At Roundtower Lime, we proudly supply a premium range of Natural Hydraulic Limes (NHLs) suitable for a wide spectrum of building, restoration, and conservation projects. Our NHL products are sourced and manufactured to the highest quality standards, offering reliable performance, excellent workability, and strong compatibility with both historic and new-build structures.
Natural Hydraulic Lime (NHL) is a traditional binder used in mortars, plasters, renders, and grouts. It sets by hydrolysis and carbonation, giving it both hydraulic (water-setting) and breathable characteristics—making it ideal for eco-friendly, breathable, and durable construction. Unlike cement, NHL allows buildings to “breathe,” reducing the risk of trapped moisture and structural damage.
We stock all common NHL grades:
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NHL 2 – softer set, ideal for internal work, pointing historic masonry, and delicate substrates
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NHL 3.5 – a balanced, versatile binder for general-purpose rendering, plastering, and masonry
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NHL 5 – a strong binder suitable for floors, coastal applications, and more exposed environments
Each grade is available in loose bagged format or in pre-mixed mortars blended with carefully graded sands. We also offer technical advisory support to help you select the right lime for your project.
Why Choose Roundtower Natural Hydraulic Lime?
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Compatible with traditional building methods
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Highly vapour-permeable and breathable – prevents condensation and promotes healthier walls
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Resilient to harsh weather – excellent durability once set
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Supports conservation standards – approved for use on heritage and protected structures
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More flexible and less brittle than cement – reduces cracking and long-term damage
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Free from additives and cement – true natural performance
Whether you're conserving a historic building or creating a breathable new-build envelope, Roundtower’s NHLs provide a dependable, sustainable solution.
Frequently Asked Questions (FAQ)
What is the difference between NHL and non-hydraulic lime?
A: NHL sets through water and carbonation and is suitable for external applications. Non-hydraulic lime (e.g. lime putty) sets slowly through air exposure and is more suitable for internal or very sheltered work.
Can NHL be used with modern aggregates?
A: Yes, but we recommend using clean, sharp, well-graded sands. For conservation work, we can advise on historically appropriate sand types.
How do I choose between NHL 2, 3.5, and 5?
A:
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NHL 2: For delicate pointing, soft masonry, and internal works.
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NHL 3.5: The most versatile grade for general use.
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NHL 5: For flooring, chimney stacks, or marine and exposed locations.
Is NHL breathable?
A: Yes. All our NHL grades are vapour permeable, promoting moisture movement through the wall to reduce trapped damp.
