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Thread: Shellac layers

  1. #1

    Shellac layers

    Getting close to the finishing stage of a bedframe project I chatted about here back last fall.
    I have some bags of flakes from the shellac shack for the colors I want, but the one thing I never had tried to calculate was pounds to coverage area.

    When using mixed flakes, do you only spray to achieve the desired color, then after that just clear shellac for added layers?

    Second, is there a general rule of how many layers of shellac are recommended prior to doing a topcoat of EM6000?


    Thanks!

  2. #2
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    One important thing to understand about shellac and other "evaporative" finishes is that "in general", there are no layers. Each application "generally" burns in/combines with the previous to create a single layer of finish. For the question you make relative to coloration, continued application of darker colored finish is going to result in...darker colored finish.

    If you are using the shellac under other finishes, such as the EM6000, it's essential that your shellac be as thinly coated as you can while still doing the job you want it to do. You can have issues with water borne finishes in particular over "thick" shellac structures, including spider-webbing/cracking in the finish which is very noticeable and unsightly. I routinely use de-waxed shellac as a barrier layer between oil and/or dye and my Target Coatings top coats; usually EM6000, but I use other Target products, too. I spray only one coat or two at the most if I need to knock down any grain raise nibs with 400 paper before moving on to my water borne top coats. Many of the times when I've broken that rule, I've had some finish issues like those I mentioned...so I don't do that anymore. Thin shellac coat unless shellac "is" the finish.
    --

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

  3. #3
    Wise as always Jim, thanks!
    Now that you mention the aspect of layers per se, I think I had read that a while back here or in another post about shellac. Just needed a refresher to get the cobwebs cleared out!
    With 2 coats max for shellac, what is your typical number of passes for the EM6000?

  4. #4
    Jeremy,

    For mixing instructions (proportions) try https://www.shellac.net/PoundCutChart.html.

    It is best to weigh the shellac but if you don't have a scale use about 1/2 of the final total volume of shellac flakes. So, to make a quart of 2 lb cut, use a pint (2 cups) of flakes and then eventually fill the container to a quart. A 2 lb cut is fairly common.

    I don't normally spray shellac. I brush it. Therefore, I do not try to tone the color using different coats the way I would with varnish. Successive coats of shellac dissolve the layers below and may tend to run. That may make streaks etc if you use different colors. Try to choose a shellac color that pleases you. You can tint shellac with a product called Trans-Tint, but if you want to go more than a few shades you will be better off if you color the wood instrad of the shellac because of the streaking that I mentioned. Be aware that colored shellac requires a bit of skill to get an even color.

    For a piece of furniture like a bed I would probably brush three coats. Some people would say that shellac does not age well if you apply many coats, others disagree. I have never found any issues with four or more coats, but from the standpoint of durability on a bed three coats should be fine. That's brushed. I can't guess how thick a sprayed coat of shellac would be.

    Finally, if you plan to apply varnish topcoats be sure to use dewaxed shellac. Varnish is also a good idea because a headboard is likely to be exposed to hair oils, hairspray, who knows what that may mar a shellac finish

    Doug

    Doug

  5. #5
    Thanks Doug.
    I probably didn't explain it the best, but I have different colors of flakes, but only one I was wanting to use on the bed frame. So I wouldn't be trying to mix different colors with different passes, just one color and a few passes.

    Good point on the headboard. No hairspray or hair oil but like you said who knows what might mess up the finish. I think the final coats of EM6000 would be the protective layer I'm looking for against things like that.

  6. #6
    Jeremy,

    After I posted my earlier response, I realized that I should have commented further about the issue of multiple coats of shellac. Since you will be varnishing anyway, the need for multiple coats of shellac may be reduced. I happen to think that multiple coats of shellac under varnish is a great way to get some "build" and increase chatoyance. I usually let varnish cure for at least 36 hours before applying the next coat. In contrast, I let the 2'd - 4'th (+/-) coat of shellac dry 12 hours to overnight So multiple coats of shellac require less time to completion.

    Some people would say that you don't need even one coat of shellac unless you want to seal in oil stain to keep it from running under varnish. One of the regulars on this forum recommends a policy of using only one type of finish and (I think) might recommend that you just use varnish. He uses a much wider variety of finishes than I do and may be right about compatibility in general. I don't necessarily agree with him when it comes to shellac because I think that "everything" sticks to dewaxed shellac.

    So, I there is a range of opinion about this that will support a varity of options.

    Doug

  7. #7
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    Quote Originally Posted by Doug Hepler View Post
    I usually let varnish cure for at least 36 hours before applying the next coat.
    Most varnishes will cross-link (form chemical bonds) between consecutive layers if they're applied within a day or so of each other, before the previous layer has fully cured. The resulting bonds are far stronger than any mechanical interlock, so by waiting 36 hrs you're weakening your finish.

    You need to wait a long time (longer than that IMO) before rubbing out or otherwise manipulating the final coat, but there's no reason to do so between coats.

  8. #8
    Patrick,

    I take your point. I have had the "witness mark" issue in the past, I admit, and my long cure time may be the reason, but I think more likely it was with polyurethane resin varnish. On the other hand, (a) the alkyd and phenolic resin varnishes that I use take a long time (OK, maybe not 36 hours) before they are hard enough to sand without "balling" and (b) I have never had any evidence of chipping (as in delamination) of an alkyd varnish finish. I rarely use polyurethane resin varnishes any longer, but if I did I would not let them cure nearly as long.

    Before you ask I am not talking about long-oil varnish. I usually use Benjamin Moore Benwood or Sherwin-Williams Classic Fast Dry. The "fast dry" refers only to the first (evaporative) stage of drying. I got started with them years ago and have tended to stick with what I know.

    Doug

  9. #9
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    Quote Originally Posted by Doug Hepler View Post
    I take your point. I have had the "witness mark" issue in the past, I admit, and my long cure time may be the reason, but I think more likely it was with polyurethane resin varnish.
    You'll get the witness mark when you rub through a coat boundary no matter what. In a reactive varnish consecutive layers that are applied within the cure time will cross-link and thereby improve adhesion, but they won't fuse into a seamless whole the way nitro or shellac will.

    Quote Originally Posted by Doug Hepler View Post
    On the other hand, (a) the alkyd and phenolic resin varnishes that I use take a long time (OK, maybe not 36 hours) before they are hard enough to sand without "balling" and (b) I have never had any evidence of chipping (as in delamination) of an alkyd varnish finish. I rarely use polyurethane resin varnishes any longer, but if I did I would not let them cure nearly as long.
    Point taken. If you need to sand between coats then that pushes you towards a longer recoat interval due to balling, and there isn't much you can do about it. FWIW my schedule with varnish is to do it over 2 days: A couple/few coats ~hours apart on the first day, then dry overnight, then level, and then the final coat on the second day.

  10. #10
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    If you must use shellac, keep it thin. What Jim has observed is an example of what happens with coating incompatibility. It's why I never recommend shellac as a tie coat. Two reasons. If a coating system needs a tie coat, it is in trouble from the start. If you need a tie coat you are taking a chance and in my work, I get paid to know how to do it right, not take chances. Cheers

  11. #11
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    Wayne, I can appreciate your point of view, but the reality of things for a large number of us is that without a barrier coat like de-waxed shellac, it seriously limits what we can do as our first steps in the final finishing process. Safety dictates we spray water borne finishes, but if we want to use oil, such as BLO, on the wood initially to add "pop" and color, we need that thin barrier coat to insure that the water borne finish will properly adhere. It's also a step used to seal a water soluble dye prior to subsequent steps. There is generally no incompatibility issue here. The majority of issues around shellac as a barrier coat appear to be focused squarely on applying the shellac thickly, either by technique or be applying more coats than are required to merely seal what's below it.

    In an ideal world, this kind of thing wouldn't be necessary, but most solvent-based finishes (which inherently "solve" the problem) are not safely usable by folks who don't have a professional spray booth.
    --

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

  12. #12
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    I really need to try shellacking something. In the past SWMBO has handled the staining/finishing work as I'm no fan of that phase of a project. I need to change that...or is it change me?
    Marshall
    ---------------------------
    A Stickley fan boy.

  13. #13
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    Fair call, Jim. Cheers
    Every construction obeys the laws of physics. Whether we like or understand the result is of no interest to the universe.

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