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body filler

4K views 18 replies 10 participants last post by  MARTINSR 
#1 ·
First....I am fairly new to body work and am getting confused at times with the process of sanding body filler...particularly at what point to stop sanding the filler area. Ive read MartinSRs Basics tutorial on fillers but here is what Ive run into....Ive welded in some replacement panels and have applied some Fiberglass (Dynatron Ultra glass) directly over the welded seams. I then sand that with 40 to 80 grit and get it "feathered" out pretty good. I then try to put a thin coat of Evercoats "lightweight" filler over the top of the fiberglass/welded area and try to feather that out with 80 grit. My problem is that I seem to sand the area too much leaving me with thinking that I need to add another layer of filler. I check the area by hand to gauge smoothness. I guess I dont know how to tell when that last "skim coat" of filler is needed. Maybe part of the problem is that Ive never experienced how much fill a 2K primer will provide over filler. So, any ideas I can think about that will help me?

Also, how do you determine when to use a filler like Evercoats Rage type or Lightweight type versus a smooth spreading filler like Evercoats Metal Glaze or Easy Sand product? Thanks.
 
#2 ·
If you're doing the majority of the filing with the ultra glass and the shape is established with only some minor filling needed then you could actually just go to a glaze from there. Think of glaze as a filler designed to fill minor imperfections like low spots around 1/16" or less, sandscratches etc. Rage extreme is also a good product that would work really well over that glass, it spreads and sands really well almost eliminating the need for any glaze.

Do yourself a favor and put a thin skim coat over the whole area, then apply either a spray on or dry guidecoat and sand it one more time. If the area blocks out without leaving any low spots identified by still visable guidecoat and the edge of the filler is feathered out you should be then ready for primer. Guidecoat also works well when you switch to a finer grit sandpaper as it'll show when all the scratches from the previous grit are gone.

A guidecoat isn't always necessary and with experience you can get a grasp on what's going on without it but for the times when you're lost it will definately show you the way, also good for really fine perfection of filler work.

Hope I helped, Bob
 
#5 ·
Its always easier to get things straight sanding with a courser grit, you only need to get down to 80 or 180 grit scratches and a filler primer will take care of them. Get it straight and the filler feathered in with 36 or 80 grit on a block, and once you have no more low spots and it feels straight, then take out the scratches with a finer grit, or if you feel you will be taking off too much of the filler by working out the scratches, then skim coat the area with a easy sanding finishing putty and use 80 or 180 on your block to sand it before primer.
 
#6 ·
Most all primers recomend the filler be final sanded with 180 grit as minimum. Some people get away with 80 grit without problems. You can take is down to as fine as 600 grit if you wanted but it really isn't necessary. The time it takes to go from 180 grit to 220 or 320 is very minimal. As a rule 180 grit is safe, 80 grit is sometimes a gamble, and 220 or 320 you're guranteed there'll be no shrinkage related scratches showing up down the road. With different primers the chance of shrinkage also varies among different products. Cure time before you sand the primer also factors in. 180 grit is the most commonly suggested grit though. Bob
 
#8 ·
#1 Be Patient!

#1 Be Patient! Body work is something that takes time to master.

#2 When using your hand to gauge your work remember to keep your hand flat and not use your finger tips but the entire hand to feel high and low spots - and feel the entire area in all directions.

#3 After your initial fill coat and knock down with 36-40 if a re-coat is needed - fill the low areas but then smooth coat the entire surface of the repair. This is because your underlying filler coat is of different hardness when you start sanding your secondary coat of filler (this technique applies to spot putty as well) - so if you coated only parts of the repair surface when you start sanding again you have to surfaces of varying hardness and they will not sand correctly to get straight.

#4 Most mistakes I see from people learning bodywork is that when doing filler work they take too much material off. Always watch for metal showing on edges or other high spot indicators - they start showing visually before you will ever feel it!

But when sanding blocking primer coats they don't take enough material off!

Especially during your initial block sanding of primer coats up to 240grit or above it is not enough to simply block out the guide coat primer - that doesn't mean it's straight - you should block until there is barely show through on the base coat or edge and always use more guide coat if there are any questionable areas.


Good Luck!
 
#9 ·
"#4 Most mistakes I see from people learning bodywork is that when doing filler work they take too much material off. Always watch for metal showing on edges or other high spot indicators - they start showing visually before you will ever feel it!"

Rambo....I think your above #4 is my major problem......THanks for mentioning that.
 
#10 ·
esahlin said:
"#4 Most mistakes I see from people learning bodywork is that when doing filler work they take too much material off. Always watch for metal showing on edges or other high spot indicators - they start showing visually before you will ever feel it!"

Rambo....I think your above #4 is my major problem......THanks for mentioning that.
You are more than welcome. Once you see high spot indicators (metal, underlying filler, etc...) when you stop and check the area decide if the high spots need more attention or is the filler area still low. Sometimes it can be a combination.

And don't forget #3 - if you have to recoat - do the entire repair area.

I see you are in the Seattle area - I'm actually in Kirkland. What kind of car are you working on?
 
#12 ·
Rambo_The_Dog said:
##4 Most mistakes I see from people learning bodywork is that when doing filler work they take too much material off. Always watch for metal showing on edges or other high spot indicators - they start showing visually before you will ever feel it!

But when sanding blocking primer coats they don't take enough material off!


Good Luck!
Man oh Man are you on the money there!

I will see guys, even experianced pros sand and apply, sand and apply over and over with the filler, yet the paint department will "block" the primer for a few strokes and leave it at that.

Brian
 
#13 ·
MARTINSR said:
Man oh Man are you on the money there!

I will see guys, even experianced pros sand and apply, sand and apply over and over with the filler, yet the paint department will "block" the primer for a few strokes and leave it at that.

Brian
Yeah, I grew up and learned bodywork and painting in the late 70's and early 80's back then you worked the whole job - start to finish - body work to painting to assembly. There was no "finger pointing" that the body person didn't do it right or the painter didn't block it enough...it was my job and in the end if something wasn't right I had to fix it!
 
#14 ·
What is really the Skim Coat?

OK, I read all the posts come people use special "bondo" to put the skim coat on other say "it's just the last coat which has not been blocked". OK I'm going to use th Evercoat Rage product plan to put my first coat down ver lightly and the sand with 80 grit for first rough out. Then check to see where I'm high or low and then re-apply the filler all over the whole line then sand as needed then if its ready just apply a l ight coat of the filler for the "Skim Coat" and then apply my two coats of epoxy primer over it. So What is really the "Skim Coat"?
 
#17 ·
#18 ·
Don't be greedy with the size of the repair area. Make it big. Take the repair to the good spots, dont try to "butt up" to the good spot. They need to blend together. You should see cat whiskers at the filler edge, or in reality, no filler edge at all just like the picture was showing. Think you got it straight? Then feel it with out looking at it. Yes you read correctly. It's amazing almost what you can feel without looking. And the finer the better. On the next repair make the metal AS PERFECT AS POSSIBLE before filling with anything. And I would NEVER fiberglass over a metal repair. F'glass is structural in nature and has no real use over a strong metal repair.

I hope I don't "sound" too bossy or arrogant here. Piling up filler leads to future problems when pimers and solvents get involved. martinsr did a post on metal finishing. Way, waaaay quicker than filler when you master it. Case in point, I was working on some big tube side boards for a prototype truck yesterday. Not thinking I grabbed the metalglaze to fill the spots that the welders didn't metal finish. I had 4 joints to do. I had 45min in the 1st joint. I then slapped myself with a 2# hammer and dragged the 110 mig over for the remaining 3. I finished the other 3 by welding and grinding in less time than I had in the 1st one. Take your time, know your surface, and do what you're already doing...ask questions. here's one of those trucks I was talkin about.
 

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#19 · (Edited)
The most common mistakes made by the newbe working with plastic filler.

1. They don't give the dent the respect it deserves. What I mean by that is the newbe will usually not look at the dent as big as it is. Not in depth, but in area. The newbe will not see that the impacts effects on the metal don't end right at the impact. There is usually a brow that lurks out away from the direct impact. First off, in the metal working stage, that brow (or many) can be holding down a low spot. This brow may be very subtle. You have to "give the dent the respect" by stripping the paint out past where you think the dent ends. This way you KNOW you are going to be spreading the filler out far enough to cover it. Going out "too far" especially with the final skim coat is not going to hurt a darn thing. That filler out here can be sanded down paper thin and won't hurt a thing.

2. Be sure the filler goes OVER the deep scratches in the metal. And for Gods sake, be sure the surrounding paint is feathered out with 120 or 180 and there are NO coarser scratches left in it. This can cause all kinds of problems as you final block out your filler and find that you "can't stop" because of them. You sand more trying to fix these scratches in the metal or the paint and ruin your blocking you did on the filler.

3. They will put the filler on to thick, and sand it with too fine of paper. Applying the filler really thick (I do this my self on the first coat to KNOW I am filling what I need) is fine, but you BETTER be using some COARSE paper to CUT it flat. If you apply too much and then "polish" it with finer paper you are never going to get it flat.

Try thinner coats applied with more pressure on the speader so press out air bubbles and press the filler into any nooks and crannies.

4. And without a doubt one of the biggest mistakes made is sanding too much filler. I can look at body work most of the time and tell you if it is smooth or not, without touching it, no kidding. If there are shiny spots in the metal in the middle of the filler or on the edges, this is a dead give a way of sanding too much. The feather edge of the filler should look literally transparent. Also, if there are different colors of filler (a little different amount of hardener with each batch changes the color) I can almost guarantee that it will not be smooth. The different applications of filler here and there trying to fix things sand different because of a number of different reasons. This means you could have some filler that is not fully cured on top of some that is. When you sand this new filler and your block runs out onto the surrounding fully cured filler, one is going to sand different than than the other. How can you get them even if one is sanding at a different rate than the other with the same stroke of the sand paper?

If you rough out the work as described in the "Basics" and then apply a THIN skim coat of filler over the whole thing, you are WAY, WAY better off. You sand the whole thing down at once and when you see that transparent edge you STOP. You will need to feel the panel, but when you see that transparent edge, you are VERY close and need to really pay attention because just a few strokes of the paper and you have shiny metal.

This is how I have put into words how you sand the whole area at once bringing down this skim coat.

Picture you have a large mound of dirt in your front yard, from fence to driveway and out to the side walk is this gental mound about ten inches higher in the middle than at the edges. You want to remove it, but without your neighbors knowing. You shave the whole thing at once every night in the dark, paying a little tiny bit more attention to the center, thicker dirt. You do this everynight, a little at a time until the whole thing is gone.

Sounds goofy, but that is something I thought of while sanding filler one day.

Anyway, practice on some test panels and strip the paint out real far so when you feel the filler you are not hitting the feather edge of the paint. Look for that transparent edge.

Brian
 
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