Alongside restoration work at the Cathedral, over the past 30 years the fixer masons at NDR have been researching historic lime mortars, more specifically medieval lime mortar.
At Nidaros Cathedral the fixer masons install the stone components produced by the banker masons, using lifting tackle, and traditional lime mortars and grouts. The precise tolerances necessary when working with accurate templates and three dimensional moulded stone make this a highly skilled job. At Nidaros Cathedral, sometimes the repair and restoration work involves the dismantling of earlier restorations, where since 1869 they have used various cement mortars, which are today causing damage to the structure. An example of this is the recent on-going restoration project, the Kings’ Entrance, a structure which has had serious stability issues. To resolve these stability problems the structure needed to be totally dismantled. The Kings’ Entrance is a highly decorated complex structure and the fixer masons were involved in an in-depth geometrical documentation of the existing structure before it was dismantled. As a government appointed national centre for the conservation and restoration of historically significant stone buildings, the fixer masons are involved in both internal and external projects; Internal projects; Alongside restoration work at the Cathedral, over the past 30 years the fixer masons at NDR have been researching historic lime mortars, more specifically medieval lime mortar. The introduction of cement in the middle of the 19th century led to the decline in the use of lime, culminating in its virtual disappearance by the mid 20th century.
Emerging evidence in the 1970s of the damage caused to historic buildings by the use of cement mortars and modern plasters has led to a worldwide revival in the use of lime over the past 40 years. Our mortar test research and conclusions at Nidaros Cathedral over the years has informed both nationally and internationally, important issues involving the specification and use of lime mortar for conservation and restoration of historic masonry. It has also given us the opportunity to develop a suitable, compatible restoration mortar to be used at Nidaros Cathedral.
Other internal projects include the development of repair mortars to restore damaged soapstone. Commercially produced repair mortars for stone are not compatible with soapstone and over recent years we have been testing and developing repair mortars specifically for soapstone.
The fixer masons are often employed as consultants to other external masonry restoration projects both nationally and internationally. In Norway we normally work in collaboration with the client, the contractor and Norwegian Directorate for Cultural Heritage (Riksantikvaren). We advise practical proceedings, specifications of materials, and offer on-site practical teaching, where we work with the masonry contractor.
The fixer masons lecture both nationally and internationally, communicating Nidaros Cathedrals on-going restoration techniques and our research regarding historic mortars in Norway.