Standing Building Recording

Date 31 March 2014 - 20 June 2014

Event ID 1014859

Category Recording

Type Standing Building Recording

Permalink http://canmore.org.uk/event/1014859

NL 66519 97944 An investigation was undertaken, 31 March 20 June 2014, on the mortar of the upstanding buildings of the Isle of Barra. The work aimed to explore changes in source materials, material sources and lime burning techniques. Buildings investigated included Kisimul Castle, the chapel sites of Cille Bharra and St Michael’s/Brendan’s (Borve), the mill above Northbay, and a number of ruined croft houses in the township of Balnabodach.

As with the rest of the Western Isles, the medieval lime mortars of Barra were manufactured by the burning of sea shells with peat fuel, and here this is almost exclusively cockleshell. Within Kisimul Castle, the lime mortars surviving from all four main historic constructional phases, from the early 15th to the 17th centuries, are cockleshell-lime mortars. The primary phase mortars of all three surviving chapels at Cille Bharra, and evidence from St Brendan’s/ St Michael’s (Borve) are also cockleshell-limes. Peat fired cockleshell-lime mortars are also evident within many of the post-medieval buildings surveyed, including many ruined croft houses.

Limestone-lime mortar, displaying large fine-grained limestone/marble inclusions and a variety of non-peat fuel evidence, is also evident within various contexts around Castle Kisimul, including within the tower house, curtain wall and crew house. However, this mortar material is only

apparent in secondary contexts, overlaying primary shelllime cores, and not overlaid by shell-lime bound mortar itself.

Other masonry evidence suggests this late limestone-lime probably dates from the 19th or early 20th century and this late date accords well with other limestone-lime evidence within surviving buildings elsewhere on Barra, such as a secondary phase at St Mary’s (Cille Bharra) and the water mill above Northbay.

Twentieth century cement mortars are also evident in some contexts at Kisimul, often directly overlying the limestonelime or earlier shell-lime mortars. A three layered mortar stratigraphy (shell-lime/limestone-lime/cement) is apparent in many masonry contexts, and is exemplified in the E parapet of the curtain wall.

Archive: Historic Scotland, RCAHMS and University of Edinburgh (intended)

Funder: University of Edinburgh

Mark Thacker – University of Edinburgh

(Source: DES)