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Thread: Finishing with water based poly

  1. #1

    Finishing with water based poly

    After applying the final coat of water based polyurethane and after it dries it is still not perfectly smooth and silky to the touch. What can be done to get a very smooth surface without changing the sheen (satin) ?

  2. #2
    Join Date
    Mar 2003
    Location
    San Francisco, CA
    Posts
    9,738
    Here's my finishing process with waterborne lacquer. Sand to 320. (320 seems to reduce the nibs.) Spray two coats with HVLP. The surface will feel awful here. De-nib. This means resanding lightly to knock down the little nibs on the surface. I usually power sand with 600 grit, and hand-sand in the corners where a ROS can't reach. Or sometimes I just handsand everywhere. I'm not doing a big sand here -- just knocking off those little nibs. The surface will feel smooth, but will not have a consistent sheen. Spray one or two more coats. Let dry for a couple of days. It will have a few nibs. Hand sand with 1800 grit. That's abrasive enough to take off the nibs, but not change the sheen. In the old days, people used to use brown paper bags for this last step. I think it depended on the clay in the paper.

  3. #3
    Join Date
    Oct 2007
    Location
    Cache Valley, Utah
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    1,673
    I use a similar procedure. I generally apply a 1 or 2 lb cut of shellac first to pop the grain and seal the wood. Sand with 400 grit or a Superfine 3M sanding sponge pad. Then two to four coats of gloss WB poly, sanding between coats with the 3m Superfine. Then one to two coats of satin WB poly, sanding between coats with 800 or a 3M Ultrafine pad. After the final coat, rub down with a gray Scotchbrite pad. I wipe the project down with a tack cloth after sanding between coats to remove all the dust.

    The 3M pads and Scotchbrite are available on line or at a commercial paint store.

  4. #4
    For light dust nibs, which I believe you are describing, I still use the "paper bag" method, but over the years realized it had nothing to do with the bag material itself. Years ago, an associate had cut down rolls of white butcher paper from Sam's Club (no wax) for a client who simply needed narrower rolls. Gave me a few of the 6" cutoffs which left a length of a couple hundred feet on the carboard core. I put them on a dispenser in the finishing room, peel off palm sized sheets and buff things down. No effect on sheen, even with dead flat finishes. Works amazingly well, and I'm not burning cash on super-high grit products. Won't cure improperly leveled surfaces, but I suspect that's not what you're describing.
    Bottom line: any fresh, clean piece of paper will de-nib quite well without the need to re-spray or purchase 1,000+ grit abrasive specialties.
    (though I'm not criticizing those who prefer them in their finishing schedules)

  5. #5
    Join Date
    Feb 2003
    Location
    Doylestown, PA
    Posts
    6,665
    Quote Originally Posted by Dave Cav View Post
    I use a similar procedure. I generally apply a 1 or 2 lb cut of shellac first to pop the grain and seal the wood. Sand with 400 grit or a Superfine 3M sanding sponge pad. Then two to four coats of gloss WB poly, sanding between coats with the 3m Superfine. Then one to two coats of satin WB poly, sanding between coats with 800 or a 3M Ultrafine pad. After the final coat, rub down with a gray Scotchbrite pad. I wipe the project down with a tack cloth after sanding between coats to remove all the dust.

    The 3M pads and Scotchbrite are available on line or at a commercial paint store.
    A coat of dewaxed shellac sanded makes a really nice base for waterborne finishes. No grain raising and really smooth surface. Spraying the shellac does help.

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