non bed liner finishing of the fender flares

[gummycarbs]

So the body guy said he would use a fiber glass patch to fill the holes and then paint/blend. $700 in total. I've hear conflicting opinions on using glass to fill body holes. Does anyone have experience or opinions they can share? I want to prevent my fairly clean body from rusting... will glass/paint hold up ok?

It depends on what he's actually doing and how he does it. If he's going to use fiberglass cloth and resin from behind the panel, and doesn't expose bare metal while doing so, then it will likely last until the panel gets bashed. But I doubt he can get access to the back side of every hole to do it that way.

If he roughs up the holes, exposing bare metal, and just smears in fiberglass reinforced polyester filler, and doesn't seal up the back side, then it's going to absorb water and rust from the back side out.

 

[Lumpskie]

It depends on what he's actually doing and how he does it. If he's going to use fiberglass cloth and resin from behind the panel, and doesn't expose bare metal while doing so, then it will likely last until the panel gets bashed. But I doubt he can get access to the back side of every hole to do it that way.

If he roughs up the holes, exposing bare metal, and just smears in fiberglass reinforced polyester filler, and doesn't seal up the back side, then it's going to absorb water and rust from the back side out.

Thanks for the useful reply! This is the kind of discussion I was hoping for. I believe that the body guy was going to access the backside of all the holes... except for those 2 small holes on the back door. I haven't pulled the door card but getting to the back of those might be tricky. (we will discuss our approach more tomorrow) From what I understand, an epoxy based fiberglass resin doesn't have the adhesion limitations or water adsorption that polyester has. West 105 is one product I was considering. West claims that West 105 does not shrink like polyester. Are you familiar with this product or anything similar?

WEST SYSTEM #105-A Epoxy Resin | West Marine


Also @LINUS I read about your pop rivet approach. Do you have any pictures or more information? I'm not against welding everything, I just want to know what's out there.

 

[gummycarbs]

From what I understand, an epoxy based fiberglass resin doesn't have the adhesion limitations or water adsorption that polyester has. West 105 is one product I was considering. West claims that West 105 does not shrink like polyester. Are you familiar with this product or anything similar?

I've made some things out of carbon fiber and epoxy. I don't think that polyester actually absorbs water. I think the issue is Bondo, or other polyester-based body filler. I think it's the other stuff in Bondo that compromises it. And even then, I think that if the 'skin' isn't ever broken, it might be impervious.

If you put down a layer of fiberglass, then tried to wet it out with polyester *or* epoxy, if you didn't fully wet it out then the exposed glass fibers could wick water in. So, I'd say technique is more critical than the resin you use.

I welded up my fender flare holes. I used MIG and .030 filler wire, which is really to big to do delicate sheet metal work. I probably distorted my panels a bit, but I'm not going for a show-quality finish, so it doesn't really matter. I've said before that if I were doing it over again, I'd:

1. Use TIG. You can much more precisely control the heat you're putting into the body panel. If you don't have a proper TIG machine, you can use any DCEN stick welder and add on a WP-17F torch (~$90 from Amazon) along with a bottle of argon (~$80 from Harbor Freight with a 20% coupon, around $25 - $40 to have a welding shop refill it).
2. Use nail heads to fill the holes. They're handy for filling body holes, since they're effectively a chunk of flat steel with a built-in handle. You find nails with about the largest head diameter that will fit into the hole to be filled. Grind off any galvanization. Tack weld it, then finish with minimal filler metal. Cut the body of the nail off and grind the weld flush.

 

[User Name]

How picky are you about the holes? You have a few options.. You can DIY various ways including the fibreglass or plug welding. And if you aren't extremely picky about the holes you can get colour match in either a tin or aerosol that will do the trick. You don't have to buff and paint a whole panel.

If you're going to glass them (or get someone else to do them) just use mat and resin. A thin layer of bog to level off will be fine.
It's not a lifetime repair, but I've had filler in vehicles that's been there 20 years without harm.

 

[jpoole]

Water absorption can be an issue with the "ester" resins though it seems academic in the context of this discussion of a painted layup in a fender and is more relevant in boat hulls where the layup is exposed to water, under pressure, for long periods of time.

Epoxy will do a better job of bonding, both short and long term, and there aren't any situations that I can think of where you'd want to use a polyester based product in a small layup unless you need to put polyester over it later (Poly over Epoxy isn't a good idea from what I know). Polyester does shrink and doesn't retain the elasticity of Epoxy over time which could both contribute to a failed bond to your fender, should you go with Polyester. The main benefit of Polyester is probably it's lower cost at this point though it's also nice to be able to speed/slow it with varied hardener levels which you can't do in the same way with Epoxy. You can read more below but in short, use Epoxy.

https://www.mjmyachts.com/images/stories/pdf/sp advantages of epoxy resin.pdf

 

[Lumpskie]

Thanks for the useful feedback and informative discussion, guys. I talked with my body guy this morning. The approach will be to use an epoxy resin based system without any bondo or body filler. The top surface will be a short fiber reinforced putty that is sand-able and epoxy resin based. (again, no body filler) After applying that product, he will sand, prime and paint the body panels as one would normally do. I'll post up results and, in the case of any long term failure or draw backs, I'll be sure to share that as well.