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Body Filler Issues

4K views 19 replies 11 participants last post by  adtkart 
#1 ·
Sorry to keep bothering you guys with my body work but I've hit another road block and would love a little bit of assistance.
Here’s the problem; I have a door with rust on the lower end. Instead of cutting the rust out and putting in new metal I decided to use a rust converter and some body filler to hide the mess. The problem is that everytime I apply filler and sand it down it is always lower then the surrounding area. I have applied "bondo" about 5 times and sanded it down, the results are the same, primer reveals lower areas.
Would this be an issue with how I am sanding the material, how I am applying the hardener or what? I'm confused and my arms are starting to look like popeye.

I am starting out with 80 grit sand paper to break the material down, then 100 for a slight while, then 220 to feather the edges.
I'm sanding in an X motion, then side to side, then up and down over the material with the sanding block touching the surrounding metal.
I am applying hardener to the filler in the form of a thin strait line over the width of the filler.

Some spots to be filled are on the edge of the door skin, causing me to send the sanding block off and away from the surrounding metal. This could be the cause for low spots in these areas but spots that are in the middle of the door are also low.

Thanks for any assistance.
 
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#2 ·
You are over sanding the product. Try mudding the lower panel the full length. then glue two pieces of straight line board paper to a straight 2x4 piece of wood. Use this to knock down the excess mud, leaving a thickness of about 1/16" at the bottom. then use your DA to sand this JUST SMOOTH, don't over sand. This will leave a straight surface. Most inexperienced guys tend to oversand panels.
 
#5 ·
Milo goes to a bunch more trouble than I do (getting old and can't afford the time for all those steps!) but the principle is sound. Bondoing is done is several steps, not just slathering it on and hand sanding before primer. Treating the entire area as a unit, not just the bad spot, using block sander EVERY time, frequent use of guide coats, finishing with spot putty/glazing putty, and a couple rounds of priming/guide coat/block sanding before finish paint are all necessary for a perfect repair.
 
#7 ·
Oddball, Be sure that you are not pressing down on your sander, what ever you are using, as this will make the repaired area give and the results will be an uneven surface.

Troy
__________________
If you don't make mistakes. your not doing anything.

69 ss rs full custom camaro 98 ISCA grandchampion
69 ss rs bb camaro wifes driver
66 Elcamino 350/all dz parts,ac,windows,loaded,my driver
69 ss chevelle bb conv.fresh frame off
26 T sedan street rod
 
#8 ·
I always thought the more you sanded a area the straighter it would become, I suppose I was wrong lol.

Anyhow, I'm using a drywall sanding board with a foam backing. its about 9 inches long. I was told the foam backing was a good idea for the contour of the door; its soft but not to soft. I will switch to the 2 x 4 though as soon as I buy some bigger sand paper.
I have been applying the filler to the whole bottom half of the door and applying two primers between coats of filler.

Also thanks a lot Milo for the info for my inexperienced mind.
 
#10 ·
I use a air long board and a hand long board, they use the same paper.

Did you say you was spraying primer between layers of filler? If so this could be giving you a problem. Do not put any thing between the layers of filler. If you prime then sand the high places off and add more filler over the primer it will not adhere right, and you will have different sanding characteristics, in other wards a mess.

Troy__________________
If you don't make mistakes. your not doing anything.

69 ss rs full custom camaro 98 ISCA grandchampion
69 ss rs bb camaro wifes driver
66 Elcamino 350/all dz parts,ac,windows,loaded,my driver
69 ss chevelle bb conv.fresh frame off
26 T sedan street rod
 
#11 ·
Opps, yes I have been priming between the layers of filler; two coats at that. I was hoping the filler primer would fill tiny imperfections. Thanks for the information

Also is there anyway to quickly break down filler, I'm extremely sore from sanding the stuff down and I was hoping for some tips besides using 40 grit sand paper that would scratch the metal. I’m beginning to think it is the filler itself, not sure what kind it is but it’s a gallon jug with a red mustang on it, (cheap stuff). Thanks again.
 
#12 ·
Not an expert by any means but trying. Use the 36 grit to start. The scratches in the metal (not much) will fill fine when you get to the prime/glaze steps. My board is about 14 inches longx 3 inches wide. 3M has paper in any grit to fit it. Get your contour with the 36 grit. Then go to 80 ( scratches in metal/filler will get much lighter). Finally 180/200. Then prime and sand. If more filler is needed, apply it then. The primer will/should have been scratched deep enough with the 80/180/200 to allow bonding.

When satisfied with the countour or flatness of the panel, prime it and sand with 180/200. Finally, use glazing putty to get fill for the scratches and pits . Glazing putty will only work correctly on primer.

Scratch it till it fits.......
 
#14 ·
Chev38... I don't know what glaze putty you are using, but the ones that I use can go directly over body filler or even over sanded paint. If you are using a 1 part putty, that is applied directly out of the tube, you should stop. That stuff will shrink up later and show it's ugly head.

Aaron
 
#16 ·
I like to get novices thinking in different terms.Have you ever spread black dirt in the yard? First you get it where you want it with a shovel(spreader). then some quick leveling with a hard garden rake (36 grit).You get the drift,the advice here is right on track. Work smart not hard. Joe
 
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