Spray foam in boats....any good?

jollysailor17

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I went to see a boat with a friend the other day and the owner had used spray foam in the bottom of a cockpit locker to fill the void so a square fuel tank would sit upright. I had never seen this material used before in a boat, so could not comment when my friend asked me if it was alright to use it and if it was safe to use in a boat? He then asked me if the material would float and I had to say that I supposed it would, but I did not know if it would soak up water like a sponge.
Has anyone any knowledge of using this material in boats and the pros and cons of its use?
 

prv

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Same stuff is supporting my fuel and holding tanks.

Clearly it floats and I can't imagine any way it would be dangerous. The only question is whether it soaks up water. I don't know the answer to that, but I do see it exposed externally on buildings from time to time. But then maybe the kind of builder that has to use lots of spandy-foam to fill in gaps is also not going to care whether the foam is damp.

Pete
 

TopDonkey

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I can answer this one !

Single part foam that comes in a spray can is useless on boats, its open cell and soaks up water like a sponge and can retain it and go mouldy and disintegrate when it gets wet, it also doesnt deal well with vibration or movement and eventually breaks up and turns to a powder.

2 part foam which comes in 2 cylinders and has 2 hoses that connect to the mixing and application gun is closed cell foam, this is waterproof and floats and is very resilient, it is an excellent insulator for heat and noise too and is ideal for boat use, but its drawback is that its expensive and its difficult to buy it in small quantities
 

vyv_cox

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Even two-part foam sold by grp suppliers (like Glasplies and Strand Glass) absorbs water. Years ago I built lots of canoes and added P/U buoyancy. A couple of years later we had to dig it all out, as it was saturated. Admittedly these boats had been full of water many times, a far more arduous duty than a yacht would receive (hopefully).

I have used the builders' spray foam around my cool box but I'm hoping this will never see water.
 

oldharry

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Another problem with ordinary builders foam - its inflammable, so not a good idea in the fuel locker, or anywhere.

Screwfix sell a one part non-inflammable foam (to whatever BS applies for fire proofing) which is also waterproof and works well in boats.

Only One disadvantage - its bright pink!
 
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ianabc

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foam

Spray foam
usually sprayed in polyurethane foam
is used extensively in metal boats to the waterline.
One inch or more usually sprayed after painting steel with zinc and then multiple coasts of epoxy.

BUT

Polyurethane foam should contain a very inexpensive fire retardant

MAY

be coated with multiple coasts of water based acrylic paint containing hollow glass beads as used to thicken resin, quite inexpensive and the combined layers act as a serious fire retardant on top of the already added compound in the original foam mix

BEWARE

Polyurethane foam on ignition, releases cyanide gas

SO

Jumping overboard has been seriously considered by those faced with a fire in fishboat holds that are often lined with sprayed in polyurethane foam.

I have while sailing seen in the distance a fishboat fire, huge column of black smoke, with the 60 foot coastguard vessel rapdly closing in.
 
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prv

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Another problem with ordinary builders foam - its inflammable, so not a good idea in the fuel locker, or anywhere.

Surely if a locker is already full of petrol (or spare diesel cans, or whatever else you keep in a "fuel locker"), a bit of foam that may burn along with it is neither here nor there?

Pete
 
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