Lime render and limewash to prevent damp towers

— 24 Oct 2024

Jonathan Rhind Architects have been involved in the assessment, monitoring, analysis and management of damp towers across the West Country for over 25 years. Moisture penetration in traditional solid masonry buildings is a key factor in decay, and it is felt particularly acutely in church towers.

Combating damp towers is an ongoing effort involving the technical research department of Historic England, builders, environmental engineers, architects and other specialists. Research to understand the movement of water and its characteristics is essential.

With climate change comes warmer wetter winters with greater frequency of showers, less frost and greater humidity. The greater frequency of showers gives fewer opportunities for towers to dry to the outside between wetting cycles with water penetration as a result. Much of the water penetration in masonry is by capillary suction through micro cracks with gravity and condensation all playing a part.

Approaches generally considered are:

• repointing in lime mortars
• grouting the core of walls
• external rendering and limewashing
• internal plastering.

Assessing the performance of previous repair projects and different approaches informs future repairs to church towers.

One such example is Holy Trinity Church, Challacombe. In a remote hamlet high on Exmoor, it has a 15^th Century tower which had its render stripped in the 19^th Century and stonework heavily pointed with cement. This was allowing water into the tower walls which were exceptionally wet, frost damaged and supporting a luxuriant growth of ferns inernally. It was agreed, with English Heritage support and funding, to render the tower with lime putty gauged with hydraulic lime and lime wash. The additional render mortar layers and thin coats of limewash have been successful in reducing the water penetration through the walls to the inner face, and the inside of the tower is stable and significantly drier and free from organic growth after replacing cement pointing with lime-based pointing.

The specification was for the limewash colour to closely resemble that of the underlying render so that when the sacrificial top coats weathered back differentially between sheltered and exposed locations there was not a stark contrast.

The render has not been re-limewashed since its initial application in 1998/99 and it is only now, 25 years later, the five coats of limewash have weathered back to the render on the very exposed west and south faces. The Parochial Church Council (PCC) have not had to undertake any expensive maintenance with the associated access difficulties, during this time which is a very impressive lifespan compared to c.4-8 years for the less effective modern acrylic masonry paint.

Plans are now being put into place to relimewash the tower to minimise further erosion of the render and ensure the future of Challacombe Church.