by Dearbhail Keating
Week 6 brought us away from Wales and back to the south taking in Somerset and Dorset. Two days were spent with Andy Ziminski, Fellow and director of Minerva Conservation and two days with Philip Hughes, Scholar and director of Philip Hughes Associates.
At the Church of St Peter and St Paul in Kilmersdon Andy showed us conservation work that is about to begin. The works will involve cleaning and conserving stonework, replacing the lead roof to the tower and repairs to the inside of the tower where a bell had fallen during a ringing exercise earlier in the year.
We carried out a trial area of stone cleaning around the doorway in the forth bay of the north aisle. The staining on the stone is due to air pollution and acid rain; this reacts with the stone creating calcium sulphate which forms a hard surface crust leading to subsequent blistering as salts expand behind.
To repair and conserve, initially the stone is brushed with water and phosphor bronze brushes, this can remove the sulphate salts which are soluble and with them, a degree of staining. But further cleaning is often required using a poultice.
In this case the poultice was a mix of paper pulp, water and ammonium carbonate. This is mixed together and pressed on to the area of stone requiring cleaning. Once the poultice is applied a chemical reaction takes place reverting the calcium sulphate to calcium carbonate which is the original make-up of the stone, thus stabilising it and slowing down further erosion
Following the poulticing we carried out mortar repairs to help support fragile edges of existing stonework. This method of cleaning and stabilisation will be used on several areas of the churches façade when works commence.
Later in the week, during our time with Philip Hughes, we were fortunate enough to visit St Giles House in Wimborne St Giles, Dorset. Built in the 17th century the house has been occupied by the Earl of Shaftsbury for many generations. Works are being carried out to a grotto in the grounds by Sally Strachey Historic Conservation. We spent the day on site getting involved in a very unique type of building conservation.
The fabulous shell grotto, dating from the early 18th century, is located to the south-east of the house. Grade II* listed, the grotto is an important example of its kind and has unfortunately fallen into disrepair. A grant from Natural England has allowed work to commence on the conservation of the grotto and the works are well underway.
Comprising of two main compartments and two side wings the grotto sits over a spring that feeds water to the ornamental lake. The building is of random rubble and flint construction with a slate roof. Internally the walls and ceiling are adorned with shells, flint, coral and fossils fixed to the walls, and the lath and plaster ceiling. Timber branches encased with shells were also suspended decoratively from the walls and ceilings.
The condition of the grotto when works began was quite bad indeed. A huge amount of work was carried out to save as much of the existing fabric as possible. All shells, coral etc. that had fallen were carefully removed and stored. Photographic evidence of the grotto before it fell into disrepair is available and the various options for reinstatement of the internal finish were debated.
The roof covering of the grotto had been removed; there are a number of roof structures that have built up over the life of the building through previous repairs. It was possible to view the condition of the ceilings from both above and below. There were problems with decay of timber laths and this was resulting in the plaster and shells falling from the ceilings. Some of the walls were studded out and decay had set in here, again resulting in loss of historic fabric. The timber branches covered in shells were also in need of attention.
Guided by the site team, we removed damaged laths and a wire was put in its place. This wire was fixed to the timber rafters on either side of the lath and secured with screws and washers. The wire ran along the line of the old lath and was a few millimetres above the plaster work. Following installation of the wire a water based epoxy resin was applied along the full length of the removed lath and built up into a peak along the line of the wire encasing it fully.
This method ensured the plaster work would have the best chance of remaining in situ, limiting the risk of it falling. Discussion is ongoing as to how repairs to the studded walls and decorative shell covered branches are to be carried out – we certainly did not have all the answers!
Thank you to all at Minerva Stone and Philip Hughes Associates for being such fantastic hosts, allowing us get our hands dirty and tutoring us in the world of stone and shells!