Kevlar or bondo?

[Digger89L]

Some body repair threads are touting Kevlar-based body fillers as being superior to 'standard' Bondo type fillers ....what's the real story here??
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I guess it depends on what you are wanting to do with it? Are you wanting to skim a low spot that’s 1/16th, or 1/32nd of an inch thick, or trying to fill a cavern that has more than a 1/4 inch difference? There are A LOT of products better than the actual Bondo brand you get at Wally World. Evercoat has high quality fillers that work well for most repairs. Most of the “reinforced” fillers are fiberglass based, and have “long”, and “short” strands of fiberglass/kevlar in them. While they are more durable, they’re not going to be sanded/feathered out thin as easaly/nicely as a polyester type filler.

The primer you put over the fillers is just as important as the fillers. I know a lot that used a primer filler, that’s basically a liquid body filler, over the finished filler work. Then a final primer over the sanded filler primer before paint.

You also may want to consider the workability of a filler. Evercoat’s Corvette Panel Adhesive is just about indestructible once it’s cured. While this makes it extremely durable, your arms will fall off sanding it if you don’t start shaping it before it’s cured.

[bluebus86]

For most repairs, it dont matter if it is kevlar or glass fiber. It is likely a marketing gimmick. For some repairs, hollow glass beads are better, shapes easier. For the resin, epoxy is oft better than polyester. But again, it likely makes no difference for most application.


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[heimlich]

Kevlar definitely sounds better doesn't it. I've seen fiberglass made with Kevlar and you can supposedly use less of it when making something structural. As far as for slapping it onto a car to fill a blemish I doubt it makes a difference what you use.
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[Kiper]

I have seen that too. These are "Reinforced" fillers, meaning they have the fibers to hold them together. These work great for areas that need the added strength and because most of these are fiberglass based they are waterproof as well. Typical body filler is very porous and will soak up water causing rust issues.

Usually over welded areas I will put a skim coat of a fiberglass based filler over the top of these areas before I use body filler. This gives the area moisture resistance so the body work will last longer.
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[Digger89L]

OK ....so let me understand this: 'regular' body filler (with brand names like Bondo) are porous and can absorb water, while body fillers with additives like fiberglass or kevlar (even though they have SAME base material as a regular, Bondo-type filler) are less prone to absorbing moisture. Is that basically what we're talking about here ..or do these 'additive' fillers use a different base material, as well as additives??
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They’re different. The white “plastic” filler is usually a talc based powder, while the gray reinforced is usually a fiberglass stranded resin. It’s my understanding the fiberglass/resin portion of the reinforced is what makes it more water resistant. They ALL absorb water if you leave them uncoated to the elements. That’s where the primer/paint comes in.

[Onceler]

I try to avoid the fiberglass strand fillers just cause the huge air pockets that can come back to haunt you after it’s painted. I usually just fill deep crevices with traditional filler in skim coats, even though it’s taboo, I’ve had better luck. Ymmv
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[67ctbug]

I use the fiberglass fillers for big dents and evercoat gold for thin stuff. The bondo fiberglass filler is waterproof. I've used that to go over welds where the panels bow in. then over that with a skim of evercoat to feather out. Works well.
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[63 vwnotch]

Yeah all hype and marketing.. even evercoat is overhyped, dynolite with 1/3 or less poly filler (glaze coat) makes for an excellent final coat.. Dynoglass, kitty hair, fiber hair or whatever you want to call it from any brand is all basically the same chemical makeup...

Kevlar, lol

whats next??
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[Evil_Fiz]

[63 vwnotch]

[sologhia]

Kevlar fibers are woven in such a way that they actually wick moisture. Duraglass and other fibrous fillers are used for structural areas. Often in repairs around windscreens . I don't think this is so much for the moisture resistance of the substrate but the strength of the materials.
The best stuff I have used for filler is probably 3m platinum. Seems to go further, sand easier and less or no pinholes.
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