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QUOTED FROM: Fiberglass Repair - Composite Repair - Fibre Glast Developments

"A new composite material is gaining widespread use in the automotive, industrial, and personal watercraft markets that presents unique repair problems. It is called SMC, or Sheet Molded Compound. Recognizing SMC from other types of FRP composites is critical so the proper repair can be performed. Parts made with SMC are produced in compression molds, so they are smooth on both the inside and outside. That is the first clue to look for when identifying them. Next, SMC parts do not have an outer gel coat, but they are usually painted or color molded. When the paint is sanded off, the underlying surface has a marble appearance. Finally, when damaged SMC is sanded, short coarse fibers are exposed and a dryer powdery dust is produced compared to conventional materials. These hints will make SMC identification quite straightforward.
SMC is a polyester-based material, but it cannot be repaired with polyester resin. This is due to the mold release agent that is present throughout the entire SMC part. Unlike conventionally molded parts where release agents are applied to the mold surface, SMC is compounded with them in the resin mix for quicker processing. This means that as the damage is sanded to prepare a good bonding surface, fresh mold release agent is exposed. Polyester resin products are not strong enough to adhere to this surface. SMC SHOULD ONLY BE REPAIRED USING EPOXY-BASED RESINS, FILLERS AND ADHESIVES. When painting, use only catalyzed type paint systems."

BMW fairings as used on the RS and RT are Sheet Molded Compound, SMC.

Thanks. I use epoxy as a matter of preference anyway, but the info about the paint is really useful.

R85/8 wrote:For the reinforcement idea, I was planning on using a 200gsm twill laid on the inside of the existing fairing parts. That way if it didn't conform well enough, I could just cut darts in it rather than get too fancy - it's going to be hidden by paint any way. It also means that the original surface of the fairing remains undisturbed.

I would be doing this to undamaged fairing parts as a preventative measure rather than a repair. However, once I have enough bits to sacrifice one, I'll experiment with repairs on the cracked bits - maybe a heat gun and some plastic welding rod will do the trick.

Anyone know what exactly the fairing material is? It looks like a thermoplastic to me, but I didn't pay attention at the time they were released because I didn't like fairings - now I'm older and gone soft...

As far as making a whole fairing from c/f, I'd expect that to throw up a few challenges.

My experience has been that to remain repaired a crack must have fiber re-inforcement spanning the crack, on both sides. Otherwise, flexure will re-open the crack.

For a reasonable chance at success epoxy resin is a must.

Native /5 wrote:...My experience has been that to remain repaired a crack must have fiber re-inforcement spanning the crack, on both sides...

Agree, but I'm intending to use unbroken fairings parts as much as possible and reinforce them with c/f to prevent cracks, as opposed to repairing them.

If I do use repaired parts, it will only be after testing the repair strength on some sacrificial pieces.

(I've made f/g components as well as repaired them satisfactorily before)

I used some carbon fiber scraps to reinforce parts of the seat base I made for my cafe racer. As stated earlier, it is a very uncooperative material for someone used to working with fiberglass. Of course, the reason I was using cf in the first place is for its stiffness but that's what made it harder to use.

The technique that I used to make it lay down was to lay some fiberglass cloth over it. The next time, I'll buy a vacuum clamping system. Sometimes they are called vacuum bagging systems.

Chuey

vanzen@rockerboxer.com wrote:QUOTED FROM: Fiberglass Repair - Composite Repair - Fibre Glast Developments
SMC SHOULD ONLY BE REPAIRED USING EPOXY-BASED RESINS, FILLERS AND ADHESIVES. When painting, use only catalyzed type paint systems."

BMW fairings as used on the RS and RT are Sheet Molded Compound, SMC.

I have an S fairing I preparing to install, but first I have to do some work to the fairing because the paint job buggered. Now I know why and have a better grasp on how to make it better.