Historic Churches 2022

BCD SPECIAL REPORT ON HISTORIC CHURCHES 29TH ANNUAL EDITION 29 without the use of chemicals and without abrading the surface. While the temperature of the steam is high, the volume of water used is low and the surface will be dry within minutes. The dry ice blasting method of cleaning uses a solid form of carbon dioxide commonly known as dry ice. Particles of the compound are sent through an air stream at a fast speed, and when they make contact with the surface they expand instantly from a solid to a gas. The expansion causes momentary freezing at the surface and the thermal shock helps to remove the dirt and grime. The combined effect reduces the amount of abrasion to the surface and no water is introduced, so the only residue is the dirt. This was the principal cleaning method used on the masonry and the only one used on the timbers. CONSERVATION OF TIMBERWORK AND ROOFS In preparation for redecoration, dry ice blasting was used to clean all burnt timbers in the nave roof which had suffered significant fire damage. As well as removing the softer charred timber without damaging the sound timber beneath, this method of cleaning was also ideal for removing the odour left after the fire. Bakers of Danbury’s team then repaired the original inner wall plate and introduced a new secondary outer wall plate to give additional support to the rafters across the width of the wall. The principal rafters are over 200 years old, each measuring approximately 400 x 400mm and 10m long, and were from very large oak trees. It was important to restore and retain these principal rafters as they are very rare, and it would be difficult to source a replacement. The team restored all seven principal rafters which form the main structural frame within the nave roof. Some of the principal rafters were badly damaged, particularly near the tower where the fire had been concentrated, some required additional support to engage the beam ends onto the new timber wall plates which was achieved by using large stainless steel flitch plates and brackets weighing in excess of 175 kg each. The common rafters were repaired and cleaned, or replaced where beyond repair. On the tower a new suspended timber roof was installed with steel supporting girders spanning seven metres. This was covered in sand cast lead (code 7) and the rainwater goods were replaced with cast aluminium. CARVED INSCRIPTIONS AND ROOF BOSSES When all timbers were being ice blasted to remove fire and smoke damage, it was realised that it would be impossible to remove the charring without losing some of the carved inscriptions, historical graffiti and fine detail of the roof bosses. The inscriptions on the roof timbers record former church wardens, reverends and people within the community as far back as 1601, and although damaged by the fire, they are still legible. Bakers of Danbury employed conservators Hirst Conservation to carry out a survey, analyse samples and provide a review of treatment options. The conservators recommended that the historic graffiti should be stabilised and their appearance retained. For the carved inscriptions and roof bosses Hirst Conservation adopted a tailored treatment for each, as they were fire damaged to varying Installing new stainless steel flitch plates and brackets to extend the principal rafters across to the new outer wall plate Not all the roof timbers could be salvaged. One of the carved inscriptions that would have been lost if the whole timber had been cleaned