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Does "direct to metal" paint mean no primer?

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  • Does "direct to metal" paint mean no primer?

    I will be painting my milling machine soon. Right now I am exploring paint options. I see some paint says it is direct to metal but there is also a listed primer to go with it. Does it mean you need the primer or is direct to metal paint ok to use without it. FWIW the paint I am talking about is Rustoleum 7400 industrial. Thanks.

  • #2
    After researching this, I painted some machines with Rustoliem
    using good surface prep and no primer. Many years later I am
    still happy with the adhesion. I am sold on Rustoliem oil based
    paint and hope they never change it.
    After cleaning, be sure and use phosphoric acid as a metal etch.
    This really helps adhesion.



    • #3
      DTM can be put on without a primer but you will generally get better results if you use one. I've done it both ways - it depends on the existing surface etc. if you've ground it back to bare metal paint away. If there are remnants of old paint, filler etc, prime it first. From the 7400 series technical data : "If abrasive blasting cleaning is used, then two coats of recommended primer is required. See the primer Technical Data Sheet for more information" and "If desired, the 7400 System DTM 450 VOC Alkyd Enamels can be applied direct-to-metal (DTM), however optimal corrosion protection is achieved when the finish coat is used in conjunction with one of the recommended primers". If you want a custom color, they only offer full gloss bases.

      The DTM I use is Benjamin Moore "Super Spec D.T.M.", but I HATE the water based version - oil alyd only. I don't like full gloss; the BM product has many sheens available in their tintable bases; all are rated for exterior use. I use P24 (semi-gloss).
      Last edited by lakeside53; 01-13-2014, 12:14 AM.


      • #4
        I used one of those Rustoleum "paint & primer in one" paints for a project, actually refurbing a crank ice cream maker. Wanted an off-white.

        The paint was crap, blew chunks and looked like sawdust in the paint... So I removed it for re-painting with decent paint.

        It was REALLY easy to remove the paint, it jumped off the surface. But the surface had been cleaned and had had a phosphoric treatment.

        I was NOT impressed, and will not try one of those paints again.

        Keep eye on ball.
        Hashim Khan


        • #5
          Originally posted by oxford View Post
          I will be painting my milling machine soon. Right now I am exploring paint options. I see some paint says it is direct to metal but there is also a listed primer to go with it. Does it mean you need the primer or is direct to metal paint ok to use without it. FWIW the paint I am talking about is Rustoleum 7400 industrial. Thanks.
          From the research that I have done, there seems to be a general consenus that it's better to not use a primer on cast iron as the paint tends not to flake or chip off that way. I expect sheet steel would need a primer though. I'm creeping up on a pile of painting with a little mill and lathe completely torn apart at the moment, and will be watching this thread for any useful info.


          • #6
            The primary purpose of a primer is to fill and level the surface and provide for an even color so as to have a uniform final color without "shadowing", most primers adhere little better than most paints, that's not what they are meant for. The exceptions to this are the specialty self etching/self adhering primers which have a mild acid (usually Phosphoric acid in the case of self etching) content so as to etch the metal and provide a "grip", the paint can then stick to the primer and overall adhesion is greatly improved. Almost all modern automotive primers, with the exception of lacquer primer, is of an adhering type while most general purpose types are not and they provide almost no improvement in adhesion.
            Last edited by radkins; 01-13-2014, 09:55 AM.


            • #7
              OK addendum to my previous post...
              I used Rustoliem from the quart.gallon.
              I brushed it in between the bed ways of my lathe
              and sprayed the rest of the machine with the paint
              in the spray gun (air compressor). It is thick so a
              pressure cup helps a lot, (even thinned 10%).
              I have also heard that Rustoliem in the spray cans
              is not the same these days as in the quart/gallon.
              I think it has some to do with the ****ty spray tips
              that they invented to "improve" things. I use the
              old style tips when I use rattle cans. I store them
              when not in use in a jar of lacquer thinner to keep
              them clean. I also heat the rattle cans with a
              100watt light bulb till almost too hot to hold.
              This prevents the spits and spatters that most
              people have problems with when they use Rustoliem
              in the spray can. But spraying with the spray gun
              works well, if you pressurize the cup to 5psi and use
              the big primer tip in the gun. With a regular siphon
              feed gun, you have to jack the pressure too high and
              the overspray becomes too much. If you use a brush,
              go to the artist's supply store and get a soft, fine
              polyester, paint brush. One that almost feels like a
              makeup brush against your skin. They hold paint
              well and lay it soo smooth with no brush strokes.
              Oh, use xylene to thin Rustoilem. It seems to work
              the best. It is an ingredient, read the can.
              Hopefully you read this and get better results using
              Rustoliem paint. Lots of products get a bad rap
              from users that don't know exactly what they are doing.
              Painting something and doing a good job is a little bit
              more difficult than eating a hamburger. Not everyone
              has the patience to control all the variables. Most
              people say, "Fuk it", to every little small detail thinking
              it will not matter. And then whey wonder why "the paint"
              does not do a good job. Well hello? Did you follow the
              instructions?? Happy painting.



              • #8
                As much as I would like to I don't think I will be able to spray this job, at least not the big parts. I was actually thinking about using a roller for most of the base and knee and a brush for areas I can't get with a roller. It looks like they are flat enough to cover most of it with the roller. Any comments on using a roller? I was thinking a fine nap 3" trim roller. Even if the texture from the roller didn't flow all the way out I think it would look better than brush marks that didn't flow out.


                • #9
                  I have had pretty good success with using "Linzer" rollers, 4" wide and 6" wide (maybe others as well) really small diameter, I recognize them by the blue helix running around the roller. These are a woven product and that is a large part of the reason I like them, so few, if any, issues with hair/lint/nap/bristles in the paint.
                  Now I did not use them for painting any of my machinery (I used a good brush) but I also like them because they are such a small diameter, just the feel and seem to be very easy to maneuver that to mean you can go fast and get as much done as with a typical wider roller. You do have to get a bit used to the end of the roller holding paint (the surface wraps around and is not cut off square) and so be very, very careful next to the adjacent wall/corner say but normally I cut that in first with a brush anyway...


                  • #10
                    I painted a steel door with oil paint and a foam roller.
                    It turned out great.



                    • #11
                      I have been paying more attention to what product I use for a last wipe down. I used to use whatever solvent was close at hand-mineral spirits/lacquer thinner/acetone. I have had better luck recently with water based products like Marine Clean from the POR company. Even hot (dish) soapy water. Often, I squirt some detergent on a Scotchbrite pad and scrub away with hot water. I've never had good luck with DTM waterborne acrylic without primer. Jay


                      • #12
                        Anything waterborne that goes direct to metal makes me think it is rusting the surface.
                        I had a paint man tell me even though he uses waterborne paint, that he uses a
                        solvent based primer to avoid rusting. I am not saying I don't believe what the
                        can you are using says, just seems illogical to me.



                        • #13
                          I think I will be using a primer, I don't know if all of the old filler will be off and I may add some new if it looks real bad.