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Sealing underside of plywood floor..


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I will do some core samples of the foam to see if it is saturated. If it is and I rip it out how do you get new foam in. Manufacturers put floor down then drill holes and pour in the foam. I could do it that way but it looks like it would defeat the purpose since the foam would once again be touching the under side of the plywood.

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If your boat is under 20 foot length you must by law have flotation foam, so if you remove it, you must replace it. One cubic foot of foam has 62 pounds of upward force, but one cubic foot of saturated foam weighs 62 pounds. It is good to replace saturated foam. Removing it makes the boat a lot lighter and gives you a chance to inspect the hull for possible leaks. As for pouring in the replacement foam. It is ideally done in a 70 degree Fahrenheit environment for perfect expansion of the foam . when it is colder there is less expansion. Just go to I-boats.com and search "pouring foam". Not only the manufacturers do what you just described. Everybody does it that way. It prevents the foam from "boiling over". The foam ideally glues itself to the floor and there should not be any room for water in there, no matter how much water you get on the floor. A boat with the foam removed or replaced by noodles or other nonsense will no longer be covered by insurance no matter how much you pay to insure it.

Edited by rolmops
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I wouldn't be sealing anything unless I'm completely encapsulating it. If you don't allow it to breath on the bottom where the water will be getting to then it will rot quicker than anything, pressure treated or not. I would just do as the original was it lasted long enough.

Edited by Chas0218
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Look up Aluthane from epoxyprodrcts.com. used it on the floors and hull of my Islander when I re did the floor. It is not cheap but it goes. A long way. Used one gallon for my floors and transom. Ditto on the foam. Mine was saturated. Removed it and found a small hole below the waterline that I repaired. I was going to top coat the aluthane but I left it and 3 years later the floors look great. Epoxy Products were great to deal with. Answered questions quickly. I did have to ship to a US address because I live in Canada. No big problem as I go to Buffalo often.

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I bought new gas lines. Livewell is solid plastic. Drain molded in. Not really anything to seal on it. I'm not doing the front of the boat at this time. Floor is solid up front. Probably do it in a year or two. The foam that I'm replacing had some areas that were completely saturated. Mainly under the rear deck. The rest of the foam had the bottom soaked but not completely saturated. Went ahead and removed it

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Looks like you are going a bank up job with the details. I would now pay attention to not letting any water even thinking about getting to the underside of your floor. Caulk all screws before installing and Caulk the edge of the floor before and after you lay it down. Good for another 75 years!

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Yeah, gonna try to seal it. A little undecided on what to use for caulk. Would like to have something I could paint over with the epoxy. Have a big tube of 5200 but I dont think its paintable. Am also condidering just using 40 yr. Paintable Dap with silicone. It would remain flexible and about 3 coats of epoxy over it would seal it. I'm going to put at least 3 and maybe 4 drains that will flow directly into the v part of the hull and run directly into the bilge.

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