[drcrash]

(Sorry if you saw this question on the vacuum forming forum... didn't get an answer there, so I'm trying here.)

I'm looking for advice on priming plastics and reinforcing them with fiberglass. (Mainly high-impact styrene and ABS, but others too.)

The idea is to selectively reinforce thin vacuum-formed parts by putting some fiberglass on the back side, where it won't be seen.

(In some cases, the plastic would be just a very thin shell and the fiberglass would be the structural part, but in other cases the plastic would be thicker, and only reinforced where it's thinnest, or at attachment points and fitting holes.)

My understanding is that the solvents in polyester resin will eat styrene, but I've seen somebody recommending using polyester resin on ABS because it makes a better bond than epoxy. I'm guessing that's fairly thick ABS, and that it does dissolve the ABS a bit and fuse with it, but that thin ABS might get funky if you did that. (?)

I gather that epoxy doesn't make a chemical bond with polystyrene, or not a good one, and surface prep is everything because you're relying on a mechanical bond. I'm wondering if that means that parts that flex may delaminate eventually, even with good (rough) surface.

I'm hoping to find a primer of some sort that bonds well to styrene and ABS, and that epoxy can actually bond well to. That might be a "plastic primer" or something like "Plastic Fusion" paint, or a thin coat of a urethane, but I don't know whether epoxy will stick well to those, either.

Thanks for any advice.

Paul

[svenakela]

Polyester has a very short pot life and there's no problem with using it on plastics, as you said the solvent will effect the plastics but with better bonding. The solvent in Polyester is styrene, it's bad-ass strong so use good ventilation.

One drawback with polyester is the shrinkage, somewhere between 2 and 10% depending on which one you use. Choose a polyester with reduced styrene, smell less and shrink less.

[drcrash]

Polyester has a very short pot life and there's no problem with using it on plastics, as you said the solvent will effect the plastics but with better bonding. The solvent in Polyester is styrene, it's bad-ass strong so use good ventilation.

One drawback with polyester is the shrinkage, somewhere between 2 and 10% depending on which one you use. Choose a polyester with reduced styrene, smell less and shrink less.

Thanks for the tips.

I did a preliminary experiment with regular (Bondo brand) fiberglassing resin and glass cloth, and a 50/50 mix of plain resin and Bondo body filler.

The resin/filler mix didn't adhere as well as I expected... I could peel the plastic (1/16" HIPS) away from the (hollow) cast. (Fairly easily in some places, less so in others.)

The glass (one layer) seems more thoughly stuck on, but maybe only because it flexes with the plastic a little, making them harder to peel apart.

Or maybe that's because the glass stabilizes the polyester and keeps it from shrinking as much in the directsions parallel to the plastic, so there's less shear stress on the joint as it cures...? (Maybe a reduced styrene polyester would be better that way, too.)

I was a little disappointed that the resin/filler mix didn't adhere indestructibly like a good solvent weld, but I'm guessing it will be fine with good surface prep. (I intentionally didn't roughen the HIPS surface for this experiment, just cleaned it with alcohol and let it dry.)

[svenakela]

I'm repairing a lot of plastics for motorcycles, and if someone wants a quickfix I do it with polyester. I rough the surface up a lot, not only sandpaper style - I use the grinder. Then I put a layer of fabric on and wet it. It sticks like crazy.

[DylanF]

Just found this site. Does anyone have an experience with this stuff and why is it so different from normal polyester resin?

[DylanF]

Ah! seek and ye shall find

I'mlooking to do a similar thing DrCrash, but I need to learn how to vacuum form the plastic first