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Thread: How long can I wait to paint after primer is sanded?

  1. #1
    Join Date
    Jan 2008
    Posts
    16

    Default How long can I wait to paint after primer is sanded?

    Hello, I am repairing a BC/CC hood. I have repaired the dent and sanded entire hood with 600 grit paper. Then sprayed k36 primer over repaired area. I am ready to block out the primer up to 600 but have heard that you really should not wait too long between final sanding and painting due to the primer "healing" itself.

    I plan on repainting this next week, I would love to get out in the shop and sand but will wait if I need too.

    Any advice would be great

  2. #2
    Join Date
    Nov 2006
    Posts
    1,590

    Default

    Iíve never heard of that. The one issue that may come up is dirt. If you sand it and let the car sit then dirt and dust can settle on the surface. This would be an issue if you let the car sit for months or if you set it aside and do a sanding job on another car. Other wise sand away and just do a good cleaning as always before you paint.

    Bob K

  3. #3
    Join Date
    Nov 2005
    Location
    lower Michigan
    Posts
    8,102

    Default

    I agree with Bob (as I usually do because he gives good advice). I've been painting for a living for a long time (40 years) and my experience is there really isn't a time frame for top coating primer. If the car is sitting in the garage (not out in the weather) then do whatever works out for you, sand it now, sand it later. It really don't matter. If the car is driven with the exposed primer the problems there are primer being porous will soak up whatever road crap lands on it and can cause problems later. The only other thing is that primer has no UV protection so the UV rays from the sun will deteriorate the primer over time (noticeable after a couple weeks and really noticeable after a couple months). That can cause adhesion problems later also.

    As far as the car sitting in your garage the only problem I can see from sanding it now and painting it later is that its open to contaminants from other sources (oil, silicone etc etc) that are normally used in most garages. If you sand it now then it would be a good idea to cover the car with a painters type plastic sheeting to keep any contaminants off the primer. Thats based on the fact that the primer has dried/cured for at least a couple days since being sprayed on the car. Thats also based on the premise that you shot 2K urethane high build primer. If you sprayed epoxy primer then its not a good idea to cover it for several days to possibly a week or more.

    Long story short - go ahead and sand the car now if you want and paint it next week, just be mindful of possible contaminants landing on the car in your shop/garage. Thats also based on the fact that the car will be in your garage til its painted.

  4. #4
    Join Date
    Nov 2005
    Posts
    27,566

    Default

    I'm with Bob, there should be no window of time unless you plan on spraying your color over unsanded epoxy primer and then you need to be within the time window. If it's a filler primer you should be able to sand anytime and spray anytime because the bond between the primer and paint is a mechanical bond and not a chemical bond. If you're using a brand name primer and paint you should be able to get technical information from the manufacture that gives you this information so it might be best to check it out because most of us only know the variables of the products we are accustom to using.

  5. #5
    Join Date
    Jan 2008
    Posts
    16

    Default Thanks


    Thanks for the help everyone...I'll get it sannded and then make sure it stays cleaner than a walmart chicken!

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