Making new plug, is expanding foam ok??

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#1

Hi there guys, Im currently making some new plugs and there are some corners/edges on them that I want to smooth out. Now I was wondering if its ok to fill these up with some expanding foam then sand it to shape? Im talking about the stuff you can buy from hardware stores that comes in a can or those tubes used with a caulking gun.

With this method would I be able to just put bondo over the foam afterwards, sand, primer, paint and mould etc…? Or would bondo not be compatible with the foam???

Also can anyone recommend any other methods?? I cant think of how else to fill these corners up since they are quite large/deep I think just using fibreglass will take forever :confused:

Thanks.

#2

Polyester filler will desolve most expanding foam…way round this is to the seal the surface of the foam before applying the filler.

#3

Thanks for the info, now what would one use as a sealer?

#4

You can use epoxy resin, or depending on the shape tape of some sort.

#5

I’m quite sure that all the expanding foam I’ve seen around here is polyurethane. In that case, it would be safe to apply polyester resin or Bondo over it.

#6

Thanks alot guys, I’ll pass by the hardware store later and grab some. :slight_smile:

#7

Through experience, I have found the yellowish expanding foam that you can buy in the aeresol cans melts when exposed to poly resin.

#8

Same here, thats whay I suggested sealing the surface in some way.

#9

I used expanding foam for the ribs on a car hood I made with PER. It did melt, but luckily I wasn’t going for looks with this piece.

Now I’m lazy and just use epoxy.

#10

I made this using expanding foam. Its a plug for a 7 foot golf ball. Used A/B type foam, not aerosol. And if you do go the A/B route make sure you mix it with a drill as the consistancy will be much better.

We used polyester filler, and duratec primer.

#11

Two part expanding foam is polyurethane, so will works fine with poly resin. Aerosol foam isnt and it will melt…

#12

JRL; What brand of A/B foam do you use?

#13

That was US Composites foam. The drill mixer made a world of difference in the consistancy/bubble size.

The only thing I dont recomend is using styrofoam stringers as yor initial shape.