Lime has been used for thousands of years and we see many examples of historical buildings and structures which are still standing today. In recent history, with the expansion of the railway industry, we saw lime mortar used extensively in the construction of bridges, tunnels and viaducts.
Lime mortar is being specified once again and successfully being used in many new modern buildings. So why is lime mortar being used instead of cement? The key differences in lime and cement is the lime mortar is weaker than the masonry, stones or bricks; yet able to support the weight of the wall. This is due to the mix composition incorporating sharp sand with the particles interlocking together when in compression. Being weaker than the surrounding stones, lime mortar has the ability to move and flex with the building without the use of movement joints. As for buildability, there are numerous examples of modern buildings that have used lime mortar and achieved and maintained a satisfactory build program. It is possible to lay in lifts of up to 1.5m high.
When laying in winter conditions it is not recommended to lay mortar, either sand and cement or lime, in temperatures of 5 degrees C or less, it can be possible if adequate protection is given. (Winter Guidelines for Lime Mortar)
Benefits of using Lime Mortar
- Movement is accommodated in the bed joints, reducing the need for vertical movement joints; which greatly improves the aesthetics of buildings.
- The building will have more tolerance to movement particularly in high buildings / structures.
- Lime will improved breathability, which allows moisture vapor to move freely through the mortar joint effectively reducing the likelihood of frost damage in the brickwork.
In the manufacturing process lime produces less carbon dioxide than cement, due to being burnt at lower temperatures; saving on fuel consumption and emissions of pollution and greenhouse gases. Co2 emissions are around 20% lower than in cement manufacture. Lime mortar will also absorb Co2 during the hydration process (carbonation) and over a period of time become carbon neutral.
Due to the lower bond strength the bricks / masonry can be easily cleaned and recycled at the end of the building’s life. Lime mortar also offers several usage and mix advantages over sand/cement mortars and site mixed lime mortar:
• Reduces the need for movement joints.
• Uses less energy to produce than cement.
• Re-absorbs CO₂ when it cures and sets.
• Allows masonry to be recycled at end of life.
• Provides a breathable form of construction.
• Provides a water shedding barrier for walls.
• Enhances brickwork and masonry
• Consistent mix proportions.
• Consistent quality and colour of mortar.
• Correct choice of sands.
• Mortars can be re-worked for up to 24 hours.
• Reduces wastage when using silo option
• Productivity savings
• Mortar is produced as and when needed
Lime mortar are considerably more flexible than Portland cement mortar; which means that movement joints are not necessary in most circumstances. Lime mortar provides good vapour permeability, which enables the building to “breathe”.
Mortar should not be used if the temperature is at 5°C and falling [see working with lime mortar in Winter Conditions or check with Limetec for advice]