Fiberglass over spray foam?

[twannabe]

I have searched the forum and have not been able to find a clear answer- is it possible to use polyester resin over the hardware store spray foam? I am modifying a fiberglass grille shell and while i have used the florist foam in the past, what i want to do in this case, the spray foam would work much better.
thanks,
bill

 

[EX JUNK]

Not knowing what the spray foam is made of, once you have "carved" it to the desired shape, cover it with foil, masking tape or duct tape. Then make your fiberglass layups. After the fiberglass has cured, the foam should easily release from the fiberglass.

Jim

 

[twannabe]

Jim, thanks for the reply, I was planning to leave the foam inside. I have glassed over the florist foam before, but the area i want fill in this case is too small to mess with carving pieces of foam to fit. I know that some types of foam (Styrofoam for instance) will melt under resin application, didn't know if somebody here had previous experience. I guess i will test a small area and see what happens.

 

[ellis8500]

If you use urethane foam it should be OK. Another option is to use epoxy instead of polyester resin. The epoxy does not attack anything. Check US Composites for good prices.

 

[Mr. Fixit]

Polyester resin over polyurethane spray foam (like "great stuff") is fine. Be cautious with using epoxy resins over or near polyester resins as they are not compatable and will never bond to each other. It may seem like they do, but will quickly delaminate from one another causing a failure.

 

[PotvinGuy]

Serendipity! I'm ripping out the upholstery in my car this winter and doing a smoothy interior something like Ex Junk's. I was pondering the best way to do it, and the spray foam sounds great. Carve, sand, cover with 'glass and paint it. Any tips will be most appreciated.

 

[fordsbyjay]

Anytime I have used spray foam it is real spungy. It doesn't cut well because of this so I would think it would be hard to shape unlike the florist foam.

 

[ellis8500]

In the boat repair world they use epoxy on polyester all the time. The surface has to be well scuffed. New polyester will not adhere well to an epoxy surface but new epoxy will adhere well to scuffed polyester. Epoxy is stronger and more moister resistant than polyester. Boat builders do not use it because it is much more expensive and the cure times far too long for production efficiencies. One can find all of this to be true with some web searches. I've also built a couple of boats and did extensive research into the subject.

 

[twannabe]

Thanks for the replies, i decided to just give it a try. here are a few pictures of the process. It actually worked fine. I used my harbor freight oscillating tool with a saw blade to rough shape the foam, then sanded it with some 40 grit. View attachment 5784

 

[twannabe]

My plan was to tie the bottom lip of the grille shell to the inner valance with fiberglass so that i could cut a groove thru the fiberglass to nest the wire mesh down into to hide the edge of the mesh because it is unfinished.

 

[twannabe]

Sorry i don't have a picture of the finished product, i will try to get one up asap.

 

[jimbo01]

WoW, that spray foam worked out well for you. I usually end up wearing more of that foam on me then the intended project. The grill looks nice too. What did you use?

 

[twannabe]

It was the "great stuff" like you get at the hardware store. It was pretty messy to use. I have learned to wear gloves any time I use it.

 

[putz]

I have a buddy that can't have great stuff in his house according to his wife. He had the top break off a can dropped it dog grabbed it and rand through the house. That was a mess. Grill looks great.

 

[madmike8]

Laugh, that's funny Putz! Did the dog survive the ordeal?

 

[Mr. Fixit]

Laugh, that's funny Putz! Did the dog survive the ordeal?

Probably did, but he was foaming at the mouth. Okay, sorry, I coundnt help it...

 

[RocknT]

Now thats funny right their !!!!

 

[twannabe]

Pictures of the final result. The first two show the groove i was able to create so that the mesh could nest down in while the inner valance is still attached. The third shows a temporary screw to hold the mesh in, but this is how i intend to attach it by screwing into the new layer of fiberglass with the foam underneath. last pictures show the final result.

 

[Keeper]

That looks great.

 

[PotvinGuy]

I did a test; squirted 2 cans of Great Stuff in a box, about 2" deep. After a while the surface had hardened, but it was still uncured underneath. I pulled off the hard part and let the interior cure. The next day it was completely hardened and I could cut and sand it. So the lesson is to build up in thin layers, maybe 1" max, allowing each to cure. And it really is tough; a power carving knife and rough sandpaper or maybe a cheese grate will ease the job. And it is sticky until cured; gloves recommended. I noticed they have several varieties of it; one is made for filling large voids and might be better if you have lots of space to fill.