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Thread: When and where to use high build primers

  1. #16
    Join Date
    Nov 2005
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    lower Michigan
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    Feather Fill is basically spray on bondo or more precisely polyester spray primer (same as plastic filler). I haven't used spray on polyester filler (like Feather Fill) in many years. The bodywork should not be that rough that you need a spray on plastic filler.

    My sequence of body work (1) Strip to bare metal. One or two panels at a time if in a humid area of the country. (2) repair metal as best you can then use premium grade plastic body filler (spread out with a squeegee). Sand starting with 36 or 40 grit to 80 grit to 160 grit and finish off with 220 grit. Should be very straight panels at this point. (3) epoxy prime the whole panel. (4) 2K high fill primer guidecoat block sand with 180 longboard sander (air to start with, by hand to finish it off) (5) When the panel(s) are block sanded to your preference then two more coats of 2K high fill primer. Hand block sand with 400 and finish off with 600 grit. (6) on to the base coat/color coat. Finally 3 coats or clear. Don't need a "flow coat" if you spray the clear correctly. Block sand the clear with 1200 grit and finish off with 2000 grit and wheel out with a buffer using the rubbing compounds of your choice.

    One big mistake that novices do is using too fine of a sand paper for initial blocking of high build primer/guidecoat block sanding. The panel will come out flatter faster if you use around 140 to 160 grit sandpaper for the initial 2k high fill primer block sanding. I use an air orbital long board sander like a Hutchins 3800 for the initial 2k block sanding in areas where applicable. Hand sand inside curves and rounded contours. You need to work smarter, not harder. All fill primer has to be finished off by hand sanding. Can't cheat the hangman on that one if you want the panel flat.

  2. #17
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    Nov 2006
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    Thanks for clearing that up Phil. You told me to start sanding surfacer with 180 grit some time ago when I posted something and I thought you were talking about finishing filler before you sprayed surfacer. I didn't get that you are applying the surfacer a second time after the 180 grit sanding. I'll try that next time.

    It takes a good long time to sand the surfacer with 400 grit wet when there are 2 or 3 full coats on but that's what I've been doing. Sometime it takes a long time of doing it wrong to finally get the mind set changed. That one little detail clears it all up.

    Bob K

  3. #18
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    Quote Originally Posted by Bob K View Post
    Thanks for clearing that up Phil. You told me to start sanding surfacer with 180 grit some time ago when I posted something and I thought you were talking about finishing filler before you sprayed surfacer. I didn't get that you are applying the surfacer a second time after the 180 grit sanding. I'll try that next time.

    It takes a good long time to sand the surfacer with 400 grit wet when there are 2 or 3 full coats on but that's what I've been doing. Sometime it takes a long time of doing it wrong to finally get the mind set changed. That one little detail clears it all up.

    Bob K
    Bob, it reminds of basically the same thing as working a larger area of filler/bondo. I rarely do any filler work with just one application. Usually two or maybe three depending on how large the filler area is. My first coat of filler has a single purpose of just "roughing in" the repair area. I don't spend much time finessing the first coat of filler, just buzz it down without removing too much filler. That is the secret to working filler. Most novices (me included when I first started body work) was to put way more filler on than needed the grind too much filler off then put too much more filler on and grind too much back off. A vicious cycle that wastes a lot of time and materials. After you buzz down the first coat of filler then you should know if there are any high spots (metal showing) and where the low spots are. Tap down the high spots and fill in the low spots and put a butter coat of filler over the whole filler area.
    In most cases I can finish off the repair with the second coat of filler but sometimes it takes a third time in large areas. Never more than 3 filler applications. Anyway, the same goes with sanding filler as sand high build 2K primer. The first application I use a relatively coarse sandpaper and don't even attempt to finesse the area until the second coat.

  4. #19
    Join Date
    Mar 2007
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    True that, Phil...

    people gotta learn how to use cheese grater and 36 and 40 grit...it is a time saver....and it shapes panels straighter....

    after that, second coat is easy.....and third coat should be just a skim coat , but that is the hardest trick of the trade....i treat it as a primer coat....

    even today i sometimes over apply skim coat....

  5. #20
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    Nov 2005
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    Quote Originally Posted by baubau View Post
    True that, Phil...

    people gotta learn how to use cheese grater and 36 and 40 grit...it is a time saver....and it shapes panels straighter....

    after that, second coat is easy.....and third coat should be just a skim coat , but that is the hardest trick of the trade....i treat it as a primer coat....

    even today i sometimes over apply skim coat....
    I agree, a cheese grater and coarse paper save time and material and three coats usually finishes the job.

    cheese grater.jpg
    Cheese Grater LINK

    It should be noted that using a cheese grater you will want to wait until the filler is about as hard as hard cheese before using the grater. Using this file too soon and it will clog the file or pull the filler off the panel and waiting too long will make it hard to level the surface.
    Last edited by Len; 03-15-2018 at 06:33 AM.

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