Hi Guys,

I have someone asking me the best way to fill some bolt holes in fiberglass. It is a Touring Box for the back of a Harley Davidson bike. There are 4 bolt holes and 2 larger ones that used to be for a rack and an antenna. He wants them filled and then a glossy black bc/cc job. What's the best way to fill them?

Thanks!!

Cover the hole with tape on the inside then fill with resin from the outside. If you overfilled just right they should sand down level, otherwise a little fine fill or glaze to make perfect. Prime and paint.

NFT5 wrote:Cover the hole with tape on the inside then fill with resin from the outside. If you overfilled just right they should sand down level, otherwise a little fine fill or glaze to make perfect. Prime and paint.

Sounds good...Thanks!!

I think those boxes are just done open lay up style with their fiberglass work. Just make sure that it isn't an SMC (sheet molded compound) fiberglass. Any resin or filler materials would have to say "SMC safe" on them if it is. SMC looks a lot different on the backside than open lay up stuff. The texture is really fine and can become kind of "chalky" over time.

How abut this for the small holes: https://www.amazon.ca/Bondo-Hair-Strand ... 212&sr=8-7

I don't care for Bondo brand stuff too much. USC makes a much better version of that called Duraglas.
https://www.amazon.com/24035-Duraglass- ... 169&sr=8-2
I've been using that in kit car builds and rebuilds for 28 years now, no failures....

Just keep in mind that none of the body fillers are totally waterproof,
even the Duraglass and the like so if you use one make sure the back side
is sealed against moisture, like primed and painted.

JCCLARK wrote:Just keep in mind that none of the body fillers are totally waterproof,
even the Duraglass and the like so if you use one make sure the back side
is sealed against moisture, like primed and painted.

Good thought, I was thinking a smear of silicon on theinside but maybe your idea is better.

^^^^^^^^^^^^^^^^^^^Yep, what he said, proper priming to seal them.... then paint....

Well, I hate to be the nay sayer here BUT! If the holes are still being used for mounting the bags, then just resin, or a canned 'glass filler, isn't going to be strong enough. IMHO, I would do the usual fiberglass fix, of grinding the holes, tapering the depth, and re-glassing with cloth, resin and matte. If this is a recurring problem, or you want to be real safe, using a sheet metal 'backer', fiberglass inside the repair, will strengthen it more than it was in the first place. I do this on cars a lot, where it's a stress point. The metal backer has holes drilled or punched in it, so resin (or resin with a bit of thickener) can get in, and behind it well, and make a stronger bond. Cloth over this., too.