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Old 12-12-2012, 06:29 AM
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not enough hardner

Last night I glassed the seem of the fenders that I just spit and widened. On the first fender I used a moderate amount of hardener thinking that I may need extra time to work. The color of the Bondo brand long hair fiber glass resin did change after adding the bondo and I did mix it real well. On the second fender I was more confident so I used quite a bit of hardner. The color went from green to brown and it set up in about 30 minutes. I sanded it down and now she is ready for bondo filler. the first fender stayed tacky for about two hours. I started to worry, but then I realized that it was getting harder than a brick. At three hours she was still very very slightly tacky but definitely as hard as the second fender. I turned up the heat in the garage and it seemed to help. This morning I checked the fender and the tackyness is almost gone. Am i good to go or do I have to try and remove all that glass. I dont think it's gonna just come out. This stuff is tuff, not at all like regular filler. Obviously there was enough hardener to start the curing process or else it would still be soggy.

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Old 12-12-2012, 07:06 AM
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sounds good

I was putting bondo (3 M brand ) to finish up a rolled rear pan I built and because of the cold weather it didn't harden, It was a mess to get off and clean up.
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Old 12-12-2012, 07:16 AM
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Polyester resins absorb water, and do not surface cure. You can control the cure time of polyesters, within a range, to compensate for temperature, to a limit.

No need to heat the whole garage, you can also use a radiant heat source on the panel. Infrared lamps, or something similar.

It is just going to take more work to sand. If you can get a good feather edge, you are probably good to go.

Because polyester resins do absorb water from the air, I have decided it is necessary to put a good epoxy primer over the metal before using polyester filler. I believe the polyester can absorb enough water to start metal to rust under it in some conditions.
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Old 12-12-2012, 07:48 AM
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Thanks, That is what i was thinking also. The heat source is actually a radiant gas heater, so it worked rather well. When i start sanding it tonight I figure if it sands smooth then there is no problem. If it balls up then I guess I am screwed.
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Polyester resins mixed with hardener have to be above 65 degrees to harden properly.

If you lay Saran wrap or similar tightly over the uncured resin it will not have the "sticky" on the surface when first hardened.

I have been laying up some large fiberglass panels. To keep from having to race against the hardener to the finish. I have been laying up the parts in a 50 degree room and then bringing them into a 75 degree room after layup is finished. No more partially hardened polyester/hardener mixture on pert/equipment before the part is done.

I use a "waxed" gel-coat and resin to keep the "sticky" down. Then remove wax before finishing up the part.
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Old 12-13-2012, 04:01 AM
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My question is did you weld the entire seam of the split fender?
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fiberglass, hardener, not enough hardener, tacky

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