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Finishing Tips?

Discussion in 'Luthier's Corner' started by topper, Jul 12, 2005.


  1. I'm working on my second project bass. For my first, I just used some tung oil on the maple body and got a nice look, but for this bass I want something with more gloss.

    The body is mahogany with a padauk top. I'd like to apply some poly but don't really know anything about wood finishes.

    Is there a particular type of poly I should look for?
    Should I use a brush or I've seen some "wipe on" poly at Lowes?
    What about "clear coat" spray paint?
    How long does it take the poly to "cure"?

    Any suggestions you have would be appreciated.

    Thanks!
     
  2. justateenpoet

    justateenpoet Have you...killed the Venture brothers!?!?

    May 14, 2005
    Connecticut
    - Type: Polyurethane comes in so many varieties that it's not even funny. Read the cans...they'll tell you what you're looking for, to a degree. Look for a poly designed for outdoor use. Since you'll be handling the instrument a lot, you want something that'll withstand a lot of contact with different...stuff.

    - Brush...all the way. If you're good, brushing will result in the smoothest finish with little or no bubbling. I find brushes make it easier to regulate the amount of poly you're putting on, and give you better control. Try both, if you can, see which works best.

    - Spray paint is just what it says, paint, not poly. It might look good and offer some protection, but in the long run, a "paint" product won't stand up nearly as well. Besides, sprays are thinned down to make using them easier, so it'll take a lot more coats to get to the final product.

    - Most woods treated/finished with polyurethane can be "lightly" handled after drying overnight. Still, you need to work in layers, and don't forget to sand after each one dries. Depending on what you end up using, you'll probably need about 3 or 4 coats to reach the finished point, which will probably take 1 or two days. The final coat needs to dry overnight (8 hours minimum) to settle.


    All of this comes from my experience with general woodworking (furniture and cabinets), so some of what I've said might not be true for guitar making.
    Good luck
     
  3. I've heard a horror story from another intrepid luthier who applied his poly in several light coats. Then four or five days later he used some masking tape to lay out the final bridge position. When he pulled the tape up the poly came with it. He stripped the bass and just went with tung oil.

    Any ideas what would cause something like this? Four or five days sounds like plenty of time for the poly to cure.
     
  4. In consumer grades there is essentially only one type of polyurethane and that's the single component coatings like Varathane (the original), Minwax Poly, and the dozens of other spray, brush, and wipe on finishes. These finishes, all are very similar to any other type of solvent based finish in that they rely mainly on the evaporation of the solvent to dry. So when you use one of these, you'll have to be concerned with the relative humidity where you live. I live in Georgia and right now, I could spray one of these and it would be tomorrow before I could even think of handling it because we are in 90%+ humidity conditions here. Someone living in Arizona would have a wonderful time with the 40% humidity and could probably safely apply 2 coats a day and handle the subject in a couple or three hours after coating if the film were thin enough.

    The only spray can poly I use is Minwax and I only use it for small pieces where it's impractical to pull out the full gun rig. I've done necks and body's with the Minwax rattle cans and I've been able to get decent results but it took a lot of worrying over the piece to get right. I prefer a two part catalyst hardened poly. I'm using a PPG high solids clear right now and love it completely. Talk about a wet look! But this type of poly requires special training, handling and equipment to spray and isn't for the casual builder.