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Thread: Bare Metal Prepping/Cleaning for Primer

  1. #1

    Bare Metal Prepping/Cleaning for Primer

    Some common mistakes I've seen people make is not prepping bare metal properly for good primer adhesion. Keep in mind epoxy and DTM type primers need the metal to have some texture and it also needs to be perfectly clean. The perfect texture is achieved by sandblasting or sanding with 80 grit on a DA, some fiber discs like 3M's Clean-n-strip discs also work well. Failure to texture the metal and clean it well can lead to less than adequate adhesion. Blasting jambs and similar areas is usually no problem but outer sheetmetal should be left to a professional to avoid warpage-(Shine should do a thread on blasting techniques). Hand held gravity fed spot blasters are an economical way for anyone to clean small areas-they work well. When sanding change your paper often so it produces a sharp scratch pattern and not a shiny polished surface.

    Clean the bare metal with solvent based wax and grease remover then follow that with waterborne wax and grease remover-spray the cleaner on and wipe it off while it's wet, or you can pour the cleaner on one towel then wipe it on and wipe it off with a clean towel. Why two cleaners?-they each offer their own benefits. Should sandblasted metal be cleaned-definitely and especially if you recycled your sand. I've seen primer fall off of sandblasted steel when the person didn't clean it before priming. You'll end up with some towel fuzzies on a blasted surface as the texture grabs the fibers-no big deal just give it a light scuff with a red scotchbrite and a blast with the blow gun and they are gone and they need to be gone!

    Simple Green, 409, Dawn dish soap, Ajax, Fast Orange, Engine Degreaser????-- these can all be handy during the precleaning stages of a job but you shouldn't be cleaning your bare metal with them for the final clean before primer.

    Will a wire wheel work for texturing the metal-No they mostly provide a polished or burnished surface, they do work well for rust removal though.

    Will an acid etched surface provide enough adhesion? No, if you use acid make sure to neutralize it well and then mechanically texture the surface with sanding or blasting. Acid works great for rust removal but needs to be completely removed for any primer application.

    Safety concerns? you need to understand the safety concerns for all autobody products and tools-every one is dangerous in one way or another.

    Feel free to add or modify as needed.
    Last edited by crashtech; 03-05-2011 at 03:56 PM.

  2. #2
    Oldtimer
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    Bob,

    Thanks for the tip about using a red scotchbrite and a blow gun to get rid of those darn fuzzies!

  3. #3
    Paint Fanatic
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    Bob,
    That was just perfect, thanks.

    I have a lot of shops that do clean the metal with 710 first and then the 700, like you say, that is the perfect way, perhaps when I talk to people I should stress this way but I have tended to neglect mentioning the two steps and really should offer that advice more.
    Barry@kives.net
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  4. #4
    Member cjetmech's Avatar
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    This is where I'm at right now. The car is 80% blasted and I've been thinking about the prep before primer. I was going to blow off all the sand that I could with a blow gun, wash the car with warm water, Dawn soap and a red scotchbrite pad, and then follow with waterborne w/g. Thanks for the info, now I'll hit it with solvent based w/g also. What type of towels should be used?

  5. #5
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    Cjetmech,

    Whatever you do, DO NOT wash sand blasted metal with water. It will rust in seconds!

  6. #6
    Oldtimer Senile Old Fart's Avatar
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    I use my electric weed blower to dry the car with, never thought about using to to defuzz it before primer! ( is defuzz a word,lol)

  7. #7
    Quote Originally Posted by cjetmech View Post
    This is where I'm at right now. The car is 80% blasted and I've been thinking about the prep before primer. I was going to blow off all the sand that I could with a blow gun, wash the car with warm water, Dawn soap and a red scotchbrite pad, and then follow with waterborne w/g. Thanks for the info, now I'll hit it with solvent based w/g also. What type of towels should be used?
    Any nonprinted towels, your basic kitchen style paper towel will work, or you can spend some money on lint free type towels designed for prepaint cleaning. The cheaper towels will leave fibers that you'll have to deal with. I've seen people have fisheye problems using printed paper towels.

  8. #8
    Member cjetmech's Avatar
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    Thanks bob. Whats the general opinion on washing with soap and warm water? I've heard others like shine say its no big deal. I was going to knock off any flash rust with a scuff pad when I go over it with w/g.

  9. #9
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    I was thinking that if you do wash with soap and water, a gallon-jug or two of distilled water from the store might be in order. Tap-water has so many 'chlorides' in it its closer to seawater than anything else. I'm exageratting obviously, but you get my drift, it's isn't just the oxygen in the air that creates rust, but also the salt or chlorides in the water used, which are plenty in tap-water.

    In the power-plant business, water isn't the enemy of iron, but any kind of salt is, in a big way...

  10. #10
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    In my garage I like the "Box of rags" you get at Lowes or Home Depot. They are real heavy paper type towels in a box of about 250 I think, and cost about $10. I use them for everything. They are great for use with W&G remover and even washing the car. Cheap enough that you just throw them away. Usually once I put one down it is going in the trash. Only way I can make sure I don't wipe the wrong thing on a car or me.

    Aaron

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