Glossary

Aggregate

Additives to plaster designed to make them lighter and/or stronger, usually sand, vermiculite, or pumas/volcanic ash. Aggregates prevent shrinkage by making efficient use of binder materials.

Blue Board

Like drywall, a gypsum-based board with blotter paper to accept modern plaster to adhere to.

Brown Coat

Base coat plaster in a multi-coat system. Sometimes applied over the scratch coat in a 3-coat application, or the base before a topcoat of plaster.

Calcimine

A water-soluble coating comprised calcium carbonate (carbonated chalk) that was used as a quick and economical coating over walls and ceilings.

Corner Bead

Plastic or metal termination of an edge that can be either 90 degrees or bullnose (rounded). To withstand impact without ruining the plaster that joins it.

Cornerite

Goes in interior corners beneath the plaster to prevent cracking.

Durabond

A brand name for a setting joint compound. Has gypsum crystals that make it set like plaster, and bonding agent that makes it stick like joint compound.

Gypsum

An organic material, called calcium sulfate in its original form. It is mined and processed crystal that is the industry standard for modern lath wallboard plaster It is a substrate material as well as an active ingredient in modern plasters.

Hawk

A one-handed tool used to hold plaster for hand tooling and troweling.

Joint Compound

Designed for use with drywall, a water-soluble binder with inert, non-reactive compound used for filler.

Keys

Parts of plaster that go through openings in wood or wire lath and curl over to assist the plaster in holding onto the substrate.

Lath

A substrate material for plaster. Wood or wire or gypsum core board, it provides the base for plaster to adhere to either through use of keys or other mechanical bond.

Polishing

Final step in finishing the plaster topcoat involving a final scrape with the trowel to remove irregularities, fill void, compressing the surface of the plaster to create a glass-like finish.

Reattachment

An adhesive process whereby plaster that has pulled away from its substrate is glued back in place with the use of acrylics and mechanical means push the plaster back in place.

Scratch Coat

The first coat of plaster in a multi-coat system. The wet plaster is “scratched” with the trowel or a comb to provide a rough surface to give tooth for the next layer of plaster to adhere to.

Skim Coat

Coating an entire area with a thin coat of material.

Slaked Lime

Also known as active lime or lime putty. Lime that has been processed (burned) and had water added to it, but has not received its final set through chemical reaction with carbon dioxide to bring it back to lime stone (calcium carbonate).

Substrate

The physical base that plaster or other finishes attach to either mechanically or physically.

Top Coat

The final coat in a plaster system, which could be veneer plaster, lime or lime and gauging plaster, or lime and sand plaster depending on the system.

Veneer

A thin coat of plaster, designed for newer blueboard plaster systems.

White Wash

A coating made of active lime and water used to coat plaster, wood and masonry. A home brew, it was sometimes used as a germicide, including such chemicals as formaldehyde and copper sulfate.