PML Expanding Foam VS GreatStuff Fireblock

I went to order some PML 2-part expanding foam ($18) a few weeks back and as told my shipping would be about $15. Now, I don't mind paying $15 if I feel like I'm getting my money's worth, but this seemed over the top with the cost of shipping nearly the cost of the item. What??! I questioned it, and PML told me they could "try" to send USPS Priority Flat Rate at about $9 or so as I recall. Even that seems high.

I suggested to them that I'd just use something like a crack filler to which PML replied that it "wouldn't meet the heat requirements for HP rocketry". While I'll buy about 10% of that argument, the 90% has me looking to other options.

Walking through Home Depot the other day, I saw GreatStuff's Fireblock. I've had electrical and plumbing contractors I've hired to assist with remodels and new construction use a similar product to seal holes in framing to meet current building codes (the idea behind sealing the holes being that fires can't jump floor to floor and wall to wall as easily if there is not an open portion of a hole that connects separate areas). To my question:

Is there any good argument that this could not be used in the same way that PML's expanding foam is used to fill and strengthen voids in the non-used parts of high power airframes (i.e. fin cans)? If it is made to stop fires from moving, wouldn't it stand the heat of a rocket launch?

Will it cure in a air tight space?

Try wildman- he carries the PML stuff, and might be able to do better on the shipping.

FYI- i think crossfire's comment is right- great stuff won't cure in an airtight location, I think.

Please search the forum. You'll see you are headed down a slippery (more like gooey) slope. If you don't like PML prices, you can get a better price/oz from US Composites but probably will trade off larger minimum size containers.

From the Ether...

Yeah 2 part foams cure and do not need air. The spray can stuff at the hardware store dries (needs air).

crossfire said:

Will it cure in a air tight space?

Click to expand...

Yes, I've used the HD spray foam on several Lev 2 and 3 rockets. Ironically, I just repaired a PML 6" FG nose cone that took a bad fall on no main chute. I wrapped the outside of the damaged area with electrical tape to keep that area from pushing out as it expands. Bondo'ed the outside, real strong and looks like new.

I also had an older RW 6" concept fincan. The triangular fins were hollow and flimsy. I dirlled a hole in the center of the hollow section and an air bleed hole on each end of every fin.
Inserted the foam tube, pulled it back as it filled all around as much as I could fill.
Once cured, trimmed off the excess. Fins are real strong now.

Been in the hobby since '99, never bought 2-part foam, only used spray can foam.

Does not match my experience. Typically you will get a hard crust where the spray foam is in contact with the air, but internally the foam transforms to goo.

From the Ether...

Don’t do it every spray foam I have seen will expand with heat.
I have seen a level 3rocket destroyed by great stuff


Sent from my iPad using Rocketry Forum

I got The PML 2-part foam. My on-site vendor (Wildman) had it in his trailer. I think that's the best way to avoid expensive shipping.

The PML foam works very well and density is adjustable. Just say no the the spray can stuff.

There are other brands, and other suppliers. if you care to shop around (Google) ...for example - https://www.amazon.com/dp/B00O5FBQJK/?tag=skimlinks_replacement-20

Ok. That is what I was looking for - good suggestions and experiences.

I may purchase some to try a simulation using some old Bluetube scraps and bulkhead plates to seal a cavity and spray it in to check its ability to cure. Then I'll cut it open after a few days to see how well it cured. If it's NOT goo or gooey, then I'll do a heat test.

I won't be at a launch close to Wildman until probably MDRA's April launch, assuming it happens.

Internet searches came up with this after a redirect to FeeBay - this LOOKS just like the PML foam in color anyway and is a polyurethane 2-part foam. I do need to check on the DENSITY however (PML foam is 6# density).

https://www.ebay.com/itm/POLYURETHA...d=331908913626&_trksid=p2047675.c100005.m2219


Here's another on Amazon:
https://www.amazon.com/dp/B01C7S6OD4/?tag=skimlinks_replacement-20

The other question being, does the stuff provide any structural benefit? It’s designed to stop fires, not hold houses together

DavidMcCann said:

The other question being, does the stuff provide any structural benefit? It’s designed to stop fires, not hold houses together

Click to expand...

Probably not... :-\

dixontj93060 said:

Does not match my experience. Typically you will get a hard crust where the spray foam is in contact with the air, but internally the foam transforms to goo.

From the Ether...

Click to expand...

back in the 90's i used the canned expanding foam for a fin can on a 6" rocket. had the aft centering ring off. sprayed it,watched it start expanding, went to the store, came back and i had a goo on all surfaces and no expanded foam.
iirc, the foam we want to use is a urethane foam? if so, could the urethane foam used in boat building be used?

SammyD said:

Probably not... :-\

Click to expand...

This actually depends on the application. Adding any measurable strength to internal fillets, probably not, but I have used it in at least a half dozen applications to firm up hollow boattails and tailcones. This application works great as it reduces any bending/cocking you might otherwise get during landing impact, thus preserving the smooth transition from tail to airframe that we "all" strive for (well at least I strive for).

Try these folks: https://www.fibreglast.com/category/Foam

Try these: https://www.fibreglast.com/product/2_Lb_Polyurethane_Mix_and_Pour_Foam_24_25/Foam; https://www.fibreglast.com/product/6Lb-Mix-and-Pour-Foam/Foam. Yeah, it is a lot so split it with your rocket pals. I transfer each part into smaller plastic bottles for easier handling.

tomsteve said:

back in the 90's i used the canned expanding foam for a fin can on a 6" rocket. had the aft centering ring off. sprayed it,watched it start expanding, went to the store, came back and i had a goo on all surfaces and no expanded foam.
iirc, the foam we want to use is a urethane foam? if so, could the urethane foam used in boat building be used?

Click to expand...

Its the same urethane 2 part foam used in boat building, we just tend to use the lighter density versions.

I fooled with the canned stuff and for my applications didn't turn out that bad. After I tried two part (from Giant Leap, I have no idea about the density) I wouldn't go back. My canned stuff was use in applications where the area being filled wasn't closed. I would partially fill then wait, add more, and then trim the overflow. One problem is it seems to expand in random directions so I doubt I ever got the area 100% full. If you are making a rocket out of found junk (WHO would do such a thing), that's one thing. If you spend money on a nice kit, I wouldn't scrimp.

dixontj93060 said:

Please search the forum. You'll see you are headed down a slippery (more like gooey) slope. If you don't like PML prices, you can get a better price/oz from US Composites but probably will trade off larger minimum size containers.

From the Ether...

Click to expand...

I purchased from US Composites years ago, and more recently from an on site vendor. My caution to anyone purchasing the 2 part foam would be to take into account shelf life. Don't buy more than you can use in a "reasonable time." The liquid components degrade faster once you open the containers. As I recall, the dark amber colored liquid (I think it is the "A-Side") solidifies over time when exposed to air. The "B-Side" is lighter in color and is not as susceptible to aging. I have managed to get 5 years of shelf life out of an open "A-Side" can but it was only because I punctured the bottom of the container and drained the liquid out. The top inch or so of the liquid inside the can had solidified making it impossible to pour out. I also recall that the amount of expansion of the aged components was less than the amount when the chemicals were fresh.

This is why I store as many things as possible (paints, stains, varnish, etc.) upside down. You open the lid, and you still have access to the liquid side of things.

dshmel said:

I purchased from US Composites years ago, and more recently from an on site vendor. My caution to anyone purchasing the 2 part foam would be to take into account shelf life. Don't buy more than you can use in a "reasonable time." The liquid components degrade faster once you open the containers. As I recall, the dark amber colored liquid (I think it is the "A-Side") solidifies over time when exposed to air. The "B-Side" is lighter in color and is not as susceptible to aging. I have managed to get 5 years of shelf life out of an open "A-Side" can but it was only because I punctured the bottom of the container and drained the liquid out. The top inch or so of the liquid inside the can had solidified making it impossible to pour out. I also recall that the amount of expansion of the aged components was less than the amount when the chemicals were fresh.

Click to expand...

Great Stuff and two-part expanding foam are both polyurethanes. According to its MSDS, Great Stuff contains an MDI (isocyanate) derivative and a polyol. The dark brown component of two-part is the isocyanate, which is why it goes bad fairly quickly. It reacts with water vapor in the air. Which, incidentally, is the same thing that Great Stuff reacts with. Water reacts with isocyanate to produce CO2, which is the blowing agent. The two-part has some water in the polyol part; Great Stuff reacts with water vapor in the air.

Significantly better results MAY be obtained with Great Stuff if a number of very thin applications are used, with plenty of time (a day or more) between applications to allow water vapor to diffuse in and react with the goo underneath. So if you're not in a hurry... I did this with my 4" Patriot and did not get a gooey inside. Unfortunately I don't know the long-term results, as the Patriot was lost on its maiden flight.

Incidentally there are at least two flavors of Great Stuff, one is more flexible and is intended for applications that may expand and contract significantly. The cheaper, more rigid stuff should be better for rockets.

Best,
Terry