Foam

I have seen many people build with 2 part foam. I don't have any available and it appears to be a little more effort than I care to put into my Gizmo build but I am curious if there would be any benefit or hazard involved with using canned foam similar to the Great Stuff product. It would be used post epoxy in the fun can and nose cone.

Do not use canned spray foam as it will not cure properly (it needs / expects full air exposure versus the confined cavities we have in our rockets).

I tried this canned stuff in my 4" Goblin, have seen no adverse effect thus far. It was used very sparingly, so as not to overflow. I also put it in before the aft CR was permanently installed, to allow maximum air exposure. I tried it mainly to see if it lives up to it's claim of being reusable, and it is. No such luck with Great Stuff.

chadrog said:

I tried this canned stuff in my 4" Goblin, have seen no adverse effect thus far. It was used very sparingly, so as not to overflow. I also put it in before the aft CR was permanently installed, to allow maximum air exposure. I tried it mainly to see if it lives up to it's claim of being reusable, and it is. No such luck with Great Stuff.

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Dang, i like the way you used dowls to reinforce the Airframe on the inside.

ClayD said:

Dang, i like the way you used dowls to reinforce the Airframe on the inside.

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Thanks, seems to make everything rock solid. They're actually bamboo skewers, way cheaper (and stronger) than dowels of the same diameter.

Thanks guys... That is kind of where I am. My internal filets are done and I am about to put the aft centering ring on. I have a can of the Great Stuff expanding foam on the shelf from another project and was just curious if it was worth spraying some in there before sliding on the aft CR.

Disaster_Guy said:

Thanks guys... That is kind of where I am. My internal filets are done and I am about to put the aft centering ring on. I have a can of the Great Stuff expanding foam on the shelf from another project and was just curious if it was worth spraying some in there before sliding on the aft CR.

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I don't know regarding the stuff that Chadrog used but about 8 or 9 years ago I did a test of 3 different types of spray foam and did different applications, i.e., layers, opened CR/bulkhead, long/short wait times, etc. In the end they all deteriorated. Maybe the stuff that Chadrog has is different somehow? I know for a fact Great Stuff did not work, ever. So unless they changed the formula, I would not use it.

I know there are several types of canned foam, some doesn't expand as much, some was advertised as filling large voids and still curing fine. I filled up a paper cone with some cheap stuff lying around so I could make a nose cone. It did take several days to cure.

The thing to remember about the aerosol stuff is that it's designed as a gap filler, and really nothing more. So if it leaves a bit uncured in the middle, as long as it has filled the gap, it has done its job.

The polyurethane foams we're using are meant to be a bit more structural.

-Kevin

What are you guys using in the way of two part foam? Pro Line?

I use two part foam from US composites - I put it it F/G nose cones, makes it less prone to shattering the gel coat on landings.

Bob

Word to the wise:

If it is not 2-part foam, DO NOT USE IT! The good stuff is only 12-13 bucks & will do many small projects.

The canned stuff is moisture cure for filling holes. It does not have any bonding/gluing/structural capabilities compared to 2-part.

Heat from motor can cause it to keep expanding months or years later.

Sitting in hot sun can do same. High humidity can activate it when sealed in airtight compartments.

Every know & then someone gets lucky. Is your rocket worth the gamble?

If so ..... go for it.

I was one of the first to "foam & fly a gizmo". It don't get any simpler than that one. You can build it in 20 minutes with foam, start to finish! Mine still flies and I have beat the He$$ out of it.

I have foamed tons of stuff & learned the hard way. My 2 cents.

I tried the great stuff fire rated foam out of the can on a 4 Inch. It is the orange foam. It seemed to work fine. Great Stuff Brand about 2 bucks more a can.

Larry W said:

I tried the great stuff fire rated foam out of the can on a 4 Inch. It is the orange foam. It seemed to work fine. Great Stuff Brand about 2 bucks more a can.

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What you can't see is what it did, or did not do, inside the gaps.

In my experience, it doesn't fully cure all the way through.

There's also the question of how well it will hold up to heat, as it's not at all designed for it.

-Kevin

I remember reading a post somewhere about a guy who had a rocket for several years and one day he looked at the rocket and the fin can had burst open. He said he had used spray can foam in it years ago and that was the only reason he could think of that caused it. Amazing after several years it still expanded for whatever reason. It was a completley sealed fincan as well.

...Fudd

I can tell you this about the Great Stuff foam, don't use it when wearing flip flops. I got a drop of it on the top of my foot and didn't notice it until later in the day. It took the skin with it when I peeled it off.

Like C/J said, The 2 part foam has a "structural" strength to it. When it is fully cured, it is ROCK hard. The canned stuff from the home improvement stores is not the same density, it is "spongy" at best when cured. I would stick with the 2 part for ANY rocket build.

Jason

If foam in a can is more flexible than the epoxy used, and I bet it is, then it will simply flex as the epoxy fails, offering little additional strength. This is something that makes me question even the lighter epoxy foams that are out there.