Mold gel coat repair?

General Composites Discussions Equipment Talk
#1

:worried: I had an unfortunate chain of events that damaged an essential and (expensive) mold!
A couple weeks back, I applied a gel coat on a carnauba waxed mold in preparation of a CF cloth layer. I left the mold overnight at shop with plans on returning the next day. A bad flu took me out most of the week (never made it) and I scrambled to get my momentum back; sprinting at urgent other tasks and the mold, well, just sat. (not good!) Unfortunately the long time in the mold (about 2 + weeks!). I decided I did not Like the application and wanted to abort the gel coat. To my horror, it was brittle and in some sections bonded to tooling gel coat. :cry: . I have removed 99% of the gel layer but not without collateral damage in a few places. Dental plaque removal tactics and some careful heat gun blasts were required. The takeaway? An expensive lesson: leaving a gelcoat on too long can burn through wax layer and bond!

I am wondering, has anyone successfully repaired a compromised mold? :sad2: Can a bondo approach (or?) tooling gel coat putty be made with a talc, sanded to micro grit buffed in affected areas? Any hope? Any tricks? Thanks

#2

Bondo no. Maybe a few pulls but it will eventually fail. Best is to use maybe some gel coat mixed with some chopped up strands of fiber to thicken it, or maybe carbosil? But I’ve never used carbosil with gel coat.

They make mold repair kits but I’ve never used them. I usually do gel coat, then more gel coat after it shrinks some depending on the repair. I’m sure there’s an easier way but I have yet to want to buy new products just to have hem sitting around.

#3

Just apply tooling gelcoat over tooling gelcoat, until you are satisfied with the amount of material applied. Wipe wit acetone, sand and buff. (invest in a buffer and the stuff that goes with it)

After that, break in your mould like new, so first 2 pulls with PVA.

I am surprised the gelcoat bonded. You tried to laminate a piece of fabric over it, then yank it out? Mostly the quickest and least invasive way to remove unwanted gelcoat.

#4

Fill any low/damaged areas with a strong filler and fair smooth. Next do a spray gelcoat repair with the same tooling gel (with wax), then sand to 1200 or better and polish. Like new.

For really small bits or chips I just carefully fill them with the same straight gelcoat (with wax) using a toothpick like tool so that it is slightly overfilled. Make sure you tease the air out of the filling as it is applied so that you minimize porosity in the repair. Once cured cut back with wet dry to 1200 or better and polish.

#5

I don’t believe the extra time of gel coat has anything to do with it sticking ,
its you release system that failed.

#6

As above. The time the tool was left gelled up played no part in the adhesion of gel to the tool. Depending on the size/amount of repair a good quality mould repair putty would be a good option.

#7

Thank you all for your replies!

I’ll give it a go!