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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 06 Aug. 2021 at 6:30pm

Good question Nofender,


This debate has been going on since I started doing body work in the 80s and I was curious if someone would bring it up. Thanks for mentioning it, and now that you have, here are my thoughts:


I am not a fan of applying filler over primer in general.


The paint reps would come around the shop and tell us “that’s how they do it in Europe”. I would counter that with saying something like “in Europe, bodymen likely belong to a union and it doesn’t matter how long the repair takes and here in the good ol’ US of A, we work on a flat rate basis and need to get these jobs out the door”. So besides it adding time to each and every repair, I don’t see how to feather edge the primer under the filler. You can’t sand the filler without sanding through the primer and exposing bare metal, so what’s the point? That primer edge under the ring of filler can’t be smoothed out and feather edged, and may react or shrink with the topcoat over it. If the primer isn’t fully cured, it could trap solvents under the filler and possibly fail later, which could easily happen in a production shop ‘cause everyone’s in a hurry. 


Now with that said, I have done this many, many times successfully, but only for small dings and hail dents with the OE paint not broken. For these, scuff up the existing paint with a finer grit sandpaper (150 is perfect) and apply a spot putty very lightly just covering the ding. Then, very carefully sand just the spot putty with the 150 and carefully blend it out without going through the existing paint. Do not sand through the paint, because now you can’t feather the paint away from the repair and risk sand scratches showing up in the topcoat when everything shrinks. 


Done correctly, filler over bare metal is a fine practice and can last for many years without issue. Done wrong and all bets are off.


Hope this adds some insight.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote rocnroll Quote  Post ReplyReply Direct Link To This Post Posted: 06 Aug. 2021 at 6:47pm
Its easy....follow the directions on the side of the can. 

Bondo brand  (admitedly a cheaper brand) states bare metal.

Manufacturers generally know how their own products give best results. Wink


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Post Options Post Options   Thanks (0) Thanks(0)   Quote nofender Quote  Post ReplyReply Direct Link To This Post Posted: 06 Aug. 2021 at 7:50pm
Fantastic insight! Thank you!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 07 Aug. 2021 at 7:27pm

OK, so putting the stuff on is the easy part. Now, how to finish the filler so it looks great:


For me, it boils down to three key ideas:

  • Sharp sandpaper

  • Letting the tool do the work

  • Know when to stop!

My first move is to knock down the bulk of the filler with my 8” sander, this will be the tool of choice on flat panels. After fitting the sander with a new piece of 40 grit and taking off most of what was applied, the left ¼ panel is at this stage:




I like to use a guide coat through the sanding process, especially with the coarse grits. A new stick of 36 grit on the air board takes off most of the guide coat and flattens out the panel. I’ll follow this up with another dusting of guide coat and moving to hand tools; 36 and 80 grit on the long boards. I’ve never been good at machine finishing filler and had good results hand- finishing my work. Again, new sandpaper makes the work easier. After going over with the 80 grit and following with a little 150, the panel looks like this:




You can see some of the lows have diminished and some metal is starting to show through where the filler is getting thinner. It feels pretty good at this point, but it’s not flawless. I’ll use some spot putty to fill in the lows and pinholes to finish. This is where knowing when to stop sanding comes into play. If I keep going with sanding, I risk undercutting the filler where the metal is starting to emerge. I’ll show this the next time I screw up and sand too much. 


Some tips on sanding using the long boards: I’ll push the boards across the filler in line with the predominant curvature but not in a straight line.




Switch and sand in the opposite direction so that you create kind of a “cross hatch” with the sandpaper- sort of like a honed cylinder. Also, I’ll switch positions from where I’m standing, kneeling, etc. so I’m not just sanding from one side. And I’ll turn the board around and use it both ways in case I’m putting more pressure on one end. It might seem obvious, but this really does get stuff straight. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote bobevans Quote  Post ReplyReply Direct Link To This Post Posted: 07 Aug. 2021 at 10:03pm
Thanks for all the detail!  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TMRoper Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2021 at 6:01am
Thanks for the time and effort of putting this together! For us novice body men ,this is very helpful!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2021 at 12:42pm
You're welcome. If it leads to straighter and shinier jeeps, all the better.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug. 2021 at 11:34pm

Some thoughts on sandpaper: 3M Green Corps sandpaper is the best, hands down. It’s very expensive, but worth it because it’s so productive as it stays sharp longer than other brands. Second tier papers like Norton, Mirka and others are OK but don’t stay sharp as long. Really cheap sandpaper won’t save you any money because you’ll go through so much of it. Also don’t try to use the paper past its useful stage; it’s false economy because you can’t really make stuff straight with dull sandpaper. Sandpaper from the hardware store is just garbage-don’t bother with it.


The key here to remember is: coarse sandpaper makes things straight, finer sandpaper makes things smooth. Get stuff straight with the coarse paper and quit, leaving something for the finer grits to do. It’s more difficult to straighten filler with the finer grits so get that done with the coarse grits early and focus on making your straight filler smooth with the finer grits.  


Here’s a tip that I find helpful: when finishing a panel that has a hole in it (like an ignition switch hole), I will place masking tape on the back side of the hole and apply the filler over the masked up hole. Finish the repair completely, and then remove the tape and drill out the hole. It will be easier to sand straighter and the sandpaper won't snag on the hole.





Edited by otto - 21 Aug. 2021 at 7:43pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 21 Aug. 2021 at 10:37pm

This is a new product I tried out last year on my van project. It’s a spot putty in a tube that the label states is “self leveling”. I was dubious but tried it and glad I did, it is awesome for filling small defects, pinholes, low spots, screw ups, etc. I remember spot putties from ye olden days and they sucked- hard to sand, plug up sandpaper, had to dig it out of a small can…


This stuff does none of that; won’t plug up sandpaper and sands almost as easily as drywall compound ! Love it.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 01 Sep. 2021 at 11:35pm

Since it’s been a while since I’ve done this work on a regular basis, I’ve forgotten some tricks that used to save me a lot of time. One of them is to use masking tape before spreading filler in order to keep it out of hard to sand areas. Sore fingertips reminded me of the tape trick while working on the tub and getting bondo in spots that were difficult to sand.

 

Here’s a good example- I don’t want to get filler in the seams on the tail light panel so I place a strip of tape just on the radius of the panel bend.




Then when the filler is all applied and still wet, pull the tape off. Makes a clean edge that will be easy to sand.






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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 04 Sep. 2021 at 9:18pm

I mentioned undercutting filler earlier, but didn’t take a good photo because there wasn’t a great example to show. I’ll use this pic to try and show what I’m talking about.




The red marker is circling an undercut spot where the metal is higher and the filler has been sanded below the metal’s height and is “undercut”. Sometimes this means the metal is a high spot that needs to be brought down and sometimes it just means too much filler has been sanded away. You can usually visually see this as well as feel it with your hand. The filler will exhibit a definite line between the metal and the filler’s edge. Compare with the section below the circle where there is a very gradual transition at the filler’s edge. What you want is that edge of the filler to be very thin where you can almost see through it.


The best way to avoid undercutting is to keep your sandpaper on the filler and let the edge of your sanding tool just reach out beyond your swipe. When the edges of the filler are brought down to the metal’s level, start checking your work more often with your hands and looking for metal showing through the filler. If you sand from the metal onto the filler, there is a much better chance of undercutting.




Edited by otto - 08 Sep. 2021 at 1:04pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shadow Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep. 2021 at 12:41pm
I just went through your post start to finish and loved it, you have lots of helpful tips and tricks to make our jeeps look better.  THANKSTongue 
lets go for a rip eh bud

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Post Options Post Options   Thanks (1) Thanks(1)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep. 2021 at 2:50pm
Thank you.

I hope the thread has lived up to its name and been helpful; it's not done yet, I still have a few things up my sleeve and we haven't even covered painting yet.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 07 Sep. 2021 at 7:12pm

With all the work on the outside of the tub, no paint has gotten in the way of the filler work. For the wheelhouses the original paint is still in good condition, and I’ll use that as a substrate for applying the new coatings. I like to find original paint and try to keep as much intact as possible because it’s the best foundation you’ll find. Paint put on in the factory is applied in near laboratory conditions and is a very different product than body shop paint- it’s much better, so if it’s stickin’ it’s stayin’.


I broke a cardinal rule of not clearing enough space around this repair, this makes it tough to feather edge the paint around the filler without getting into it.  




I like to start the feather edging process with a coarser grit and step up to the finer grits; here in 80 grit:



I feel it goes faster using this approach and uses less sandpaper than just using a 180 or 220 grit throughout the process, especially if there are many layers of paint to deal with. After 220 grit:



The wider the bands of paints after sanding the better. Shoot for at least ¼ to ½” for each layer as a rule of thumb and you shouldn’t be able to feel the transition from the metal surface to the paint. My goal here was to just smooth out the scratches and chips, not remove more than necessary. The DA is the go-to tool for this because the pad wobbles as I mentioned earlier. Try to lay the pad as close to flat as possible- it won’t like to be laid perfectly flat and will jump around if it is. Most of the sanding is done on the outside of the sandpaper; it’s kind of like a monster truck show ticket- you pay for the whole seat, but just use the edge. 


 Prep work like this is my least favorite part of the project, mostly because it’s the messiest with the fine dust; also 1940s paint may likely contain lead.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep. 2021 at 7:21pm

Once the bodywork and paint feathering are finished, I like to cover everything with a coat of catalyzed epoxy primer. Before that, if I have any new steel or metal that was completely sanded smooth to bare metal with no filler, I like to use something to etch the metal so the paint will stick well.


For example: the floors and hat channels were new steel and no filler was applied to them. I used OSPHO on the steel as an etching agent after wiping them down with some solvent. The directions on the OSPHO container instruct the user to apply liberally and let the stuff sit until dry. I don’t use it this way- what I do is to just wipe it on, let it sit for maybe just a minute and then wipe it off until dry. Keep it away from paint or body filler- it’s of no use on these and they may absorb product. As OSPHO is phosphoric acid it works immediately to etch the metal; you can see the metal turn color almost instantly and feel the difference in how the rag drags a little more as you run it across the metal. It’s done it’s job at this point and I don’t see any reason to let it sit longer. Now if you’re painting ocean going ships that’s another thing…


Etch primers are not recommended for over fiberglass or body filler and I don’t use them on my projects.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote rodfrey Quote  Post ReplyReply Direct Link To This Post Posted: 24 Sep. 2021 at 12:39pm
I finished the "body work" on my 48 CJ2A several years ago.   Before it was painted I was advised that imperfections would become more visible.  And they did!  I wish this thread had been available because it gives very helpful advice.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 24 Sep. 2021 at 8:45pm
Originally posted by rodfrey rodfrey wrote:

I finished the "body work" on my 48 CJ2A several years ago.   Before it was painted I was advised that imperfections would become more visible.  And they did!  I wish this thread had been available because it gives very helpful advice.

Well, there's always next time! There's always a next time right? Next upgrade, next project, next iteration...

Thanks for tuning in.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 24 Sep. 2021 at 9:08pm

Last time I mentioned epoxy primers- this is what I use:




It’s OMNI which is PPG’s house brand. PPG’s DP line of epoxy primers are excellent (but cost more), but this product is offered in the same colors, smells the same, sprays the same, etc. so, I’m not sure of the difference.

Sort of makes me think of this:



As my project is winding down for this year, I never did get to the painting portion of this thread which will have to wait until next spring/summer. I hoped to share how I prep stuff for paint and get the final coatings on the jeep but just ran out of time. My project will be assembled in primer and everything will get checked for fit and fine tuned so after paint will go together smoother. 


That also means updates to this thread may slow while my project is mothballed. I’ll try to add items that may be of interest in the meantime, or if there are thoughts, comments, or questions just post away.




Edited by otto - 24 Sep. 2021 at 9:24pm
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