Lime

Lime has been a cornerstone material in building construction for millennia. Its unique properties make it particularly well-suited for the conservation and restoration of historic buildings. Lime mortars, plasters, and washes are vital to maintaining the structural integrity and historical authenticity of heritage structures. There are two main types of lime: hydraulic and non-hydraulic. The basic difference between the two? Hydraulic lime cures through hydration and non-hydraulic lime cures through carbonation when exposed to air. There are appropriate areas for both types of lime in conservation work and this is carefully considered with every project that we undertake. Lime is a vapour permeable product which means that it is excellent at moisture management. It allows moisture to escape, in turn preventing damp, decay and even structural damage. Lime is also an extremely flexible product, meaning that it accommodates the thermal and structural movements of historic structures without leading to cracking, as is the case with many harder, stronger modern materials. One of the more visual benefits is that lime provides a much more traditional finish, consistent with historic building practices. Where required, it can also be easily pigmented with natural minerals to match original colours found throughout historic structures. Not to mention the environmental benefits of working with lime and implementing it into our buildings, both new and old.  

Pointing and Bedding Mortar

The application of lime pointing and bedding mortar is a crucial process in the correct restoration of historic structures. There are many reasons why lime mortars of various backgrounds should be used and carefully considered when working to preserve the masonry of which it surrounds. 

Just some of the benefits are: 

1. Breathability

• Moisture Regulation: Lime mortars allow moisture to evaporate from the masonry, reducing the risk of damp and associated damage.

2. Compatibility with Historic Materials

• Chemical and Physical Compatibility: Lime mortars match the properties of traditional masonry materials, ensuring compatibility and preventing damage from differential movement.

3. Flexibility and Durability

• Accommodates Movement: Lime mortars can accommodate thermal and structural movements, reducing the risk of cracking and structural damage.
• Long Lifespan: Lime mortars are durable and can last for centuries with proper maintenance.

4. Aesthetic and Historical Authenticity

• Traditional Appearance: Lime mortars provide a finish that is visually compatible with historic structures, preserving the original aesthetics.
• Colour Matching: Lime mortars can be tinted with natural pigments to match the historic colours of existing masonry.

5. Environmental Sustainability

• Low Carbon Footprint: Lime production has a lower environmental impact compared to modern cement, contributing to sustainable building practices.
• Natural Material: Lime is non-toxic and environmentally friendly, promoting healthier living environments.

A worryingly common reason for needing our services in lime pointing is due to an excess of traditional and historic properties with incorrect cementitious mortars applied around brick and stonework. This often leads to issues such as internal damp, spalled bricks and cracked masonry. The cementitious mortars are much harder than many traditional masonry building materials, is non vapour permeable and does not allow any natural movement of the structure. We aim to carefully remove the cement mortar ad replace with a thoughtfully chosen lime mortar based on the original bedding mortar within the structure. In some circumstances, we will also send off a sample of the original mortar to a laboratory for an exact chemical analysis, aiding us in obtaining as close a match to the original historic mortar as possible. 

Rendering

Lime renders have been an essential component of historic building finishes for centuries, providing protective and decorative layers to masonry structures. The use of lime render in conservation and restoration work is crucial for maintaining the structural integrity, breathability, and historical authenticity of heritage buildings. As with pointing and bedding mortars, we use mostly the same mortars for rendering. These mortars can be split into two main categories when considering options: non-hydraulic and natural hydraulic. Both have their place in the conservation of historic structures, and we work with our clients, architect and conservation officer to ensure the correct material is chosen. Proper assessment, preparation, and application of lime renders require specialised knowledge and skills to ensure successful outcomes. Despite the challenges, the benefits of using lime render, including compatibility with historic materials, environmental sustainability, and long-term durability, make it a vital material in heritage conservation. 

Plastering

There are many different techniques of lime plastering but our aim is to always do what is best suited to a property or if possible, match any existing original plaster. Internally we can apply lime plasters on to a variety of backings such as solid brickwork; lathes; sustainable insulation boards; natural plasterboard alternatives; cob; plasterboard. Both non-hydraulic and hydraulic limes can be used, depending on what backing substrate is either existing or chosen. With traditional non-hydraulic lime plastering, we like to use horsehair in our backing coats to give a strong bond throughout the coating, as has been done for hundreds of years. In some cases, we have found that it may be appropriate to replace the horsehair with goat hair to match original haired plaster. In situations where laths are present or have been specified, there are usually two options: riven or sawn. In pre 19th century buildings through until mid to late 19th century buildings, then riven laths will be the preferred choice to keep the correct features and feel of the original techniques used at the time of construction. Towards the end of the 19th century sawn laths gradually became more common as steam power helped to power sawmills throughout the country. This will always be considered with lath work and special consideration given to the age of the building to inform decisions on whether to use riven laths or sawn laths. 

Sustainable Insulation with Lime Renders

Perhaps a more modern improvement for traditional and period properties when it comes to lime plastering and rendering is the use of sustainable and breathable insulations that can receive lime plaster with ease to improve the thermal performance of these previously poorly insulated structures whilst maintaining the correct functionality of traditional wall construction. Two of the more popular sustainable insulations that we install are corkboard and wood fibre board. The insulating benefits of each of these are similar and options will often be dictated by area of application and cost. 

We also relish in opportunities that allow us to use decorative features of lime plastering such as rolled in corners, birds beaks as well as styles of pargetting and hand formed patterns. See Architectural Details for more information.