Sand the wood surface to prepare it for a coat of shellac. If you intend to seal a different material with shellac, then sanding is unnecessary. Shellac will seal and protect live tree stumps, asphalt, metals, craft projects, and small wooden objects. For most wood surfaces, hand-sanding the wood with 120-grit sandpaper with or without a sandpaper block, followed by a lighter sanding with 220-grit sandpaper creates a smooth surface to work with. For wooden floors, use a floor sander with 80-grit paper at first, then a 100-grit finishing paper.
Clean up the sanding dust with either a vacuum, or a tack cloth for wood surfaces.
Moisten a rag with mineral spirits and wipe down the floor you wish to seal. For any other woodwork or carpentry, fill any noticeable holes in the wood with wood filler.
Select a brush to use with the shellac, depending on what sort of surface you wish to cover. For most open, flat areas, it is best to use a 2- to 3-inch china bristle brush or a premium-quality synthetic bristle brush. A 1- to 2-inch angled sash brush works best for crevices or detailed areas.
Thin the shellac with alcohol, if the instructions call for thinning. Follow the package directions.
Pour some shellac into another container. This way, you can work with that smaller quantity of shellac without getting contaminants into the entire can.
Sink half of the brush's bristles into the shellac in the new container and tap off the excess by knocking the end of the brush against the edge of the container. Do not wipe the brush on the edge of the container.
Brush on the shellac with full pressure and even strokes. Do not brush the surface excessively, just enough to coat it, and brush in the direction of the woodgrain. Also, work at a quick, but not reckless, pace. Load the brush with less shellac for vertical surfaces, since gravity will take its toll on an overly thick coat of shellac.
Add another coat of shellac. For each coat, do not try to go back and brush over places you have missed, simply wait for the next coat. Mind the edges of the woodwork to avoid accumulation of shellac. A rule of thumb for how much shellac to use is 1/4-pound of shellac for every 10-square-feet of surface area. For light sealing job prior to wood staining, one or two thin coats will suffice.
Clean the brush or any spills with denatured alcohol.