View Full Version : Reinforcing vacuum-formed parts with fiberglass?

09-16-2007, 01:38 PM
Does anybody reinforce vacuum-formed parts with fiberglass on the back side? (Maybe just in the thinnest places, or at places where it's attached to something else?)

I've been under the impression that epoxy would stick to styrene, ABS, etc., and I could put a little epoxy fiberglass on the back side of parts and it would stick.

Now a few things I've made are coming right apart, and I assume the others will. Oops.

(I guess I thought it would stay because a lot of people epoxy-coat PS foam... but maybe that's only giving them a mechanical bond to the texture of the foam.)

Does anybody know a very good primer for styrene or ABS that you can epoxy to? (I know some people use flat "latex" housepaint to prime PS, but I don't know if that's really good enough---maybe good enough for a thin layer of flexible paint, but not a layer of FG?)

Has anybody tried polyurethane-resin fiberglass on PS or ABS (or anything else)? There are moisture-cured prepreg fiberglass repair tapes sold for various purposes that seem promising, but they're not cheap and I haven't tried them.

There's also a Super Glue (brand) UV-cured polyester FG patch material that you can allegedly use on "plastic." My understanding is that regular liquid polyester resin will just eat styrene plastics, but maybe this stuff won't. (Maybe it'll just dissolve the surface enough to bond really well?)

I've also seen people saying to prime styrene with CA glue, but I'm not clear on how to do that easily and well---seems like you'd want an extremely thin layer and immediately bond it to something else. (?)

Thanks in advance for any tips/advice.

11-14-2007, 01:03 PM
The best manner in which to fiberglass-reinforce ABS, Styrene, etc. is to
first sand the "back side", and then to utilize a urethane resin to layup the
glass. Ensure that you do the *entire* piece- otherwise, I have found that
often enough the fiberglass "part" will pop off. Don't be discouraged if it
happens ;-)

A easy tip / trick I've learned also, is to overlap the edges *slightly* with
the resin- not the glass matting. It seems to help prevent the part popping
off a little more often.

These techniques are often used in hot tubs, bathtubs, etc. for added
An excellent primer is made by dupont for plastics- although now you can
buy much lower cost plastic "spray paints" that work fairly well, as well as
rustoleum's plastic products..

For the paint itself, I stick with urethane based paints- as they seem to
grab the plastic slightly better. They do cost a bit more, but- for the added
shine, as well as durability- I think it's worth it.. That whole "Do it right one
time- as opposed to wrong several" concept. I tend to ignore most of the
latex users myself. .....

And before you start worrying- especially if you talk to the special people
in dupont's sales department.... You do NOT need a "Flexural additive" for
the urethane based paints. The urethane paints are the same ones used
on cars these days- and everyone knows you can *usually* dent a door
slightly - and pull the dent out- and keep your paint intact, if you're careful.

I use the polyurethanes - not the polyester resins. I have put a coat of
polyester resin over a fully cured polyurethane layer in the past, as a test-
without adverse results.

Priming styrene with CA glue is just overall more expensive and time
consuming than some generic polyurethane resin, 'glass, and sandpaper.
Plus the whole factor of being able to spread the resin with the right roller
quickly- and have a little more "working time" than the CA glue....

-- I love your website by the way. It has some great info.

11-19-2007, 03:20 AM
Thanks very much for the info.

Is there a suitable urethane primer that's easily available in a spray can, or do I need to deal with spraying 2-part stuff?

Where would I find polyurethane laminating resin? (I did some googling and didn't find much.)

High Seas
11-19-2007, 05:34 AM
Here's a thought - well maybe a link anyway:
I've been looking for a similar product and came across this. I will try it next April - May when Back in the USA.
:cheers: Jim
PS -- I plan on making a thermoforming machine then too - you've been warned Dr Crash!

Note - this stuff "reads" like a styrofoam coat - but it seems to bind with acrylics and styrenes - so might be a brush-on option.

11-19-2007, 09:54 AM
Thanks very much for the info.

Is there a suitable urethane primer that's easily available in a spray can, or do I need to deal with spraying 2-part stuff?

Where would I find polyurethane laminating resin? (I did some googling and didn't find much.)

Unfortunately, it's the 2 part stuff that I use, have not found a suitable
laminating primer yet that's even remotely affordable.

You don't *have* to spray- I've found that brush or roll-on works okay. There's neat resin rollers available from Tapplastics or Professional.

11-29-2007, 08:55 PM
I have reinforced Styrene and ABS many times. I use a regular waxed styrene resin used in boat building. Use unwaxed if you are going to do multiple layers of glass. You need to use a waxed resin on the last coat or it will remain tacky. Make sure you don't go overboard and put too much resin in one shot or the heat reaction of the curing will distort the plastic. I have reinforced 1/16" to 1/8" styrene and the resin will actually melt into the plastic creating an awesome bond that will not peel. I have tried many things on Styrene and this is the only thing that I found that works.

11-30-2007, 02:51 PM
I recall seeing an article in High Performance Composites in which a company was producing hoods and large composite panels for John Deere farm tractors. The process consisted of thermal forming PETG sheet, and reinforcing with fiberglass applied with a chopper gun. I believe the 2-part epoxy was “tinted” prior to being shot through the gun.
The benefits included fast cycle times, the use of lower quality molds (the PETG “bridged” minor mold imperfections), and easy release from the mold, the PETG also offered a formed a bonded clear top cap, eliminating the need for gelcoat.