St. Mary's Church Conservation

INTRODUCTION

Conservation works at St Mary's were commissioned by Galway County Council, the Employer; Mathieu & Mitchell Ltd was appointed Contractor; the consultants were John Britton, Structural Engineer; Dominic Delaney, Archaeologist; Brendan Slevin, Project Manager; Gerry McManus, Conservation Architect. The works received grant aid, administered by Galway Rural Development.

GENERAL DESCRIPTION OF WORKS

Works were generally carried out as described in Engineer’s drawings and Conservation Architect’s specifications and schedule of work. As the time of year was not favourable for the use of lime, particularly not fat or feebly hydraulic lime, it was necessary to use moderately hydraulic NHL3.5 in the mortar and grout mixes.

The contractor sourced his sand from Cannon Quarry, Loughrea and used a mix of sharp plastering sand and concrete sand with a large chip. This proved to give a successful mix which set well and gave a satisfactory appearance. While the proportion of large chip was probably a little greater than in the early mortars, the mortar gave the desired grainy appearance and matching grey colour tones. The repair and consolidation work can be identified on close inspection while toning in well from a distance.

Sand used was limestone sand with particle size from 0-6mm, larger aggregate had particle size from 0-14mm. Neither were from crushed aggregate but from pebble aggregates which matched fairly well with the original mortar. Due to the time of year the contractor made provision for protection of the lime work using straw, hessian covers, and used plastic and electric tracer wires hooked up to a metered electricity board independent of the Heritage Centre. The tracer wires were placed over and around the completed work below the straw protection. These wires heat when the temperature falls below a certain point (in this case the setting was 0 deg C)

It is notable that the archaeologist considers that there are probably 4 or more different phases of building at this site as well as a certain amount of modern 20th century repair. His report will discuss this and pinpoint different styles of building corresponding to the different phases. The historic mortar mixes also show subtle variations associated with the different phases. However the colour of the mortar is fairly consistent due to the general use of local grey limestone sand. It was decided to use the one repair mix throughout for the consolidation of rubble stonework because of its desirable properties described above, particularly the good setting properties conferred by the coarse aggregate, useful at the time of year. Of course, a much finer mix was used for repair of cut and carved stonework, and for grouting. The lime used was Otterbin from the Traditional Lime Company which has a creamy rather than a very bright white colour.

Mortar mix for building rubble stonework generally and rough racking: 2 parts NHL 3.5 : 3 parts 0-14mm aggregate : 2 parts 0-6mm sand

Mortar mix for re-pointing: 2 parts NHL 3.5 : 3 parts 0-6mm sand : 2 parts 0-14mm aggregate.

Mortar mix for limecrete capping where required: 2 parts NHL 5 : 5 parts 0-14mm aggregate.

Mortar mix for repair of cut stonework: 2 parts NHL 3.5 : 5 parts silica sand 1mm down.

Mortar mix for grouting: 2 parts NHL 3.5 : 5 parts silica sand 1mm down. 7kg of casein used per 15 bags of lime, approx.

The grouting technique adopted by the contractor as the most appropriate in the particular circumstances is described as follows. Wall was cleaned down and loose mortar and clay removed from joints. Water tests were carried out to establish if and where there were voids in the core of the wall and where the water was escaping on the wall face. Escape holes and joints were plugged temporarily with a clay daub and the wall grouted in shallow lifts as per usual practice. Re-pointing was undertaken where necessary following setting of the grout and washing away of the clay daub plugging. Where it was necessary to rebuild stonework the stone used was sourced from collapsed stone at the base of the particular piece of wall being rebuilt, or where sufficient was not available in situ, stone was sourced in the stone dump against the boundary wall in the north corner of the graveyard. The archaeologist supervised all reuse of stone. No cutting or dressing of stone was done.

CONCLUSION

Extent of work undertaken was limited by financial constraints but the works which were completed were substantially as set out in the tender documents. Despite the unfavourable time of year for the use of lime, the repair work was successful and mortar has set well. This was largely as a result of the careful protection of the works which the contractor put in place. The winter of 2014/2015 was not severe which probably also helped. Repairs are readily identifiable at present but should blend in well in the future as the mortar ages. Aggregates are from native local limestone which is appropriate, and appearance, while not identical to the original, is similar in character. Written and photographic records clearly identify repairs undertaken.

Every effort was made to specify and undertake consolidation and repair works which would ensure the stability and preservation of the ruined remains of St Mary's into the future. However the work was constrained by the funds available and not all parts of the structure were the subject of works and works which were undertaken were limited. On-going monitoring of the structure must form part of a management plan for these important remains.

Prepared by Gerry McManus B Arch, M Arch Sc (Building Conservation), MRIAI.