THIS to learn why button shellac is harder and better for floors.
Make the Shellac.
Measure your denatured alcohol. I bought a bunch of paint mixing buckets and lids. It made it so easy to measure the right amount of alcohol! Since I was mixing a 2-pound cut; I needed 1 quart per 1/2 pound of shellac. (A pound cut refers to how thick one makes the shellac. A 2 pound cut is a standard starting point. It is really personal preference and project preference. Shellac.net has a handy chart HERE.)
I used just about every type of brush on these floors and really couldn't tell much difference in the finish. The one type I didn't try was a lamb's wool applicator. I have used this in the past and did not get the knack. Too many drips and lines. Foam sponge brushes work fine, but it goes on thin. A chip brush works good and I used it for the majority of the floors. I felt like I could get it on quite thick for the first coat, which I liked. Then I invested in an expensive natural hair brush which I used for the top coat downstairs. It put the shellac on a little tiny bit thinner than the chip brush which was fine for a top coat.