Insulated Lime Plaster

We specified an insulated lime plaster finish to replace polystyrene insulation products which had been causing the walls of this property to sweat for many years. This was damaging finishes and creating an unhealthy internal air quality.

Lime plaster is the traditional wall and ceiling finish found in most UK buildings constructed before the early 20th century. Unlike modern gypsum or cement-based plasters, lime plaster is designed to work with older masonry and timber-framed buildings by allowing moisture to move through the fabric of the building rather than trapping it.

Lime plaster is a more time-consuming process than modern plasters; it is slower to apply and can require more coats with drying time in between, requiring several visits. It also hardens differently from gypsum plaster which becomes firm within hours, as it initially dries, then continues to harden by absorbing carbon dioxide from the air (a process called carbonation).

Although the process is slower than modern plastering, lime plaster offers several important benefits for historic buildings, reducing the maintenance requirements and cost of repairs in the long term.

Its benefits include:

• Breathability: It allows moisture to evaporate through the wall, helping reduce damp problems.
• Flexibility: It can accommodate small movements in older buildings without cracking as readily as rigid cement plasters.
• Compatibility: It bonds well with traditional stone, brick, cob, wattle and daub, and timber lath.
• Repairability: Damaged areas can often be patched without replacing entire walls.
• Historic authenticity: It preserves the character and performance of listed and period buildings.

On this project, the main contractor’s plasterers undertook a morning with Baumit, the lime product supplier and the company’s field engineer. They undertook training on the specific products and techniques involved in the process. The engineer’s advice about drying times and techniques ensured the optimum application of the products and the plasterers really enjoyed learning more about this historic and important technique.

The process of creating a lime plaster finish in this property involved: