Roundtower Insulating Plaster is a lightweight, highly breathable lime plaster designed to significantly improve the thermal performance of solid-walled buildings while managing moisture naturally. Acting as a plaster, insulation, and dehumidifier in one, it offers a practical, low-impact solution for both heritage and sustainable construction projects.
Formulated with Natural Hydraulic Lime (NHL 2) and recycled ultra-lightweight mineral aggregates, this plaster combines low strength, high flexibility, and advanced vapour permeability with excellent insulating performance.
✔️ Thermal Conductivity (K-value): 0.12 W/m·K
✔️ Breathable & Vapour Open: Functions like NHL2 render
✔️ Application Thickness: Up to 30mm in a single coat
✔️ Binder: NHL2 with mineral, non-organic additives
✔️ No framing or boards required – direct to wall application
✔️ Suitable for internal and external use
✔️ Pack Size: 25kg paper bags
Key Benefits
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Work Faster, Apply Thicker: Apply up to 30mm in one pass, reducing labour and curing times compared to conventional lime mortars.
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Breathable & Flexible: Performs like a traditional NHL2 plaster—highly vapour permeable, reduces risks of damp and decay.
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Superior Insulation: With a K-value of 0.12, a 25mm coat improves U-values by ~40%, while 50mm improves by ~60%—making it Part L1B compliant without compromising fabric breathability.
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Moisture Buffering: Regulates indoor humidity by absorbing and releasing excess moisture—acts like a passive dehumidifier, improving air quality and comfort.
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Space-Saving: No need for boards or frames; can be integrated into boarded systems for greater insulation.
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Robust & Durable: Utilises a three-dimensional recycled aggregate that doesn’t collapse under trowel pressure, ensuring both thermal performance and longevity.
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Reinforced Without Mesh: Built-in fibres improve flexural strength and distribute stress, often eliminating the need for mesh reinforcement.
Versatile & Sustainable Applications
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Suitable as a backing coat or full plaster build-up on:
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Hemp, straw, rammed earth
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Lime render backgrounds
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Solid masonry substrates
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Internally: Use alone or finish Heritage Lime Skim, Heritage Finish or BreathAplasta Smooth.
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Externally: Finish with Roundtower NHL2 Coarse or Fine Render
✅ Also suitable for high-suction backgrounds such as cob—please contact us for guidance.
Why Choose Roundtower Insulating Plaster?
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Part L1B compliant for thermal upgrading of historic buildings
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Delivers over 50% U-value improvement at 50mm thickness
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No VOCs, no organic content, no synthetic binders
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Safer, healthier and more sustainable than cement-based alternatives
Each project is unique. Please consult the Roundtower Insulating Plaster DataSheet and seek professional advice before specifying or applying.
