I googled the art of slats and plaster and this is what I found. Plaster and lath was the method craftsmen used in the early 1900s and before that to construct interior walls. Plaster was mixed by hand and spread over the lath--wooden oak slats nailed close together that held the plaster in place. Old houses were all constructed this way. Master craftsmen working on old houses used plaster and lath to construct all interior walls. Plaster walls were smooth and silky, and when cured were paintable. Plasterers were skilled craftsmen who worked long hours perfecting interior walls. Plaster and lath walls took 30 days to cure, although craftsmen advised waiting a period of a year before painting. For this reason, many homeowners chose to wallpaper their walls so as not to ruin the plaster work by painting too early.
Plastering involved placing three layers on top of the other. The first coat stuck to the oak strips and was called scratch coat, which was troweled carefully into the lath to form a bond. The second coat was called brown coat, then a finish coat was applied thickly and pressed firmly to form a half-inch wall of silky-smooth lime plaster.