Expanding Foam (split from Launch Pad topic)

Hahaha….

I use GLR expanding foam, and I haven’t had that experience, but I learned early on to use only a little at a time. A lot is asking for disaster.

Makes for some great stories though 😆

There are a variety of formulations of 2 part urethane foams out there. PML happens to be a pretty agressive formula with approximately 25:1 expansion ratio for the straight up 50:50 mix. I ALWAYS foam any thru the wall fin can assembly. Might be overkill, might be a good idea – I can’t prove it either way except to say I had an EZI-65 kit come in ballistic from a J350 flight and the only part of the bird that was intact and flyable was the section of airframe that was foamed. Fins, motor mount and airframe around them was 100% intact and the rest of the bird was essentially fragmentary.

DON’T use too much at a time. Never mix more than a full cup at a time because you will barely have time to place it given it will be reacting before you can even get it properly mixed. You literally have 90 seconds or less from the moment you pour the materials together to stir AND place the foam. At 90 seconds you’ll almost certainly have a mess on your hands. I wrap masking tape on all surfaces that can’t get foam on them so I can peel it off cleanly afterwards. By the way, don’t breath the vapors of this stuff before or after its mixed… these are urethane cyanoacrylates… VERY bad juju for your eyes, nose and lungs.

There are also a number of less aggressive formulations out there; slower reacting AND less expansive. The 4:1 ratio foams give you as much as 8 or 10 minutes to place the foam.

Warren

Sounds like it’s the same stuff as the GLR foam then. Very fast, and I have yet to mix more than 1/2 of a dixie cup at once. Still foamed up quickly and aggressively.

I know I’m not as experienced as anyone on this topic, but I learned my lesson real quick. The first rocket I used foam on, I did so without really testing how it would react. I tried a little bit in a paper cup and it was slow, so I figured that increasing the amount would be the same. Big mistake. It was more like soda and vinegar. Got all over everything and I ended up sanding the inside of the MMT with the handle of a long socket wrench wrapped with sandpaper, the fins, the outside of the airframe. Everything. It was a royal pain and took forever. The last rocket I built I papered and taped every surface that shouldn’t be exposed to the foam – inside and out – fore and aft. Poured the foam, let it cure, cut it down, Dremmel’d what I didn’t need and removed the paper and tape. Other than some very minor sanding It worked great. The only cleanup was the garage floor – easily scraped off with a putty knife.

The great thing about foam is that my kids love watching it blow up all over the place – it’s a great science experiment!