Somebody scared me away from using this once as they said it was HIGHLY FLAMMABLE...

So I went searching for the official 2-part expanding foam and couldn't get past the price.

So I did a little experiment with a $5 bottle of great stuff... With a direct flame on a completely cured foam sample, it only mettled a bit and scorched.

I don't see what the big deal is about using this to fill in nose cones and even possibly fin cans.

Or maybe I'm missing something? Looking for everyone's thoughts on "Great Stuff" by Dow.

Thanks, Andy in Houston

It never fully cures. When you fill a nosecone or a fin can, it will eventually expand enough to distort the shape or even bust the rocket. It might take a few days or several months, but it will usually do it. I've been there, done that.

BTW, I filled a fin can once, flew it several times, and several months later it expanded enough to collapse the motor tube completely.

Lovely... Wish they would've mentioned that part to me...

Oh well, I guess my caffeinator is toast. Luckily, I have some extra styrofoam cups :-)

Polyurethane glue ("gorilla glue") also expands, and I've seen many recommendations to use it with through-the-wall fins for reinforcement.

Never done it, though. Strictly LPR, don't need that much reinforcement. I do use it with noseweight, but you have to be careful and not use too much...

... I'm still cleaning it out of my Star Watcher.

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Yep, agree with what TBZep said..Also, the 'Great Stuff' stuff is what is called 'open cell' foam and will soak up any moisture in the atmosphere and expand also(just like a sponge)...Get the 2 part foam, it is well worth the $'s!

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Jon
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NAR 86940
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I'll agree with the others. The canned foam requires moisture to cure while the 2-part does not. I have used the canned and haven't quite had the disasters others have. However, I had heard enough to move on to 2-part. The 2 part is easier to use as you can pour it before it begins to expand. I've used it large (5.5" cone) and small (small paper tip on a cone) applications with no problem. I also found it far less messy. Well, I have to recant. I've never had a fin can or cone blow up, but I have had some terrible messes to clean up and I'll count them as disasters . One of the problems with the canned foam seems to be that, in order to get it to the far end of a gap, you have to keep spraying, which leads to way too much product being used.

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I was going to buy the canned foam for a home improvement project once but stopped when I read the label. First, what's for sale (discounted) in the home improvement stores is often past it's expiration date and second it specifically says on the label that once opened you are supposed to use the whole can. Once opened, somehow it doesn't "keep" or something. I recall my father having an "open" can and when we went to use it at a later date, nothing would come out.

I might be able to use it to fill a crack or two or to foam an outdoor outlet box, but use a whole can in a day or three? Not likely.

The problem is that a small amount of the foam is left in the valve and nozzle, and it hardens, blocking the flow the next time you try to use it.

Unfortunately, you can't turn the can upside down and vent some propellant to clear the nozzle after use like you can with spray paint.

The manufacturers really should sell smaller "single application" cans of the stuff, but of course that isn't as profitable...

I understand completely. I have been using it (up until last night) and then waiting two hours and picking the soft semi-dry chunks out of the nozzle and base tube.

Thanks for you help everyone! -Andy in Houston

Andy,

2LB density is the one I use:

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

Not that expensive @ $20.50 for the kit and it produces about 2 cubic feet of foam. Seems pretty close to what Giant Leap and others are selling.

I used it to fill the fin can on the 4" dia. rocket below between the 54mm motor mount and the six fins. Two small pours of a couple of ounces filled all that volume to the rear centering ring.

.

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