Repointing is a critical aspect of heritage and restoration stonemasonry, a process that involves renewing the external part of mortar joints in a masonry construction. Over time, weathering and decay cause voids in the joints between masonry units, usually bricks, allowing the undesirable entrance of water. Water entering through these voids can cause significant damage through frost weathering and from salt dissolution and deposition.
Repointing is designed to prevent this, by carefully removing the damaged material and replacing it with new mortar, usually applied with a pointing trowel. The process can dramatically improve the visual appeal and stability of a structure, and is a common task in the restoration of historic buildings. However, it requires a high degree of skill and knowledge to perform correctly.
History of Repointing
The practice of repointing has been around for centuries, as long as masonry structures themselves. The Romans, for example, used a form of repointing in their architectural works, and evidence of the practice can be found in ancient structures around the world. However, the techniques and materials used have evolved significantly over time.
During the 19th century, for example, it was common practice to use a very hard, cement-based mortar for repointing. This was done with the belief that the harder the mortar, the better the protection. However, we now know that this can often do more harm than good, particularly in the case of historic buildings made from softer materials such as lime mortar or soft brick.
The Evolution of Techniques
Over time, the techniques used in repointing have become more sophisticated. In the past, it was common for the old, damaged mortar to be removed with a hammer and chisel. This was a laborious and time-consuming process, and could often cause damage to the surrounding masonry.
Today, however, more advanced tools such as angle grinders and pneumatic chisels are often used. These make the process of removing the old mortar much quicker and easier, and can also reduce the risk of damage to the surrounding masonry. However, they must be used with care, as they can easily cause damage if used incorrectly.
The Evolution of Materials
The materials used in repointing have also changed over time. As mentioned earlier, in the 19th century it was common to use a hard, cement-based mortar. However, this can often be too hard for historic buildings, and can cause damage to the surrounding masonry.
Today, it is more common to use a softer, lime-based mortar for repointing. This is more compatible with the softer materials often used in historic buildings, and can provide a better level of protection. However, it requires a greater level of skill to apply correctly, and can take longer to dry than cement-based mortars.
Importance of Repointing
Repointing is a vital aspect of maintaining and restoring masonry structures. It helps to prevent water ingress, which can cause significant damage over time. It can also help to improve the visual appeal of a structure, by giving it a more uniform and cared-for appearance.
However, repointing is not just a cosmetic procedure. It can also help to improve the structural integrity of a building, by replacing damaged or missing mortar and helping to secure loose bricks or stones. This can be particularly important in the case of historic buildings, where the original masonry may be fragile or deteriorated.
Preventing Water Damage
One of the main reasons for repointing is to prevent water ingress. Water can cause significant damage to masonry structures, particularly in climates where freezing and thawing are common. When water enters the masonry and then freezes, it can cause the masonry to crack and crumble. This is known as frost weathering.
Repointing helps to prevent this by filling in the voids in the mortar joints, preventing water from entering. This can help to prolong the life of the masonry, and prevent costly repairs in the future.
Improving Structural Integrity
Repointing can also help to improve the structural integrity of a building. Over time, the mortar in masonry joints can become loose or crumble away, leaving the bricks or stones unsupported. This can lead to instability and, in severe cases, structural failure.
By replacing the old, damaged mortar with new, strong mortar, repointing can help to secure the masonry and improve the stability of the structure. This can be particularly important in the case of historic buildings, where the original masonry may be fragile or deteriorated.
Repointing Process
The process of repointing involves several steps, each of which requires a high degree of skill and knowledge. The first step is to remove the old, damaged mortar. This must be done carefully, to avoid damaging the surrounding masonry. Once the old mortar has been removed, the joints must be cleaned and prepared for the new mortar.
The new mortar is then mixed and applied to the joints using a pointing trowel. The mortar must be pressed firmly into the joints, to ensure a good bond with the masonry. Once the mortar has been applied, it is then shaped and finished to match the original style of the building. Finally, the new mortar must be allowed to dry and cure, before the building can be used again.
Removing Old Mortar
The first step in the repointing process is to remove the old, damaged mortar. This can be a difficult and time-consuming process, particularly in the case of historic buildings where the mortar may be hard and brittle. The old mortar must be removed to a depth of at least 2.5 times the width of the joint, to ensure a good bond with the new mortar.
There are several methods that can be used to remove the old mortar, including mechanical methods such as using a hammer and chisel, or more advanced methods such as using an angle grinder or pneumatic chisel. However, care must be taken to avoid damaging the surrounding masonry.
Preparing the Joints
Once the old mortar has been removed, the joints must be cleaned and prepared for the new mortar. This involves removing any loose or residual mortar from the joints, and ensuring that the masonry is clean and dry. The joints must also be dampened before the new mortar is applied, to prevent the masonry from absorbing water from the mortar and causing it to dry too quickly.
The process of preparing the joints is critical to the success of the repointing process. If the joints are not properly prepared, the new mortar may not bond correctly with the masonry, leading to a weak and ineffective joint.
Applying New Mortar
The new mortar is then mixed and applied to the joints. The mortar must be mixed to the correct consistency, and must match the original mortar in terms of colour, texture, and composition. The mortar is then applied to the joints using a pointing trowel, and must be pressed firmly into the joints to ensure a good bond with the masonry.
Once the mortar has been applied, it is then shaped and finished to match the original style of the building. This can involve several different techniques, depending on the style and age of the building. Finally, the new mortar must be allowed to dry and cure, before the building can be used again.
Common Challenges in Repointing
Repointing is a complex process that requires a high degree of skill and knowledge. There are several common challenges that can arise during the repointing process, each of which requires careful consideration and planning to overcome.
One of the main challenges is matching the new mortar to the original. This involves not only matching the colour and texture, but also the composition and strength. If the new mortar is too hard, it can cause damage to the surrounding masonry. If it is too soft, it may not provide adequate protection against water ingress.
Matching Mortar
Matching the new mortar to the original is one of the most important aspects of repointing, particularly in the case of historic buildings. The new mortar must match the original in terms of colour, texture, and composition. This can be a complex process, requiring a detailed analysis of the original mortar and careful selection of the new materials.
There are several methods that can be used to match the new mortar to the original, including visual matching, chemical analysis, and physical testing. However, even with these methods, it can still be difficult to achieve a perfect match, particularly in the case of older buildings where the original materials may no longer be available.
Protecting Surrounding Masonry
Another common challenge in repointing is protecting the surrounding masonry during the process. The process of removing the old mortar and applying the new can be messy, and can often result in damage to the surrounding masonry if not done carefully.
There are several methods that can be used to protect the surrounding masonry, including using protective coverings, careful handling of tools, and thorough cleaning after the work is done. However, even with these precautions, there is always a risk of damage, particularly in the case of historic buildings where the masonry may be fragile or deteriorated.
Dealing with Deteriorated Masonry
In some cases, the masonry itself may be deteriorated or damaged, making the repointing process more difficult. In these cases, it may be necessary to repair or replace the masonry before the repointing can be done.
This can be a complex and time-consuming process, requiring a high degree of skill and knowledge. It may also require the use of specialised materials and techniques, particularly in the case of historic buildings where the original masonry may be unique or rare.
Conclusion
Repointing is a critical aspect of heritage and restoration stonemasonry, helping to prolong the life of masonry structures and improve their visual appeal. However, it is a complex process that requires a high degree of skill and knowledge, particularly in the case of historic buildings.
Despite the challenges, repointing is a rewarding and fulfilling process, allowing us to preserve and restore our architectural heritage for future generations. With careful planning and execution, and a deep understanding of the materials and techniques involved, it is possible to achieve excellent results, ensuring the longevity and beauty of our masonry structures for many years to come.
Preserve Your Heritage with Expert Stonemasonry
At A F Jones Stonemasons, we understand the importance of preserving the integrity and beauty of your historic masonry structures. With over 160 years of experience, our in-house team combines traditional craftsmanship with modern technology to deliver exceptional repointing and restoration services. Whether you’re overseeing a large-scale restoration project or require bespoke masonry work, we’re equipped to bring your vision to life. Embrace the true potential of stone and ensure the longevity of your buildings by making an enquiry with us today. Let’s protect and enhance your architectural heritage together.