Roundtower SuperTherm is a high-performance insulating lime plaster designed for the internal insulation of solid wall buildings, particularly where breathability, moisture management, and heritage compatibility are essential.
Formulated with hydrated lime, natural pozzolan (metakaolin), and a cutting-edge ultra-lightweight aggregate, SuperTherm delivers superior thermal performance (λ = 0.0395 W/mK) in a fully vapour-permeable, cement-free system. It is ideal for upgrading the thermal comfort of traditional masonry walls — without trapping moisture or compromising the integrity of older buildings.
Benefits:
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Exceptional thermal insulation with a K-value of 0.0395 W/mK
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Highly breathable – μ-value of 4.2, allowing walls to release moisture
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Moisture buffering – absorbs and re-releases moisture to stabilise humidity
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Non-organic & rot-proof – suitable for damp environments
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Lightweight (density ~260 kg/m³), reducing structural loading
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Natural composition – free from cement, VOCs, and synthetic additives
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Conservation-grade formulation – compatible with historic buildings
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Areas of Application
Roundtower SuperTherm is suitable for use as an internal wall insulation plaster in:
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Traditional cottages, period homes, and solid masonry walls
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Listed and protected structures where breathability is essential
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Retrofit projects in stone or brick buildings
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Damp or poorly ventilated interiors
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Conservation and restoration works requiring lime-based, non-invasive solutions
Typical application thickness ranges from 30mm to 100mm, followed by a 5mm Heritage Lime Finish (CLM35) with mesh reinforcement.
Roundtower SuperTherm Usage:
SuperTherm is an extremely low density and highly insulating plaster designed to significantly improve the thermal performance of masonry.
SuperTherm excels as a remarkably low density, high insulation material, offering superior mechanical resistance relative to other products with similar density and thermal characteristics.
It delivers outstanding thermal insulation for masonry and can achieve this at much thinner layers, whilst also maintaining exceptional vapour permeability.
SuperTherm offers a viable solution for Part L legislation, meeting the requirements for improving the thermal performance of a wall, while maintaining a permeable fabric which absorbs and readily allows for the evaporation of moisture.
With a measured K Value of 0.0395, a 50mm application of insulating render will improve the U value of a solid wall by 115% or more, significantly reducing heat loss.
Fibre additions improve the flexural strength of the render, distributing stresses across the surface and negating the need for mesh in most applications.
Due to its lightweight nature, SuperTherm can be applied at depths of up to 50mm per pass.
It can also be applied green-on-green through to the finish with appropriate suction, making the application significantly easier and faster than most available plasters.
SuperTherm can also be used in sustainable construction and renovation projects as a basecoat onto building materials such as hemp, straw, rammed earth and woodfibre boards. The insulating properties help reduce the thermal expansion differentials between the background and any subsequent coatings.
For internal applications, it should be applied as backing coat/s and finished with Heritage Finish.
Suitable for application onto most host surfaces with suction.
If working on weak or friable backgrounds such as cob, please contact us for further application information.
Do not use this product if the temperature is above 30°C, below 5°C, or if frost or snow is expected within the next few weeks. This includes temperature drops from wind-chill.
