SMC project

P

Panelwagon62

Hey guys, its winter time and that means its time to do some paint work on my jet ski. Its a KAWI stand up and is completly SMC. There are alot of larger holes from the exhaust and fuel filler cap that i would like to shave off. I know with SMC i have to use epoxy resin, but how exactly can i bridge a hole that is about 3-4 inches in diameter without it cracking later on? I know there is a science to SMC repair in doing it properly i would just like for someone to give me alittle insight before i start sanding away. Thanks alot for any advice!
 
Epoxy resin doesn't stick long term (if at all) to SMC.

I've done many of these back in the day with liquid urethane adhesive from Duramix. Grind (50 grit) the exterior perimeter of every hole to a shallow ~25 degree bevel and grind the back side of each hole (about an inch out from the hole. Find a suitable backer such as a SMC panel and cut to overlap the hole by an inch all the way around. Grind the side of the backer panel where adhesive will be sticking to. Find a quick set Duramix product like 4040/4050 and apply bead around the perimeter of the hole and the perimeter of the backer. Spread it smooth with filler spreader then quickly mate the backer. You may slide the backer to reposition but never pull apart and re-mate the backer to the hull. Let the adhesive kick for 30 minutes then grind away any excess adhesive visible on the front side of the repair. Fill the void with a known quality SMC filler such as Vette Panel Adhesive. If you end up needing a skim coat, either re-skim with the filler you just used or an SMC compatible filler to prevent mapping. Sand then prime with epoxy primer.

Lets say you are working around a radius and a backer isn't feasible. Prep those holes like above and apply masking tape across the front side of the hole creating a backer if you will. Fill the hole with Duramix 4040/4050 and let it set 30 minutes. Pull the tape and look for any voids in need of filling. Do not use any type of filler directly over Duramix. Use the Duramix adhesive to fill any of these top side voids. Let it set 30 minutes then DA smooth. Apply 2 coats of epoxy primer over the Duramix and top coat appropriately. This is a bit more risky repair than if you had a solid backer but I've done it many times with Duramix since being a liquid urethane the adhesive will be as strong as the SMC.

Under no circumstance would I trust filling a non-backed hole this size with an epoxy type repair adhesive.

Also note, since 3M bought Duramix ~10 years ago, the line has been changed a lot and many old products went away. 3M kept some original Duramix liquid urethane product but also threw some of their epoxies in the line as well. You only want to use a liquid urethane in a high stress situation like this. A quick search shows 3M replaced 4050 with #04240 which is the same as 4040. That's the number I would personally select.
 
For structural repairs on SMC you want to use the SMC spec'd right product. For cosmetic repairs I've often sanded the area, applied epoxy primer, and then used basic polyester products, filler, glazes.... and never had any problems or mapping-the epoxy primer is key. I've also bonded fiberglass parts to SMC panels using polyester products and the key was using epoxy primer for the tie coat.
 
Also just to avoid confusion, Andy is talking about a two part adhesive and epoxy is different in a two part glue vs a epoxy resin.
 
I have not had much time to be messing around with my ski so i'm just getting started on it again. Now i also lurk around on most of the jet ski and PWC forums and some guys are using the two part epoxy adhesives your talking about but ALOT of them are also using epoxy resin and mat for major structural repair/modifications with no problems. These are all on SMC hulls to. in that situation is that a stronger repair VS epoxy adhesive?
 
Forget fiberglass resin....buy the more expensive SMC resin and be done with it...I did yrs ago. Now it don't matter anymore whatever I'm working on what I use works... ;)
 
I'm not talking regular polyester resin I know that won't work. Isn't. Epoxy resin compatible with fixing SMC?
 
I can't respect the method shown on their website as it does not include repairing the backside, also I believe glass mat should be the first step on both sides so the part will be strong.
 
I am sorry. But the most important things happen between steps 10 & 13. I should just probably just keep my mouth shut.
 
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