The time saver with this process is that a third coat, the scratch coat–normally required in a normal lath and plaster wall–and its drying time are eliminated from the process. The finish coat of plaster is applied after the brown coat has dried. When all the Rock Lath is installed on the wall a brown coat (or undercoat) of plaster approximately 1/2′ thick is applied to the Rock Lath. These sheets were applied to the wall in the same fashion as Drywall. The Rock Lath itself comes in sheets 16″ x 48″ and 1/2′ thick. These keys harden to hold the plaster veneer to the Rock Lath. Installing drywall requires fewer tools compared to plastering. (This might also speak to why even though submerged during Katrina for several hours the rock lath did not mold the same way Drywall does.) The most obvious difference between today’s Drywall and Rock Lath is that in Rock Lath a 5/8″ hole is cut to allow the brown coat of plaster to spill through and create a key. Cost-Effectiveness: Drywalling over plaster walls is cost-effective because they are typically cheaper than plaster walls due to their simpler construction process and the availability of ready-made components and supplies.

While similar to modern Drywall (Sheetrock) as a gypsum material, rock lath was treated chemically so it would be capable of accepting a wet veneer of plaster. The material is called Rock Lath and much like our past MissPres Architectural Word of the Week “ Grounds,” if it does it job correctly and without interference it will never be seen. The technique derives from an earlier, more primitive process called wattle and daub. It consists of narrow strips of wood ( laths) which are nailed horizontally across the wall studs or ceiling joists and then coated in plaster. Have you ever seen a material attached to a wall that looked like drywall but maybe had some holes in it and possibly some plaster stuck to one side? It’s possible you never have. Lath and plaster is a building process used to finish mainly interior dividing walls and ceilings. Here we will illustrate several types of gypsum board lath. Rock Lath Detail from Preservation Brief 21: Restoring Historic Flat Plaster-Walls and Ceilings Rock lath or button board was used as a base for wall and ceiling plaster systems as early as 1918.

Rock lath walls