Front elevation of Balnacraig House.

Front elevation of Balnacraig House with its reinstated lime harling.

Degree of deep voids to substrate at Balnacraig House.

Preparation works to walls at Balnacraig House.

Beautiful finish affect created by lime harling and lime washing.

An example of a ‘rick’.

Balnacraig House

Balnacraig House is an exceptionally beautiful early 18th Century building located in rural Aberdeenshire.

Scope of works

Works included reinstatement of traditional lime harling to original building and new extension, lime washing to all newly applied harling, selected masonry repairs and construction of slate vents.

Technical and philosophical solutions

The original lime finishes that had been removed many years ago had been replaced with a hard, dense and impermeable cement harl coat. As a consequence of this inappropriate finish a catalogue of defects had become apparent. These included moisture entrapment within the mass masonry walls, internal dampness and decay of in-built timbers such as joist ends and internal wooden safe lintols.

Laing Traditional Masonry were brought in to advise upon the repair project, working in conjunction with the client and Historic Scotland inspectors. The solution that was felt to be most sympathetic, technically sound and aesthetically acceptable was to reinstate the traditional lime harl coat. The decision to reinstate the harl coat was also guided by analysis undertaken by the Scottish Lime Centre Trust who gave advice on the materials and limewash finishes to be adopted. This intervention enabled the building to once again perform in the way that it was always intended, namely to ‘breathe’. Lime based materials whether used in the form of harl coats, mortars, or lime washes all have the ability to handle moisture allowing relatively free dissipation to occur, they are also relatively soft (however, that doesn’t mean to say that they are not durable!), act sacrificially and have the capability to accommodate movement within the structure as it changes in size with alterations in temperature and moisture levels. For all the technical benefits that are associated with lime harling and limewash coating it is always important to recognise them as the truly beautiful finish that they are.

When Laing Traditional Masonry undertake a project of this nature it is not a simple case of executing the works in a dogmatic manner. As a part of Laing Traditional Masonry service it is always necessary to establish those parts of the structure that are considered high risk, both in terms of the degree of climatic exposure and or their potential vulnerability to deterioration due poor design or maintenance. A visual survey is always undertaken to help to guide the type of materials and processes selected.

For the works to be successful it was necessary to undertake a comprehensive and methodical repair strategy. The most important aspects of this included, meticulous documentation and recording of the fabric, painstaking substrate preparation, through deep void packing, pinning and mortar ‘flushing out’, application of the harl coat and lime washing and finally, essential aftercare and protection. The mortars used for the project were specified by Laing Traditional Masonry using the most appropriate binders and well graded aggregates. All pinning stones were retained for later use and were in situations were they were missing the replacement stones were geologically compatible.

The lime harling was hand cast to give a traditional finish and the most desirable aesthetic possible. It was applied in 2 coats with an overall thickness of approximately 10-15mm. The coats were composed of a tack / pricking up coat of approximately 5mm, followed by an even 8mm finish coat. The harl was finished with 6 coats of pigmented lime wash. It important to understand the significance of limewashing onto lime harling it fulfils three functions, namely, to consolidate the freshly applied mortar, to give colour to the harling and to act as a sacrificial layer to the underlying harling.

Beautiful finish affect created by lime harling and lime washing.

Laing Traditional Masonry are clearly committed to the use of the most appropriate materials possible. This ethos was taken one stage further by Laing Traditional Masonry and the Scottish Lime Centre Trust when we manufactured local lime wash from the indigenous sources of limestone at Balnacraig. The burning of the lime was undertaken using a self contained timber constructed kiln known as a ‘rick’. The resulting quicklime was then slaked and used to make a creamy coloured lime wash.

Project

Balnacraig House, Aberdeenshire.

Client

Ballogie Estates.

Consultant

Ballogie Estates.

Solutions

Reinstatement of traditional lime harling, lime washing, masonry repairs and construction of slate vents.