# flotation/insulation foam under floor get soggy with water?



## rancocasrich (May 27, 2009)

I am replacing the wood floor and carpet on my aluminum boat. The entire floor has been removed and we are cutting the plywood pieces to re-assemble the floor. The boat is in the back yard uncovered. A friend told me today that the rain is probably totally saturating the foam where the skin has been removed. It will make the boat heavier and is unlikely to evaporate. He thinks I may have to remove the foam and replace it. Can that be? If it does get water-sodden, can it dry out? There is now a cover on the boat. Any suggestions are appreciated.


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## Quackrstackr (May 27, 2009)

If your floor was originally wood, I doubt that it was watertight to begin with. Most aluminum boats with floors are designed to drain down the very bottom of the hull.

It is possible for foam to absorb moisture and become somewhat waterlogged. If it dries out, it will take months and not hours or days to do so. How quickly the foam absorbs water really depends on what type of foam it actually is.


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## rancocasrich (May 27, 2009)

I have a '93 Lund 14' aluminum boat. Is there any way to find out about the foam? Will it dry out eventually if I put in the new floor?


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## Quackrstackr (May 27, 2009)

If you are replacing the floor, you should be able to tell pretty easily. The foam underneath it would be the first to get waterlogged.

I'm not sure if the foam will dry underneath a new floor or not. At the very least I would expect mold to set up under your new wood before it does.

It would be best to let the foam breathe without being covered for it to dry.


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## 2007NNBS (May 27, 2009)

what foam is waterproof/water resistent?


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## ben2go (May 27, 2009)

If foam gets wet it will stay wet and absorb the water.Almost all foam will do it over time.Using a thick coat of polyurethane water seal on polyurethane foam will slow down the soaking up of water.Another thing that I have seen done is a thick plastic laid in the hold,filled with expanding foam,and then sealed with something like 3M 5200 marine sealant.I wouldn't put fresh wood over wet foam.It will rot faster and get infested with mold and mildew,and spread to the carpet and seats.


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## sparkbr (May 27, 2009)

If you have to replace the foam, the best stuff I have found is the blue or pink closed cell foam board insulation. it can be found at any lowes/menards/home depot, ect. It is inexpensive, very rigid, and does not absorb water. I personally stay away from the spray in foam, but if you were to use it, wipe the hull down with oil or a coat of Pam cooking spray. Otherwise you will form a barrier between the bottom of the boat and the foam that will prevent water from draining to the rear of the boat until it is deep enough to go over the foam.


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## 2007NNBS (May 27, 2009)

what size and thinkness does the foam board come in?


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## sparkbr (May 27, 2009)

I have only used it in 2" and 4" thicknesses, but I know it comes in 1/2", 1", 1.5" and might be available in 3/4", and 2.5" Sheets are typically 4'x8' and a sheet of 2" costs around $20. To calculate boyancy (if swamped) calculate the volume of foam, divide by 231 (231 cubic inches in a gallon) and multiply by 8.34lbs (the weight of a gallon of water). 

For example - a full 4x8 sheet of 2" foam is 9216 cubic inches, which equates to 39.89 gallons and would float 332.73lbs (assuming it didn't break appart of course.)


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## sparkbr (May 27, 2009)

I forgot to mention, you can usually find decient sized scraps in the dumpster at just about any new building construction site.


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## rancocasrich (May 27, 2009)

This seems a really workable and affordable situation for me. So --just take out the old wet foam and replace with the blue sheets? Does it need to be glued to the bottom or just sit there under the flooring? If I cut it so I created a channel down the middle of the bottom, would the drainage be good enough?


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## sparkbr (May 27, 2009)

That should be work fine for the water. I wouldn't glue it down though. Not really needed, plus and bonded surface under that foam has an opportunity to obstruct the water... one other thing to mention, cut this stuff with a fillet knife. I was getting impatient and used a circullar saw on about 2 sheets worth and am still finding little foam debris all over the garage. lol.


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## Ranchero50 (May 27, 2009)

I got two sheets of 3/4" blue foam from Lowes yesterday for $12 a sheet. I plan on painting them to keep the water at bay.

Jamie


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## dyeguy1212 (May 27, 2009)

sparkbr said:


> I have only used it in 2" and 4" thicknesses, but I know it comes in 1/2", 1", 1.5" and might be available in 3/4", and 2.5" Sheets are typically 4'x8' and a sheet of 2" costs around $20. To calculate boyancy (if swamped) calculate the volume of foam, divide by 231 (231 cubic inches in a gallon) and multiply by 8.34lbs (the weight of a gallon of water).
> 
> For example - a full 4x8 sheet of 2" foam is 9216 cubic inches, which equates to 39.89 gallons and would float 332.73lbs (assuming it didn't break appart of course.)




Wow is that accurate? Seems like sound logic, but it still boggles my mind to think one sheet could float my entire boat... Makes the cost of that foam seem worth while...


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## sparkbr (May 28, 2009)

Ranchero50 said:


> I got two sheets of 3/4" blue foam from Lowes yesterday for $12 a sheet. I plan on painting them to keep the water at bay.
> 
> Jamie



Watch what paint you use, spray paint will disolve the foam


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## sparkbr (May 28, 2009)

dyeguy1212 said:


> sparkbr said:
> 
> 
> > I have only used it in 2" and 4" thicknesses, but I know it comes in 1/2", 1", 1.5" and might be available in 3/4", and 2.5" Sheets are typically 4'x8' and a sheet of 2" costs around $20. To calculate boyancy (if swamped) calculate the volume of foam, divide by 231 (231 cubic inches in a gallon) and multiply by 8.34lbs (the weight of a gallon of water).
> ...



It is accurate, in order for anything to float, it just has to displace it's own weight in water before going completely under.


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