kortensi

Hey guys,

Need some more help and advice, again.

So I've been patching some areas on the front and rear clip of my 71 coupe and so far so good.

Now I tried to patch these two spots on the doors that were missing chunks. I glassed it as I did both the front and rear clips, however, once I started sanding the area down, both of these just came right off.

I ground both areas, cleaned with lacquer thinner and tapped them off just like I did for the front and rear. Then I layered the new glass and resin (same ones that I am using for the front and rear, Daytron), used the cheep brush with cut bristles and roller. It seemed to set up but didn't bond to the old glass.









These are the patches that came off





Anyone have any suggestions?

Thanks
KO

zwede

No thinner BEFORE laying the glass. Just grind, you want the panel to be dry so it absorbs the resin. Paint the ground area first with just resin, then add mat and resin on that.

samsonb

Aren't you supposed to wipe it down with Acetone before and after you grind before you lay the resin/matte?

kortensi

The thinner was used nearly 24 hours before the area was taped off and then it was dusted off with compressed air. I did coat the roughed out area with resin before adding the 1st layer of the new patch.

Does the thinner cause this much of a problem a day later?

If so, what should I do to clean up the thinner to fix the doors?

Thanks
KO

Scott Marzahl

Clean it with acetone, course sand it and use some epoxy resin.

zwede

Not sure how much of a problem the thinner is, we just never put anything on the ground area before the resin. Personally I would grind a little bit more off so you have a fresh surface to bond to.

Another thing: Could you have gotten oil or water on the panel from the air hose?

mapman

What material are you using?

Perhaps the doors are SMC - I believe the SMC contains a release agent and regular fiberglass won't stick.

Try a fiberglass kit that uses an epoxy resin compatible with SMC.

Do a CF search there are several threads on this topic - seems like Chevrolet began using SMC on some parts in the early 70s. Also, if damaged, the door skins may have been replaced with SMC.

These other threads describe fiberglass repairs "popping off" panels just like your description.

zwede

Dynatron polyester resin sticks just fine to SMC. I have patches like that on my SMC panels and they are stuck good.

kortensi

I've cleaned the areas with acetone and I will let them set overnight.
I'll grind out a bit more of the area and try again. I'll let ya'll know what happens.

KO

ikwhite

Hmm thats what they say, think I'll try a test patch myself on an SMC panel and see how it goes. I just used Dynatron on some regular Fiberglass aftermarket pieces and like how that turned out, but have always used West Systems epoxy resin for my SMC panels with great success. As already stated my guess would be either of the above incorrect prep perhaps not enough tooth, or using the polyester resin on SMC.


ikwhite
http://www.vettemod.org/index17.html#


Fiberglass Resin and Accessories
Dynatron® FIBERGLASS RESIN is a high-quality polyester resin for use in the repair and restoration of SMC, metal, wood, fiberglass and masonry. Repairs can be reinforced with Dynatron® FIBERGLASS MAT and FIBERGLASS CLOTH

lushdrunk

Lacquer thinner will actually leave a layer of oil behind. If you want to see it in action, pour some lacquer thinner on your hands and then go wash them. The water will bead off just like if you had motor oil on your hands.
When lacquer thinner evaporates it leaves a film similar to that of oil based products. This can some times be an issues with fiberglass.
To correctly clean a surface before using fiberglass you need to use a product called
Methyl Ethel Keytone or MEK for short. Very careful with this stuff, it is very strong and will make you very sick. Wear a organic cartridge mask and gloves when working with MEK.

Also the other other reasons fiberglass wont stick is from a poor mixture. Too much hardener will cause the fiberglass to become hot, and vapor to form between the new and old fiberglass.


mapman is correct about SMC panels, although SMC was not invented until 1975 and was not used for automotive body panels until 1980. GM started using them in 1984 on the C4 corvette. The C3 fiberglass is just normal, compression molded fiberglass. It should not require any special materials. But it is possible that a panel could have been replaced over the years with one that is made from SMC fiberglass. 95% of automotive grade fiberglass resins are now approved for SMC repairs. So as long as your not using production resins you should be fine.

From looking at your repair, it looks to me that you did not use enough resin. Fiberglass resin must be 1/16" thick above the mat used before it will bond and turn into fiberglass. If it is done too thin, the fiberglass mat will wick the resin and not the hardener. Leaving a sticky mat covered by a hard shell.
For thin repairs such as the repair to the door. You should try and use some wax paper. Wax paper will keep the outside area smooth thus needing less sanding, and it will hold the fiberglass mat firm against the panel.
Just like with paint, Be sure to use quality products and don't mix brands.
Evercoat makes a product for just about every need. The Vette-glas and the SMC panel adhesive are both great to have when working on a C3.
Good luck

zwede

There are two types of SMC. The early type was used on the C3 starting in 1971. Not all panels were SMC, they started with just the rear quarters in '71 and then went more and more to SMC each year.

The second (newer) type of SMC was never used on a C3. It was first used on the C4.

The dynatron resin referenced above will work on the early, C3 style, SMC. It will not work on the later SMC used on the C4.

lushdrunk

You happen to have any reading material on the 1st style SMC? Ive been doing a lot of reading and research about SMC over the last year or so trying to put fact and fiction in their place. The 1st form of SMC panels Ive found where used for boats in the mid 70's. Before that I cant find any info other then rumors of it being used in the C3 like you said, or I read once that it was used for some Aston martin cars of the 60's. But can't find any real evidence that it is true.

zwede

I haven't seen documentation either, this is info I picked up over the years that came from (to the best of my knowledge) reliable people. I can tell you that a NOS replacement rear deck I bought for my '71 was clearly SMC as it had a gray/marbled color, very unlike straight fiberglass. It still had the original GM subcontractor sticker on the bottom.

lushdrunk

That's about all I got as well. Im really hoping to find some info about the 1st SMC panels. Do you happen to remember the name of the Subcontractor? I may be able to do some research on them.
I do know for a fact that a few company's make replacement body panels out of the SMC fiberglass for the c1,2,3,4 corvette. It's a faster, higher quality and stronger fiberglass then normal hand laid or compression molded fiberglass.

wombvette

A product called Genite made by General Tire Co. was first used on `69 doors.

A new product SMC was introduced at General Tires Marion in 1970. The `71 rear quarter panels were the first SMC component use on Corvettes. By 1974 the change over to SMC was completed with the last panel being changed, the `74 rear deck.

Many SMC panels were sold as over the counter replacements and may show up on any car that has had repairs.