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Metal Prep Question

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  • Metal Prep Question

    Quick question on metal prep/preservation. I am going to be starting on multiple pieces (tins, tanks, rims, parts) that are eventually going to be painted. My hope is to hang and paint them all at the same time when ready for paint. I have purchased an etching primer that I will use on everything. Since I am a one man show, prepping all this for paint will take a while, so are there any tips or guidance on how to manage this to prevent rust from building back up? If I have to spend days or weeks prepping parts, how can I keep them from rusting without having to spend more time cleaning it up when ready for paint? Is there a protectant I can use after the metal is ready? If so, do I then have to remove it before priming? Or should I only prep what I can in a day and prime the same day?

    Any tips are appreciated. Thanks!

  • #2
    There's a lot unanswered or implied in your question.

    First, what are you doing for preparation? This can mean anything from sanding old paint to media blasting to chemicals.

    Second, what is the material? All steel, some alloys, some mystery metal?

    Third, what's your work environment? How much space, how long can you leave parts to dry, etc. is it dry or humid. Dry means less than 40 percent humidity year round 24/7.

    Fourth, are you doing repairs to parts? If yes, how. Body filler?

    Fifth, match your primer to your paint system. Etching primer is a generic term. You need to know what type of primer and whether it will be compatible. For example, if you shoot many urethane paints over many phosphor base self etch primers it will craze pretty rapidly.

    generally, in a dry environment using dry air, you can media blast most mild steels and have a few days to a couple of weeks before surface rust is an issue. It will start instantly, but won't necessarily cause a bond issue. The easiest way to deal with that is to use a two part epoxy primer. About 90 percent of epoxy primers can be sprayed over panels that were left bare for a bit. N, they can't go over big splotches of surface rust, but they can handle prep that isn't microscopic. It was not unusual to see cars in bare metal for weeks as body techs blocked filler. In a dry shop, the talc dust left on the panels did most of the work of absorbing moisture. Blow off the dust, wipe the panel, and tack it off.

    Keep in mind your primer is your foundation. cheap primer gives cheap results. You can cover good primer with cheap paint, but the opposite rarely works well.

    In terms of protectants for bare steel, yes several exist. They range from ospho which is a general phosphoric acid converter which works for lacquer based primers to various waterborne washes that Ward rust off and are supposed to be fine with polyester sprayable filler. But, again, you have to make sure this stuff is compatible with your primer and your paint. Don't buy some cat on the internet saying it's fine. Almost all professional painters stay in a family of products for a reason. Most amateur issues are from mix and match to save money.

    In other words, you can use products to protect before priming, but your results may be a bigger pita. Easier to plan and keep dry.

    Also, it can be difficult to have enough room. I find it takes about four hundred square feet to hang and prime a whole bike, including chassis, and still have enough room to move and not be constantly shooting overspray on other parts. Sometimes, batches are your friend.

    ps this makes it sound hard, it's not. Just keep asking questions and it will become clear very fast.


    • #3
      I use Kirker DTM Acid Etch Wash after blasting. It is compatable with the Kirker epoxy primer I’m using. I’ve had blasted parts for at least a month, and we have been having really high humidity, so far the parts haven’t shown any signs of rust. I am a believer in using all paint products from the same manufacturer. I would recommend you check with your paint manufacturer for a similar product, also check the “Technical Data Sheet” for their recommended procedure.


      • #4
        Thanks chuckthebeatertruck for the tips. They are all good. Majority is all metal parts either being blasted or sanded. I live in Texas, so there is a bit of humidity. I'd have to wait for a cold front to pass to get a really low humidity day. But, I do have a climate controlled shop area that has controlled humidity which I keep right at 45%, so parts can be stored there until painted. I guess if I had a lot of parts, I could bring it down some, but then it gets too dry to even be working in there.

        I bought the paints a while back. PPG epoxy primer, a 2K high build primer to use where needed, and PPG DCC Acrylic Urethane. That is what was suggested to me a while back when the CAIMAG forum was still running (the PPG line, that is). What kind of shelf life does this stuff have if unopened?

        I think I will do this in batches. Since I am working on two at the same time, I'll just do the frames and forks together, fenders together, so on and so on to keep from having too much to do all at once.