Cracks in plywood

[Alden]

I recently purchased a homebuilt Penguin Class sailing dinghy that has been stored in a barn for over 10 years. It has some longitudinal cracks in the paint on the outside of the hull. When I scrape it down the cracks are in the outer lamination of the plywood hull. They are not delaminating, just small cracks here and there. I think it's probably due to being over dry for so long. I would like advice as to how to proceed with fixing and refinishing the hull. I would appreciate both epoxy based and non epoxy based ideas on this. A couple ideas I have had is to use some kind of filler (I've used Bondo for boat repair before) for the cracks then proceed with regular painting. Or possibly an epoxy clear coat over this filler or a thickened epoxy filler for the cracks, then paint. Has anyone dealt with this?

[cs]

Would these cracks be checks? If so you may want to consider putting a layer of glass on it.

Chad

[Wayne Jeffers]

Alden,

I assume the cracks you speak of are very small. My best guess is that the Penguin is made from fir plywood. Fir plywood checks. Epoxy "encapsulation" or paint will not prevent it.

One proven way to prevent checking is to cover the fir plywood with glass cloth set in epoxy. Expensive and adds unwanted weight.

I've read that giving fir plywood a liberal coating of raw linseed oil before painting will prevent checking, but I haven't tried it yet (although I intend to with the boat I'm now building.)

On vintage plywood, you may be able to strip, sand, and re-paint without "filling" the existing checks with anything more than paint with the result that the plywood will not check in the future nearly so much as it has already checked.

Wayne

[Alden]

The largest cracks are approaching a 16th of an inch. I would much prefer to avoid glassing the hull for both reasons you mentioned, Wayne. I like the idea of the paint filling the cracks but I'd also like to make sure I don't get into dealing with a continuous and ongoing problem year after year. Should I expect the checking to continue to increase over the life of the boat unless I take preventative measures?

[Roger James]

I have a Penguin Dinghy my father and I built over 50 years ago from a Chris-Craft kit. The plywood is douglas fir and though it has stood up all these years sitting in a barn, sitting outside full of water, ice, leaves, etc. The plywood still looks like new except for all the checks. I do not want to add the weight of any cloth set in epoxy, so I have learned to live with the checks. smile.gif

[Alden]

Roger, what do you do to maintain it? What I've worried about is that the checks would be an entry to moisture and eventual delamination or rot. If yours has lasted so long without further deterioration maybe I can drop that fear ... ? I can certainly live with the checking as long as it doesn't lead to something worse. I would like to know what kind of a paint system and schedule you use.

By the way, I had no idea I would get such quick and thoughtful response so quickly on this forum. Thanks guys.

[Wayne Jeffers]

Alden,

Nothing will prevent moisture from entering the wood. Even epoxy and glass will allow moisture to pass into the wood, albeit slowly.

If you store your boat so that it doesn't have water sitting in it and so that it gets fresh air circulation so any moisture can dry out sooner rather than later, it will likely be around for your great-grandchildren to enjoy.

A risk in glassing an older hull is the possibility of trapping moisture between the glass and the wood and thereby hastening rot, rather than preventing it. My own feeling is that moisture is easier to trap in places you don't want than it is to keep it out. Ventilation! Ventilation!

Wayne

[NormMessinger]

I can't get paint to bridge the checks in the fir ply in our first MacGregor. Some filler is required. I'll either use laquer putty or epoxy filler when I get around to repainting.

--Norm