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Polyurethane on top of factory flat finish

Discussion in 'Luthier's Corner' started by placedesjardins, Mar 3, 2016.


  1. placedesjardins

    placedesjardins

    May 7, 2012
    Okay, i have an ibanez bass with a red flat finish. I'd like to make it a gloss finish.
    Is it as simple as removing the neck and hardware and applying the polyurethane and buffing it?
    I'm guessing they used a dye to the color the body, but it is a flat finish. So does that mean they just dyed the body or is there a flat clearcoat on top? Or some sealing material that will not allow the poly to bond properly to the surface?
    It is a sr1400 premium model so it isn't cheap, to me. Thanks.
     
  2. ehque

    ehque

    Jan 8, 2006
    Singapore
    A flat finish is almost definitely a clear coat that has not been buffed to a shine. You could actually buff that to a shine without spraying more poly on it, depending on how thick the finish is.

    I'd leave it alone if I were you.
     
  3. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars
    I doubt it, I would assume the factory uses a clear with some type of matting agent instead of simply not polishing it to a gloss. That is how I would do a matte finish on a body so that it doesn't develop polished spots from the players body rubbing against it.

    It should work fine, just make sure that your gloss clear is compatible before spraying the whole bass. Test it in a pickup or control cavity to make sure you have no problems.
     
    StreetScenes and GKon like this.
  4. earlysecond

    earlysecond In Memoriam

    Jan 26, 2016
    I agree with Hopkins. Commercial production has them adding a flattening agent to the clear. It MAY buff. I would sand it first. You could test a spot on the back. Wet sand and then buff! If not then you can clean with a good cleaner, scuff with a scotch brite and apply new coats. Then, of course, you will have to wet sand and buff. Fortunately, the color is already done for you!!

    Hope that helps

    PS- what kind of poly are you considering. Not sure if you will get away with water based over solvent based IF indeed the product on there currently is solvent based (which I would guess that it IS)
     
  5. placedesjardins

    placedesjardins

    May 7, 2012
    Well, I was thinking of some oil-based polyurethane in an aerosol spray can. I saw this youtube.com video of this guy who dyed this wood-lathed piece and then he sprayed polyurethane, and then buffed with steel wool and paste wax; and the piece turned out with a really wet-looking glossy surface, which is what I want.

    My bass has a quilted maple top with a transparent red finish, so I'm guessing they used dye instead of stain (if there's a difference).
     
  6. placedesjardins

    placedesjardins

    May 7, 2012
    Just to note, I'm a total noob when it comes to finishing. I don't want to sand the surface before applying the polyurethane. I can just clean with mineral spirits and then spray?
     
  7. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars
    You are never going to get a nice gloss finishing without wet sanding and polishing.
     
    placedesjardins likes this.
  8. PDX Rich

    PDX Rich

    Dec 19, 2014
    Portland, OR
    I believe you'll have adhesion problems if you don't sand first. There is no real quick'n'easy approach to finishing. It takes patience and sore hands, arms and back. The more effort you put into it, you'll see how worthwhile all the work was once it is done. Otherwise, you'll likely have wasted your time and find that you need to sand down to the wood and start over. :)
     
    placedesjardins likes this.
  9. JustForSport

    JustForSport

    Nov 17, 2011
    Agreed- too much chance of the finish lifting later.

    First, wipe it well with naptha.
    I would lightly wet sand using 400 grit on a flexible rubber block all the relatively flat areas, drying periodically to see when it's all been scratched.
    Then, hand wet sand (w/o the block) the same way all the rest of the areas, drying periodically to check how it's progressing and where it needs a little more.
    The reason for the light sanding and frequent checks is to have all the surface scratched, but not to go thru the clear anywhere.
    Be extra careful on the sharper turns and edges.

    Then, re-wipe with naptha and when completely dry, wipe with a tack rag, then spray the poly. I use MinWax poly spray cans, and you can get a few coats on in a day if you start early.
    Give it at least 72 hrs before level sanding and re-coating at least 1 coat.
    After 72 hrs (or more to be sure) you can buff and polish it out.
     
    placedesjardins likes this.
  10. earlysecond

    earlysecond In Memoriam

    Jan 26, 2016
    What shortcuts you can get away with is largely a function of which type of clear you choose. Any flaw in the current surface will likely show through your final coats of clear UNLESS. the clear builds a whole lot between coats OR you apply a lot of coats of a thinner product.

    Almost no matter how good you are a spraying, what equipment you have and where you spray. . . .there are a lot of reason that you will want/need to wet sand and the buff the finish to a flat surface with a great gloss. If you choose to spray an let it, I'm gonna guess that you will not be fully satisfied. To be clear, I am talking only about the original finish you requested which is poly. It is my understanding that you could do a satin, oil finish a lot more easily BUT that is not what you are looking for.

    There are few shortcuts to a deep, high gloss finish. It requires a lot of work!

    Brent
     
    placedesjardins likes this.
  11. placedesjardins

    placedesjardins

    May 7, 2012
    Thsnks for all the tips. I guess i meant i feel hesistant to sand before applying the polyurethane because i might remove some color.I don't have any dye of the same color to fix it. Is 400 grit too gritty to sand with before appkying the poly?
     
  12. earlysecond

    earlysecond In Memoriam

    Jan 26, 2016
    What you will sand off, depends totally on what is there for a top coat (if it is clear on top of color you want to only sand clear). Sorry if that is overly obvious. IF it is single stage paint, you WILL be sanding color, which puts you at rist of removing color. NOW, my caveat is that my experience is from auto refinishing and NOT guitars.

    If I am you and I want a gloss finish enough to pursue it. I would:

    Disassemble the guitar

    Clean the entire project with spray foam glass cleaner get rid of all dirt, oil grease and junk

    • Start on the back of the guitar and gently scuff with a gray colored scotchbrite pad (this is supposed to be the same as wet sanding with 500 or 600 grit paper) See if white powder comes off or powder with color. If it is white you are sanding a clear coat.
    • This will be a decent scratch for your new clear to stick to
    • Wipe again with foam glass cleaner
    • Decide on a poly. I cannot help much here as my go to products are solvent based and require a compressor, guns and a learning curve to pull off others have suggested spray bombs with different choices.
    • Apply several coats, allow to dry sand it level with a sanding block and 320 - 500 grit paper (if you do it dry, I'd go with at least 400)
    • Clean it again
    • Spray some more coats
    • Wet sand the body with 1200, 1500 and 2000 grit paper
    • Buff back to a gloss with compound of your choice (I can give a couple of suggestions when you get to that point). At minimum, I would use a decent drill and a wool buffing pad (others use foam or cotton)

    The bottom line is this- I believe that as much as building anything, finishing is an art which requires some practice a mastery to get good results. There are many ways to get great results but there are few shortcuts AND there is no 1 right way to do things. (some methods are a bit easier than others but that is about it)

    Finally, if you are not scared to sacrifice a small spot on the back of the guitar. You MAY want to try wet sanding a small spot with 1200, 1500, then 2000 grit paper and attempting to buff it back to a shine. One can take many finishes which are flattened, satin, matte or flat and sand, buff and bring it to a high gloss.
     
    PDX Rich and JustForSport like this.
  13. JustForSport

    JustForSport

    Nov 17, 2011
    From the photos I've found, it looks like the clearcoat is tinted, which means if you sand too much, you'll be removing color.

    The idea here is not to remove mat'l by sanding too much, but only to scuff the surface for adhesion. That's why you go carefully, and dry periodically to watch your progress, and only sand to get 'tooth'.
     
  14. earlysecond

    earlysecond In Memoriam

    Jan 26, 2016
    agreed! If it has a decent coating you will be hard pressed to sand through anything with a scotchbrite pad. As pointed out by JustForSport you are scuffing NOT sanding!
     
  15. Primary

    Primary TB Assistant

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