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Am I over sanding?

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  • Am I over sanding?

    I'm trying to finish my epoxy river table and twice now I've ended up with swirls and scratches in/under the first few layers of wipe on poly.

    What I'm hoping will fix the problem is sanding the wood sections using 180 to 220 going with the grain. Then sanding the epoxy section from 180 to 220 to 400 (I don't have anything between 220 and 400 so I may need to remedy that.

    Is 400 too high a grit for the poly to get good mechanical adhesion? Are the scratches created by 400 grit too small for the poly to sink in to leaving the scratches visible?
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  • #2

    Re: Am I over sanding?

    These swirls were likely left by a random orbit sander with medium grit paper....like 100 - 150 grit. There are many potential reasons why, but I will cover a few of the most common options here.

    1-you might not be sanding thoroughly enough with each grit.

    2-you might want to consider hand sanding (strictly WITH the grain) after you hit the wood with a random orbit sander and a 120 grit paper.

    3-belt sanders won't leave swirl. Maybe hit the surface with a 150 belt, before moving to some hand sanding. Just keep the belt sander moving at all times, so it doesn't dig in anywhere. If you're not familiar / confident with belt sanders this might not be a good option for you.

    As an aside.....if you're trying to get rid of swirl marks use a fairly course grit - like 100 or so, depending on how deep you feel the swirls are. Hitting the swirls with a 220 grit paper will not do anything to actually get rid of them. The 220 will just make the swirls feel smooth to the touch.
    ______________________________________________
    Rob Brown
    Editor - Canadian Woodworking & Home Improvement

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    • #3

      Re: Am I over sanding?

      I have had good results using a random orbital sander with the following process. 1. 80 grit for initial removing the biggest imperfections. 2. 120 and 150 grit in sequence to get to a relatively smooth finish. The key is to avoid putting pressure on the sander but let the sander do the work. Try to keep the sander level to the work so the edges of the sandpaper will not gouge the work. Excess pressure can create swirls that weren't on the surface initially if there is any loose grit left from the previous grit or created from the current grit. 3. "VACUUM' the surface thoroughly between each grit. 4. I then used a 180 and a 220 grit. Again vacuuming between each grit. This may be overly paranoid but I don't rely on the sander vacuum picking up all the loose grit. Using this process, I have not found it necessary to go above 220 grit. One thing to note, I personally have not finished a river table so I am not sure how the random orbital sander works on large surface areas of epoxy. That is where a finer grit may be required.
      This process has worked well for me and I built custom furniture for several years so for me it was a tried and true procedure.
      Your mileage may vary.

      Good luck, Murray
      MartyFromKingston likes this.
      This wood is all clear between the knots.

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      • #4

        Re: Am I over sanding?

        Would a scraper work?? Just a thought.
        Egon
        from
        The South Shore, Nova Scotia

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        • #5

          Re: Am I over sanding?

          Both of the posts from Rob (post #2) and Murray (post #3) are what I'd recommend. Not all ROS operate the same: some have such large swirls that they're quite difficult to get rid of. If everything Rob & Murray have suggested are still leaving you dissatisfied, hand sand your second and final grit sanding by hand, ensuring you go only with the grain so your scratch patterns won't be noticeable.

          Egon's suggestiong to use a scraper is also certainly valid. Ensure you figure out how to properly "sharpen" your scraper and learn how to effectively use it before trying that method. There are a few tricks to figure out and once you've got the knack, you'll wonder why you're reaching first for your sander! But... you have to invest the time necessary to develop the necessary skills.
          All the best,

          Marty

          Secretary of Kingston Wood Artisans Inc. https://kwoodartca.wordpress.com/

          Master Mistake Fixer (because I've made them all... at least once)

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          • #6

            Re: Am I over sanding?

            Here's a good video on sharpening a scraper.


            https://www.youtube.com/watch?v=0L4Ij-xMuNU

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            • #7

              Re: Am I over sanding?

              With wipe-on poly, I find that anything under 1200 grit will telegraph scratches... even with a flood coat

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              • #8

                Re: Am I over sanding?

                The quality of sandpaper used has a lot of influence on the number of scratches/swirl marks imparted onto the surface.
                Cheaper sandpaper has a variety of grit sizes in it compared to the more expensive varieties, so the chances of getting scratches etc greatly increase the less one pays. A cheap 180 grit could have any percentage of 80 to 180 particles in it compared to a much more uniform abrasive size range in more expensive paper.
                In the grand scheme of most projects, sandpaper really isn't that expensive a component, so I have never understood why folks cheap out on the one material that can literally make or break the final appearance.
                FWIW, I use Norton Adalox for hand sanding prior to and during finishing, as I have found this the most reliable, and either Norton sanding disks or Mirka mesh discs on the ROS.

                Paul
                stotto likes this.

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