Working with Bondo on Styrofoam tips?

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TylerHam

Well-Known Member
Hi All

I like the theory of Bondo over foam, etc - But I can NEVER get it to work right - It always hardens too fast, wont sand well (too hard) etc -

Is there a trick to using it? Is Bondo-glass easier to use (The Bondo fiberglass)

Any help would be great! Thank you!
 

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slimesquare

Well-Known Member
RPF PREMIUM MEMBER
try using rondo....mixture of fiberglass resin and bondo. use a half and half mixture and adding a little extra resin to it will make it pourable, or brushable
 

TylerHam

Well-Known Member
never heard of doing that! So do you add the hardener to the "rondo" that the bondo uses after its mixed? Or do you add the hardener to the bondo before mixing?
 

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aron42486

Well-Known Member
If memory serves me well...

You want to use the resin catalyst as opposed to the bondo hardener for the mixture.

Double check that just in case I am mistaken
 

b26354

Sr Member
RPF PREMIUM MEMBER
I use a coarse half-round file or rasp on bondo to get the basic shape then sand. Also several thin layers to build up the shape you want is better than one thick layer.

If it sets too fast you're probably using too much hardener.

For foam I'd be tempted to apply a layer of fiberglass first for strength then bondo over that. Then you could melt the foam with solvent to leave a hollow shell.

Hi All

I like the theory of Bondo over foam, etc - But I can NEVER get it to work right - It always hardens too fast, wont sand well (too hard) etc -

Is there a trick to using it? Is Bondo-glass easier to use (The Bondo fiberglass)

Any help would be great! Thank you!
 

Leigh

Sr Member
RPF PREMIUM MEMBER
I'm assuming your Bondo is basicly the same thing as our P38 or Easysand, A polyester resin with chalk dust ?

I've been using it in the motor trade for many years & on my foam based project. I also would have thought it would melt Styrofoam being styrene based, I used insulation foam on mine & PVA to seal the foam prior to using the filler.
I've personaly not found the need to add more resin but you can reduce the curing time by using slightly less hardener & as said build it up in thin layers. I also always take advantage of the Semi cured time when its setting but not quite set its a bit like cheese, when its like that you can carve it really nicely to knock down the sanding work.
I always use 80 grit aluminium oxide paper for the bulk of the shaping & then a finer 180-240 grit to remove the 80 grit scratches.
Also if your covering a larger curved area use a rubber spreader to apply it & Dont play with it too much looking to get the perfect finnish first go.

HTH
 

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Contec

Master Member
you can cover the styrofoam with aluminumfoil before useing the rondo/bondo... Also there is another typ of foam that some people use (pink foam?) that do not melt when resin is applyed.
 

Sean

Sr Member
I'm assuming your Bondo is basicly the same thing as our P38 or Easysand, A polyester resin with chalk dust ?

I've been using it in the motor trade for many years & on my foam based project. I also would have thought it would melt Styrofoam being styrene based, I used insulation foam on mine & PVA to seal the foam prior to using the filler.
I've personaly not found the need to add more resin but you can reduce the curing time by using slightly less hardener & as said build it up in thin layers. I also always take advantage of the Semi cured time when its setting but not quite set its a bit like cheese, when its like that you can carve it really nicely to knock down the sanding work.
I always use 80 grit aluminium oxide paper for the bulk of the shaping & then a finer 180-240 grit to remove the 80 grit scratches.
Also if your covering a larger curved area use a rubber spreader to apply it & Dont play with it too much looking to get the perfect finnish first go.

HTH

what is PVA?
 

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