// Frank ///

[notwoodbut...]

I believe that at least one of the old A-cats in NJ was completely covered in fiberglass both inside and out. Seems they could pull rotten wood out from between the glass layers but it worked and added years to the life of anotherwise dying boat. Those boats have huge stresses especially in the bow but the glass job worked. I also read, I think in WB, of an old lobster boat being fiberglass sheathed(sp?) to buy her a few more years. Maybe not the best on a new project with heavy timbers but for an inexpensive fix, seems to be an option.

[plyboat]

I would do glass sheathing for a plywood hull only.
---Joel---

[creddin]

Hi all,
I have a similar question. The sides of my dog house are new solid mahogany. I'll fiberglass the top because it's made of plywood, but am debating what to do with the sides .... I already have a lot of bright work to maintain, so I'm contemplating painting or fiberglassing ? It's 1 1/4 thick. Will it move to much with fiberglass? It's vertical sun exposure, so it might do OK with varnish.
Chris

[wizbang 13]

If the planks are 1 1/4 " thick AND 1 1/4 " tall it would work.
if the planks are 1 1/4" thick and 6" or 8 " tall, that is a different story.
It is possible to make solid wood stable,( as in strip planking), but then, if it is stabilised, why glass it?

[skipper68]

Wood moves. Varnish breaths.Wood is still alive aboard. If you epoxy one side, while varnish the other, the moisture is trapped. Either or, in my opinion. I have proved it on my girl. Against my advice.Long story... All better now.EDIT: Was cabin sides. NEVER use anything on a Caravel but oil paint outside.(Ya Ya Ya.. new water based...Blaa Blaa Blaa) The boat must move. The oil paint will crack, but the water is what makes the boat flex. If you epoxy the frames or planks, the trouble will run like the wind. You can try to encapsulate a ply bottom, but you better do it right. I've seen the "good enough" with the stand pop through.

[Todd Bradshaw]

Considering that the primary functions of adding fiberglass are to increase tensile strength and abrasion resistance, this wouldn't be a case where you would be using it for what it's good for. If your wood and its installation are sound, paint or varnish would probably do the job just fine and glass doesn't have much to offer.

[James McMullen]

A big consideration is how much money and time are you throwing on top of a poor foundation. Epoxy ain't cheap. And neither is a tired old boat once you're done "fixing" her up.

I wouldn't do it. If you start out right you're more likely to end up where you want to be, on time and in budget. There have been too many reported failures with trying to sheathe old solid wood boats for me to want to risk it.