Dubbing-out

Dubbing-out is a technique used in building conservation, particularly in the repair of historic masonry and plasterwork. It involves the application of one or more preparatory layers of mortar to fill deep voids, irregularities, or damaged areas before applying the final coat. This method ensures a stable and even surface while maintaining the structural and aesthetic integrity of the original material.

The process is especially important when working with traditional lime-based mortars, which require careful layering to prevent shrinkage and cracking. By building up the missing material gradually, dubbing-out allows for a more compatible repair that blends seamlessly with the existing fabric of the building. This approach helps maintain breathability, which is essential for moisture regulation in historic structures.

One of the key benefits of dubbing-out is its ability to support and reinforce delicate or weakened areas. In cases where masonry has suffered from erosion, impact damage, or previous inappropriate repairs, it provides a sympathetic and non-invasive solution. It ensures that the final coat of plaster or render adheres properly and functions effectively without causing undue stress on the underlying structure.

Dubbing-out also allows conservators to reshape lost details and ensure smooth transitions between old and new materials. The careful application of mortar in layers prevents abrupt changes in texture or depth, preserving the craftsmanship and character of historic façades.

As with all conservation techniques, the success of dubbing-out depends on the use of appropriate materials and skilled craftsmanship. Traditional lime mortars, mixed to match the original composition, are preferred over modern cement-based alternatives, which can trap moisture and lead to further deterioration. By applying the technique with care and precision, conservators can help extend the lifespan of historic buildings while respecting their original construction methods and materials.