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Thread: Filling Pores with Finish

  1. #1
    Join Date
    Jan 2008
    Jay, Maine

    Filling Pores with Finish

    I posted this in another forum and the only answers I received were to use pore filler - no one actually addressed my questions. I'm sure we can do better here, right?

    All you experienced finishers out there -

    When finishing a porous wood such as walnut, oak, mahogany, etc. how do you fill the pores? I've read about filling them with finish (shellac, varnish...) and the author always says that after the finish dries to "sand back" to level the finish. However, I have never found a definition of "sanding back". Do you add several coats, then sand through them until you achieve a level finish - doesn't this leave obvious marks on your finished product even if you add an additional coat after "sanding back"?

    Please explain this to me. Also, when sanding the finish on a swirling grain pattern, how is it possible to sand "with the grain"?



  2. #2
    Join Date
    Oct 2006
    ABQ NM
    Jim, "sanding back" is pretty much as you described it. I'll put on a coat or three of finish, then sand it lightly by hand with 220 or 320 grit, just to the point where I get back to bare wood in the high spots. You can often tell when you are at the right point when you see most of the surface is dull, but the pores still look shiny, since there is still finish down in them. Wipe off all the sanding dust, then put a few more coats of finish on, then repeat the sanding. It's important to use a finish that will "burn in" to the previous coats of finish. Shellac and lacquer are two that come to mind. I'll let someone who knows more about finishes than I do offer more examples of finishes that burn in well.

    After a few cycles of this, you'll see that the pores no longer show up as shiny spots when you sand the surface. (Because they are now full of finish, and the wood surface is level.) One more coat of finish, left unsanded, and you're ready to buff or polish after the finish cures. If I'm looking for a very high gloss finish, I will often start the polishing with wet 400 or 600 grit paper, to get an absolutely flat surface. I have to be careful though, because I can sand right through the finish if I'm not careful.

    I've never had problems with the sanding leaving scratches in the finish. The subsequent coats of finish fill the scratches, in my experience. (I'm talking fine, light sanding scratches, not the 80 grit kind.) Also, I've found some papers clog with finish more quickly than others...Norton 3X seems to do pretty good. If you sand before the finish is somewhat cured, it'll gum up and turn into little balls.

    On swirling grains, I sand in all directions. But then again, I tend to do that on all grains, since I prefer to use a random orbital sander when I can.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

  3. #3
    Join Date
    Oct 2006
    Tokyo Japan
    Yep, I do what Vaughn is describing, I use a product called "Lacquer Sanding Sealer" it is, to my understanding, a lacquer finish, with more solvent than normal lacquer, so it flashes off real fast and it is about half the price of normal lacquer. On some wood, I need to do a good dozen coats to get the surface level, on others 4 or 5, it also depends on what you want. If you are going to go for a hand rubbed or polished surface, you need to make sure everything is real smooth, no low, half filled pores

    A bit of work, but it works well, and the sanding sealer is really quick, 5 minutes to wait before you can sand.

    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  4. #4
    Join Date
    Oct 2006
    like stu, i use sanding sealer. it`s lacquer with aluminum striates in it to make for easier sanding, it`ll powder up white with very little effort but is softer than a lacquer topcoat.
    as to sanding with the that in preperation to begin finishing, on burls or wonky grain use a random orbit sander and progressivly finer paper, dampen with spirits to see if the piece is scratch free and if so apply stain/dye if you`re going to, let dry 24hrs and start laying on the sealer. i usually sand after 4-5 coats with 120 paper and at this stage it doesn`t matter which direction you sand in relationship to the grain. (sand by hand!)
    blow off the sanding dust and look at the poors...if they`re not full either sand more or apply more sealer and sand`s a subjective thing hard to discribe in print.
    once the surface is smooth (usually 1 day) then start laying on topcoat.
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  5. #5
    Join Date
    Feb 2008
    Cedar Park, TX
    Subsequent coats of finish will fill in the scratch marks left from sanding, leaving a clear smooth finish.

    I've found that by padding on shellac (dewaxed, of course) in a manner similar to french polishing using circular motions the grain gets filled much more quickly than any application along the grain. I think the wiping motion, of either a pad or a brush, along the grain actually pulls some of the finish out of the grain. Adding a drop or two of mineral oil (available at the drug store with the laxatives) to the pad occassionally lets you work it without the pad sticking to the shellac on the wood. The circular motion across the grain works more shellac into the lower areas. You can then apply your choice of filming finish on top of the shellac in your normal fashion.

    "If politics wasn't built on careful deception it wouldn't need its own word and techniques. It would just be called honesty, education, and leadership."
    Bob "Phydeaux" Stewart one day on Woodnet

  6. #6
    Join Date
    Oct 2006
    The Heart of Dixie
    Working with mahogany in boats, filler stain is commonly used. It's a thick almost paste like stain that is rubbed in with burlap or some coarse cloth. Let dry, sanded and then varnished over.
    God grant me the senility to forget the people I never liked anyway,
    the good fortune to run into the ones I do,
    and the eyesight to tell the difference.

    Kudzu Craft Lightweight Skin on frame Kayaks.
    Custom built boats and Kits

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