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How To Prep Aluminum For Paint

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  • Paul Alciatore
    replied
    Well, after a light sanding and cleaning, I cooked it for a couple of hours under the heat lamps. I used two 125W ones as one did not seem to be enough. This seemed to help harden the first two coats. Then I put on two fresh coats and left it under the heat lamps to dry. After 24 hours it was fairly hard but I left it for another day. Now, after about 48 hours it is DRY and hard enough that I can not scratch it with a finger nail. And there is no paint odor left.

    It would seem that the drying procedure is a lot more important than the preparation before painting it. I have no doubt that it is ready for assembly now. Even in the 95+ degree temperatures here in South Texas, the heat lamps do make a big difference. I am really surprised.

    And I guess I do not need to install an AC unit to dehumidify the storage shed. I still plan to install an exhaust fan: you can see my other thread about that. But I think I have a functional spray painting booth now.

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  • darryl
    replied
    Not about painting, but someone mentioned gluing- and sanding the aluminum using the glue as a 'lubricant'. Done that myself, and it does work well. Jb Weld can be very strong on aluminum and so can Goop, or ShooGoo.

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  • Paul Alciatore
    replied
    Well, I have some heat lamps and I am going to try them. 125 Watts were the smallest size I could find so I will try one of them first. I will first bake the present paint to try and harden it before I add more.

    If south Texas wasn't enough, it is going to get hot in that shed.

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  • wierdscience
    replied
    Originally posted by Paul Alciatore View Post
    I am concerned about the fact that it did not completely harden. Even today, as I was sanding it, I could see that it was still a bit tacky. A fingernail could scrape it off. At least the top coat, if not the primer. I suspect the high humidity here in South Texas is the problem: there are warnings about the humidity level on the can. But, I would have to wait for months for the humidity to be lower. Southeast Texas is like that. I have had other problems with paint drying properly in this area.

    So, I am wondering what I can do in that lawn shed to improve the drying situation. Two ideas have come to mind. First, I could install an inexpensive AC unit in the window of the lawn building. This would be used as a dehumidifier, not to cool the building. There is zero chance of actually cooling it in the summer sun here. But if it runs almost constantly it should do one heck of a job of drying the air in there. If that works, I would probably want to add some form of remote control so I can control it from the house. That way I could turn it on an hour or two before I plan to paint and turn it off the next day when the paint is properly dry, even if I can't get out there right away. So probably about $100 for the AC unit and another $100 or so for the remote control. I would give this option a good chance of working.
    I'm almost certain it's the humidity Paul.I usually let my stuff hang for 3-4 days before even thinking about moving it in the summer here.If it's something I have to have in a hurry for work,I will go down to the local automotive paint store and fork out for a quart of urethane and catalyst.
    A small window AC would probably do the trick,but might be an ignition source while spraying???

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  • wierdscience
    replied
    Originally posted by MattiJ View Post
    I doubt how much the humidity level has to do with drying speed. It's only problem if dew forms to the surface. (Blushing: http://www.paintproblems.com/general_problems.htm )
    Heat helps to speed up the process, but Texas should cover that. I have used propane BBQ for parts that fit in, "cook" the parts on lowest temperature for couple of hours and they are ready for assembly after cooling down.
    Actually,where Paul and I live,Southern US humidity does make a big difference in paint drying times.Our humidity ranges from 80+% in the Summer to 15% in the Winter.Winter time most brands of rattle can paint will dry to touch in 30 minutes or less,almost too fast,in the Summer it can take days.

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  • MattiJ
    replied
    I doubt how much the humidity level has to do with drying speed. It's only problem if dew forms to the surface. (Blushing: http://www.paintproblems.com/general_problems.htm )
    Heat helps to speed up the process, but Texas should cover that. I have used propane BBQ for parts that fit in, "cook" the parts on lowest temperature for couple of hours and they are ready for assembly after cooling down.

    Leave a comment:


  • Puckdropper
    replied
    I had some Rustoleum paint that took forever to dry. All the other colors dried just fine, but this particular one had trouble. I think it was green. My solution was to change to Krylon where possible.

    This is just an idea... They make oversized bags of desiccant for dehumidifying spaces. You could make a tent with the desiccant bag and your part inside and maybe it'd dry faster?

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  • epicfail48
    replied
    Im with Jim on this one, itll dry, it just takes a while if its humid. Ive had some Rustoleum enamel take the better part of a week to fully dry in my rather humid basement. Id say wait it out, an ac unit or dehumidifier in the shed seems like a little too much money to drop for relatively little reward. Heat lamps could work, but ive never had any luck trying to accelerate the drying or curing of any finish. Heat could also dry the outermost layer of the finish before the inner gooey bits have a chance to, which can cause some trouble with bubbles. Still though, the heat lamps would work, but youd have to be careful not to get them too hot.

    Id be more inclined to wait it out, unless youre on a deadline

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  • Jim Stewart
    replied
    Paul, my experience with Rustoleum in spray cans is that it will harden. Eventually. It can stay soft for weeks. Heat lamps will help a great deal, both reducing humidity and speeding the curing.

    I avoid Rustoleum for finish coats - seems to me the red and yellow primers are OK...

    -js

    Leave a comment:


  • Paul Alciatore
    replied
    OK, more adventure. I did paint it. First the Rustoleum self etching primer. Then two coats of the Rustoleum Metallic Gray Hammertone. I do all my spray painting in my lawn shed which has no AC and little ventilation. My wife gets migraines if she smells paint odors so I can't paint in the attached garage/shop. I let it dry overnight and started to assemble it. I noticed that the paint was still a bit tacky, but I just handled it carefully.

    When I tried to install the front panel switch assembly, I found that the rectangular cutout was too small and needed to be enlarged at the top and bottom. So back to cutting metal. When that was done, the front paint was messed up so now it needs to be resprayed.

    I am concerned about the fact that it did not completely harden. Even today, as I was sanding it, I could see that it was still a bit tacky. A fingernail could scrape it off. At least the top coat, if not the primer. I suspect the high humidity here in South Texas is the problem: there are warnings about the humidity level on the can. But, I would have to wait for months for the humidity to be lower. Southeast Texas is like that. I have had other problems with paint drying properly in this area.

    So, I am wondering what I can do in that lawn shed to improve the drying situation. Two ideas have come to mind. First, I could install an inexpensive AC unit in the window of the lawn building. This would be used as a dehumidifier, not to cool the building. There is zero chance of actually cooling it in the summer sun here. But if it runs almost constantly it should do one heck of a job of drying the air in there. If that works, I would probably want to add some form of remote control so I can control it from the house. That way I could turn it on an hour or two before I plan to paint and turn it off the next day when the paint is properly dry, even if I can't get out there right away. So probably about $100 for the AC unit and another $100 or so for the remote control. I would give this option a good chance of working.

    My other thought is heat lamps. Commercial painting facilities use heat lamps to bake the paint on so it seems it may help here. But I don't know if that would actually help to control the humidity. And how much wattage would I use? 50W, 100W, 200W, or even more. I am using a shelf in the building for the paint area. It is about 2 feet deep, 2 feet tall, and 6 feet wide. It is open in the front and one side, where I store the paint cans. The building itself is about 8 feet by 16 feet and has a sloped roof which is not insulated. I do not know if the walls are insulated, but would bet against it. It was built as a storage building, not a work area. There is no ventilation in the building but I am thinking about installing an exhaust fan in the outside wall behind that shelf to draw the paint odor and excess spray out. I would add a filter to that exhaust fan so it does not become clogged up with paint and so that the wall of the house that it would face also does not get any paint spray on it.

    Any comments about these two ideas or any additional ideas would be welcome.

    Oh, and yes, I did shake the cans well, VERY WELL.

    Leave a comment:


  • Paul Alciatore
    replied
    For the edification of all, the Alodine is apparently the same thing as the Bonderite recommended by Polaraligned in post #10.

    BTW, the job is not that well done. For instance, the 5/8" hole near the top-most corner in the photo is actually somewhat oval shaped and too big for the strain relief that goes there. I had to enlarge it even more and make a patch plate with the correct size hole. I had to make that plate twice as the first one also had a hole that was too large. I need to install that patch plate before painting. Live and learn.

    Yes, it is nice and shinny, but I just want it painted. I'm a glutton for punishment I guess. I will be looking at it and using it for the next 20 years. Oh, and it is not a power supply, it will house a contactor to control the power feed to my lathe. My drum switch is somewhat exposed to accidental activation and I want to be able to add some E-Stop switches at several locations on the bench. It allows external E-Stop switches to be added. It will sit on a shelf above the lathe headstock. I hope to get myself in the habit of using it start and stop the lathe and the drum switch just for direction control. We shall see.



    Originally posted by Joel View Post
    You are probably thinking of Alodine. My local automotive paint store stocks it at a reasonable price and a bottle lasts a very long time.

    Scotchbrite/sand/bead blast the item, clean it thoroughly right away, then wipe on the alodine. If it really needs to last, follow with zinc chromate primer or one of the newer substitutes.
    Last edited by Paul Alciatore; 07-17-2017, 01:54 PM.

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  • bob_s
    replied
    To etch the surface of aluminum parts for painting, I use household bleach. It works faster than lye.

    For simple flat surfaces, use Comet powdered cleanser w/ water; with orbital sander with flat rubber mat

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  • lakeside53
    replied
    Originally posted by Paul Alciatore View Post
    So, is there any real evidence that the oxide on an aluminum surface will actually prevent paint adhesion?
    Not really... the oxide is extremely well bonded well to the the surface and hard. Anodizing first (thick aluminum oxide) is a perfect way to get paint to stick.

    Aluminum oxide forms almost immediately the AL is exposed to oxygen and is protective for the base metal.

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  • epicfail48
    replied
    Wait, theres more than one grade of green? Ive only ever seen one... At any rate, the green that im talking about is the one they sell at loves with the sanding supplies, next to the grey and white pads.

    Leave a comment:


  • Mike Burch
    replied
    Originally posted by Paul Alciatore View Post
    So, is there any real evidence that the oxide on an aluminum surface will actually prevent paint adhesion?
    Without being dogmatic about this, Paul, I would think that painting the oxide means that one would then be relying on the paint's sticking to the oxide AND on the oxide's sticking to the aluminium.

    Painting directly on the aluminium, on the other hand, would seem to halve the possible failure modes.

    As far as I know, primers for aluminium are designed to go on aluminium, and are not designed to go on the oxide. My understanding of the situation is that any paint job on aluminium must exclude atmospheric oxygen to prevent that irritatingly active metal from forming its oxide layer again. I may, of course, be completely wrong, but the foregoing makes sense to me.

    Leave a comment:

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