The three-coat lime plaster wall of the traditional New England house is not a building technique that has been superseded. It has been replaced — by drywall, for cost and speed — but it has not been improved upon. The three-coat plaster wall is harder than drywall, more durable, better at acoustics, better at vapor management, and more appropriate in a historic building. In a restoration context, it is the correct specification. In new traditional construction, it is the correct aspiration.
A three-coat plaster wall has a quality that drywall does not. It is harder — you cannot push a finger through it as you can through drywall. The surface is slightly irregular — the float marks of the finish coat produce a texture that varies slightly across the wall, catching the light differently at different angles. It feels solid because it is solid. An inch of lime plaster over wood lath has mass and thermal capacity that 5/8" drywall does not approach.
Three-coat lime plaster over wood or metal lath. Scratch coat: lime putty and sand with animal hair fiber, applied to the lath and scratched to create a key for the next coat. Brown coat: lime putty and sand, floated level, the main thickness coat. Finish coat: lime putty, marble dust, and white cement in various proportions, depending on the desired finish character. Total thickness: 7/8" to 1" over lath.
Lime plaster is vapor-permeable — it breathes. In an old building with inherent moisture movement, this is the correct wall material because it allows the building to dry. Drywall, being paper-faced, can support mold growth in moisture-prone conditions. Plaster does not. Lime plaster is also resistant to impact damage in a way that drywall is not.
Historic plaster walls should be repaired rather than covered or replaced with drywall wherever the plaster is structurally sound. New construction in the traditional vernacular should specify three-coat plaster where the budget and the building merit it. The wall material is part of the building's character.
A skilled plastering contractor with three-coat plaster experience. This is not a common skill — find a plasterer before designing around it. Materials: lime putty from Virginia Lime Works or The Lime Works.us; mason's sand; animal hair fiber; finishing materials from specialty suppliers.
Three-coat lime plaster — scratch, brown, and finish coats — over wood lath for interior walls in traditional New England buildings under restoration or new traditional construction where the budget supports it. Lime putty from domestic manufacturers. Finish coat: lime putty and marble dust for smooth finish. This is the wall the house was designed to have.
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