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Username Post: bondo        (Topic#365868)
bobb 
Super Senior Member
Posts: 5846

Loc: paradise
Reg: 09-05-03
07-21-21 07:23 AM - Post#2823615    

why does bondo harden with a sticky surface? how can i avoid this?

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


 




paulo57509 
Senior Member
Posts: 511

Loc: CA
Reg: 07-18-00
07-21-21 04:39 PM - Post#2823652    
    In response to bobb

  • bobb Said:
why does bondo harden with a sticky surface? how can i avoid this?



I've wondered the same thing. Must have something to do with the mix ratio of filler to hardener. Even though the ratio is supposed to be 50:1 (filler:hardener) it's mostly an eyeball estimate.

I've found that once you start sanding through the tacky surface layer, there's hard filler underneath.

Someone once told me not to mix on cardboard or other porous material because it will absorb some of the filler/hardener and throw off the ratio.



1987 IROC-Z 5.0L
1992 Lumina Euro 3.1L
2003 GMC Safari


 
bobb 
Super Senior Member
Posts: 5846

Loc: paradise
Reg: 09-05-03
07-21-21 08:13 PM - Post#2823660    
    In response to paulo57509

as i understand it. bondo is made of resin and talcum powder. so the porus material will suck up all the resin. if i mix it hot its not as bad, but working time is like 1 minute or less.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5214
Mel Foye
Reg: 09-29-00
07-22-21 02:57 PM - Post#2823707    
    In response to paulo57509

Several body classes said nothing porous. I use a rear side glass from a VW. Cleans up easy.



 
wagonman100 
Site Ambassador
Posts: 15244

Loc: Baltimore, MD
Reg: 11-27-04
07-22-21 07:21 PM - Post#2823726    
    In response to Mel Foye

I’ve mixed body filler on cardboard for decades with no adverse effects. Telling people not to use cardboard was mainly so that the filler didn’t pick up contaminates from the cardboard.

As for filler having a sticky surface, it can be from many factors. Hardener to filler ratio, ambient temperature, and humidity can all play a part. And yes, you can usually knock off the very top, sticky layer, and get to hardened filler.

Jay
Friends don’t let friends drive Fords.

1999 Silverado Z71 4X4 extra-cab short bed
1983 Malibu Fauxmad - tubbed
1978 El Camino Kustomized
1972 Monte Carlo
1957 210 handyman wagon
1957 Nomad sport wagon
1957 Cameo Carrier


 
kool53 
Member
Posts: 849

Loc: Mukwonago, WI
Reg: 06-18-04
07-24-21 05:37 PM - Post#2823835    
    In response to wagonman100

... also using quality body filler (usually not containing the letters b, o, n, d, o) helps.

Jay


 
Belair-o 
Contributor
Posts: 138

Reg: 03-26-07
07-27-21 05:24 AM - Post#2823959    
    In response to kool53

So what do you consider quality fillers, and what is wrong with Bondo?



 




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