Bondo tech claims that you can use poly resin on early SMC.

[enkeivette]

So when I first found out that 3rd gen Corvettes were made of SMC I called Bondo tech line to see if I could still use the fiberglass poly resin and short strand filler that I bought. This was before I asked questions over here. They called me back this morning and they claim that their fiberglass polyester resin will work on ealry SMC (3rd gen Corvettes) but not later SMC (4th gen Corvettes). Can anyone either confirm or deny this?

I plan to finish the job with SMC compatible adhesive and filler, but I'm still curious to see what you guys think about this.

 

[MYBAD79]

I have used polyester based Bondo filler and fiberglass jelly with the "hair" in it, no problems but none of this was a structural repair.
Same applies to the hole that you fixed on your hood, it'll most likely be fine because the Bondo doesn't take any load or force and from what you're describing you shoved it into a hole (cavity) so it has a large area to stick to.

The bumper that you show on your pics in the other thread is fiberglass, polyester resin is fine for that.

I have used Evercoat SMC adhesive as a base and then used the (cheaper) Bondo on top of that, again, no problems so far.

I have also used bondo resin and mat on SMC and it didn't stick... :suicide:

Do you have a area on the body that needs repair? Glue a small piece of mat and Bondo resin on the SMC panel and see how easy you can pull it off, almost like a sticker :smash:.

 

[SMYDA]

So when I first found out that 3rd gen Corvettes were made of SMC I called Bondo tech line to see if I could still use the fiberglass poly resin and short strand filler that I bought. This was before I asked questions over here. They called me back this morning and they claim that their fiberglass polyester resin will work on early SMC (3rd gen Corvettes) but not later SMC (4th gen Corvettes). Can anyone either confirm or deny this?

I plan to finish the job with SMC compatible adhesive and filler, but I'm still curious to see what you guys think about this.

Adam, I appreciate you posting this info. Learn something new everyday. :drink:
I've known that there is a difference between the 3rd and 4th generation
SMC but have yet to find out "exactly" what it is. I'm no Chemists so if anyone
has any info I'd love to hear it.

 

[010752]

Here is some interesting facts that are little known

1966: First sheet-molded composite (SMC) used for front body panels and hood.
1970: Plenum and instrument panel support panels switch to SMC.

1971: Rear quarter and end panels switch to SMC.

1984: One-piece, lift-off SMC roof panels with massive rear glass introduced.

1993: Rear inner panels molded from recycled SMC, an industry first.



Most everyone seems to get hung up on this SMC stuff.
It really means very little.

What is important is that epoxy has a far, far more adhesive strength than any type of polyester or it's hybrids. Since all bonds (glueing and fillers) only have a mechanical bond, then this is the product that will adhere the best to any type of composite, bar none.
It's really just that simple.

Here is from the GM Repair Manual. Remember that they used the adhesive as a filler at the factory.

Description and Operation
Sheet Molded Compound (SMC) Panel
Bonding
This is intended to provide general guidelines for
sheet molded compound (SMC) and carbon fiber
adhesive bonding of full panel replacement in regards
to collision repair procedures.
Sectioning, partial panel of full panels, is not supported
by General Motors unless specifically documented
in a Service Bulletin or Manual.
Important:
• Prepare the surfaces to be bonded according to
adhesive manufacturer’s recommendations.
Many adhesive manufacturers have different
preparation methods. Do not intermix adhesive
manufacturers systems. Mixing materials
from different manufacturers can produce
unsatisfactory results.
• DO NOT top coat any adhesive bonding mating
surface. Use primer only on bonding surfaces.
Refer to adhesive manufacturer’s
recommendations for priming applications.
Adhesives currently meeting the performance
requirements include General Motors materials and
products manufactured by Ashland and Lord Fusor. At
this time, ONLY the adhesive products listed below
meet this guideline:


Sheet Molded Compound (SMC) Panel Bonding

Medium Set
GM Goodwrench® 89020330
GMSPO of Canada 8902332
Ashland Pliogrip Structure Adhesive 7770B
Lord Fusor Structural Adhesive Product Type 127 EZ

Fast Set
Ashland Pliogrip Structure Adhesive 7779B

 

[Twin_Turbo]

That is EXACTLY what I have always belived. The C4 material is very different. However, the 82 also uses that foir the doors and hood. I even did a test repair years ago and posted pics on CF. Epoxy will bond, regular polyesters won't.

I have always used regular resins and never had a problem with cracking. I bonded the entire front clip, bumper and hood together and it's still rock solid after having been abused. I hav e taken it off many times and it glexes wen you do so, it has been droped on the floow, dragged across the floow, sat straight up on the nose.,...and so on. I doubt it sees that much abuse when on the car.

The 82 up glass is mostly resins and very little fibers. I don't have the pics anymore unfortunately, they were on the old crossfire server. It's a very distinctive difference when you grind it. It's light gray and there are no visible fibers at al. It's more like actual plastic.

As for epoxy you really can't use it as it does not contain styrene to dissolve the fiberglass binders, however there's probably some special formulated stuff out there. If you use ordinary epoxy resin your matte will not " wet" and you'll end up with an epoxy matric with a loose bunch of glass strands in it that really do nothing.

 

[Belgian1979vette]

The info that I've found never stated any difference, but I never had the chance to work on an C4 either, so don't really know.

The info that I've found stated that the 'early' smc should be repaired with epoxy also, due to the fact that with the resin there were products incorporated to get the part releasing from the mold and when you grind the panels, those incoporated products start to release again producing a bond that has a possibility in failing, epoxy would not have that problem presumably.

Anyway, you still can use epoxy on polyester and epoxy based materials but you cannot use polyester on epoxy, so when in doubt...

Don't know about the fiber thing, but VOSSchemie over here doesn't produce any matts different for either epoxy or polyester and does not state that there should be any difference. They are one of the biggest producers over here.

 

[010752]

Been using it for years.
Here is the proper mat for epoxy with no styrene soluable binders in it.
Should be available at any serious composite supply.

I'm lucky, US Composites (formerly Joe's Auto Marine)) is in town.

 

[enkeivette]

When I first bought this car 6 or 7 years ago, the fender was cracked on the bottom corner near the gill. I took it to a bodyshop and they fixed it, I went to that same shop today and asked the manager if they used fiberglass resin or special SMC resin, he said they use typical fiberglass resin.

It's been 6 years since the repair, still looks good.

 

[Belgian1979vette]

I always used epoxy and never had a problem neither.

Anyway, I looked in my workshop manual (79) and it specifically states that you should use a epoxy resin...(section 2D-27 left page). After looking at it again, they talk about epoxy solder-adhesive, but you can ask yourself why using an epoxy solder if not necessary...regular polyester based adhesive is a lot cheaper.

 

[MYBAD79]

When I first bought this car 6 or 7 years ago, the fender was cracked on the bottom corner near the gill. I took it to a bodyshop and they fixed it, I went to that same shop today and asked the manager if they used fiberglass resin or special SMC resin, he said they use typical fiberglass resin.

It's been 6 years since the repair, still looks good.

Could you post a photo of that area now that the paint is stripped ?