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Thread: Rubbing out a polyurethane finish

  1. Rubbing out a polyurethane finish

    What is the best method to rub out a polyurethane finish?

  2. #2
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    Best method to rub out will depend on what you want to achieve.

    A few things to know about poly...

    1. it takes 30 to cure
    2. it cannot be buffed up to a mirror high gloss, the gloss you get off the brush or gun is the glossiest it will ever be.
    3. buffing will produce a semi-gloss finish at best

    The above facts are due to poly being tough; poly is not hard, mirror gloss needs a hard finish.

    Hope this helps...
    Scott

    Finishing is an 'Art & a Science'. Actually, it is a process. You must understand the properties and tendencies of the finish you are using. You must know the proper steps and techniques, then you must execute them properly.

  3. #3
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    I'd offer a different opinion.

    A guy on a drum forum I post to regularly takes oil based poly to an immaculate, deep 'n glossy wet, scratch-free shine. There is plenty of hand work, followed up by machine based polishing.

    He uses Varathane brand poly, and lays on multiple coats, relatively thick. Drip control is best, but the sanding will ultimately remove small drips, sags 'n such. Sanding removes approx half the thickness of the finish.

    Use wet/dry paper, starting with 600. You can always drop to 400 or 320 if the 600 is too fine. The sandpaper is soaked in water for 5 minutes or so prior to sanding. Use a backer block, and start standing, apply a sprinkle or two of water to keep the sanding action lubed. Rinse the paper periodically to clear away swarf. Poly will give off a milky white slurry, so occasionally wipe it away and check your progress.

    (I've discovered that felt chalkboard erasers, available at Office Max or Staples or whatever, make an inexpensive and relatively firm backer block.)

    Progress thru grits up to 1200 or 1500, polishing and buffing will take it the rest of the way.

    I use Megwire's brand of automotive cleaner / polisher / wax system and hand rub the compounds using a microfiber cloth. Drum Finishing Dude uses 3M brand Perfect It 3000 and wool pads on a motorized buffer. One pad for each glaze is best.

    Naturally, practice first on a sample board before taking your process to the actual project.

    Cheers,

    Seth
    Play drums!

  4. Is that 30 days to cure? A semi gloss finish is what I am trying to acheve. What should I use to rub it out?

  5. #5
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    Quote Originally Posted by MICHAEL S HILL View Post
    What is the best method to rub out a polyurethane finish?
    Polyurethane doesn't like to be sanded. Even after it has cured for a couple of weeks, it has a bit of a gummy quality when sanded, which feels very different from a finish like shellac (which rubs out very well). I would try to minimize the amount of sanding.

    If you want semi-gloss, start with semi-gloss. Sand as necessary to remove runs, brush marks, and other flaws. The problem areas you sanded will probably end up with a different sheen than the rest of the piece, so lightly sand the rest of the piece with the same grit. Probably, you won't want to go higher than 600, but you can experiment on a hidden area or a piece of scrap. The mechanics of sanding as described by Seth above are good.

    Jim

  6. #6
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    Quote Originally Posted by James Scheffler View Post
    Polyurethane doesn't like to be sanded. Even after it has cured for a couple of weeks, it has a bit of a gummy quality when sanded, which feels very different from a finish like shellac (which rubs out very well).
    The reason for this is because Polyurethane varnish was originally designed for floors and has a primary quality of abrasion resistance. "Rubbing out" is an abrasive process so poly will fight it. Ideally, using an alkyd or phenolic resin varnish that contains no poly is the best way to have a hard finish (poly is actually softer, too) that you can rub out to get a sheen less than high gloss or to level and even out the gloss for a mirror shine. Unfortunately, the retail market is saturated with poly and even some well known personalities pull it out, rather than using a more appropriate furniture finish.

    So I have to concur that if poly is the choice for the finish, do your coats up to the last one with gloss and then us satin or semi-gloss (well stirred...) for the final coat.

    One silly thing that's counterintuitive about poly is that it doesn't like to be abraded, but has to be abraded between coats if you wait too long to insure that the next coat will actually stick to the previous coats...
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  7. #7
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    Quote Originally Posted by Seth Dolcourt View Post
    He uses Varathane brand poly, and lays on multiple coats, relatively thick.
    I have had very good luck with Varathane poly as well. I usually do 3-4 coats. The first 2 coats lite, and the last too moderate. Sanding in between with 220. For brushing I like varathane much better, but I have trouble spraying it. For spraying I use minwax. Most wont spray poly because of the sticky mess that can be left afterwards. But if you have good ventilation and the spray gun set right, you have no mess when done. I have 3 large bathroom fans in my finishing room that suck most all the vapors and airborn materials out before they have a chance to settle. Just pick the sheen you want and wax when you are done. As others have stated you dont really accomplish anything by rubbing out a poly finish. If you want a durable finish the high gloss is the toughest, Start with 2 coats of that and put the semigloss or satin on top.

  8. #8
    how long is too long? sounds like, if i do it soon enough, i can recoat without sanding. correct???

  9. #9
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    I would say a good rule-of-thumb is to read the label and use the recoat time listed on the label as to how long you can wait between coats and NOT sand. You may be able to go a bit longer.

    Do you realize that non poly varnishes don't have the "MUST sand" between coats requirement?
    Scott

    Finishing is an 'Art & a Science'. Actually, it is a process. You must understand the properties and tendencies of the finish you are using. You must know the proper steps and techniques, then you must execute them properly.

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