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Thread: Spraying wet mil, dry mil drying time

  1. #1

    Spraying wet mil, dry mil drying time

    Looking for a little confirmation that I'm on the right track.

    I bought some ML Campbell aqualente. Here is the product information sheet.
    http://www.paintdocs.com/docs/webPDF...7318706&lang=2

    First question:
    Application film thickness is 3-4 wet mils. I have a wet mil gauge so I can check that I'm applying it about that thickness. Percent Solids is 32 to 35% so I assume the rest is "solvent" that evaporates off and dry mil thickness will be a little over 1 mil if I spray between 3-4 wet mils. (Yeah, I probably won't be that accurate, but it gives me something to strive for)

    dry film thickness is a minimum of 2.5 mils and a maximum of 5 mils. If I do this correctly I should plan on 3-4 coats?

    Second Question:
    The time for sanding dry is 30-45 minutes at the specified temp. Stacking dry time is 4-6 hours. The doc says not to apply the second or third coat until the previous coat is completely dry. Is "completely dry" the sanding dry time of 30-45 minutes or the stacking dry time of 4-6 hours? I'd like to apply the 3 coats all today if possible but I don't want to push it and have to do it all over again....

    The product was tinted a dark blue so I'm trying to be extra careful as dark colors seem to be less forgiving then just spraying clears. I used a similar (earlier generation of ml Campbell) product years ago for a project that was painted black. That experience was very frustrating getting it to look good and I think my wet mill application was off along with some other rookie mistakes. The piece I'm spraying today is a big panel with only one face showing so I can do a little practice on the back side to refine my process.

  2. #2
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    9,647
    Your plan sounds fine. Results when spraying paint are highly dependent upon how well the substrate is prepared. Any little defect will show, although dark colors are less of a problem than light ones.

    You should have no problem applying three coats in a single day, even four if needed. You didn't mention a primer, but I would use one, and I would want it tinted dark.

    John

  3. #3
    Tinted primer would have been a great idea but I already put down white BIN shellac primer. I sanded through the edge on a few spots on a few coats and that white line jumped out like a laser beam. I have more of these dark blue pieces to spray coming up and I'll find a tinted primer for those.

    The ML Campbell stuff is very thin. The last stuff I sprayed (a few months ago) was some WB clear poly on 20 drawers that I had to thin way down. Gun cranked up to let more air and fluid through and slow passes. So I started that way by mistake and got lots of runs on coat 1. Sanded them all out but then I was gun shy on runs so the next coat was probably too thin. Third coat I turned it up a little and went slower so it was better but uneven coverage. Fourth coat was a little better and other than one run in an inconspicuous spot I think it will be good.

    This is a larger panel that goes under the breakfast bar so it won't be real visible with the brackets on it and barstools in front of it. Thank goodness as my spraying technique needs some work....

  4. #4
    Join Date
    Mar 2007
    Location
    Kingston, ON, Canada
    Posts
    223
    Here's answers to your two questions:

    1. You're right about how to roughly calculate the number of coats needed to achieve your desired thickness. Incidentally, you'll pretty well fully sand off all the first coat to get rid of those "fuzzy whiskers" your first coat of the waterborne finish will cause, so that'll mean an extra coat.

    2. For purposes of applying another coat, if it's ready to be sanded, it's ready for another coat. The trick here is to understand that drying time for waterborne finishes is related to the relative humidity (the higher the humidity, the longer it'll take for the finish to dry) as well as the temperature (if it's colder than 60F it'll take longer; higher than 85F and the upper-most part of that coat will probably dry too quickly, complicating matters for the finish in that coat below the upper-most part to set as it'll take nearly twice as long as it should. If that happens, then be patient and wait approximately 1 full hour beteween coats. In other words, the environment you're spraying in, as far as temperature and humidity is concerned, is important.

    Hope this helps.


    Quote Originally Posted by Mike Berrevoets View Post
    Looking for a little confirmation that I'm on the right track.

    I bought some ML Campbell aqualente. Here is the product information sheet.
    http://www.paintdocs.com/docs/webPDF...7318706&lang=2

    First question:
    Application film thickness is 3-4 wet mils. I have a wet mil gauge so I can check that I'm applying it about that thickness. Percent Solids is 32 to 35% so I assume the rest is "solvent" that evaporates off and dry mil thickness will be a little over 1 mil if I spray between 3-4 wet mils. (Yeah, I probably won't be that accurate, but it gives me something to strive for)

    dry film thickness is a minimum of 2.5 mils and a maximum of 5 mils. If I do this correctly I should plan on 3-4 coats?

    Second Question:
    The time for sanding dry is 30-45 minutes at the specified temp. Stacking dry time is 4-6 hours. The doc says not to apply the second or third coat until the previous coat is completely dry. Is "completely dry" the sanding dry time of 30-45 minutes or the stacking dry time of 4-6 hours? I'd like to apply the 3 coats all today if possible but I don't want to push it and have to do it all over again....

    The product was tinted a dark blue so I'm trying to be extra careful as dark colors seem to be less forgiving then just spraying clears. I used a similar (earlier generation of ml Campbell) product years ago for a project that was painted black. That experience was very frustrating getting it to look good and I think my wet mill application was off along with some other rookie mistakes. The piece I'm spraying today is a big panel with only one face showing so I can do a little practice on the back side to refine my process.
    Marty Schlosser
    Kingston, ON, Canada
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  5. #5
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    9,647
    The viscosity of Agualente is low so that you can spray it with common gravity feed HVLP guns; that's the beauty of it. Bin shellac primer is pretty close to the same viscosity. Most WB polys are higher, some are much higher, so the settings you use on those, even the gun, are probably very different. It's just a matter of knowing the viscosity of what you are using, using an appropriate gun with the correct N/N, and practicing on scrap until you are happy with the result. Short cuts are often unrewarded.

    John

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