In the Smooth On racing car seat video, they use their Epoxamite resin with a fiberglass mat. With just two coats of their Epoxacoat gelcoat and one heavy layer of CSM, they make what appears to be a high quality part. So why is this practice frowned upon? It looks like pretty simple and reliable process, minus the reusable silicone bag.
CSM fibreglass is held together with a binder and the binder is designed to be disolved by the solvents in polyester or vinylester resins.
Epoxy resins do not have any solvents to dissolve the binder so the CSM does not wet out very well.
Not according to Smooth On
“Epoxamite 102 Laminating System can be used with reinforcements such as Fiberglass Mat, E-Glass, or even Chopped Strand fiberglass for lay-up applications or composite parts.”
This is also demonstrated in their video
I would never use csm for a seat. Why go through the process of making something when it’s such a critical part of safety. Even s or e glass is better then chop strand. Unless you are making something you don’t care about I would stay away from that stuff in components that matter.
Look at the big air bubbles in the intake line at 3:54
The part may appear to be “high quality”, but as I always say, everything looks good in a picture.
I’ve used plenty of CSM and epoxies, building stiffness in a mold for example. No problems with that at all. That said, I agree that it’s the least efficient category of composite reinforcement for strength/weight, it’s stiff but weak.
That “matting” looks like Rovicore or Saercore (there are other brands as well). These are actually stitched products so they don’t have binder in them. Both of these products have a polypropylene flow media in the center with chopped fibers stitched on either side of the core. They allow good flow rates and are very conformable as can be seen in the video. They can also be supplied with various structural fiber configurations although the material in the video looked like a plain chop product.
Also, for those that questioned it, I don’t think the idea of the video was to show an actual lam schedule for a race car seat. Rather, I think it was to show the possibilities of the process.
And finally, before this soap box collapses right out from under me, the reason you hear the admonishent to not use CSM with epoxy really has more to do with the sizing than the binder. Sizing is a treatment for the surface of the fibers. It is used to help bond the resin to the glass. Binders hold fibers together prior to lamination. Some sizings are not compatible with epoxy. Most CSM is made as inexpensively as possible because of what the bulk of it is used for. There are sizings that are compatible with multiple resin types but, as I understand it, they are more expensive. No sense putting expensive, multi resin sizing on a product that will never take advantage of the upcharged material.
If you want to read more, here is a link to an article about sizing: http://www.compositesworld.com/articles/sizing-up-fiber-sizings
Thanks for everyone’s responses.
CSM can indeed be compatible with Epoxy resin although it will need to be of the ‘powder bound’ type. The usual Polyester compatible CSM is generally ‘emulsion bound’ although powder bound is also Polyester & Vinylester compatible.
It’s also a bit of a material mismatch to use the expensive epoxy resins with the cheap short fibre CSM that would also be resin rich if done as regular hand laid part.
Usually bottom end cheap fibreglass parts = CSM and polyester or vinylester resins.
High end parts use better quality materials with better processes.
As Roger said if the material used there is rovicore then thats another material type (not CSM) usually used in closed mould processes.
I appreciate the help. I think I understand now why it just doesn’t make much sense to use these two products together. It may happen, but it’s the exception to the rule.