The ISSE recognises that older buildings, especially those built before 1890, are constructed with lime mortar and lime plastered walls.
Over the years many general and specialist surveyors have been responsible for the use of sand and cement in repairs of such masonry. This is inappropriate and the use of internal sand and cement renders, or external repointing in sand and cement, should never be undertaken in heritage properties. Many damp proofing manufacturers and companies have not enjoyed a good reputation in this respect leaving a legacy of rapidly deteriorating buildings which had previously stood for centuries unmolested.
Lime mortar masonry joints and internal lime plaster act as a sponge for internal moisture and water vapour. The internal moisture inside the living accommodation of a structure emerges via the mortar joint and evaporates off. When cement is pointed over the original lime joint the system of passive natural drying out is interrupted and moisture instead penetrates the edges of the masonry and spreads throughout the internal plaster as stubborn damp patches.
This is often mistaken for rising damp that may be present too, but which was also removed via the mortar joint. Ground salts brought up by rising damp may however be a problem.
When lime plaster is removed and the external mortar joint is repointed in cement this conspires to cause a deterioration so severe it can be equivalent to centuries of normal wear and tear within a few years and from which the building may never recover.
The ISSE is researching and developing products and methods which can remove the ground salts from the wall or provide a cavity product to replace lime plaster, when and if this desirable which introduces a means of drying and drainage void between the substrate and the internal surface.
Nano stone preservatives are currently being researched to deal with salt crystallisation and deliquescence.
Sand and cement used to point lime joints in masonry, especially old and porous masonry, is much harder than the masonry substrate itself thus rapidly accelerating erosion of the stone or brick leaving the cement pointing protruding as an unsupported lattice while the masonry behind erodes through moisture and salt damage exacerbated by cyclical freezing and thawing over winter. Many an ancient edifice is now at risk or has already deteriorated so badly as to need major restoration works which would never have been required in the first place.
Alternative materials and methods can be used which respect the historic fabric and which do not interfere with the delicately balanced function of the fabric, which is to allow buildings to dry out naturally via breathing out damp air through mortar joints and porous masonry.
The ISSE Home Log features a comprehensive conservation and regulatory section. A narrative contains a full description of conservation features with table of materials such as traditional paints and different types of hand made glass.
The ISSE has appointed an experienced and well known conservation specialist to Board Level in order to lead to greater awareness of conservation requirements in the industry.
Conservation issues are likely to arise in the implementation of repairs to older and listed buildings, for example, replacement of timber lintels with timber where there is a recurring risk of dry rot. The ISSE can advise in these situations.
Salt analysis of historic building fabric can be provided in order to support and validate a recommended course of treatment.
This is especially relevant in internal plaster or decorative surfaces.