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Rotting Plywood between fiberglass shells

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monty0
1st Mate

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USA
51 Posts

Initially Posted - 05/05/2008 : 19:25:10

Our windows out we find the plywood sandwiched between the fiberglass shells is rotting. We're thinking of squeegeeing in some thickened penetrating resin just before we put in the windows with frames. We've used this 1:1 penetrating resin on other projects before and it doesn't seem to stick, but does seem to thicken.

Or does someone have other suggestions on what to do, like injecting the plywood with wood-rot?

Monty

1977 Catalina 25 #66 SRSK "Prana"

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 05/05/2008 : 20:18:47

You mean "Git Rot"? I think that's also penetrating epoxy. Can you tell how far the rot has gone from the perimeter of the windows? Is it above as well as below the openings? If above, your hand rails or hardware on the cabintop might be partly to blame. Some penetrating epoxy (not thickened so it soaks into the rotten wood) is probably your most practical solution, and will help avoid future damage if more moisture finds is way behind your frames some day.

Edited by - Dave Bristle on 05/05/2008 20:20:04

Happy D
Admiral

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921 Posts

Response Posted - 05/05/2008 : 20:50:24

I replaced the plywood core between the fiberglass skins because it was totally rotted. I removed it 100% and put in new plywood. It is a huge job.
I have never used git rot or the penetrating epoxies but I would think since they are very thin, they would just run out before they stuck to anything.
To do it right, if the wood is missing, it needs to be replaced. If it is just delaminated, you can wet it with un-thickened and then glue it back together with thickened epoxy reinforced with microfibers. I can give you all the gory details if you want. I'll need a few days because I'm working around the clock.
Dan

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monty0
1st Mate

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USA
51 Posts

Response Posted - 05/05/2008 : 21:38:52

Yes, I meant Git-Rot.

I don't think we're equipped or ready to replace the plywood core. There is some delamination and the rot, I'm thinking, goes down about 3 inches; however, I need to investigate that more for accurancy.

We tried to putting a laminating epoxy putty in the gap with clamps on the sides to hold the shape while the putty dried, but that didn't work.

Hence we're looking for other options.

Thanks!

Edited by - on

Sloop Smitten
Master Marine Consultant

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USA
1181 Posts

Response Posted - 05/06/2008 : 09:11:15

Why don't you fill the gap with some aerosol insulating foam, let it dry, scoop out the top inch or so and replace it with resin. That should reduce the area you need to fill appreciably.

Edited by - Sloop Smitten on 05/06/2008 09:11:47

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 05/06/2008 : 11:21:50

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Sloop Smitten
 Why don't you fill the gap with some aerosol insulating foam, let it dry, scoop out the top inch or so and replace it with resin. That should reduce the area you need to fill appreciably.
<hr height="1" noshade id="quote"></blockquote id="quote">

Or maybe liquid nail? Would that harden more? It would depend on how much torque needs to be on the window frame screws to keep the seals from leaking.
I would ooze something in or look at that pink high density insulating foam and fill with custom cut slabs. I would try a lot of solutions before I cut my headliner.

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Voyager
Master Marine Consultant

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USA
5445 Posts

Response Posted - 05/06/2008 : 21:21:39

Quoting the "bible", Don Casey advises to find the extent of rotten plywood by tapping the skin, then cutting the inside fibreglass just below the rot, cutting out the wood, replacing the wood, reattaching the fibreglass and filling the seam.

He makes it look easy -- but if I were doing it, I might be done by August! And I'm certain that the seam would be visible by even the most casual observer.

If the rot is only a few inches down below the window, I might try to pick out or drill out the rotten material, use penetrating epoxy to seal the good edge of the plywood down below, then try and slip a new piece of plywood down between the interior and exterior skin.

If I could get the right size and thickness to fit snugly, I might coat the insides of the skins with epoxy, slide the plywood in, trim off the edge of the plywood a little shy, and then coat the top of the plywood with a layer of glass and epoxy.

On this foundation, I would mount the window in the side of the cabin.

Sounds easy, but it would be time consuming and tough to get right.

Edited by - on

Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 05/06/2008 : 21:56:51

<blockquote id="quote">quote:<hr height="1" noshade id="quote">If the rot is only a few inches down below the window, I might try to pick out or drill out the rotten material, use penetrating epoxy to seal the good edge of the plywood down below, then try and slip a new piece of plywood down between the interior and exterior skin.

If I could get the right size and thickness to fit snugly, I might coat the insides of the skins with epoxy, slide the plywood in, trim off the edge of the plywood a little shy, and then coat the top of the plywood with a layer of glass and epoxy.<hr height="1" noshade id="quote"></blockquote id="quote">

I think he nailed it. That is the right way to fix your problem.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 05/07/2008 : 00:05:53

Obviously we're flying blind here--we don't know what it looks like after the things you've done so far... If the rotten wood still has essentially its original dimensions, and if you can dry it out reasonably thoroughly (I don't think it has to be perfectly dry), then penetrating epoxy (maybe a couple of doses) could retore its strength and hardness to the degree you need there, which isn't that much. It isn't the ultimate fix, but it might be the practical and sufficient one. I don't know.

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Douglas
Master Marine Consultant

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1595 Posts

Response Posted - 05/07/2008 : 13:07:23

www.rotdocktor.com

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Voyager
Master Marine Consultant

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USA
5445 Posts

Response Posted - 05/07/2008 : 20:22:13

Dave -
I think you might be on to something, which is a lot less work than I described. If the material is not completely shot, the penetrating epoxy might be the answer. My main concern would be the strength of the area above the window if you were to walk on it (as I frequently do)

Edited by - on

Happy D
Admiral

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921 Posts

Response Posted - 05/07/2008 : 20:38:05

I didn't cut any fiberglass to put in new core. I cut the new core down the center and slid it in through the window openings. Then I pumped the gap full of epoxy and clamped the whole sandwich together. I finished the hole openings with epoxy and gelcoat and they look great.

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Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 05/08/2008 : 00:06:28

Happy D, very creative. Nice work!

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