Pounds of shellac per gallon is a "cut"
Hi,
Bob Flexner indicates in the chapter 'washcoats' that a shellac washcoat
is: 'shellac with denatured alcohol to a 1-pound cut.
Does this mean that I have to mix it up 1/1???
for other washcoats as water-finnish based and others he mentions the proportions by example 2/1 but the shellac - of course just the one I need - hat to be ' a 1-pound cut' with alcohol.
What can be the meaning of that?
Squirrel
A "pound cut" of shellac is that amount of dried flakes of shellac added to a gallon of denatured alcohol. To make a 'one pound cut' of shellac, you would add one pound of shellac to one gallon of denatured alcohol. I use shellac in a one pound cut routinely as a sanding sealer as part of my standard finishing procedure - most of my pieces are sprayed with lacquer, and the shellac provides a very acceptable "primer" coat for this, or for polyurethane finishes.
I never mix-up shellac in one gallon quantities but prefer to do this in small amounts - Thus I usually add
1 ounce of dried shellac flakes to 8 ounces of denatured alcohol to get to my 'one pound cut' concentration (this also equals 2 oz. dried flake per pint). I use ultra-blonde shellac, which is the highest (and unfortunately, the most expensive) grade of shellac flakes, because it is purified to such a high level. I much prefer using the ultra-blonde (or blonde) grade compared to lower grades of shellac (e.g. garnet, button, orange, etc.) since the blonde grade alters the color of the piece very little, yet allows for improved final sanding characteristics and surface preparation for the final film coats. This also helps strengthen the softer wood fibers in those species that are ring porous, or with pieces that are made from woods that are generally somewhat soft overall (i.e. spalted woods).
I have had very good success with the de-waxed shellac flakes made by Hock - I think Woodcraft sells this brand. I have not used the pre-mixed shellacs (e.g. Zinsser) for turned items, but have used them for flat woodworking projects. If I recall, these are sold pre-mixed in a 'two pound cut' concentration (but check the label to be sure) if you elect to try the pre-mixed version. To get to a one pound cut, you simply mix equal amounts of two-pound cut shellac and denatured alcohol. regardless, the shellac used should be de-waxed.
A few other hints: Avoid the temptation to sand too soon after applying your shellac wash coat..... be sure it is good and dry before you begin sanding to avoid rapidly gumming-up your abrasive. When doing an initial sanding immediately following a shellac application (after it is totally dry), I find that a fairly quick and aggressive rub-down (with the lathe spinning, or off the lathe by hand) with #1 steel wool
first quickly removes excess shellac on the surface of the piece - this significantly extends the life of the sandpaper used in subsequent pre-finishing sanding operations. I usually sand to at least 400 following the steel wool cleaning, beginning at 150 or 180 and working up to 400 to get to the stage where I can spray the lacquer (or water-based polyurethane).
If you want to use a shellac-based friction polish (e.g. Mylands) instead of sprayed finishes, the 1 pound shellac wash coat, followed by careful sanding, does an excellent job of getting the surface prepared for a smooth final "friction rubbed" finish.
Hope this informaton has helped.....
Rob Wallace
