Hardtop smc repair
Posted: Sat Apr 05, 2014 9:11 pm
I recently repaired a cracked hardtop for my track car. I suspect it had blown off a car at speed. After googling SMC (sheet moulding compound) repairs, I decided on using West system epoxy...because I had some left over from a yacht I rebuilt in 1999 in the shed going to waste. There is a huge amount of bull sh$t on the net about repairing this stuff, largely generated by companies that sell allegedly special smc compatible products at exorbitant prices.
After a bit of research it appeared that ANY epoxy is totally compatible with the polyester SMC matrix. I used some left over 15 year old west system epoxy and hardener and it stuck like you know what to a blanket. Fairing was done with West and Q cells, mixed to whatever consistency I needed for the particular application.I used the bog to glue, to rebuild the broken/chipped bottom edge of the roof ( a common weak spot), and for fairing.
I didn't think of taking pictures, and they would be irrelevant anyway...but I will download some before I paint it.
Repairing these smc hardtops is a doddle. Dont even think of a polyester or vinyl ester resin, they wont stick. Just go straight to epoxy and it will be fine, and an easy job even for someone with no experience in composites.
Cracks should be ground through to air( i.e. No material left at all) in a u shape, not a v shape. The glass cloth must then be laminated into the u shaped gouge the grinding left.Build layer upon layer like a pyramid...largest on the bottom working up to smallest on the top to fill your void. This will now be about 20 times stronger than the surrounding smc which is a really low strength crappy elcheapo matrix .
Sand the glass flush and bog with epoxy + Filler medium ( I had left over Q cells and a bag of talc.I chose Q cells as they are easier to sand) Any filler medium is OK, eg talc , if you want to save a buck . I suspect talc is the filler medium in the SMC Mazda used, just by its feel when sanded to dust.
After a bit of research it appeared that ANY epoxy is totally compatible with the polyester SMC matrix. I used some left over 15 year old west system epoxy and hardener and it stuck like you know what to a blanket. Fairing was done with West and Q cells, mixed to whatever consistency I needed for the particular application.I used the bog to glue, to rebuild the broken/chipped bottom edge of the roof ( a common weak spot), and for fairing.
I didn't think of taking pictures, and they would be irrelevant anyway...but I will download some before I paint it.
Repairing these smc hardtops is a doddle. Dont even think of a polyester or vinyl ester resin, they wont stick. Just go straight to epoxy and it will be fine, and an easy job even for someone with no experience in composites.
Cracks should be ground through to air( i.e. No material left at all) in a u shape, not a v shape. The glass cloth must then be laminated into the u shaped gouge the grinding left.Build layer upon layer like a pyramid...largest on the bottom working up to smallest on the top to fill your void. This will now be about 20 times stronger than the surrounding smc which is a really low strength crappy elcheapo matrix .
Sand the glass flush and bog with epoxy + Filler medium ( I had left over Q cells and a bag of talc.I chose Q cells as they are easier to sand) Any filler medium is OK, eg talc , if you want to save a buck . I suspect talc is the filler medium in the SMC Mazda used, just by its feel when sanded to dust.