I'm going to rivet my fiberglas flares to my car (like this):



But, my flares are full of holes (previously attached with Dzus fastners):





The backside of the flares have to remain flush as they will be resting against the body. I'm guessing I use masking tape on the backside and fill the holes with Kitty Fur, then resin. Sand, repeat?

Sand the backside down to good clean glass, lay up one piece of fiberglass MATT once setup, bevel the holes out on the opposite side. Cut several discs gradually increasing the diameter. Starting with the smallest disc, apply a light coat of resin to your hole, lay in the first ( smallest ) disc, wet it until it becomes transparent, then repaet with each larger disc until the hole is fairly level. Once setup fully sand the glass with 80 grit and give it a wipe of bondo.

BTW If you do not bevel the holes the new glass will have nothing to really bond to and you will end up seeing the outer perimeter of each hole

If I put a layer of matting on the backside, won't that keep the flares from sitting flat/flush with the (metal) fender?

that's why you sand it down first ...
Andy

Once the front side has setup you can also go back and sand the backside completely smooth. You MUST have something substantial on the backside to begin with though

Got it. Thanks.

Also invest in a box of latex gloves and wear them. Fiberglass sucks on the skin

Oh yeah. I buy them by the 100 when on sale @ Harbor Freight.

Depending on the person/type of resin, it's more than just your hands, particularly if it is green resin (not fully cured) I got sensitized part way through building my kayak at it is now a real pain working with fiberglass. Painter suit and a respirator is not overkill particularly if you are working indoors. IMHO of course.

I have a table set-up outside for spraying and stuff like this.