Problem With Nitrocellulose Lacquer

Discussion in 'Guitar Building' started by vonbeck2, Nov 1, 2018.

  1. vonbeck2

    vonbeck2 New Member

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    Greetings everyone,

    I am new to guitar building and have completed 2 guitars. On both guitars I have finished them with Mohawk Classical Instrument Lacquer. I am an experienced wood worker but have not had much experience at all with lacquer. After some trial and error and by the 2nd instrument I feel confident that my application technique is sufficient. I am able to apply a level coat, sand and buff it to a nice finish after a 2 week dry time.
    The problem I am having is that the lacquer seems very soft. So soft that the finish is being removed by contact. I first noticed in where my arm rest on the instrument on the lower bout while playing. All of the lacquer rubbed off to bare wood. I thought that perhaps I had sanded to thin so I repaired the area. I began to notice that the lacquer is dulling on the back of the instrument as well where it rest against my body. This problem repeated itself on the second instrument as well.

    Has anyone else used Mohawk Classical Instrument Lacquer? Is it too soft, I was under the impression it is the same as Behlen. Could this problem be the result of adding to much retarder? Any ideas or suggestions would help.

    Any suggestions on another lacquer brand? Would it be better to switch to a conversion varnish for my next build?
     
  2. GuitarBuilder

    GuitarBuilder Member

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    I'm not familiar with Mohawk, but have used Stew Mac, Behlen, and ReRanch with excellent results.
     
  3. vonbeck2

    vonbeck2 New Member

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    So after some research I think I know what I did wrong. While spraying I think that I added way to much retarder which affected the drying time of the lacquer.
     
  4. Cagey

    Cagey New Member

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    Usually, too much retarder results in numerous sags/runs as the material is very thin and doesn't set quickly enough. Eventual cure time doesn't change, but immediate dry time while shooting lengthens just a bit. But, we're talking seconds/minutes, not days/weeks/months.

    Lacquer is somewhat sensitive to environment when shooting. Too warm or cool, or too high a relative humidity will show up right away in the results. Retarder is used to compensate for those conditions, and needs to be used sparingly, if at all. It's kinda like octane additives in fuel - you're trying to compensate for short timing issues. If it's too warm where you're shooting, the vehicle (acetone) boils off too fast and you'll either get a dusty, non-building finish that doesn't adhere well, or you'll trap moisture in the finish creating "blush", or both. We're talking short times here - I mean, lacquer starts drying almost the instant it leaves the gun. So, small adjustments by the addition of retarder slows down the dry time by raising the boiling point of the reducer/thinner/vehicle.

    If you're abrading the finish off quickly, it could well be that you didn't add enough retarder, so the material was hitting the subject half-dry to start with. Doesn't stick well, and doesn't "melt" into the previous coat.

    It could also be too thin overall. Color coats usually are thin - no sense wasting material - but the clear coats have to be sufficient to provide some protection. It's not unusual to apply 6-8 coats of clear. When you hear of "thin" lacquer finishes, usually they're talking about some time down the road. Lacquer tends to shrink. Doesn't mean it was applied thin or sparingly.
     

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