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Witness Lines with Crystalac Brite Tone?

Discussion in 'Finely Finished' started by thecrushr, Sep 23, 2020.

  1. thecrushr

    thecrushr TDPRI Member

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    I am trying to switch over to water base finishes and have tried Crystalac Brite Tone on a couple of guitars. When I level sand, I got what looks like witness lines in the finish on both guitars. The picture below shows what I get on one of them. It was hard to photograph and much more visible than the picture indicates. Everything I have read indicates witness lines are not a problem with this finish.

    So why am I getting this?!? What am I doing wrong? For background, it was sprayed in ideal conditions around 70-80 degrees and low humidity using a 4 stage HVLP turbine. I scuffed with a gray scotchbrite between coats.

    Once I understand what went wrong, the question is what to do about it. I can buff it out and see if it is visible but I imagine that will just make it pop more. I already put on more coats once. The lines went away with the additional coats but came right back when sanding. I'm debating just putting some 2K urethane over it since I know that won't have the issue but I don't know if that will hide the lines like the additional coats did before or just magnify them under the different clear.

    I appreciate any advice or insights people have.

    [​IMG]
     
  2. Speedy454

    Speedy454 Tele-Holic

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    Most finishes do this. Lacquer and shellac do not. It has to do with mechanical bond vs chemical bond. New coats of lacquer and shellac dissolve the existing coats and bond chemically into one thicker layer. Almost every other finish the coats just sit on top of each other. Then when you sand and cut into the prevous layer, the witness line is visible.
    Usually a thin top coat will hide the witness lines. That is the only way I have been able to get rid of them.
     
  3. fleezinator

    fleezinator TDPRI Member

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    Crazy coincidence @thecrushr. I came here to post the exact same problem because I didn't know what this was called. I could only describe it as a peeling sunburn effect lol. I had a hard time capturing it on video/photo, but it's kinda like this:
    [​IMG]

    In my case I'm only seeing it in certain spots and it's not so evident from front on, but you can definitely see it from lower angles.

    I too am using Brite Tone and after three weeks of curing the final top coat (8 coats), I started to level sand last night. I'm wet sanding with Micro Mesh sheets and a foam block starting from the lowest grit of 1500 (equivalent to regular 400 sandpaper or P800) going thru all the way up to 12000.

    I wasn't sure if it was my technique or if I waited too long to level sand or if I was moving up in grits too quickly but I thought it might resolve itself on the way up to 12000. It didn't so I took it back to 4000 and worked small sections over again a little more all the while being mindful of not sanding thru. I'd work a section for 10-15 seconds, wipe dry and analyze. repeat. Since mine has a mid coat of pearl, I really had to view the spot from different angles to see what was going on.

    I think I evened it out for the most part with 4000 and tried to repeat that all the way up in grit. I've got it completely gone or minimized except in the back of the neck pocket:
    [​IMG]
    [​IMG]

    and in the belly cut. This part is harder since it's not flat. I think I might just leave this part.

    [​IMG]

    I don't know what grit(s) sandpaper you're using but the Micro Mesh sheets seemed to have done the trick. Hope that helps!
     
  4. stratisfied

    stratisfied Tele-Meister

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    First off, those are not witness lines. Witness lines or witness marks are found on mechanical parts resulting from mechanical interference. Say you over-revved your engine and floated the valves. A valve may strike a piston and leave a mark as a witness to the interference, called a witness mark.

    In the OP's case, it looks like there was sanding dust present that was finished over leaving white spots. In the Blue poly example, it is a chemical reaction resulting from being recoated outside of the recoat window. The new coat partially dissolve the old coat which may have not been fully cured as a result of the paint being thicker in that area.
     
    Last edited: Sep 24, 2020
  5. Freeman Keller

    Freeman Keller Friend of Leo's

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    Over the years I have experimented with water born lacquers and as much as I want to like them, this is one of the reasons I don't. I have only tried the old stuff that StewMac was selling (10 years or so ago) and KTM-9 (which LMII was selling and is not longer)_. I have not tried any of the Target finishes or Crystalac, I guess I'm reluctant to experiment when I know I can get good results with lacquer.

    What I have learned is that each coat of water born lacquer does not melt into previous coats like solvent lacquer (or shellac) does. When you level sand you cut thru the layers and get witness lines (that is what I've heard them called so I'll continue to do so). Subsequent coats don't hide the lines, there doesn't seem to be a way to remove them.

    I had best luck when I was spraying KTM-9 of doing my level sanding between coats to say, 400 grit, then right before spraying the finish shooting a mist coat of DNA. When I cleaned my gun with hot water I would put some DNA in and shoot that into a rage to clean the water out of the passages. I'd just leave the cup full of DNA, the next day do the sanding and mist coat, dump the alcohol into a container, pour the finish into the gun and shoot. The mist coat on top of the scruff sanding seems to make the surface slightly tacky and the subsequent coat seemed to bond better. I don't believe I ever had witness lines when I did this.

    I see beautiful finishes with some of the modern water born products and I tell myself I should try them again but I have a hard time breaking away from tried and true nitro.
     
    Speedy454 likes this.
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