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Thread: Pimples/dimples/inperfections

  1. #1
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    Pimples/dimples/inperfections

    The wood is curly maple. I followed "the Creeks" advice and followed the suggested sanding regimen through hand sanding @ 220. Wood smooth as silk. Wiped it down with naptha, let dry and then applied a coat of Transtint dye. One coat of BLO ,and one coat of Seal Coat at something less than full strength. So far so good. Three coats of Rockhard at approximately 90/10 and now I see imperfections that look like pimples/dimples. I sanded the first coat of Rockhard with 220 premium on a Festool 125. I wet hand sanded subsequent coats with 400 w/d and the finish is smooth. What should/could I have done better to not have dimples/pimples? Short of returning to square one is there a fix?

  2. #2
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    I'm a bit confused. You say the finish is smooth, but that you see dimples/pimples. How are both statements possible--I'm missing something I think. Are you seeing something in the wood underneath the varnish that looks that way, or has the varnish developed these bumps and dips after being originally smooth sanded with the 400 grit.

  3. #3
    Can you post a pic?
    When using Rockhard Table Top Varnish, after my research, it is best to follow the directions. 3-4 coats if I recall. Use 320 grit then recoat. That should help you out. Don`t sand by hand, I tried that and I think that is exactly what I had happen to me. I just turned to my orbital. Problem solved.
    I used Behlen`s Rockhard per directions on a Red Oak dining table 2 months ago. I sanded with 320 between coats with random orbital. Wiped with mineral spirits then tack cloth. One month after it cured, i sanded with 1800 to 12000 micro discs, then I used pumice and then Rottenstone. I then foloowed that up with a coat of paste wax. I did not have any dimples in mine.

  4. #4
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    I'm going to seriously disagree with using a ROS for sanding between coats of varnish. Particularly on the first coat it is just too easy to cut through in places, and when you do the next coat is absorbed differently in those places. Consequently, the surface can become less level. Hand sanding, with a sanding block, is about the only way to go. Yes, if you are highly skilled with lots of practice in using the ROS with a very light touch you can save a couple of minutes that way. But for non-commercial situations that time savings isn't worth the risk, in my opinion. I do agree that 320 grit is the best choice. 220 is way to aggressive for sanding between coats. 400 grit is OK but anything finer risks lessing the adhesiion between coats.

    I'm not too fond of wet sanding either, at least until the final rubbing out stage anyway. Sanding dry ensures that you aren't rushing the process, and until you are really sure of having sealed the surface, water and wood don't mix well. A small cut through can result in additional raised grain.

    Until John gets back with a bit more on exactly what the dimples/pimples look and feel like I won't speculate on a fix. Ought to be fixable though.

  5. #5
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    Without seeing the finish it is hard to say. Could be dust nibs missed, could be air bubbles popping, could be application problems.

    Did you shake the finish per chance? That is one of the major causes of air bubbles in varnish finishes.

    I haven't used Rockhard but hear it is good stuff. When using waterlox (the varnish I generally use when not spraying) I scuff with 320 or 400 between every coat to remove any nibs, etc.

    Joe
    JC Custom WoodWorks

    For best results, try not to do anything stupid.

    "So this is how liberty dies...with thunderous applause." - Padmé Amidala "Star Wars III: The Revenge of the Sith"

  6. #6
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    A pic wont show the problem.
    For Steve: I see the imperfections when looking slant wise at the piece. They appear to be beneath the surface which is smooth. Your comment regarding sanding with a ROS is correct.

    For Joe: I stirred the mix, applied with a "wet brush (Jim) and tipped the strokes off. The sides are only 12" x 8" so application is not a big deal although I am not expert at brush work. I do not have the problem on the "practice" piece.

    I have not rubbed it out. It is in the curing process. The Rockhard is not new so product freshness could be a factor. The product is probably a year old.

    I neglected to mention in my original posting that I applied a coat of Minwax Natural as the final coat before the Rockhard. Thanks for the interest. JFK
    Last edited by John Keane; 05-03-2008 at 10:47 AM. Reason: Added comment

  7. #7
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    Could you actually be seeing "figure" that is not quite a regular part of the curly pattern--almost a birdseye or the like? If the varnish is smooth over them it isn't a sanding or planing defect--that would have revealed itself clearly after the first coat or two as irregularities in the surface of the finish, not just under the finish. It maybe you have an example of the charm of working with natural materials instead of printed plastic.

  8. #8
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    Steve, you have an interesting point. I picked up on your sanding with 320 and gave the jewelry box a good workout. My perceived problem diminished dramatically and my conclusion is that the remaining imperfections are a natural part of the wood. I am going to apply another coat of varnish and see what the results are tomorrow. I will post my impression here. Thanks again, as always you are most helpful.

  9. #9
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    Sanding at 320 has resulted in a major improvement in the removal of the pimple/dimples. I suspect that what I was looking at appeared to be worse because of the depth aspect of the gloss. Rubbing them out at 320 has resulted in a significant reduction in the gloss. I am presuming that rubout after curing will result in the high gloss that I am looking for. The finishing learning curve is a long frustrating education.

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