A building of historical, cultural or archaeological interest will often be the subject of a preservation project and it requires a methodical and precise process to ensure that it is carried out in the right way. Companies who specialise in building preservation not only need to be familiar about the preservation process, they need to be able to research, assess and identify the type of building so the correct techniques and products are used to achieve the best results. It is only after careful assessment of the building can the team determine what needs to be done to carefully preserve the building. The work of a building preservation team will combine a number of specialist areas from geology and law through to understanding the chemical makeup and history of the building.
Maintenance and repair are carried out to address the deterioration and decay of a building that can be caused by wear and tear, neglect or changes in the weather over a long period of time. Maintenance is routine work that is undertaken to retain the overall fabric of the building and to keep it in the best possible condition. Maintenance tasks are carried out to reduce deterioration of a building. Good maintenance is the key to building preservation.
Repair on the other hand is work that falls outside of general maintenance, often to address defects as a result of damage, decay or general use. Repair is usually carried out to preserve a building and ensure that it can be used in the future and it is an approach that will reduce the long term deterioration of a building by addressing any defects as soon as they arise.
The preservation process should only use techniques and materials which are suitable for the fabric of the building. These materials will be as close to the original materials as possible both from a technical and aesthetic perspective. Regular preventative maintenance should be carried out on older buildings which will maximise their lifespan and retain the fabric of the building.
When undertaking building repair it is important to understand how the building functions and why the materials have started to fail, as well as understanding what can be done to prevent the same level of deterioration occurring in future. This may require detailed testing and sampling of the building over a period of time.
Different buildings will present different problems so each project will be different. Unsuitable or repairs undertaken without the correct knowledge may result in failure and an increased rate of deterioration. This is why it is so important to not only use the right materials but to ensure that the preservation process is undertaken by a skilled and experienced team.
In the UK there are countless historical buildings, many of which are listed. However, over the years many of these buildings with historical significance have fallen into disrepair over the years due to neglect, abandonment, poor management or just lack of money.
Historical building preservation is a time consuming and delicate process but it is an important task. Whether it’s an elaborate cathedral or a grand stately home, the process is the same and each project would need a careful assessment to determine the best approach. It would first be necessary to understand the goal of the preservation work, whether it’s to repair, restore or simply preserve the building.
The goal of a building repair would be to ensure that the original architectural elements are preserved as close to the original as possible. This is usually undertaken when the building is still in use. The restoration process is slightly more complex and it involves a complete restitution of the architectural structure prior to any damage occurring. Restoration is often undertaken if a building has been left in a state of disrepair for a long period of time and usually doesn’t meet building regulations.
Many historical buildings are affected by ground movement, the degradation of building materials and structural inadequacies at the time of construction and when subject to alterations and repair over many years, this can affect the original fabric of the building. Preservation is designed to ensure that the building is safeguarded against any further movement, weathering or issues that could affect the integrity of the structure. Preservation techniques will focus on retaining original structures while restoring as many of the original features as possible. Preservation will preserve and strengthen the structure of the building.
Lime is often used in the building preservation process because of its strength and durability.
The Use of Lime in Building Preservation
Lime is used to describe slaked lime or quicklime, frequently used for render, plaster and mortar before the mid 19th century. When limestone is heated in a kiln, it becomes quicklime. Slaked Lime can then be made by mixing this quicklime with water to create a soft putty. Once they have been applied, a lime based product will harden to form a strong compound useful for repairing brickwork, stonework and most other types of masonry which is why it is a popular material used in building preservation work.
Benefits of Lime
Lime based materials are great because they allow the structure to breath and absorb gentle movement as the ground expands and contracts with changing seasons and temperatures.
In most traditional plasters, renders and mortars, lime is the principal material used to bind the materials together and it is a product that is used in countless building preservation projects throughout the UK. Lime products may seem a little daunting to work with at first, because there are so many different types, mix ratios and options that you can choose from but once you begin using the product and understanding its properties and benefits, you will develop your own systems and techniques to apply the product to your own building preservation projects.
There are three types of lime that you can purchase including lime putty based mortars, natural hydraulic lime and hydrated lime. A lime putty based mortar is best suited to buildings that require breathable mortar, typically this would be on a solid wall building. Hydrated lime products are not recommended for use as a binder for lime mortar because they will be too weak and won’t provide a suitable material for building. Natural Hydraulic Lime is more complicated still and can be divided into three main categories. These categories have different strengths and chemical properties. The first is NHL2 which is the weakest product that you can purchase and is usually applied on soft materials such as internal repointing. The second category is NHL3.5 which is for general use suitable for internal and external use. NHL5 is the strongest lime material and is recommended for anything that will be underwater or in an exposed environment.
Two types of lime are used in preservation work and these include non-hydraulic lime and natural hydraulic lime.
Non-hydraulic lime is created from pure limestone and the hardening process takes place by carbonation. In its purest form, it is referred to as ‘fat’ and in the least purest form it is known as ‘lean’.
Natural hydraulic lime is derived from limestone that contains reactive silica and aluminium impurities.
During any building preservation project, it is important to select the lime as close to the original as possible. In older buildings, non-hydraulic lime was more frequently used because it was considered to be softer and more flexible. Each job is different, so it should be evaluated on its own merits, such as exposure and location, a suitable mortar or render would then be recommended based off these qualities.
It is recommended that English and German lime-based products are used for internal preservation work because they have a higher proportion of free lime. This means that they will set at a much slower rate. French lime products are stronger and the setting time is quicker so they are better suited to external preservation work. Careful assessment of the building should be undertaken before any lime is used to ensure that the product you choose is weaker than the masonry that the lime is used on.
If lime is a product that you intend to use in your preservation project, you should make sure that you have assessed the breathability of the building. This is because there have been some instances where full breathable lime render has been applied but acrylic masonry paint has been applied over the top, sealing the building and retaining moisture in the fabric of the building.
Care should also be taken when applying lime mortars. If moisture is removed from the lime too fast, large shrinkage cracks can occur. The same will happen if the mortar dries out too quickly or a heavy downpour could wash the lime render away.
As with all building preservation projects, the most important thing to remember is to use materials on the building that are suitable for the era in which it was built. If lime was not originally used in the construction, it wouldn’t be wise to introduce it to the fabric of the building as part of a preservation project.