Lime mortar repointing is the process of renewing the pointing–the lining between bricks or stone–of a building. This method can improve the waterproofing, structural stability, and appearance of brick or stone walls. It is essential that this procedure is conducted properly to ensure the steadfastness of your home or building.
Lime mortar buildings usually have solid walls without a cavity. The stones or bricks are not as permeable as the lime mortar, which results in moisture passing through the mortar joints. Over time, this process can begin to wear the mortar away, and cracks and gaps can develop between the stones. Improper pointing can lead to water becoming trapped within the mortar, and damage can occur to brick and stonework. It is crucial that this practice is carried out correctly, and should only be conducted by knowledgeable DIYers or professionals, to ensure longevity and wellbeing of aged buildings.
A frequent mistake is to remove and replace lime mortar with cement mortar. When this is done, due to the lower absorption rate of cement mortar, water does not escape the stones as effectively. This can lead to damp issues, with observable chipping of bricks and stones. Additionally, lime mortar is a flexible material. It can withstand movements in a property that may occur over time, which is expected with older buildings. These movements can create fine cracks or splits in the mortar. When this happens, the lime mortar has a self protecting quality. As the lime takes in moisture and CO2, it begins to form calcite crystals which seal and protect the crack from further damage. Cement mortar does not have this quality, and as older constructs naturally shift, it just begins to wear, crack and fall away. For these reasons, cement mortar should never be used in place of lime mortar under any circumstances, and is often considered the fault of damage, particularly with damp, in older buildings.
Lime mortar repointing requires properly raking out the original pointing, and correctly mixing and applying the new lime mortar. Lime mortar is also known as natural hydraulic lime and comes in different grades, (NHL 2, 3,5 and 5), which can be dependent on the type of wall and strength required; it essential to use the correct grade for the intended purpose. With resulting structural soundness in mind, it is important to hire a professional lime mortar repointing company, or ensure you fully understand the method and feel confident before attempting it yourself.