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Old 24-06-2013, 11:29   #1
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Join Date: Jun 2012
Location: Ventura, CA
Boat: Horstman Tristar 38
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Repairing Failed Foam Deck Core

Good day all,

Was hoping to solicit some advice on the best approach to repair a failed section of the deck on my trimaran. I have about a 1ft x 1ft section near a hatch which I believe has failed likely due to the hatch leaking. The section immediately near the hatch is very soft and spongy and appears to have sagged a small amount. From what I can tell the construction in the area is partially foam and partially balsa core with plywood/fiberglass on top. The only damaged area looks to be the core and the top plywood, the bottom is dry and straight still.

The choices i've come up with are as follows and was wondering if some with more experience could give me advise.

A. Cut out the 1x1 section of deck from top and replace balsa and foam as appropriate.

B. Drill and fill the section of deck with epoxy and refiberglass top to bring deck surface back to level.

C. Since the section of deck is accessible from the cut out for the hatch I might be able to scrape out the foam and/or balsa from there and slide new foam and balsa between the damaged section.

I understand that cutting out the deck is probably the best approach, but is a lot more work and I've heard that it can compromise the overall strength of the deck requiring you to pull a much much larger section of deck out.

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Old 24-06-2013, 11:43   #2
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Join Date: Jan 2010
Location: Fort Washington, Maryland
Boat: 1971 Rhodes "Discoverer" - 44' Motorsailer
Posts: 49
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Re: Repairing Failed Foam Deck Core

I did this (option A) for the entire accessible section of deck of my flybridge-- a 4' x 5' rectangle. When in doubt, go big. A 2' piece of foam is the same amount of work as a 1' piece, and costs only a little more. In fact, you'll be buying a 4' piece at least anyway, and cutting it down to fit. Don't skimp and miss some spongy balsa.

I was able to re-use the top fiberglass layer-- cleaned up the under-side and drilled some vent holes to let the air out and the epoxy squeeze through when I re-placed it. I mixed the epoxy with colloidal silica to about pancake-batter thickness: spread a layer of epoxy on the bottom layer of fiberglass (still in place but cleaned), then the new foam-core, another layer of pancake batter, then the top layer of fiberglass. Weighed it down with concrete blocks and braced from below with a 2x4 so the epoxy squeezed through the holes and made little pools to grind off later. Don't epoxy the concrete blocks to your deck-- might sound like good anti-skid, but you'll stub your toes. Trust me.

Good luck!

"If it ain't broke, fix it 'til it is."
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core, deck

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