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Thread: Sanding Sag from BM Super Spec P22

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  1. #1
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    Apr 2022
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    Default Sanding Sag from BM Super Spec P22

    Hi guys,

    First post - I am a painting rookie here. I have learned quite a bit from this forum already including gun adjustments, basics of body work, and the value of a stainless steel cafeteria tub to assist with clean-up. I am working on repainting a piece of machinery, and I am using BM Super Spec Urethane Alkyd Enamel (P22). I reduced it by 10% with mineral spirits to get it to go through the gun (Iwata LPH50 1.0mm fluid tip). I use the touch up gun because there are several hard to reach places.

    I painted the last Sunday and the job turned out good, however I have one vertical spot that developed a small sag. I was reading on this forum that enamel should be dry before attempting to sand. I went out there last night, and the paint is not longer tacky and is however it is still a little soft. I was able to dent the sag with a finger nail. The TDS shows a pretty cure time of 2 weeks. My question is can I sand it now or is it still to wet?

    The machinery is a temperature controlled room, and it is set 75 degrees F. Thanks for any feedback it is very much appreciated.

    Patrick

  2. #2
    Join Date
    Nov 2005
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    Quote Originally Posted by Patrick_ View Post
    Hi guys,

    First post - I am a painting rookie here. I have learned quite a bit from this forum already including gun adjustments, basics of body work, and the value of a stainless steel cafeteria tub to assist with clean-up. I am working on repainting a piece of machinery, and I am using BM Super Spec Urethane Alkyd Enamel (P22). I reduced it by 10% with mineral spirits to get it to go through the gun (Iwata LPH50 1.0mm fluid tip). I use the touch up gun because there are several hard to reach places.

    I painted the last Sunday and the job turned out good, however I have one vertical spot that developed a small sag. I was reading on this forum that enamel should be dry before attempting to sand. I went out there last night, and the paint is not longer tacky and is however it is still a little soft. I was able to dent the sag with a finger nail. The TDS shows a pretty cure time of 2 weeks. My question is can I sand it now or is it still to wet?

    The machinery is a temperature controlled room, and it is set 75 degrees F. Thanks for any feedback it is very much appreciated.

    Patrick
    If there is NO HARDENER added then you should wait the recommended amount of time before sanding. Even after waiting non-hardened enamel stays somewhat soft and should be wet sanded using 1500 grit or finer.

    Are you planning or repainting that area or sanding and polishing?

  3. #3
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    Apr 2022
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    Quote Originally Posted by Len View Post
    If there is NO HARDENER added then you should wait the recommended amount of time before sanding. Even after waiting non-hardened enamel stays somewhat soft and should be wet sanded using 1500 grit or finer.

    Are you planning or repainting that area or sanding and polishing?
    Hi Len, I didn’t use any hardener. The TDS has no information about sanding, however I did call the BM tech line and they said I could sand it a couple days after spraying. I was hesitant because of what I read about enamel.

    I was planning to respray after sanding because the phone tech said that it would not polish like a traditional auto body enamel. Also, they said that wet sanding would compromise the paint integrity. If I am planning to respray do you think it is still to early to sand?
    Last edited by Patrick_; 04-23-2022 at 05:36 PM.

  4. #4
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    Nov 2005
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    Quote Originally Posted by Patrick_ View Post
    Hi Len, I didnít use any hardener. The TDS has no information about sanding, however I did call the BM tech line and they said I could sand it a couple days after spraying. I was hesitant because of what I read about enamel.

    I was planning to respray after sanding because the phone tech said that it would not polish like a traditional auto body enamel. Also, they said that wet sanding would compromise the paint integrity. If I am planning to respray do you think it is still to early to sand?
    If the work has been kept warm you may be able to sand now but then wet sanding prior to spraying would not be as good as dry sanding. I'd probably dry sand with some 800 or finer then allow it to sit for a day or two before repainting.

  5. #5
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    Apr 2022
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    Quote Originally Posted by Len View Post
    If the work has been kept warm you may be able to sand now but then wet sanding prior to spraying would not be as good as dry sanding. I'd probably dry sand with some 800 or finer then allow it to sit for a day or two before repainting.
    Got it. I will give it a go and report back how it went. One last question, because the machine is a large cast iron mass, I will have to blend the spots I am touching up. When it dries will it be obvious where the wet edge transfers to the dry edge, or should it lay down flat and not be noticeable?

    Thanks again for all the help.

  6. #6
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    Nov 2005
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    Quote Originally Posted by Patrick_ View Post
    Got it. I will give it a go and report back how it went. One last question, because the machine is a large cast iron mass, I will have to blend the spots I am touching up. When it dries will it be obvious where the wet edge transfers to the dry edge, or should it lay down flat and not be noticeable?

    Thanks again for all the help.
    Because a hardener was not used the chance of a bad reaction is possible. When blending over a hardened paint I would normally recommend applying the paint then over-reducing the paint to blend the edge of the spot then spraying a little straight reducer to melt the dry edge into the existing paint. However with fresh, non-catalyzed paint as your foundation your chances of causing the existing paint to wrinkle are much greater.

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