Sandstone repair and cleaning:

Irvine Town House

Irvine · 2016

Our role: Stonework sub-contractor
Client: McLaughlin & Harvey
Architect: Robert Potter & Partners
Value: £0.5m to £1m
Programme: April 2015 to 2016
Scope: Condition survey, specialist cleaning, stone removal and rebedding, sandstone indents, lime mortar pointing, mortar repairs, burnt sand mastic, portico and tower works

Irvine Town House is a sandstone civic building on the town's High Street, with a columned portico, arched windows, a bracketed cornice and a tall central tower. Barr Construction appointed us as stonework sub-contractor on a refurbishment designed by Robert Potter & Partners. Our package covered the survey, cleaning, repair and repointing of every elevation and the tower, and the downtaking and rebuilding of the portico stonework. The restored Town House now forms part of the Portal, Irvine's leisure, cultural and community centre, which opened in January 2017.

Irvine Town House, High Street, Irvine, Ayrshire — photograph 1

Irvine Town House, High Street, Irvine, Ayrshire — photograph 2

Irvine Town House, High Street, Irvine, Ayrshire — photograph 3

Irvine Town House, High Street, Irvine, Ayrshire — photograph 4

Irvine Town House, High Street, Irvine, Ayrshire — photograph 5

Irvine Town House, High Street, Irvine, Ayrshire — photograph 6

The challenge

Decades of weathering had left the sandstone in mixed condition. Cornices, modillions and column bases showed surface loss and delamination, balcony and cornice ledges carried biological growth, and old ferrous fixings, redundant cables and vegetation were causing damage in the joints. Earlier coatings, cement render repairs and bitumen on some elevations had to be removed before repairs could begin, and once the scaffold was up and the stone washed down, the extent of front elevation stone needing replacement rose from around 80 to around 90 per cent. The building is on a busy high street, so cutting had to be controlled to limit dust, and stone for the indents had to be matched to the existing sandstone and ordered well ahead of installation.

Our solution

We began with a condition survey, from which we prepared cutting lists and templates and ordered the replacement stone. Ferrous fixings, redundant cables and vegetation were removed, and a specialist sub-contractor treated the stonework with biocide and cleaned it using a low pressure, high temperature DOFF steam system, with poulticing to draw out salts and repeat passes to lift old coatings. Decayed stones were then cut out, roots removed and sound stones rebedded. New sandstone dressings were indented, and squared rubble was indented using salvaged stone from the downtakings where it could be reused. Open joints were cut out and repointed in traditional lime mortar, and small repairs were made in a pigmented repair mortar. Burnt sand mastic was applied at the windows once the stonework was complete. Around 90 cubic metres of replacement stone was worked in our own workshop from one to one templates taken on site, including seven carved face masks modelled on the sculpture of another building by the same architect. The portico was carefully downtaken, with each stone surveyed and weighed first, then rebuilt largely in new stone with a spider crane lifting the units into place, and the tower, where columns and capitals weigh up to 400kg, was repaired from scaffold and hoist. Over 1,100 square metres of the remaining elevations were cleaned and repointed in lime. Stone was wet cut where possible and cut high on the scaffold, away from the public.