House 7, Skara Brae, Orkney
Context
This is the remains of a stone house from about 3000BCE. It was excavated in the mid 20th Century and has been exposed to the elements ever since. Some of the stone seems as good as the day it was excavated whereas other parts have disintegrated to a large extent.
Issue
Accelerated stone decay seemed to be associated with an area of stone “protected” by glass. The glass seemed to be causing the problem and was replaced with a solid turf roof. The effect of this change needed to be recorded and assessed.
Investigation
Reliable, accurate and repeatable data gathering proved to be very difficult as the Orcadian weather kept damaging monitoring equipment.
Temperature and relative humidity inside and out was recorded by two systems at once (Tinytag & Rotronic loMoniggers) so that if one failed then there was a backup.
Fluctuations in both temperature and relative humidity were found to be very small after the glazing was replaced. A geological assessment of the stone found that it was susceptible to fluctuations in relative humidity due to clays in the stone. It is also susceptible to damage from high relative humidity due to iron oxide and sulphur in the stone possibly creating mild sulphuric acid.
Action Taken
Monitoring continues in order to establish that conditions remain stable and to provide early warning of any changes. Much of the effort and cost of this is spent on maintaining and replacing the often damaged monitoring equipment.
Outcome
Consistently high relative humidity with a small risk of sulphuric acid decay is preferable to the constant damage caused by salt efflorescence and clay expansion. Monitoring continues with visits every 6 months to check conditions and the function of the data loggers.
