dolanosa

Hi all. This could be a very easy question to answer for people.

I'm building a plug from blue foam, because I'm cheap. I decided to use the epoxy from Home Depot because I ran out of W.S. To hold the fiberglass on the part, I sprayed the cloth lightly with 3M 77 and put on the properly mixed epoxy lightly. As the epoxy dried, I noticed that my nice flat fuse started getting ripples in it. Now it has pits and ripples and generally melted. What happened? I thought that all epoxies were nfoam safe? I made a mistake a while back of using acetone to thin out the epoxy but I didn't thin it out this time. I can use filler to fix this but I'm afraid to continue on the rest of the fuse since it has a lot of compound curves and the cloth has been tacked on with 3M-77 already. I also know that the new compound of 3M77 can cause melting but there is no melting on those areas. Please help.

Thanks!

Butch

lshadow2005

My Feedback: (5)

Butch,
You should use Epoxy designed for foam.
I have taken fiberglass cloth and cover an area and then applied a light coat of foam safe CA and it works great.
Hope this helps as I have ruined a number of projects by not using the correct glues, wrong paint etc.[]

daven

My Feedback: (1)

I'm betting it is the 3m 77 causing the melting, not the epoxy.

drela

Maybe you got polyester resin, and not epoxy?

dolanosa

Thanks for the assist guys.

lshadow2005,
What foam-safe epoxy can I get from Home Depot or Lowes? I could just go back to West Systems since they have proven themselfves with other projects but I haven't tried blue foam with their epoxy, only white foam and balsa.

daven,
I don't think it's the spray. The only way I know that is because I still have raw cloth sprayed with 77 on foam right now without epoxy. I actually checked last night on those areas I just mentioned and the foam hasn't melted at all. I do know that the new formula eats foam but sprayed very lightly, just enough to tack the fiberglass won't melt it. Thanks though.

drela ,
I really don't know what resin they have at the HD. It kinda stinks so it may be polyester but I'll check tonight. It uses MEK in very small quantities...does that mean it's polyester resin? If it is, I'll have to bit the bullet and get West Systems and such.

Again, thank you for your input and I'll let you know what happens.


Butch

davidfee

Yes, this is polyester resin. The catalyst is MEKP (not MEK), and the main ingredient is styrene monomer... which is what your blue polystyrene foam is made from. So... there's your problem. Polyester resin and polystyrene foam do not play well together.

-David

dolanosa

David,

Thanks. That's what I was afraid of. Well, time to order the real deal. Thanks all for your help.