Okay, here is what I have learned with SMC Panels. You apparently aren't supposed to use polyester resin on them because they wont stick. You're also supposed to use fiberglass matte on vette panels so no checkering shows through the paint job. So, instead of polyester resin, I used west systems epoxy resin. I also used fiberglass matte with it, which is technically designed for polyester resin. The fibers are held together with styrene which dissolves once the polyester resin contacts it, and then the fiberglass matt becomes more flexible and you can work with a way better than when it is dry. when you use epoxy resin with fiberglass matt, the styrene doesn't dissolve, but instead it stays suspended in the matte. It works just fine, but the only problem is that it is hard to work with the matt because it is still very stiff after you wet it out. Epoxy also takes a hell of a lot longer to dry.

I see evercoat sells fiberglass SMC resin, which works well with regular fiberglass matte. BUt it says its polyester based...not epoxy based, so how the hell does it stick to SMC panels? Is this a marketing scheme to get us to pay more for what is really just regular polyester resin? I want to try something that works better with fiberglass matte, and which also dries faster too. Anyone out there use evercoat SMC resin? Have you had any problems with it sticking to SMC...seams like a scam to me if it is in fact polyester based...

 

I tend to agree with you Stinger. I don't believe everything I read in a book (or internet), since the day an old time engine builder told me that "a book will lay real still and let you write whatever you want in it" . That was in reference to an engine build in a magazine. Needless to say he didn't believe their hp numbers.

Things like this often get started when someone failed to prep a repair properly and the poly didn't stick so they conclude that poly wont stick to smc. The only problem I see is that vendors do put it on their labels if it is appropriate for use on smc or not, so I don't know. What I do know is that it is too big a risk on body repairs for me to use anything that isn't labeled for smc. There is just too much work involved to chance it for me.

 

I dont think you need to over analyze this. On SMC, use SMC or epoxy resin with regular matt. The results will be fine We have never had a problem with this procedure

The matt has a starch that makes it stiff. just before you lay it down squish it once LIGHTLY with your hands to make it a little more pliable.

 

Hey, that's a good idea! What I do know is that this west systems epoxy stuff dries harder than a rock - its a pain in the but to sand afterwards. Epoxy bonds mechanically, not chemically, so when you want to lay another layer, you really need to rough up the surface. I have a whole box of fibrglass from a forum member, so its good to know that it won't go to waste. What boggles my mind is that most fiberglass books don't cover this kind of stuff in much detail - they just say to use regular resin. I'm sure lots of people use regular polyester resin on smc panels and don't ever have issues. Like Kevinator said - one guy probably started the "myth".

 

I'm using some polyester based resin from a local boat yard (with the matte).....I have never had a problem with that stuff sticking to my 79. the fender anels I've molded in are indeed not going anywheres. I've pulled and tugged on them pretty well and the thin aftermarket fender piece gives a little, but where it's bonded to the panel at it is definatley not going anywheres.....

i was getting worried when I fest started reading this, but hey i guess if it's sticking there's really not much to worry about.


ryan

 

Like I said, its probably a "myth". One guy probably had issues with it sticking due to improper prep, then everyone else followed and said it was no good. This being said, I have had success with my epoxy resin, and I will continue to use it.

 

I use only the Evercoat SMC, and it works great with both kinds of fiberglass material.

 

I might resort to using evercoat smc resin - it will make life a lot easier for me.

 

I figured out the difference between regular resin and smc resin, Evercoat just replied to my email.

Thank you for contacting us. I was unclear on some of the issue you had so I sent it on to our Senior Tech. Below is the response that he sent. I hope this answers all your questions. If not, please feel free to contact us again. Thank you for your interest in Fibre Glass-Evercoat products.

The reason that SMC Resin work on SMC panels where regular polyester resin won’t is because SMC resin contains a small amount of Methyl Methacrylate (MMA) that help to increase the bond. The MMA works to compensate for the mold release that is in the SMC panel. SMC stands for Sheet Molded Compound/Composite.

In order for the material to be molded it is placed inside of the mold which has a positive and negative side. The material is compressed between theses two sides during the manufacturing process. After the part is cured the positive and negative molds are separated and the part is removed. In order for these parts to come out of the mold a release agent is incorporate into the resin that allows the parts to easily removed, otherwise they would stick to the molds. It’s this release agent that causes the issue for traditional polyester resins to not stick.

 

I'm not so sure it is just a myth. While only slightly related to this post...I had a jetski once that I "bumped" into a dock pylon with at a pretty good pace. I took it to a boat repair place to fix it and they did a great job. It lasted about a year before the repair just started coming apart. The guy was completely stumped as to why. He repaired it again and I sold it shortly thereafter. I found out later that the jetski was made out of SMC. I'm guessing the new owner had the same problem later.

 

The concern over using fiberglass mat with epoxy is really of no concern. Buy the proper mat that is made for epoxy and you don't have to worry about the styrene and other binders in the mat. They are just not there.
If your supplier is unaware of this, it's best to find another supplier. It's likely they are also lacking other important knowledge about the resins that goes beyond just being a vender.

Cloth is much much stronger than mat and there should be no problem with "checking" using the proper grade. Additionally to avoid this you should paint the top layer a couple of times with straight resin before the original layer is cured to give you a sanding buffer and avoid any small shrinkage.

Any time you do a repair or build with resins, you should always continue to the finished product so that there are chemical bonds. Anytime any type of resin has cured you only have a mechanical bond not chemical.

There only a very few companies that produce resins, and West Systems is not one of them. They repackage it as most do with their own additives. West is very good, but far too overpriced. Comparable or better resin can be had for less than 2/3 the price.
As a result there are also many different curing rates available.

Polyester has a molecular chain that looks like a snake wraping itself around a tree limb only contacting in several spots.
The epoxy chain is like a cobweb strangling the tree limb, thousands more contact points.
That is basically why polyester is a poor glue and epoxy is a very good glue.
Epoxy based glues are used to bond car metal together with today instead of welding. epoxy bonds somewhere in the neighborhood of 2000psi and polyester at less than 500psi.
There is also vinylester but why bother.
Any repair is just a glue job so use the best.

For best repairs,
Prep with a 20 grid abrasive disk
Use the proper cleaners and wax removers ( I don't mean for the paint wax)
Use a good epoxy and compatable mat or cloth and don't stop until the finished product. You can always grind off the excess.

 

I have used the evercoat SMC resin and have had no issues, hard as a rock once cured. I have had no reason to use anything else

 

Evercoat SMC works fine on C3 panels. The C4 and later SMC formulation is different and requires different materials.