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Surface Rust Pitting

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  1. Martin

    Martin Member

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    Post blasting, I have lots of little areas of rust pitting that got uncovered. So whats the best practice on fixing these types of spots? Cuda.jpg
     
  2. Steve340

    Steve340 Well-Known Member

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    Etch prime and use a little filler if they are not to deep?
    Whatever you do get some etch on there ASAP to seal the metal. You can then use filler over primer if you use the correct etch primer.
     
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  3. Martin

    Martin Member

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    That is the primer. PPG gray! Too much light in the picture. Those were my thoughts on the matter, so thanks.
     
  4. moparleo

    moparleo Well-Known Member

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    What area of the car are you working on ?
     
  5. Adam

    Adam Well-Known Member

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    As Steve340 noted you can use filler over some etch primers, but if you get it wrong the filler will soften. If unsure topcoat the etch with primer/sealer. If you have topcoated the pits with epoxy it will be fine as alone as the metal was clean.
     
  6. budascuda

    budascuda Well-Known Member

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    Hey Adam, could you please say a little more on the filler softening over the wrong etch primer,.
    I use the Sem metal etch,. Does getting it wrong have to do with the type of etch or the way it applied?
    Thanks.
     
  7. Adam

    Adam Well-Known Member

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    I like SEM products and have never had a problem with them. I have used several different brands and I remember reading the directions that it may cause “softening” of body filler. However, a quick search and I found the following on Sherwin-Williams website:

    Etch Primer Selection and Protection

    The purpose of an etch primer is to provide rust and corrosion protection to the bare body of your vehicle.

    Seems simple enough, right?

    Well before you start applying any paint products, it is important to know whether you need to apply body filler to improve any imperfections. If that answer is yes, then nine times out of ten you will want to apply the body filler prior to using an etch primer. Many body fillers will not adhere to etch primers.

    After the body filler application and necessary sanding is complete (or if it wasn’t needed to start with) you can begin applying an etch primer.

    Etch primers (or sometimes referred to as wash primers) use a phosphoric acid to attach zinc to a bare metal substrate. The zinc within the coating provides a protective and sacrificial layer to moisture. Without the protective layer, moisture would penetrate into the bare metal and cause corrosion and rust. But with the etch primer, there is a barrier that will absorb the moisture and prevent damages.

    In most circumstances a primer surfacer or sealer will be applied directly over the etch primer prior to a color topcoat.

    We also have direct to metal (DTM) urethane and epoxy primers to choose from. DTM primers provide excellent adhesion to the properly prepared bare metal and can be directly topcoated.

    Regardless if you choose to use an etch primer and then a sealer, or go straight to a DTM primer, proper surface preparation and film thickness must be met to ensure your vehicle has the protection it needs.

    When you get to point where you are making paint purchase decisions, make sure to ALWAYS request the product data sheet. This easy to follow form will give you the instructions necessary to be successful!
     
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  8. Adam

    Adam Well-Known Member

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    SEM’s etching primer directions state that it can cause paint “lifting” if applied too thick, or top coated too soon. It doesn’t specify about fillers, but why chance it when you can shoot a sealer over it.

    I like sealers anyway, just to get one color under the top coat. Often times the car will have several different color patches of primer or original paint showing after the bodywork is done, and the primer color does effect the appearance of the color coat.

    I use Transtar Speed Sealer. No mixing and lays down smooth with minimal texture or overspray.
     
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  9. budascuda

    budascuda Well-Known Member

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    Thanks Adam, as always, excellent advice.

    I did get a chance to apply a coat of (SEM) etch primer on an old quarter panel with body filler patches on it and it seemed as if the feathered edges of the body filler were dis-coloring. It might be the age of the filler or it's quality grade, I don't know what was used originally.
    I will have to check it in a couple days to see if the edges will lift or what happens.

    In the past when I used SEM's , i always treated the metal first, rubbed it lightly with a Scotch pad ( to remove residues and loose particles) and then applied the body filler , my reasoning was that the body filler will have a more porous surface to adhere to. I never had any problems but it seems I might have to put that practice in the not to do list.

    Thanks again!