Lime mortars allow traditional stonework to breathe, transporting moisture away from the structure. Cement mortars can be impermeable to moisture, trapping it within the stone leading to dampness and eventually internal decay. Cement also sets harder than stone, so naturally the two materials will eventually detach from each other.
When replacing lime mortar it’s crucial to ensure the new joints have been raked out properly. This is to allow the new mortar enough space to bond and set. Once cleared, the open joints should then be soaked with water. Again this gives the new mortar the best conditions to set. Depending on the time of year, an NHL 3.5 lime mixed with sand usually works great for most stone work. Once the lime mortar has been applied, we would then cover the stonework with a material called hessian. This natural material creates the ideal environment for setting while also protecting the new mortar from unfavourable weather conditions. When partially set, (time dependent on the time of year) the new mortar is ready to be brushed back. This will reveal the aggregate within the mortar and leave a watertight and breathable structure.
Stone Surface Repairs
Depending on the extent of damage or decay to the stone, a repair can be the perfect alternative to carrying out a stone replacement. Using the lime based material lithomex, we can apply this over the affected stone giving it the appearance and structure of a brand new stone.
Before applying lithomex it’s important to chisel away all the loose and decaying stonework back to a solid surface. This creates the perfect base for the lithomex to bond to. Once applied and dried, (which usually takes around 24 hours ) we rub back and shape the lithomex to recreate the desired structure.
This also reveals a stone like finish that is now watertight and breathable. Here we can dress on any surface finish to match the surrounding stonework.
If a solid surface is not found within the ideal depth due to internal decay, a repair won’t be suitable and we will advise replacing the stone.
We may also recommend a replacement or descaling of the stone due to it’s location on the building.
For example, repairing areas above ground floor level over walkways should be avoided. Although a well executed repair can last for upwards of 15 years, they are the temporary option and will eventually fail and detach from the original stone.
In this example, the original stone would of been dressed on a comfortable waist high table. Here I’m dressing the repair in situ creating a “stugged” surface finish to match the surrounding stonework.
At this stage we can also cut false joints that will be pointed in lime mortar to create the illusion of a built in stone.
Stone Structure Restoration
Garden walls, pillars, steps, windows, doorways and chimneys. We're highly experienced in bringing these structures back to life, from using a combination of restoration techniques to deconstructing and rebuilding.
This should be carried out when there is significant decay in the stone. Sometimes this is difficult to diagnose when looking at stones two stories up and above, in most cases this can only be determined on closer inspection from a scaffold. Decaying stones at height can pose a real risk to the public. Large cracks and heavy spalling are a sure sign of a stone in need of attention.