Why Use Lime Mortar
Slaked lime plasters and mortars have been used for thousands of years whereas the use of cement in construction is relatively recent. The vast majority of buildings in this country dating pre 1910 would have been made using lime mortar to lay the bricks, render the outside and plaster for the inside, either directly to the walls or on to wooden laths. There are many examples of these traditional methods going back hundreds of years that are perfectly sound.
Buildings made using slaked lime mortars are far more capable of withstanding the vibration from traffic and the movement of the ground beneath them. Lime mortar makes the ideal plaster for timber-frame and straw bale construction. It will even cope well with the movement of green oak, which can be seen in so many early Tudor houses.
Today slaked lime mortars and mortars made with NHL (natural hydraulic lime) are gaining ground with enlightened architects and contractors, as a better alternative to cement mortar in new builds. It is esthetically appealing, flexible and far less prone to cracking, it also allows moisture to be released from walls via the mortar bed. Garden designers are finding it superior for hard landscaping for the same reasons
Lime has a much lower carbon footprint as opposed to cement.
If you have a home that was built using lime mortars it is important to understand that the people who designed and built your house knew what lime could do. Its breathability is an integral part of the way the building copes with moisture from the ground, rain and from the activity of day-to-day living. Its ability to cope with movement is a fundamental part of the design of the property.
Buildings constructed with lime tend to be on much lighter footings than today’s sand/cement and concrete constructions. They were often built with a “Step foundation-footing” no more than 400mm below ground and were designed to move with the heave and fall of the land. This approach is not shoddy or bad practice in any way. It is not necessary to attempt to keep a building constructed with slaked lime mortar rigid as lime can move without cracking.
If a cement based product is used as a render, pointing mortar or for repairs to brick or stonework on a lime mortar building, it will be incapable of moving in harmony with the rest of the structure. This will inevitably cause stress and cracking in the area worked on as well as the lime construction in the surrounding area.
Because cement mortar reduces the passage of moisture there will also be a localized build up of moisture in the lime construction causing rapidly accelerating decay, known as “sick house syndrome”.
Using modern plasters, cement renders and non breathable paints can lead to damp problems as they seal the walls not allowing them to breath.
I you have a period property suffering from damp, cracking or timber decay, please consider that many of those problems are easily solved by allowing the building to function as it was designed to do. The long-term effects of using modern materials without due consideration on traditional buildings can be devastating and costly. If you have a period property I would always advocate using an experienced period building contractor.
If you have problems with rising damp, check the ground level outside, over time it may well have been raised. Examine the pointing to see if it is cracked, falling out, lifting or too hard, this will cause moisture levels to increase in the wall.
Check your air bricks (if you have any) are not obstructed.
Walking round your property when it’s raining, check the gutters are working and water is not pooling against the walls.
I hope this has been of some help, if you would like to discuss any issues that this article has raised please don’t hesitate to contact us. We have experienced and knowledgeable staff and are always happy to help.