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Thread: Polyurethane pulling away from edges

  1. #1

    Polyurethane pulling away from edges

    Hello. First time using brush on polyurethane. I am doing a long craft table top. I sanded the top down using 220 grit with ROS. In hindsight after reading here, I would have liked to have followed this up with a hand sand in the direction of grain. I did a very thin first coat of Gloss Poly (full strength) and did not have any issues. But it was very thin. After sanding, I have put down a second coat and it is currently drying (Can states 48 hours). Second coat was put on much thicker.

    I checked on it now after 12 hours and it looks like the poly has dried or is no longer there on one edge. Is this because the work piece may not be perfectly flat? Can it be resolved by doing a 3rd coat in the "low spots"? or should I go over the entire piece with the 3rd coat?

    There is a good chance that I put too much pressure when sanding between coats and I may have cut through the first coat in spots.
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  2. #2
    Join Date
    Aug 2006
    Location
    Maine
    Posts
    381
    I'm sure some of our experts will jump in but for my 2 cents, never sand between coats. Once you begun building a finish, use 0000 steel wool or the scotch brite equivalent to rough up the previously layer so that your next layer has something to grab onto. Just run over your project with steel wool and put on a 3rd coat. No harm, no foul.
    - - - - - - - - - - - - -
    Jim Mackell
    Arundel, ME

  3. #3
    Join Date
    Sep 2009
    Location
    Three Rivers, Central Oregon
    Posts
    2,340
    Ben, what specific poly are you using? How are you applying it? Difficult to tell from the pics what's going on with your finish. In particular I'm confused by "Polyurethane pulling away from edges. What does that mean? Is it peeling off?

    I use WB poly exclusively (GF Enduro). I spray at least 2 coats before sanding, and then sand very carefully either by hand with 320 grit, or if a large piece then with a small variable speed ROS with 400 grit at very slow sped....just enough to scuff the surface and knock down any dust nasties.
    Scott Vroom

    I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.

  4. #4
    Join Date
    Jul 2008
    Location
    Tomball, TX (30 miles NNW Houston)
    Posts
    2,747
    Why do I say "never use steel wool between coats (or on raw wood)?

    Reason #1 - Steel wool abrades the finish; it does not give enough "tooth" for poly to adhere well. 220 grit sand paper 320 grit at the finest.

    Reason #2 - you will leave shards of steel wool behind; then you will top coat it. Now you have steel wool IN your finish when water vapor gets to it, and it will, it will RUST - IN YOUR FINISH.


    Reason #3 - Many steel wool products have oil to keep them from rusting so now you have oil on your surface... bad idea.

    Did you wipe down the project after you sanded? Did you use a tack cloth? It could be a contaminate that caused the problem. Best to use a damp tee-shirt rag with either mineral spirits or water to wipe it down before recoating.
    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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