Permeability in lime plaster in relation to durability of covered materials
2004 (English)Conference paper (Refereed)
In restoration of old buildings, lime plasters are used for reasons of authenticity and for technicalreasons as well. In many traditional constructions, there is wood behind the plasters or there is old limemortar in the masonry. For the durability of both these underlying materials, it is important that therelative humidity, RH is not too high under a long time of exposure. This can lead to an accelerateddegradation process of wood and leaching of lime in mortars. To prevent this, the plaster must have aproper permeability.The permeability of a material determines its ability to transport gas and moisture. In lime plasters,permeability affects hardening, carbonation as well as durability of the underlying materials. In thepresent paper, eleven mixtures of lime mortar were studied. The binders used were lime slaked in fourdifferent ways, hydraulic lime and cement.The following measurements were made to analyse the permeability and the pore structure of thesamples. Gas permeability and draining curves give an indication of rate of carbonation. Vapourpermeability shows the ability of plaster to transmit moisture at different RH. Thin sections were madefor microscopically investigations of the samples.The investigations show that both the vapour permeability and gas permeability decreases with anincreased amount of hydraulic binder in the lime plasters. Even small amounts of hydraulic binderhave a significant effect.By connecting these results with examples from reality, the picture becomes clearer. In the medievaltown Visby in Sweden, there are several examples of both rotten wood and disintegrated lime mortars.It is constructions from 13th to 19th centuries and low permeable cementitious plasters have coveredthem all, during the middle of the 20th century.
Place, publisher, year, edition, pages
lime, cement, plaster, pore structure, permeability
Other Natural Sciences
Research subject Conservation (HGO)
IdentifiersURN: urn:nbn:se:uu:diva-220075OAI: oai:DiVA.org:uu-220075DiVA: diva2:704001
Proceedings of the 32nd IAHS World Congress on Housing – Sustainability of the Housing Projects. Trento, Italy 2004.