Why Wont My Filler Stick - Page 2
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  1. #21
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    bad casting you can blow air in one hole and see coolant oozing out of the surface many inches away. or pressure test and find air leaking through 2" of solid casting iron
    .
    if you must clean soaked in oil usually you bake it out in a oven, basically boiling the oil off. if soaked in hot caustic you might find caustic oozing out of the metal for a long time.

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  3. #22
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    We have great results painting old machine tools. Most, saturated with cutting oil for 50+ years.

    Media blast to remove all trace of paint and old fillers. Use an angle grinder with a 60 grit disc to smooth and remove casting flash. If necessary can selectively heat with a rose bud to burn out oil. Flush with lacquer thinner. Top to bottom until no trace of residue. Takes several gallons. Fill with a premium body filler. Block sand flat. Lay down 3 light coats of Polane, self-etching primer. Lightly block sand dry with 320. Finally, lay down 3 wet coats of Polane B. Use a retarder so paint will wet-out with minimal orange peal. Will yield a high gloss automotive finish. Can pound the snot out of it with a dead blow hammer with no damage.

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  5. #23
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    I had the same thing happen to me about 20 years ago on my bridgeport. I used some filler that a guy at work said was the greatest. He is a car body guy, i certainly am not. I did about what what the opy did but less cleaning and the stuff came off and drove me crazy. In the end I said screw it and just painted the iron. The paint stuck to it fine. I went back into work and he and my boss (both had done a lot of car body work) asked if I primed it first? I said no. And they acted like i was the idiot. So in hind site I always figured it was probably because I should have primed the iron before filling. Maybe you guys know if this is true? So, maybe prime it first then fill.

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    If filler wont stick, neither will primer. In professional paint work substraight preparation is everything. Sadly, most feedback is from hack hobbyists that refuse to sweat the details then bemoan lousy results.

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    I would like to say that I did a lot of reading on this website as to the proper process. The problem comes that no one can agree on what is right. Just like in this forum at leave 10 people have given a different process. I am not trying to cut corners and have spent a lot of time on this. If I can't use a wire wheel. What do I use. A grinding wheel would just clog with bondo. We are all learning no need to call me lazy.

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    By the way -- keep ANY silicone products far away from the areas you want to paint. Silicone contamination will result in "fish-eyes" in your paint. If you ever use automotive wax on anything, lottsa luck painting it later.

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    RE "The problem comes that no one can agree on what is right."

    No. The problem is inexperienced hacks seeing virtual, self verification posting non sense. Here and elsewhere. To filter out the fools, ask to inspect their work. My doors are always open. Have several high-end rebuilds in process at any one time. Can also show you machines we use near daily that were done over 20 years ago. If you're struggling to make filler stick, try working with Moglice.

  10. #28
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    Quote Originally Posted by mvernon View Post
    I would like to say that I did a lot of reading on this website as to the proper process. The problem comes that no one can agree on what is right. Just like in this forum at leave 10 people have given a different process. I am not trying to cut corners and have spent a lot of time on this. If I can't use a wire wheel. What do I use. A grinding wheel would just clog with bondo. We are all learning no need to call me lazy.
    This website isnt the best when it comes to painting imo.
    Its on you ultimately to find the issue, take what anyone says (including me) as a hint, youre the man on site with the job in front of him. Spend some time on here and you might find that super duper self praising 'experts' aint as great as theyd like you to think they are when rubber hits road.

    Likely the problem is oil, it could also be a residue left by something youve used on it (purple power etc) that your preclean wont remove. If theres still doubt you can test your process on a small area and go by your results. In short, body filler should have no problem sticking to bright metal thats been blown off with an airline.

    If I had the task it would probably go something like this:-
    1)Check a problem area with a torch, if oil starts to sweat straight away youll want to chase it out.
    2)Mechanically scuff up the surface dry production paper 80-120 grit / flexi sanding discs on an angle grinder/ scotchbrite green etc etc etc. Wirewheel is fine on bare cast for your situation. Theres no real need to remove old filler / paint if its sound and stable (doesnt soften with the solvent in your paint)
    3)Preclean with a precleaner instead of thinner or acetone, its cheap, not as aggressive and designed for the job. Work it with a brush on rough CI, wipe on wipe off anything else, either case wipe off before it drys.
    4)If you really feel the need to use bondo then nows the time to put it on.
    5)Shape it up and sand it out dry going no finer than 180 grit.
    6)Prime / paint or just paint depending on what youre using. A commercial line 2K sticks like shit to just about everything apart from oil.

    When I painted my lathe, I wire wheeled and scuffed it, wiped it down, first coat of 2K on with a brush (for a change), knocked off the tops with 180 dry next day, second coat on and job done. No primer no bondo etc, its a machine tool not a Bentley.
    I did it that way because I know what I can get away with having 15 years in car body.

    Keep ya chin up an good luck

    Edit:-
    Theres no such thing as the 'right way'

    img_20190723_111518.jpg

  11. #29
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    the whole idea of priming (especially if the primer is the iron etching type) is to apply it before anything else (after the iron has been degreased of course), only then one should apply epoxy or polyester filler, epoxy and polyester have only mechanical bond to the iron, so surface texture and no oils is what lets it hold on to the surface, etching primers on top of mechanical also bond chemically to the iron - so it holds on to the substrate a lot better, appropriate primers then may provide the chemical bond for the fillers or any subsequent process

    using filler on bare iron is the cheap way out, factories don't do it because it isn't strictly necessary, but if you're doing this for yourself, then skipping that makes no sense

    thermite already touched on to this when he told about using naval jelly and watching how it transforms the surface, it is phosphoric acid that does the etching (on top of converting any flash rust that might be there), and iron phosphate then serves as the primer for following prep work

    one more note - the first, etching primer you put on the bare metal also serves the purpose of being an indicator to stop sanding the filler, ideally you wouldn't want to expose the fresh iron any more

    in the OP case, the main problem was probably the surface left by the wire wheel - it is way too smooth for a filler to stick, 32-60 grit sand paper (dry) should be the last step if you go this route (after using wire wheel to get the majority of the old stuff off), the texture it leaves is what the filler is going to hold on to, and watch oil from the air tools getting on the surface if you're using air tools, after the sanding - wipe with acetone, don't need to be extremely thorough, the primer or filler is mostly glue, it will capture minute dust if there was left any on the surface and adhere to substrate, use brush or roller to help with this, switch to air spray after all the filler work has been done, but proper rollers (satin) can get you a very good, smooth and glossy finish without the mess associated with spray guns

    edit: about sanding grits, this is what I used when was younger and fiddled with cars
    1) use dry 60-80 to shape the initial applications of filler
    2) dry 120 for finish the filler work
    3) then 2k primer with air spray gun, thick coat, it should fill all the scratches left by previous sanding
    4) spray a very light mist of contrast color to help with wet sanding the primer (800 wet)
    5) repeat 3&4 till the contrast can be sanded out without going through the 2k coat
    now you're ready for base/clear, or any other glossy paint

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    Would water sand blast be a viable option instead of wire wheel and sand. Seems like it would get into all the tight areas that would be hard to clean. My concern would be how to protect the ways and machined surfaces. Would a thick tape like gorilla tape work. I would think it would stand up fine to indirect contact. The blasting should leave a clean and ideal surface for epoxy.

  13. #31
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    it is phosphoric acid that does the etching (on top of converting any flash rust that might be there), and iron phosphate then serves as the primer for following prep work

    in the OP case, the main problem was probably the surface left by the wire wheel -


    After Blast is designed to clean, degrease and etch freshly blasted or sanded metal prior to painting or powder coating. Use with a plastic spray bottle to liberally apply to the part, wipe and reapply until all contaminants are removed. The blend of aqueous cleaners and phosphoric acid properly cleans, etches the metal and leaves a zinc phosphate coating that is excellent for paint, primer or powder adhesion. Also protects the metal from flash corrosion for extended periods.


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