If you own an old home, preserving it is no simple task. True, it may look at first like it is all but indestructible, having stood the test of time following its construction way back in the past. But keeping it in good shape is not something that comes easily.
Indeed, there is no surer way of causing a building to decay and lose its structural integrity than by applying the wrong materials. The biggest threats to roof timbers are rot, caused by the ingress of moisture, and bug infestation, where wood fibres can be eaten by hungry pests that can access the wood.
A highly effective step that can be taken to preserve roof timbers and the laths used to support the roof tiles is lime torching, sometimes known as lime parging. It dissipates moisture and acts as an insecticide against bugs due to its high alkalinity.
As well as being an excellent weatherproofing material, it also helps act as an insulator by filling any voids in the roof tiles. The work can preserve the structure and protect your bank balance from big energy bills.
This is not rocket science; the method has been used for centuries, a time-honoured way of protecting roof beams from rot while regulating moisture levels and ensuring structural robustness, protection from the elements and, crucially, prevention of internal decay or infestation.
A further historical use for lime torching was helping to hold roof tiles in place against the wooden beams, fixing them rigidly so that they would not be displaced by windy weather or any other forces of nature that might dislodge them. By holding them in place, the wood beams below were protected from the elements, as was the attic space.
Many will be unfamiliar with this method, but that is because it has been superseded by modern techniques of protecting, preserving and insulating homes, especially in their loft areas, like roofing felt and nibs to hold tiles in place, not to mention the use of different materials in construction.
The fact is that in the past, this was a standard way of treating roof timbers in buildings and also a way of securing roof tiles. While it may not be the modern way, that doesn’t mean it ever stopped working.
The introduction of vapour barriers and roofing felts to historic buildings has significantly impacted their ability to breathe, as well as how moisture is handled. Unfortunately, the reluctance to conduct regular inspections and maintenance has increased this reliance, making it difficult for these structures to function correctly.
To compensate, there have been advances made in recent times, such as the development of roofing felt that is porous enough to allow some movement of water vapour through it.
However, introducing vapour barriers and roofing felts can potentially restrict the movement of water vapour, leading to possible damage such as rot and decay in timber roofs. While these materials have seen technological advances recently, more permeable options such as lime torching should be favoured when possible.
When introducing any barrier into a historic building, it is essential to consider the potential implications carefully. Blockages or other hindrances can cause severe issues for roof timbers and supporting structures.
To preserve the many beautiful buildings from our past, it can be preferable to opt for regular maintenance instead of drastically changing their initial design or performance. This approach can help prevent long-term damage and ensure these buildings can continue and thrive well into future generations.
Lime torching may sound like a process involving using fire to bake the material. Still, torching is a material made from a mix of quicklime, chalk and animal hair, the latter acting as a binding ingredient. It is then applied to the relevant areas and shields against water and hungry invertebrates. Because it is permeable, it dissipates moisture rather than allowing it to build up.
That said, heating is part of the process. The mixture will generate heat in a chemical reaction when slaking the quicklime, and it is applied while the mortar is still hot; the torching is added so that it can be malleable, adhere well, and fit in place before setting. At this point, the animal hair comes into its own, with its capacity to bind the material, minimising cracking as the material stiffens up.
When applying the torching hot, it initially stiffens up after a few hours, but it takes several months to harden fully. This process involves carbonisation as the render absorbs carbon dioxide from the atmosphere. This sets the material gradually, which is fine if the lime mortar is indoors and not exposed to the weather.
Making lime torching through slaking is not difficult for a skilled craftsperson. A lime mortar mix is made by adding enough water to the mortar, which causes the chemical reaction that includes giving off plenty of steam – something that should not be ingested.
It then needs mixing and ensuring that it has a workable consistency without lots of lumps, a process that needs just the right amount of water added. Too little leaves the mix powdery and volatile, while too much leaves you with a mortar more like soup.
Once applied, torching can last long, especially indoors, where it is not exposed to harsh weather conditions. But, like any other material, it has a shelf life. Eventually, through a lack of care, impacts and deterioration caused by moisture regulation, it can fracture and fall away, exposing timbers.
Lime torching is the preferred choice because it allows more water evaporation, reducing the risk of adverse effects on the building’s structure over time. In addition, regular inspection and maintenance help ensure that any existing issues are dealt with promptly before escalating into a more significant problem.
Maintenance also allows for early detection of general wear and tear or damage from weather conditions and climate change, which could lead to costly repairs if left unchecked. Regularly inspecting and maintaining historic buildings can help reduce long-term repair costs while preserving the building’s original structural integrity.
