Blockade White Shellac Sealer Primer provides excellent adhesion to almost all interior surfaces such as previously coated and new wood, plaster, drywall, porous wallcoverings, metal and tile and requires minimal preparation before use. Blockade is quick drying, saving time on jobs that require multiple coats or to be quickly overcoated with emulsion. The pure shellac base permanently blocks stains and odours, covering even the darkest of colours.