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Old 11-04-2005, 20:27   #1
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Soft deck - pour in hardening foam?

Okay, might sound pretty stupid, but I remember seeing the tv show monster garage where they poured what looked like syrup that turned into an expanding, hardening liquid foam. Like the aerosol "Great Stuff" you can get at hardware stores for weatherproofing/insulating houses. They used it to turn a car into a floating boatcar. The stuff dries pretty solid. Has anyone ever heard of using this to replace rotted balsa core inside the decking on a sailboat? Seems like the ideal stuff to me. I've seen old houses that have had it in trouble areas that the owners said had been there for 10 years or more. It was still stiff and solid as can be. Does not seem to rot or soften at all. Any thoughts?

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Old 11-04-2005, 22:47   #2
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It's a two part expanding Urathane foam. If it is cut or damaged, the internal structure can absorb water. The material itself does not absorb water, it is just the "lattice work" of tiny air bubbles that allow water to flood the stuff. The outer surface is usually a sealed surface. It is alos used as a core like the Balsa is used. But I can't say in your situation, if the foam is a good substitute. It depends on the structural strength and design. The only guy that could answer that would be the Designer.


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Old 12-04-2005, 02:40   #3
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Core Replacement

I’m short on time, so this will be a short & incomplete answer.
I see several problems with injecting expanding foam into rotted deck cores, including:
1. Inter-laminar bonding is required between FRG skins (inner-outer) and core. The foam is not likely to adhere sufficiently.
2. The product needs a void to fill. You’d still have to excavate all the rotted core, prior to refilling
See also “A primer on Fibreglass Construction” by JeffH

and “Cored Sandwich Construction” from Diab

and “Replacing damaged balsa cores” by WEST System (Under Boat Repair & Restoration)

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Old 12-04-2005, 10:30   #4
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There are two types of foam. The junk you buy at the hardware store will desolve of one were to put liquid poyester resin on it. Ask me how I know.

The marine, two part, foam is what one would want to use. But as GordMay, above, was saying you have to strip out the old core. And when the stuff is ejected into the void there has to be relief holes for the excess to escape or the outer layers will expand. Foam is not a good resolve.

Start with the links GordMay provided, and do some research before diving into a project like this........................_/)
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Old 12-04-2005, 17:33   #5
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I work with several foam products in residential construction and I have a few comments. First, dryrot is alive like a cancer. Filling in the voids does not get rid of the rot, and it will continue to spread. Second, most foams will resist most solvents - stuff is hard to work with - we once had a guy get it all over his hands and while trying to drive to the pharmacy to get nailpolish remover, which will break it down, he bonded his hands to the steering wheel so he could not get out of the car - he is no longer with my company since this was not an unusual error in thinking on his part - my point is - when you inject and it expands it may do more damage than good. I'm afraid you need to remove all affected wood and patch using conventional methods, but if you try it, stock up on nailpolish remover and let us know how is goes. capt. lar
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