Tackling Damp & Improving Thermal Performance At Heritage Cottage

"It’s one of the oldest houses in Allonby, on the West Coast of Cumbria" Steven explains, "and was owned for many years by the late eminent local artist, Percy Kelly. We really wanted to keep the distinctive features and characteristics of the sandstone walls."

"The house was very damp because moisture was trapped by the external cement render so we decided to remove this and replace it with a ‘breathable’ plaster. We wanted to use materials that are sympathetic to how the walls should perform and were very lucky to find Ecological Building Systems."

With this in mind, the first step in the refurbishment process was to strip back the internal and external walls to uncover the full extent of the damp and remove the extensive mould that had built up. This uncovered beautifully undulating walls that were extremely solid but far from straight. The choice of thermal plaster was driven both by the desire to keep this authentic rustic aesthetic and also by the need to control moisture levels to prevent future problems with damp and mould. Use of a conventional impervious insulation material would not only have removed the original contours and reduced the internal space; it would also have trapped moisture within the fabric of the building. Conversely, the Diathonite system of thermal plasters from Diasen offers a diffusion open solution that skims the surface of the existing solid walls and combines excellent thermal performance with a hygroscopic capacity that absorbs and dissipates humidity, preventing the potential for condensation and mould.

The Diathonite Evolution thermal plaster used as part of a combination of breathable solutions from Ecological Building Systems at Glen Cottage is based on a Diatomaceous earth formulation, leveraging the high porosity of this naturally occurring mineral which is capable of absorbing up to 1.5 times its own weight in moisture to provide high levels of capillarity. Diatomaceous earth is combined with cork particles to enhance thermal resistance and sound absorption, naturally porous and lightweight aerated clay and NHL 3.5 lime, which provides a hydraulic binder for the thermal plaster. Diathonite Evolution was used as the insulation and resurfacing plaster for both the internal and external walls. 50mm of Diathonite was applied internally and 30mm externally, improving the U-value from to 2.5 W/m²K to 0.45 W/m²K.

Externally, stripping back the mouldy and discoloured render revealed rubble sandstone which was cleaned to remove any loose particles. The naturally rough surface provided an ideal key for application of the plaster. For the timber lintels and window surrounds, however, Diasen Aquabond was used to aid adhesion of the Diathonite Evolution.

The Diathonite Evolution was hand-applied to the external walls, with the grey of the wet thermal plaster gradually turning to white as each surface dried. Once dried, the hand-applied Diathonite Evolution provided a smooth surface for the application of Diasen D20, a water-based paint primer for use on the plaster. The external walls were then finished with Diathonite Cork Render sprayed by hopper, a diffusion open finishing coat that provides both water repellent and anti-fungal protection to the newly plastered walls. This enabled a clean, white finish in keeping with the location and original aesthetic of the building.

Glen Cottage is now completed and available to rent for those looking for a coastal retreat that combines authentic charm and a creative past with a warm, dry, quiet and damp-free interior.