Harl

Technique

An example of the inadequate protection afforded by high cement harling is the Charles Rennie Mackintosh designed Hill House completed in 1904 using the newly available but poorly understood Portland cement harling. Over the years water had penetrated the harling and threatened the overall integrity of the building. The National Trust for Scotland, the building's owner, has (2019) enclosed Hill House in a transparent 'box' which will allow some rain to enter but which will eventually allow it to dry naturally. It is estimated that this will take seven to ten years, after which the box will be removed.