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Thread: Shellac then polyurethane

  1. #1

    Shellac then polyurethane

    Got a big pine table top, was going to put a shellac on first, then sand, then a few coats of Varathane poly. Any indications this is not a good idea? Will use zinsser shellac.

    Thanks
    Jim

  2. #2
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    There is always the first question; why use the shellac at all? I will assume the pine is irregular or pitchy? Maybe it has rustic coloration that you do not want to telegraph through your topcoat? If you decide to use the shellac I would use Zinsser Seal Coat which is dewaxed. I often seal things with a very thin application of Seal Coat and follow with a 1:1:1 blend which includes a modified phenolic urethane. I sometimes use this on end grain and not on the rest of the piece to unify the coloration from the oils. I have pieces going on 20 years old that still look great. Your oils will not penetrate as much as on bare wood so I would strongly recommend a test board.
    Last edited by glenn bradley; 10-25-2020 at 12:38 PM.
    "The Danish government believes that if we train 5,000 designers, and produce
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  3. #3
    The wood is very stable and dry, not pitchy at all. Was thinking it would be a good ‘sanding sealer’.

    I will try a test piece to be sure of what I’m doing.
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  4. #4
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    Jim, I think you are on the right track. Pine can be blotchy and the Seal Coat should help reduce that. Test board is best...but even a smallish test board may not indicate all the blotch you might get on the entire table top. I think you’ll be happier with the Seal Coat first results. And besides all that, it doesn’t hurt one bit.

  5. #5
    Quote Originally Posted by Jim Riseborough View Post
    ...was going to put a shellac on first, then sand, then a few coats of Varathane poly...
    That is called a science project.

    If you are serious about getting a long lasting finish, don't experiment. Begin instead with tried and true methods that have worked for professionals forever. For example, follow the formulator's instructions.
    "Anything seems possible when you don't know what you're doing."

  6. #6
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    You must use wax free shellac for this application, but it's a very common method. Zinsser SealCoat is wax free if you want pre-mixed but making from flakes gives you more color flexibility.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  7. #7
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    Quote Originally Posted by Jim Riseborough View Post
    The wood is very stable and dry, not pitchy at all. Was thinking it would be a good ‘sanding sealer’.

    I will try a test piece to be sure of what I’m doing.

    I will add that unless there is a compelling reason to add something to your finishing protocol, I would not. Using dewaxed shellac as a sealer to help with blotch control is a compelling reason. Using the shellac as a vehicle for a dye to tint the piece is also legit IMHO. I am not big on colorations so I use this method when I want a bit of toner but, not a full-on dye job.
    "The Danish government believes that if we train 5,000 designers, and produce
    one Hans Wegner, the money is very well spent." - Ole Gjerlov-Knudsen

  8. #8
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    I use shellac under poly a lot. Typically, I sand the shellac lightly and then multiple coats of wipe on poly.

  9. #9
    Been working on the table and finishing it, I have the top with 2 coats of poly. I have been thinning it, and it seems to help get even coverage.

    For the final coats, how do you guys feel about wiping it on? I think I would get better even coverage, and no thick or thin spots.

    Thoughts?

  10. #10
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    Shellac under varnish finishes is about as "tried and true" as anything in finishing ever is ;-), and used universally by every pro finisher I've ever spoken to. I do it all the time, almost reflexively.

    With varnish (including polyurethane varnishes) I get a more even coat with a brush than I do with wipe on, but that may just represent way more practice with one method over the other. Wipe on is fine when I want to leave an extremely thin coating and can wipe off virtually all of the finish applied-- of course then it doesn't matter whether it was originally applied with a brush or with a rag.

  11. #11
    "blotch" is usually not objectionable to me. If I were you, I'd make my own sanding sealer by thinning your varathane poly 25-50% with mineral spirits to make a wiping varnish.

    Your test board will be the BOTTOM of your table.

    Flood on the first coat with a foam brush.
    Knock down any nibs with some high grit sandpaper (+320).

    Then keep applying subsequent coats with a shop towel. You can look up techniques for applying wiping varnish. While it takes more time to apply a thinned finish this way, it can lead to less headache because each coat is easier to apply and control than a brushed coat.

    IIRC, Varathane is pretty thick; it's intended for floors, i think.

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