split lath the plasterer had the luxury of making lath to fit the cavity being plastered. Lengths of lath two to six foot are not uncommon at Economy Village. Hand split lath is not uniform like sawn lath. The straightness or waviness of the grain affected the thickness or width of each lath, and thus the spacing of the lath. The clay plaster rough coat varied to cover the irregular lath. Window and door trim as well as the mudboard (baseboard) acted as screeds. With the variation of the lath thickness and use of coarse straw and manure, the clay coat of plaster was thick in comparison to later lime-only and gypsum plasters. In Economy Village, the lime top coats are thin veneers often an eighth inch or less attesting to the scarcity of limestone supplies there. Clay plasters with their lack of tensile and compressive strength fell out of favor as industrial mining and technology advances in kiln production led to the exclusive use of lime and then gypsum in plaster applications. However, clay plasters still exist after hundreds of years clinging to split lath on rusty square nails. The wall variations and roughness reveal a hand-made and pleasing textured alternative to machine-made modern substrate finishes. But clay plaster finishes are rare and fleeting. According to Martin Weaver, “Many of North America’s historic building interiors…are all too often…one of the first things to disappear in the frenzy of demolition of interiors which has unfortunately come to be a common companion to “heritage preservation” in the guise of building rehabilitation.” Gypsum plaster (plaster of Paris) Gypsum plaster, also known as plaster of Paris, is a white powder consisting of calcium sulphate hemihydrate. The natural form of the compound is the mineral bassanite. Etymology The name "plaster of Paris" was given because it was originally made by heating gypsum from a large deposit at Montmartre, a hill in the north end of Paris. Chemistry Gypsum plaster, gypsum powder, or plaster of Paris, is produced by heating gypsum to about 120–180 °C (248–356 °F) in a kiln: CaSO4.2H2O \overset{heat}{{}->{}} {CaSO4.1/2H2O} + 1\!1/2 H2O ^ (released as steam). Plaster of Paris has a remarkable property of setting into a hard mass on wetting with water. CaSO4.1/2H2O + 1 1/2H2O -> CaSO4.2H2O Plaster of Paris is stored in moisture-proof containers, because the presence of moisture can cause slow setting of plaster of Paris by