OK guys, I screwed up at the end of last week. I was working on my 54 pickup (fixing a cab mount) and had the running board off. The process of reinstalling the running board didn't go quite as well as it should have... You can call me a dumb ***, I've got it coming. Anyway, when I kicked at the running board, I missed and nailed the bottom of the door pretty good, knocking a big chunk of plastic filler out. The filler was put on about a year ago in my heated garage, and covered a weld seam and was mostly about an 1/8" thick, some spots were a little thicker. The chunk that fell out was about 18" long and about 12" high. It was instantly visable to me (besides knowing how much I just screwed up) that I had improperly applied the filler because it sure wasn't stuck to the door very well. In fact, i could barely see any evidance there was ever filler there, except the missing paint and the slight uneveness of the sheet metal. BTW the metal was still clean-no rust. I ceartainly don't want any future filler work I do to fall out with a little bump. Though the work was done over the winter, my shop was 65-68 degrees. The door was off the truck and sat on saw horses. The filler was put on in layers. I used the stuff that was in the $18-$20 range (not the real cheap stuff, but not the expensive stuff either.) The door was sanded down to bare metal with 80 grit sanding disc on my air grinder. It was wiped down with Gone degreaser and the filler was put onto the bare metal. What did I do wrong? What is the best way to applie filler so it stays on? In the past I've seen filler that was so stuck to sheet metal it had to be ground off. Mine poped off in one big chunk from a little dent below the edge of what fell out. I have just slobbered some paint over the hole in the filler for now so it won't rust. Soon I will be mudding it in again and would like to improve my application process so maybe it won't fall out in big chunks again. Help. Gene
i'm not really a prime example of a body man, but my guess would be that the degreaser that you used left a residue on the metal thus not letting the filler adhere correctly. i generally just use a tack cloth on the metal after grinding/sanding and then just smear the filler on. how much filler did you put on? just the door or all over the place? just my 2 cents
I Work At A Body Shop .just So You Dont Think Im Blowing Smoke. Theres A Couple Of Reasons Your Mud Wont Stick .1 Too Much Hardner . 2 If You Try To Speed The Drying Process With Heat Lamps Or A Heat Gun . And 3 (not Enough Grip) Try Using (50) Grit Like A Roloc Disc Or Grind It -lightly- Watch Your Heat With 36 Just My Thought. Oh And I Hope You Dont Use A Cheese Grador .you Cut It Down Faster .but In The Long Run You Use Way More Material.
There are several places where there is filler on this truck. This spot on the door is the only place it has come off, and it was wacked hard enough to put a dent in the door. My concern is I have filler work to do on a few other projects. If I'm screwing up, I want to change my evil ways before I have filler falling out of 3 or 4 rides instead of just one. Gene
well I do mudwork all day on custom stuff, so heres what I know from personal experience. If you want your mud to stick to bare metal and feather out nicely, you need to grind the **** out of the metal with 36 where the bondo will be thickest. 80 works, but isnt really enough. I use either a mudhog, or buffer with a 36 grit mudhog disc on it, or a DA on grind mode. Amount of hardener should not affect it as far as I know, I have mixed it 100,000 different ratios wether its hot or cold out or whatever and never had that affect adhesion, but if some one has then I am not gonna say its impossible. And you should really epoxy the panels first, because anymoisture under the bondo will rust the metal and make the bondo fall right off. The epoxy will protect the bare metal from any moisture. If you need advice on repairing that let me know.
OK, !) How much is too much hardener? I usually put a pile of filler on my board, and make an X across the pile of filler. Usually comes out a pretty consistant pink. 2) No heat lamps here. 3) I was wondering about the 80 grit being too smooth. 36 grit sound like a whole lot? Would a 50 be a good comprimise? 4) No chease grador here, just me and my air file, air grinder, and my da. An 80 grit sanding disc on an air grinder will cut too much off too fast to. Gene
What he said. I'd bet a month's pay (which isn't much here recently I'm afraid) that the degreaser left a residue. Even if you didn't mix it right (as "2 wheeler" said) it wouldn't fall out that eaisly. Of course what he said was right too. You should grind it with 24 grit, & if you need to wipe it with anything I would use laquer thinner or wax & grease remover (the kind for paint prep - follow the instructions about wiping it off before it dries) & a clean rag - no red shop rags even though they've been cleaned. It's also better if you epoxy prime bare metal before you apply filler. It will stick better & feather easier. BTW 30+ years building custom cars & doing repair work. Nothing wrong with using a cheese grater IMHO. And...I always make sure to sand each coat prior to applying more even though most folks say you don't have to. I've had panels that I repaired cave in when hit without so much as a crack. ~ Paul aka "Tha Driver" Giggle Cream - it makes dessert *funny*!
I too have a bodyshop and will agree with most of what has already been said. You should prep with 36 or 50 but it should of held with 80grt, also make sure you press really hard on your first coat and work it in this also gets rid of air pockets. after you sand and you need more filler you should make sure to get all of the sanding dust off and take a clean wire brush and sweep over the area. the wax and grease remover may have left a film and its not needed after you grind the area. I used to put all of my filler over epoxy but ppg does not recomend it anymore they say to go over properly prepared bare metal, I've never had a problem going over epoxy by the way. When you weld a seam you must make sure you clean the seam very well I usally sandblast it after it is ground smooth you should also seal the seam from the back if it is a lap weld or if you miged it by making lots of small spot welds. If the mud is mixed to hot it can have adheasion problems especially if you're trying to put that last little bit on as it begins to get stiff. One last suggestion , even though your shop was at 65 deg if the metal was cold and the weather damp moisture can form behind the filler and cause problems down the road..
Looking closer at the pic (I didn't check the full-size one before) it does seem that it broke too easily around the edges, indicating too much hardner (but I still don't think that's why it fell out). Too much will make it brittle. It's hard to describe how to mix it; how are you coming out near the end of a gallon? Running out of hardner? ~ Paul aka "Tha Driver" Giggle Cream - it makes dessert funny!
As far as measuring how much hardner. like most have said It depends on the weather and alot of things. a good rule of thumb at least I think .is for ever golf ball size of filler use 1 inch of hardner if the temp is between 70 and 80 .But your putty is much thinner so thats diffrent too.. yea I guess it is hard to explain the process .
Do your degreasing etc BEFORE you pick up the grinder. I usually stay with the same filler/hardener ratio unless the shop is really cold or extremely hot. If its too cold I warm the shop and go with my normal ratio...if its too hot I call in sick, go to the beach and say "F it all"...LoL Really though...I hardly ever increase the ratio as it just "kicks" too fast to be workable...you can add a LITTLE less in very hot conditions. Grind with a 36 disc beyond the repair area so you don't end up applying filler to areas that aren't grinded in order to blend your repair filler application...thus having poor adhesion to the edges. Make sure the metal is slightly warm...not even close to HOT. Don't heat it with extreme lamp application etc...but do warm it slightly with a lamp. Otherwise the cold metal will form condensation as the curing filler "kicks" and heats up. If you don't get poor adhesion from that NOW, you will get filler bubbling and rust from it later. It needs to be warm for an hour or so (depending on weather conditions naturally)...no sense trying to warm it 5 minutes before application. The metal needs to radiate a very slight amount of heat or it may be sweating from the heatlamp application itself. After the first coat of filler is filed, the possibility of moisture is not a problem as the remaining filler acts almost like insulation to the panel. Is it possible the repaired door is too flexible now (did it "oil-can" before you added the filler)...and the flex and movement in the skin as you repeatedly open and close the door is breaking the mechanical bond between the metal and the filler? I've had cheap *** insurance adjusters require a skin be "repaired" when it really shouldn't be. Result...a comeback due to cracks or separation...and on OUR coin many times.
BODY, TECH Bondo 101 (Magic dent erasing compound) Check the Tech Archive. It's a long read but I'm sure you'll find some useful info. If you don't see it in the archive go to the User CP (control panel) and change your settings to view all the archive. overspray
Thadriver: I'm usually running out of mud about the same time I'm running out of hardner. When I did the body work on my truck it sat inside my shop all of the time. I have gas forced hot air heat with the thermostat set at 65-68 all the time. I have a lot of new sheet metal in my shop and I do not have a condansation problem. It really is very dry inside there. The degreaser I used was from NAPA and was the degreaser/wax remover for repainting. I wiped down the truck with new paper shop towels after I was done sanding. It sat for several minutes (maybe as long as an hour) before the filling began, then I did not use it again. Between filler coats was wiped down with clean paper shop towels. After reading all of this, I suspect my problems were too fine of sanding grit to begin with and then not forcing the first layer into the steel. Hackerbill: The door(s) was in very good shape except of rust through on the bottom curved section. All the rust was cut out and new metal was welded in. The weld area is low and the filler was used to bring the weld seam back up to level. The original door skin was flanged and the new piece was welded on with the over lap pointing down so as not to hold moisture. After the filler work was done, the back side was sealed with seam sealer. The door is solid, there is no oil caning going on with either door. Overspray: I can't ever get anything out of the archives. Guess I'm not smart enough to figure it out. Thanks for all the help guys, I knew you would set me straight. Gene
http://www.jalopyjournal.com/forum/showthread.php?t=8318 There's a link for you, lots of good information in it!
Then you must be mixing about right, then. I'm more inclined to believe there are chemicals in those shop towels that caused the problem. Use rags that you know are clean like old towels or T-shirts. However, as I said I always grind metal with 24 grit & work the bondo in well, whether I'm using epoxy or not (but I try to always use epoxy on anything decent). As I also said I sometimes use laquer thinner to clean bare metal; that's if something happens like an air tool blowing out oil or something (I'm working with some old tools). ~ Paul aka "Tha Driver" If you can't take the heat, get out of the nuclear reactor.
The filler over an etch primer is allright but not absolutely the gospel ...I commonly sand bare and apply filler to sanded bare metal and it stays fine....Id bet the degreaser is the culprit-0 remember-just cause they sell a product doesn;t mean we need it.....
My vote is that the degreaser is at the root of the problem. And if you did'nt prep the steel with at least an 80 grit disk, I think that cobo is what caused the ultimate problem. With many degreasers, it is necessary to wipe the panel with at least two cloths. One is saturated with degreaser, the other is dry. Wipe down the panel with the saturated one followed with a thorough wiping with the dry one until the degreaser is completely evaporated. If you looked at a ground panel under a microscope, even 80 grit grinder marks would look like enormous mountain peaks with huge valleys in between. The degreaser would sit in these valleys and would be very hard to get out even with a thorough wiping. When the degreaser evaporated on it's own, if in fact it evaporated all the way before you applied filler, it would leave a residue on the steel. It sounds like the filler just sat on top of the steel without actually having a chance to gain any tooth. As stated earlier, it is usually not necessary to degrease a freshly ground panel. Avoid it if you can.
Well yeah duh after all we've done that for decades before they invented epoxy (not etching - don't put filler over any primer but epoxy) primer. It always held in fine - in fact the incident I referred to before (where the bondo was fine after an accident that caved in the panel) was before epoxy & applied to bare (grinded) metal. But when technology comes along (such as epoxy) that allows better adhesion, feathering, & corrosion resistance I think it's a good idea to use it. Bottom line; it had to be the degreaser or the rags or both, leaving a residue - for it to just fall out like that. ~ Paul aka "Tha Driver" America - made in China! :-(
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