Restoring & Preserving Historical Masonry Structures: The Case For Natural Hydraulic Lime Mortar

Historical masonry structures stand as testaments to the craftsmanship of bygone eras, embodying the rich history and cultural heritage of a region. Preserving these structures requires a delicate balance between restoration and conservation, and one key element in this process is the use of Natural Hydraulic Lime (NHL) mortar. In this blog post, we'll explore the various uses and benefits of NHL mortar when working on historical masonry structures.

As a masonry company that specializes in preserving historical buildings throughout Victoria, BC, Lennox Masonry is well versed in the use of Natural Hydraulic Lime cements. We have had the pleasure of working with NHL while repointing heritage-designated chimneys, brick and stone retaining walls, government buildings, as well as private historical masonry collections. Unfortunately, there isn't a wealth of information available on the subject of NHL mortars and their uses. However, thanks to modern day mortar testing techniques, it has now become easier to replicate the initial ratios (lime to sand) used by the original builders. And, hopefully, by the end of this blog post, you will have gained enough knowledge to be confident in the use of NHL based mortars for your future masonry projects.

17th Century Limestone window from a former Gothic Cathedral which is now being used as a garden feature in Victoria, BC. NHL 3.5 was utilized in rebuilding this historical remnant.

Understanding Natural Hydraulic Lime Mortar

Natural Hydraulic Lime mortar is derived from limestone, containing hydraulic properties that allow it to set and harden through a chemical reaction with water. In fact, unless the mortar is exposed to freezing temperatures, it will continue curing as long as a degree of moisture is present. Unlike conventional cement-based mortars, NHL mortars are more breathable, flexible, and compatible with the original materials used in historical masonry structures.

1. Breathability and Flexibility

One of the primary advantages of NHL mortar is its breathability. Historical masonry structures often include softer stones or bricks, and the ability of NHL mortar to allow moisture to evaporate from the wall is crucial in preventing damage from trapped water. The mortar's flexibility also accommodates the natural movement of historic structures, reducing the risk of cracking or displacement.

2. Compatibility with Historic Materials

NHL mortar is particularly well-suited for use with traditional building materials such as soft bricks and porous stones. Its composition is more similar to the historic mortars used in the past, ensuring a harmonious blend that minimizes the risk of damage to the existing structure during restoration. It's important not to overpower the stone or brick you're working with

3. Minimal Environmental Impact

Natural Hydraulic Lime is an environmentally friendly choice compared to cement-based mortars. Its production involves lower energy consumption and carbon emissions, making it a sustainable option for those who prioritize eco-friendly building practices.

4. Historical Accuracy

Preserving the authenticity of historical structures is paramount. NHL mortar provides a visually accurate finish that closely resembles the appearance of traditional lime mortars. This ensures that the restored areas seamlessly integrate with the original masonry, maintaining the historical aesthetics of the structure.

5. Ease of Application

NHL mortar is no different to work with than any other cement while mixing it with sand and then applying it. It's important to let the mortar rest for a few minutes directly after mixing it so that you can allow the chemical process to take shape prior to mixing it again and then utilizing it with masonry units.

6. Enhanced Durability

Despite its breathable and flexible nature, NHL mortar exhibits robust durability. It can withstand the test of time, offering a long-lasting solution for the restoration and conservation of historical masonry structures.

7. Mixing Ratios

The ratio between NHL and sand does vary depending on the application it is being mixed for. Having the existing mortar in place tested will eliminate all guesswork on your end. If mortar testing is not an option, a good rule of thumb is to increase the ratio of sand based on how soft the stone or brick you're working with is. You can utilize modern cement to sand ratios which pertain to the type of masonry material you are working with while removing Portland cement from the equation.

Conclusion

Preserving historical masonry structures requires a meticulous approach that respects the craftsmanship of the past. Natural Hydraulic Lime mortar emerges as a versatile and effective solution, providing breathability, compatibility, and environmental sustainability. By opting for NHL mortar in restoration projects, craftsmen and conservators contribute to the longevity and authenticity of our architectural heritage, ensuring that these structures continue to tell their stories for generations to come.

17th century limestone doorways from a former Gothic Cathedral now being used as garden features in Victoria, BC.

Lennox Masonry of Victoria, BC has been proudly serving both Vancouver Island and the Gulf Islands for over a decade. We are small group of skilled masons with a great deal of passion towards our trade and for improving the communities we live and work in. We extend our gratitude to the lək̓ʷəŋən people for allowing us to share and work on this corner of the garden with them. We are thankful for the residents and businesses of Victoria, BC for supporting us in our endeavors!

If you’re in need of a professional and reliable masonry company for your next project, please contact us today!