Does Resin Eat Away At Spray Foam?

Hey 405 members,



My friend is making a subject delta costume just like me, and we've been exchanging ideas to make our costumes as best and easily as we can. After he fiberglassed his helmet, he covered it with some expanding foam, which he plans to carve out details in.



I was wondering, if I used some "Great Stuff" expanding foam, and resined the foam after I carved details, would the resin eat away at the foam???

I'd use the resin just to protect the foam from being dented or whatnot.



And I know, some of you are asking, "Why don't you just use rondo/bondo?"

Well, two reasons,



1) I've never used bondo before

2) I believe the foam will be easier to carve grooves into, rather than trying to carve grooves into bondo.





Any information is appreciated.



EDIT: also, for people who have used fiberglass mat and cloth, does fiberglass mat fray as much as cloth does? because with cloth, you have to be careful around the edges or you have fiberglass threads everywhere...





Heres a picture of the kind of foam Im talking about:

no it doesnt dissolve it but you know that stuff is hard to put on thinly so you're going to either be wasting a lot of foam or makeing your helmet quit a bit bigger

box o crayons said:

no it doesnt dissolve it but you know that stuff is hard to put on thinly so you're going to either be wasting a lot of foam or makeing your helmet quit a bit bigger

Click to expand...

Thanks, and putting it on thinly isn't a problem, since the model I used was striped of most detail, so I'm actually trying to build it up a bit.

At least now I know when I finish fiberglassing I can go ahead and use the foam.

In my experience, no it doesn't eat away at the foam. (Assuming the foam is cured.) If it isn't, you kinda end up with a gooey mix.









Cheers!

it will not eat away the foam that is "skinned" however it will eat away any of the foam you trim to expose "unskinned" portions. Spray paint will also eat away un-skinned parts of great stuff.

BenStreeper said:

it will not eat away the foam that is "skinned" however it will eat away any of the foam you trim to expose "unskinned" portions. Spray paint will also eat away un-skinned parts of great stuff.

Click to expand...

what do you mean by skinned and unskinned? Are you saying that if I were to resin right over it, as is, it would be fine? but if I were to carve it and resin it, then it would be a problem?



if thats right, do you have any idea why?

Jeddychan said:

what do you mean by skinned and unskinned? Are you saying that if I were to resin right over it, as is, it would be fine? but if I were to carve it and resin it, then it would be a problem?



if thats right, do you have any idea why?

Click to expand...

I have no Idea why this happens, though I am speaking from experience. That is the very reason I started using Foam-it From Reynolds/ Smooth-On. But yes when you use "great stuff" it gets hard on the outsides to "weatherproof" but stays soft on the inside so that is has some sway to it. The soft inner "non-skinned" part does not react well to resin or spray paint. I have found that bondo will not eat away at it, nor does the fiber glass jelly. Again I don't know the chemical reason behind this, but I have had to fix the results on several occasions. I found that covering the "non-skinned" areas with Dap plaster patcher and then resining was the best/ cheapest solution to that problem. The other solution I came up with was to simply stop using it and switch to Foam-it

BenStreeper said:

I have no Idea why this happens, though I am speaking from experience. That is the very reason I started using Foam-it From Reynolds/ Smooth-On. But yes when you use "great stuff" it gets hard on the outsides to "weatherproof" but stays soft on the inside so that is has some sway to it. The soft inner "non-skinned" part does not react well to resin or spray paint. I have found that bondo will not eat away at it, nor does the fiber glass jelly. Again I don't know the chemical reason behind this, but I have had to fix the results on several occasions. I found that covering the "non-skinned" areas with Dap plaster patcher and then resining was the best/ cheapest solution to that problem. The other solution I came up with was to simply stop using it and switch to Foam-it

Click to expand...

how hard is rondo to dremel? does it get as hard as bondo? because I know it has the consistency of pancake batter or something like that, but as I said before, Ive never used bondo or rondo...

Jeddychan said:

how hard is rondo to dremel? does it get as hard as bondo? because I know it has the consistency of pancake batter or something like that, but as I said before, Ive never used bondo or rondo...

Click to expand...

Depending on how thick you made it rondo isn't that difficult to dremel into. However, it sands like a dream.

Neoproks said:

Depending on how thick you made it rondo isn't that difficult to dremel into. However, it sands like a dream.

Click to expand...

do you mean how thick, as how much you put on the helmet? or, how much resin to bondo you mix together? because I would probbably try a 1:1 ratio to start with... untill I get comfortable with rondo...

BenStreeper said:

it will not eat away the foam that is "skinned" however it will eat away any of the foam you trim to expose "unskinned" portions. Spray paint will also eat away un-skinned parts of great stuff.

Click to expand...

and ben, I'm both surprised and happy to see that you found one of my topics. You're Emile helm is awesome, and I'm waiting for more updates! I'm curious how you vac-form your visor, and curious to see what your vacuumforming machine looks like... Ive wanted one for the longest time, but sadly I don't have a welder to make a decent one... nice shop btw...

if you are unsure of the reaction of foam and resin. do a test spot. i havent tried it but i have been told to use elmers white glue on foam. i have seen pictures from other prop sites.

One word of caution with the spray foam... that stuffy is sticky as all hell and wont come off of anything unless it is cut or sanded off. I have a pair of work gloves that got a bit of the spray foam on it, its been 3 years. It is still there, and I use the gloves often to clear brush and trees and what not.

Ender06 said:

One word of caution with the spray foam... that stuffy is sticky as all hell and wont come off of anything unless it is cut or sanded off. I have a pair of work gloves that got a bit of the spray foam on it, its been 3 years. It is still there, and I use the gloves often to clear brush and trees and what not.

Click to expand...

Im not worried about that, since I have a pair of kitchen gloves that are covered in resin and little threads from all the fiberglass cloth Ive been using... and once the resin gets thick enough, I just bend the glove, cracking the resin, and just peel it off...

hippo said:

if you are unsure of the reaction of foam and resin. do a test spot. i havent tried it but i have been told to use elmers white glue on foam. i have seen pictures from other prop sites.

Click to expand...

I would try a test spot, but my dad says when you open one of those cans of spray foam, it tends to be a one shot kinda thing and you gotta use up the whole can, or it all goes bad... or the foam hardens in the tip clogging it up or something...

you can use the stuff maybe twice, the second time you have to trim the straw and clean out the gunk with a tooth pick. The problem with trimming it though is the porous nature of the stuff underneath, so be careful of that.

I was thinking to myself, "Hey, why don't i just carve it out of foam and then cover it with a thin layer of rondo? Thats a great idea!"



and then I remembered that theres still resin in rondo, so if resin would eat away at the foam, rondo would as well...

Haha You've got all the same questions I had when I first used great stuff. Ok, speaking from a lot of experience with spray foam, here's my advice.



1. I would not recommend using spray foam as a "smoother" on the outside of a piece. It is definitely not made for this. I suppose if you really tried hard, you could apply a good bit, carve it, and then seal it, but almost every kind of sealer would react negatively with the "soft" core of the foam. Also, getting uncured foam on any part of your skin or clothing will become a living H311. Uncured foam becomes insanely sticky when it attaches to anything. This is because the foam is designed to "skin" itself, and the "skin" can become detached from the under layer it's protecting, and begin to stick to you, or your table, or your gloves. If you're really unlucky, you could potentially ruin any foam you have applied by detaching the protective skin. One time, I took off all the skin from a piece, and was scrubbing my hands with steel wool and goo-gone for two hours. :rolleyes



2. Now the good news! While foam may be a bad idea for external smoothing, it works very well in my opinion for internal reinforcement. As a substitute for resin and fiberglass, and when applied carefully, you can provide a 1/4 to 1/2 and inch of rock hard coating for the inside of a piece. To do this, you need to work very slowly, pressing the gun's trigger very lighlty, and getting a steady flow of foam that's like a thin line from a tube of toothpaste. You should apply this foam over the inside of a helmet, or any other pieces, going slowly back and forth, to get a consistent painting of foam over every inch of the inside of a piece. A word of caution, the only way this can backfire is if you apply the foam too thick. However, there is a relatively easy solution to the problem. If the foam begins to cure, and bulge rapidly on the inside, you must wait patiently for the foam to build up a "soft" skin. Poke it with a paper clip to see if the foam has built up a resilient skin yet. When the paper clip no longer penetrates, you can, very carefully, press the foam down with a latex gloved hand. Doing this gently de-gases the foam, and makes the de-gased portion even harder, and much more dense than a piece that has been left to expand fully. On one of my wip helms, I degassed the entire inside, and was able to get a very smooth finish on the inside.



3. Last word of warning, over applying the foam is a deadly error, and so is not de-gassing overly thick spots. If you do not de-gas, the foam is very unpredictable in the way it cures. Over a year ago, I put a ton of foam on a chest piece, and did not de-gas. The next day, the piece had bloated terribly. And then a day later, the piece had collapsed. It had literally shrunk in on itself after bloating out. The chest piece was ruined, and was unusable.





Sorry about the novel! I just wanted to make sure you were well informed before making a decision. Hope everything goes well! You can pm me if you have any more questions.