bondo hardening

[flatheadgary]

i read all the search post but, i am having a problem that doesn't make any sense. i can mix bondo and put it on steel and it sands and adhears just fine but, put it on a styrene model and it won't harden. as i try to sand it, it is soft and it will peel off in a glob and have no bonding with the plastic. i have been building 1-1 cars since i was 12 and i am 60 now. this stuff is not new to me but, this has me stumped. i have tried to mix the hardener in different ratios to no avail. i have bought other brands of hardeners, nothing. i have left it in 90 deg sun for days to no avail. i have put it in the dehydrator for days to no avail. then just mix some up and put it on my steel 1-1 and it hardens just fine. sands right down. this is the bondo from wal-mart. maybe that's the problem! does anybody have an idea why this is doing this? i think next time i'm in town, i'll pick up evercoat or something else.

[randx0]

try priming the body with a sealing primer or just go with the evercoat.

[Zoom Zoom]

A lot of people say that spot putties like to be applied to primer vs. raw metal or plastic; not sure why your Bondo won't set but if you do get a catalyzed polyester spot putty like Evercoat or Dynatron Putty Cote that it does dry and is sandable in under 30 minutes. Evercoat has gotten pricey but it's easy to find in my area through auto paint stores, though recently found the Dynatron Puty Cote for half the Evercoat price at the local O'Reilly auto parts. It's still likely more $$ than plain old Bondo, but it's a lot nicer to work with in "our" scale.

[Pete J.]

Just a word about Evercoat. It use to come in metal cans, now they are plastic. In a 1:1 shop, it doesn't matter because you use it quickly, but on a modelers bench, both the catalyst and the base eventually eat the plastic container. I have an old glass model paint bottle for the catalyst and a quart canning jar for the base. Had a mess when I left the bench for a while and came back to evercoat slowly seeping across the bench like a nasty plastic blob. Lots of acetone later it was clean but it ruined a lot of good plastic in the process. Pete J.

[bobss396]

I believe that a big can of bondo has a shelf life once you open it and so does the hardener. I can't see why so many people like to use it. Less is more sometimes, unless you're doing a wild custom and you throw it on with a trowel. I use those little tubes of what we used to call "red lead" or aka spot putty or finishing glaze. It dries fast (if you don't slather it on) and should be able to be sanded within an hour.

Bob

[flatheadgary]

well, thanks for all the replies. i have sanded it and cleaned it to no avail. i am beginning to think it is in the hardener or the cleaning. i took some pic's when a buddy stopped by yesterday and he is just as confused as i am. what i can't get my head around is, bondo is a plastic, how can it not stick to plastic? all the glues stick to the model. the stuff comes off like a silicone rtv for mold making, as you can see.

Edited November 10, 2008 by flatheadgary

[Harry P.]

There might be some sort of substance on the body that's keeping the Bondo from sticking... like grease, wax, etc. Any kind of foreign substance like that would affect the adhesion of the Bondo.

Also, try sanding the area you want to cover with coarse sandpaper. The Bondo will grab onto the rough surface better than smooth plastic.

[kustom]

the only thing i can think is maybe your putting to much on at a time. maybe when its curing it lifting off the smooth plastic instead of cracking like it would on a real car. but i have never seen anything like this unless the plastic is oily

[E St. Kruiser50]

Hey flatheadgary

I've had the same problem some time ago, and it was always because I didn't wash the part with soap and warm water, to remove the silicone mold release, and then lightly sand the surface before applying the putty.

Once in a great while I'll still get a small area that doesn't stick, and I'll just use some super-glue to stick it back in place. Works great.

Good luck - Dave

(I'll probably hear about this one. Please don't take this personal about your choices, but I put Bondo in the same catagory as Krylon paints. They are cheap, but the complaints just never seem to end here until people switch to a more expensive brand. The old addage - "You only get what you pay for still holds true.)

Edited November 12, 2008 by Treehugger Dave

[Peter Lombardo]

Well, I have used Bondo for some time now, both over primer and bare plastic, with no problem. I do two things that I think help guarantee a good result. One, I always “rough up†the surface that I am puttying onto to give it “teeth†to hold onto and two, I tend to use a little more of the hardener when mixing a small batch. Maybe these two points mean nothing, maybe it helps, but I use a lot of Bondo to do my “heavy lifting†of reshaping my models, and it works every time.

[Peter Lombardo]

I just went back and looked at your photos and something occured to me.....did the side of the VW "flex" in any way? If the surface you apply to has any flex in it, it can break the bond of the new putty. Just a thought.

[MikeMc]

try priming the body with a sealing primer or just go with the evercoat.

I always prime and sand B4 any filler...

[made007]

ive benn working with 1:1 car 6 years now, and i use evercoat, and i dont have any problem, you just cant put that much at one time, apply just the necessary and sand the plastic first, if it comes off, apply crazy glue to the surface then use the bondo

[Eshaver]

Treehugger Dave , Peter Lombardo, and all the other posters, ya'alls RIGHT! Yep I use the N A P A Tec Glaze or Duron Putty Cote . Bondo brand is jus that, cheap amateur weekend warrior stuff. Hey I use Snap -On tools for a reason.

Ed Shaver