Teach me about expanding foam

At the theater I often have a need for expanding foam to make props and things, fill in scenic gaps, etc.  The problem with buying a can of expanding foam is that once it is used for a teaspoon-sized fill, you have to flush the tube with acetone and the can has a very limited shelf life... if it will work again at all.

So I want to maybe invest in some two-part expanding foam so I can mix just what I need.  Can someone point me toward what I might need?  I can imagine that bond strength and rigidity will be preferred if that is an option.

Example.  I built this prop pickaxe for an upcoming show.  The head is 3/4" ply held on by a sandwich of luan.  The cavity on the pick side I ended up filling with epoxy and paper powder.  It was overly messy, overly expensive, and not really the right application but it's what I had on hand.  If I could have mixed up an ounce of expanding foam it would have been smarter.

Do not get on hootus.

When I re-did the floor in my 1976 Ouachita boat with 3/4" plywood, I put 2-part expanding urethane foam under each section by pouring it through holes I cut in the floor.  I ended up using a couple gallons of each part A and part B.  I used the 3 lb. density.  Fun stuff.  You'll need to calculate the volume of the space you want to fill, or there will be "overflow".  I did a pretty good job.  Be advised the stuff sticks to anything, but you can wipe it off while it's still liquid or cut or sand it off later.

After I filled each cavity under the floor, I replaced the wood plug from the hole saw and fiberglassed over the whole floor.  With carpet over it, it looks and feels rock solid.

One of the components has a pretty short shelf life.  A year, tops.  Even mostly full, in a sealed container, the leftovers started to gel and solidify, so buy what you need and don't figure on long-term storage.

Not sure where I bought it.  Definitely online.  Might have been this place:

http://www.uscomposites.com/foam.html

I'd guess you'd be looking at the 4 lb. or 8 lb. density.

Have fun!

I replaced the deck on an old Bayliner tri-hull years ago.  The boat had been through a lot of freeze/thaw cycles and had seen much rain water.  When I got the deck out, if you poked the old flotation foam with a finger, it would squirt like a watermelon.  Likely added 600lbs of lightness by getting rid of that stuff.

After I had glassed the new deck back in, went to a small boat manufacturer near me and the guy sold me a couple of quarts of two part expanding foam.  Drilled some 2" holes in the deck, mixed the stuff, and poured it in.  Foam expanded out of the holes like a glow worm firework.  When it got done, sliced off the worms and glassed the holes.

Anyway, if you can locate a boat repair facility near you, I would bet you could buy a a couple of quarts from them.  Failing that, WallyWorld has this - https://www.walmart.com/ip/Liquid-Foam-2lb-Quart-Kit/594066716?wmlspartner=wmtlabs&adid=22222222222250808055&wmlspartner=wmtlabs&wl0=e&wl1=o&wl2=c&wl3=74354554487958&wl4=pla-4577954119544925&wl5=&wl6=&wl7=&%20wl10=Walmart&wl12=594066716_10000019565&wl14=boat%20foam%20flotation%20kit&veh=sem&msclkid=a5e82c498623185701cb712c166cab62

Edit - beat me to it ;=)

In reply to CJ :

Sounds like you probably had as much fun as I did!  The old foam in my boat was just like yours.  Wet!

The 2# and 3# density is good for flotation.  I understand the heavier densities can be carved like wood.

Great stuff pro?  It comes in cans but has an application gun with a valve and lasts many months between uses.  

1988RedT2 said:

In reply to CJ :

Sounds like you probably had as much fun as I did!  The old foam in my boat was just like yours.  Wet!

The 2# and 3# density is good for flotation.  I understand the heavier densities can be carved like wood.

Had a great time on that project.  And got to grind fiberglass, too!

I have been told that just about any of this foam can be carved with a Sureform blade after it is fully cured.  Of course, denser would likely be better for durability. 

If you are making sets / props that have to be moved around, lighter might be easier to deal with.

In reply to CJ :

Still, even at 8 pounds per cubic foot, we'd be talking about some pretty lightweight objects unless they were huuuuge.

Check out Smooth-On for all your prop making needs.  I've used their A-B silicone and urethanes with great success.  They make a variety of A-B foams.

https://www.smooth-on.com/

And here's a video showing how to make a hatchet and hammer using Smooth-On products.

1988RedT2 said:

In reply to CJ :

Sounds like you probably had as much fun as I did!  The old foam in my boat was just like yours.  Wet!

The 2# and 3# density is good for flotation.  I understand the heavier densities can be carved like wood.

I had the same thing in my old boat.  I chopped it out with a shovel, and I describe mine as being just like cutting into an apple.

Some googling turned up that 2-lb foam expands to about 30 times volume, and 6-lb expands about 10-times volume.  Does that sound like about what you have experienced?

Curtis said:

Some googling turned up that 2-lb foam expands to about 30 times volume, and 6-lb expands about 10-times volume.  Does that sound like about what you have experienced?

 

That does sound about right.  The link I posted does address that.  Keep in mind that the reaction is highly temperature dependent with 75 deg. F. being the practical minimum, so if you're working outside, it's probably a good summer project, but a no-go come winter.

It might be good to get some small cans to play with, and see if you can stop it from expanding like great stuff. 

Its been many years, so formulations may have changed, but misting the foam from a spray bottle with water could be used to stop the expansion of great stuff without negative effects on the curing. 

I always wanted to foam fill the chassis on my commute attack car. Q45 had that E36 M3 from the factory iirc. Sport compact car did that to their z32 project and said it made a huge difference. 

Some products are fire resistant and some are an accelerant.

Carbon said:

I always wanted to foam fill the chassis on my commute attack car. Q45 had that E36 M3 from the factory iirc. Sport compact car did that to their z32 project and said it made a huge difference. 

I thought about that as well.  I wonder how a body repair guy might feel about it.

Duke said:

https://www.youtube.com/embed/zAIY0I5GGw4?rel=0

 

Was that 1980’s Marty from MCM?

Beware: I have heard bad things about trapping moisture with expanding foam against metal. Lots of cautionary tales of weird and premature rust, after initial ravings about improved chassis rigidity in car applications.

I often wonder if this can be easily mitigated, maybe by sleeving in plastic like they do for shipping foam, or just laying down a sealant like por15 first. I have a beat up CRX I wouldn' t mind making a test mule.

In reply to Nugi :

I think it’s either already rusty and someone used it to fill an area, or it’s plugging up a drain hole and won’t let water out of the panel causing rust. 

Nugi said:

I often wonder if this can be easily mitigated, maybe by sleeving in plastic like they do for shipping foam, or just laying down a sealant like por15 first. I have a beat up CRX I wouldn' t mind making a test mule.

I think the real rigidity comes from the fact that the foam adheres to the substrate, so I don't think the plastic sleeve would help the rigidity.  POR-15 might be the key.

We used use expanding foam in the shipping department I used to manage. A gun with two nozzles shot the stuff out.  (Don't make boxing gloves, it's exothermic.)  They make little self-contained bags of the stuff, you could let one expand and then carve it into the shape you want. 

Packing Foam

So what do I need to know about the different types?  I can pick between 2lb and 10 lb on my own, but there are plastics, urethanes, 2-part, marine, structural, flexible, rigid... too many options.

I would love to use it for things like the axe I pictured above (one teaspoon of just something to fill the gap - non structural) but also have something that will pull general duty.  For instance, maybe make some molds and cast some stuff.  Maybe make a big blob of it to carve a rock for a set.  Maybe use it to fill a hole where the mice are getting in.  Maybe use it for a custom office chair.  Who knows?

I need something that is a good, general purpose expanding foam.

Get a pro gun, cans are about the same price, produce way more, and the valve closes off the nozzle so the can lasts forever.

for some reason I am thinking of this video.