Polyurethane foam in a spray can

Quick question ( and im typing as fast as i can ), Is it ok to use polyurethane foam, the stuff they use to insulate around windows and doors, as flotation foam for my build ?


L

 

Yep, but it'll suck up moisture if the outer skin is cut, sanded, etc. When these polyurethanes cure, they form an external skin which does work pretty well at preventing them from absorbing moisture. Again, if this skin is breached, it'll absorb moisture.

The stuff they sell in cans doesn't expand much, so you'll need lots of cans, which isn't very economical. How many cubic meters are you trying to fill?

 

I would echo PAR, how much do you need? If you need more than a couple of cubic feet then using those cans will cost you a lot more than buying two part pour foam, or premade block foam.

 

Thats not what I was told. I was told its the same stuff as you buy. By its very nature of expanding bubbles it has to be a closed cell structure. I was told it is ideal for small filling and glassing work.

Glad you brought this up.

 

Thanks Par for the confirmation, I thought it might be but wasnt sure.

I was going to buy the 2-part foam (the pourable stuff) but i had 2 full cans of the insulating foam in my shed and thought i would put it to some good use.

I dont know how much of the stuff i will need , the V-hull LOA is 16' ,width @ MS is 73"

Also im not sure how i will go about getting some measure of control over the expansion rate when i start spraying. Prolly i'll just spray in short bursts and watch what happens.

L

 

The sprayable foams aren't like the two part polyurethanes, though they are similar chemically. The yield is a lot lower in the sprayable stuff and there's a fair bit of propellant contamination with the sprayable stuff, unless it's the costly two canister, two part products, designed for doing your attic (which is very different than the aerosols).

I wouldn't use short bursts with the aerosol, as you'll just introduce more voids. Just stick it in and start spraying and don't stop. It'll expand as much as it will, forcing itself into nooks and crannies. As the volume of foam begins to rise up around the tube, pull back slightly, but still keep spraying in the same spot. Eventually you'll fill the area or run out of foam. It can be moved around after it's out of the can for a few minutes, as it continues to expand, but don't get any ideas you can shape or mold it. It's fine for large cracks, tubes and the like, but big voids, such as a buoyancy chamber, well not so much. Lastly, do not attempt to contain the foam. I've seen boat side, locker sides, etc. bulged out horribly once this stuff expands. Let it over flow the top of whatever it's going into, then hot wire, saw or other wise shave it flush. Seal this cut side with a few coats of epoxy, then put what ever lid on you want, with usual building techniques.

 

There are two types of foam-in -a -can.. The regular stuff behaves as PAR describes .. you must allow it space to overflow or it will bulge whatever contains it. It is quite powerful, enough to jamb a window sash if used to insulate around a window. The other version, naturally, is the "Window and Door " type. With lower expansion rate and no pushing power ..it stops expanding when it runs into something .. and more costly. Use the regular stuff with the caveats above.

 

Look for the spray can foam formulated for wells and sewers. It forms a thicker outside skin that resists water much better than the regular stuff, but does not flow as well in narrow passages.
The cured product is not yellow but brown.

 

Brown for sewers --Ok I can remember that.

 

The window and door aerosol and the crack and gap aerosol products are the same thing, just different densities. The window and door stuff will bulge out an enclosed space, just not as much as the crack and gap versions will.

If really interested in doing foaming right, you need pourable two part polyurethane or the two part systems, designed for roof and wall insulation. They're not the same as the spray kits which have propellants, typically Pentane (highly flammable) and Enovate (the non-flammable substitute). It's the Enovate versions you see in the big box stores. These are catalyzed reactions with the propellant acting to some degree as a density control. There are a number of formulations, some even have colors, but typically only the 2 pound, thin skin stuff is commonly available. Wet area formulations are preferred, but not nearly as easy to find.



Prices for these kits are about $20 - $25 a cubic foot of foam, which isn't cheap, but can solve many application issues. The above kit is about $350 and does 16 cubic feet.

Pourable 2 pound foam is about $10 - $12 a cubic foot, which is easier to live with, but not as handy to apply. Pourable foams also can be had in various densities, if you need structural support and as a rule they are more easily found in the marketplace.

 

My air con shop sells it for foam fridge insulation in general.

They sell it in two plastic pop bottles.

They mix it for you before you leave!!!!

 

Thanks again guys,

Yes its the insulating type foam it dries to a sorta light-beige color( not the yellow stuff) . As an experiment I sprayed a small amount out and let it expand and dry.The surface texture is smooth, when i break a peice off, the inside appears dense full of tiny bubbles and is rough, feels like popcorn

Par, yes i was planning on using it as a boyancy foam under the floor. When you mentioned using a hot wire to cut the excess foam it got me thinking( hadnt thought of that). So this raises another question, will this seal the foam and be better than simply cutting or sawing it off ? another area for experimentation :idea:

 

I wouldn't hot-wire cut urethane. The urethanes I am familiar with have cyanide based compounds in them. Once cured they are benign, but I wouldn't want to hot wire cut them, as I don't know what you might release. Certainly not without an organic vapor cartridge mask rated for spraying isocyanate hardened urethane.

 

Hi fishstretcher, thanks for the quick reply.

Cyanide ! really ? Oh well there go's plan A

 

Even with the pourable stuff you should have a mask and gloves. The stuff in a can called great stuff says this about a fire, per the MSDS for "Great Stuff"

Fire Fighting Procedures: Keep people away. Isolate fire and deny unnecessary entry. Stay upwind. Keep out of low areas where gases (fumes) can accumulate. Water may not be effective in extinguishing fire. Do not use direct water stream. May spread fire. Fight fire from protected location or safe distance. Consider the use of unmanned hose holders or monitor nozzles. Eliminate ignition sources. Move container from fire area if this is possible without hazard. Use water spray to cool fire-exposed containers and fire-affected zone until fire is out.
Special Protective Equipment for Firefighters: Wear positive-pressure self-contained breathing apparatus (SCBA) and protective fire fighting clothing (includes fire fighting helmet, coat, trousers, boots, and gloves). Avoid contact with this material during fire fighting operations. If contact is likely, change to full chemical resistant fire fighting clothing with self-contained breathing apparatus. If this is not available, wear full chemical resistant clothing with self-contained breathing apparatus and fight fire from a remote location. For protective equipment in post-fire or non-fire clean-up situations, refer to the relevant sections.

And it contains diisocyanate. I wouldn't hot-wire cut it. That said, I sprayed it in my boat. With a mask and gloves. But I mostly used it to tack expanded polystyrene sheet in place under the cap/gunwale.