Compatability:Polyurethane & Polystyrene

[rgranger]

So I'm planning on some modifications to the general layout of my boat. And this will involve considerable tearing up and replacing of panels etc. When I'm done I will want to replace the foam that is in the inaccessible areas.

The 2-part polyurethane is relatively expensive so I was thinking I could rough in the spaces with Styrofoam (I have plenty of that) and then fill in the remaining gaps with polyurethane foam. What I don't know is this.... 'will polyurethane resin dissolve polystyrene? And if so does it dissolve slowly enough so that the polyurethane will cure before it dissolves too much of the styrofoam?

Has anyone out there tried this?

 

[Ross]

Allow some questions to go with some answers. Canned urethane foam such as "GreatStuff" makes excellant glue for styrene foam. The pink or blue extruded kind not the junk make of expanded beads.
now the questions. Is the foam for flotation? Are the spaces large enough to use for cold storage? Have you read the questions and answers concerning the freezer insulation thread? it is good reading.

 

[rgranger]

Nah

Just flotation. Right now I have hunks of the pink stuff jammed here and there and I want to move the port-o-potty from it current location behind the main bulkhead to a notch-out in the v-birth (like on many small cruisers)... and then move the galley to the location the port-o-potty used to be. This will open up my main salon area for loafing and make room for a queen sized air mattress

During all this remodeling would be a good time to re-think the foam. Since I'm going to lose a little volume (from the notch-out for the potty) I want to recover that volume in expanding foam. So I'm thinking all of the lost flotation capacity from gaps in the foam could be harvested if I fill in the gaps.

 

[Ed A]

Interesting idea, Styrofoam is not good to use on a boat, When it gets damp it will absorb moisture and water, if it gets wet it will retain the water.

Two part poly foam is expensive, and it takes a lot of skill to use it correctly.
it has to be mixed for exactly the right time, the temperature is also a factor,
and the amounts of material used are critical. When it is put in it will expand to a size that corresponds to the amout you put it. I have seen a little too much foam ruin a boat hull by distorting the shape of the hill the size of a basketball.
it will move and break fiberglass and wood. once in the stuff in really hard to get out. its messy and sticks to everything.

Im not sure of the math, but i am not sure you could put enough in to make the boat unsinkabe unless you filled every space available, it works ok on power boats but on sail boats they are just to heavy to float with foam unless you have a ton of it.

Spend lthe money on flotation devices and wear them would be my suggestion.

 

[rgranger]

Thanks Ed

I understand your points but my boat is a MacGregor V222. It came with flotation foam and is reportedly "unsinkable". And the pink extruded styrofoam is close celled so it does not absorb water. I do appreciate what you said about expanding and hull distortions. If I go this route I'll make the pours in stages so I don't over do it.

Fair winds,

r

 

[Ross]

Ed try and experiment. Take a block of the pink extruded foam and weigh it when it is completely dry. Then place it in a tub or bucket full of water and weight it down with a brick or some such and leave it for a week. Pull it out and air dry it for a few hours so that it feels dry on all faces and then weigh it again and note the weight gain. I believe that you will be surprised at how little water is absorbed. If he will use the canned foam he can easily controll the volume of the fill.
thirteen cubic feet of foam will float a cubic foot of lead. Fiberglass has a specfic gravity of about 1.5 so that means the in the water a cubic foot block of fiberglass and resin would weigh abou 34 pounds thus a cubic foot of foam would easily keep it afloat.

 

[Barnacle Bill]

Two part urethane foams that are used for marine applications have "closed foam cells". This means that if it is marred or puctured or damaged, moisture will not wick to other areas of the foam rendering it useless as a foam flotation device. The more weight of anything you add, including foam, will increase the displacement of the vessel, which will lower the water table aspect of it. When the vessel is holed, the idea is that the foam will keep the boat swamped, but not sinking to the bottom. It is easy to find out what foams will not hold up to fiberglass resin. Just put some resin on them and see if they dissolve or not.

 

[rgranger]

It is easy to find out what foams will not hold up to fiberglass resin. Just put some resin on them and see if they dissolve or not.

Bill. The stuff is expensive. So I'd like to know that it works before I buy it. :neutral:

So if anyone has actually tried it, I'd like to know if the resin dissolved the polystyrene.

 

[Ross]

polystyrene foam is based on styrene monomer. polyester resin is polyester desolved in styrene. Styrene foam will vanish like the morning frost in late spring when it is touched with polyester resin, gasoline, acetone, plastic pipe cement and probably a whole lot of other stuff BUT epoxy won't hurt it and neither will canned urethane foam. My ice box is made from styrene foam cemented together with Greatstuff foam sprayed with 3M adhesive and covered with very light fiberglass cloth and coated with epoxy.

 

[rgranger]

Thanks Ross

that was what I was hoping to find.

Fair winds,

r

 

[kenn]

On our boat, the original flotation foam became waterlogged (it's a common fault of that model) After scooping the wet crap out, I replaced it with Styrofoam SM, which is commonly used for below-grade foundation insulation. Not the cheapest, but very resistant to water.