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1. A liquid coat which seals wood, plaster, etc., and prevents the surface from absorbing paint or varnish; may be transparent; may act as a primer for a following coat or as a finish for the surface.
2. A coat, applied in liquid form, which is laid over a tar-like substance to prevent its bleeding through an applied paint film.
3. A finishing coat of a bituminous substance, asphalt, concrete, etc., to seal it against moisture.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.