Faster way to sand down bondo?

Fiberglass, body panels, valences. Also interior pieces like seats, dashes, etc
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Faster way to sand down bondo?

Postby Yoshi » Thu Jun 09, 2011 12:00 am

Right now I have a mouse sander and some 80 grit. You'd figure it would kill the bondo quickly but it gets gummed up really fast. I tried block sanding but the same thing happens. I get these spots of clumped up dust and crap. Should I wet sand ALL the time? IE spray surface with water and go? The few times I did that it just gummed up faster. I don't want to spend an hour just sanding down the first layer. How can I do it faster?
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Re: Faster way to sand down bondo?

Postby M20_fever » Thu Jun 09, 2011 12:53 am

get an inline sander and some course inline paper, it will take it down fast, too fast sometimes. If the paper is getting clogged up the bondo is either not fully dry or you didn't mix enough hardener in. It should be to hard for you to scratch with your finger nail.
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Re: Faster way to sand down bondo?

Postby Yoshi » Thu Jun 09, 2011 1:11 am

Even with bondo hard to scratch I still gum up quicker than I'd like. Define inline sander? I have a belt sander but that would KILL this I think.
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Re: Faster way to sand down bondo?

Postby M20_fever » Thu Jun 09, 2011 1:47 am

don't use a belt sander.

This is what Im talking about.

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Re: Faster way to sand down bondo?

Postby Yoshi » Thu Jun 09, 2011 1:48 am

I have one of those. Still slow as balls.
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Re: Faster way to sand down bondo?

Postby M20_fever » Thu Jun 09, 2011 12:50 pm

Ok, well if you are letting it dry completely and using the proper amount of hardener then my guess is you are putting it on too thick. Another trick is to use a cheese grater type planar to rough it in. You need to use it while the bondo is still a little soft.
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Re: Faster way to sand down bondo?

Postby Yoshi » Thu Jun 09, 2011 3:22 pm

on my first coats I always try to lay it on real thick. Cover up big holes and crap that I missed with the kitty hair. I'm essentially building a huge area around my sunroof. It wasn't fully flush so I have to make up some distance :(
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Re: Faster way to sand down bondo?

Postby M20_fever » Thu Jun 09, 2011 5:08 pm

don't lay it thicker than about a quarter inch at a time max. If you need to go thicker than that do it in layers, though you should never total more than about 3/8" thick. If you need to go thicker think about either doing some cut/weld repair first, or glass in the rough shape then skim coat with bondo.

Also, if your mixing the right amount of hardener in it should only take about 10 min to harden in average 60-70 degree temps. When I apply bondo I mix a lot of small batches to eliminate waste of bondo that hardens before I can apply it.
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Re: Faster way to sand down bondo?

Postby Yoshi » Thu Jun 09, 2011 5:13 pm

I got lazy with the sunroof and did it all in one go. Just kinda winged the hardener lol. Plus it was about 97F out... It dried to the touch after I was done putting everything on. at it's thickest It's only about 1/4". There are some peaks in some places but that stuff usually doesn't take too long.
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Re: Faster way to sand down bondo?

Postby Rick » Tue Nov 15, 2011 12:32 am

The thinner the bondo layer the LONGER it takes to cure. Also, use "pro gold" brand in the Bondo family for the finish layers. The reason why you're gumming paper is the thin surface layer is not cured yet ( this very thin top layer takes a long time)

All bondo or filler is basically polyester fiberglass resin + Talc (baby powder) Polyester resin (or Bondo) likes to harden the most in the absence of oxygen. "finish" types of filler have an extra agent added to take care of this.

To stop gumming paper:

1: Use finishing type bondo in the first place

2: lots of heat and more time to set. Heat is really important for hardening poly resin.

3: Wash cured filler area with acetone and a brush. This will remove the thin, top uncured surface layer (about the thickness of a coat of paint) Thats the shit thats clogging the paper up. Underneath where its oxygen free, its hard and will sand without gumming.

Happy Bondo-ing!
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Re: Faster way to sand down bondo?

Postby M20_fever » Tue Nov 15, 2011 12:40 am

Excellent first post, thanks!
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Re: Faster way to sand down bondo?

Postby Rick » Tue Nov 15, 2011 12:55 am

Ha thx :)

Just found this place. I figued Yoshi was causing trouble somewhere since the "tech" incident and now I see where he is! Cool he started his own place.
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Re: Faster way to sand down bondo?

Postby M20_fever » Tue Nov 15, 2011 12:59 am

Yep, good bunch here, welcome aboard!
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Re: Faster way to sand down bondo?

Postby Yoshi » Tue Nov 15, 2011 3:27 am

I gotta raise hell somewhere right?
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Re: Faster way to sand down bondo?

Postby Rick » Tue Nov 15, 2011 3:33 am

You're a pretty sharp DIY, wait for no one kinda guy. Like your style

Carry on! *in heavy british accent*
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