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Calsitherm system applied to solid brick wall. Lime plaster levelling coat, then adhesive, then finishing plaster, mesh and breathable paint..
Calsitherm system applied to solid stone wall. Lime plaster levelling coat, then adhesive, then finishing plaster, mesh and breathable paint.
Highly porous Calcium Silicate under the microscope, 93% of the volume is air.
Calsitherm to un-insulated ceiling joist

Calsitherm Climate Board

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I need m2 of Calsitherm Climate Board
  • Product Overview
  • Technical Details
  • Installation guide

Main purpose

High performance thermal insulation that provides a more comfortable indoor climate. Manages moisture, regulates humidity, eliminates mould and minimises heat-loss; especially in older or historic buildings or newer buildings suffering condensation and mould problems.

Use it on

Interior side of external solid stone or masonry walls, solid concrete walls or ceilings and waterproofed basements with a cement based tanking system.


Calsitherm is a remarkable absorbent and dehumidifying insulation material capable of absorbing up to 4.7 times its own weight of water. It is capillary active and hygroscopic making it the best insulation available for dealing with peaks in humidity or moisture, rising damp and penetrating damp from rain. Calsitherm is made from a mixture of lime and sand (calcium silicate), making it a natural and extremely effective mould inhibitor. It is suitable for use on solid (single leaf) walls in older buildings or any building that has condensation or mould issues.

Where to use it

Calsitherm Climate Board is used as an internal thermal insulation system for solid stone or solid masonry walls and window reveals.  It can also be used to internally insulate solid concrete walls and ceilings (of any thickness) in apartment blocks and commercial buildings. It is also suitable for use in waterproofed basements where a cement-based tanking system, with no membrane, was used.   

What it does

Calsitherm Climate Board is ideal for thermally upgrading and restoring old buildings or any newer building with solid walls and problems with condensation or mould. 

It is highly capillary active, meaning it can rapidly draw water out of the wall and store it within its micro-porous structure.  It then allows moisture to gradually evaporate into the building harmlessly regulating moisture in the wall. With conventional impervious insulations (e.g. foil covered board), there is no capillary action to move the moisture away from the surface of the wall so there is a high risk of condensation and mould forming behind the insulation board.

Calsitherm is a highly effective thermal insulation and acts as a dehumidifier helping to maintain a constant humidity level inside the building.  Regulating humidity is achieved by Calsitherm’s hygroscopic ability to absorb moisture vapour from the air. This makes it particularly useful for preventing condensation in buildings that have highly variable humidity levels caused by lots of people entering and exiting the building over short periods of time. (E.g. museums, churches and schools).  The ability to regulate humidity also helps protect precious items inside the building that would be sensitive to fluctuations in humidity such as paintings, furniture and musical instruments.  This is the reason Calsitherm is used in buildings of significance such as the Rijksmuseum  in Amsterdam.

50mm of Calsitherm Climate Board on a typical 600mm solid stone wall  reduces the thermal conductivity by nearly two thirds.  The wall goes from 2.3W/m2K to 0.80W/m2K.

The combined effect of thermal insulation, moisture control and humidity regulation provide a much-improved level of comfort and indoor climate for the building’s occupants.

Why we love it

Calsitherm is an excellent insulator and improves the air quality, temperature and humidity within buildings. These are the key components of the climate within a building and the reason Climate Board got its name.

When Calsitherm is installed internally, the exterior features of the building can be retained. In this way it is ideal for listed, historic, brick or stone fronted buildings where the original appearance must be preserved.

Calsitherm is naturally non-combustible with an A1 fire rating. It is also incredibly robust and impact resistant. Due to the alkalinity of the material, it is also quite toxic to mould.

The raw materials are sourced from sustainable resources and a full Environmental Product Declaration (EPD) is available.

A Calsitherm board is extremely porous; 93% of its volume is air.

As part of a complete internal wall insulation system  the boards are also available in a narrower 15mm size for window reveals and as a tapered board  for eliminating thermal bridges at junctions with internal walls and ceilings. 

If the wall being insulated has a ceiling cornice, tapered boards can be used to minimise the visual impact of the insulation.  The insulation thickness can taper off towards the cornice so there is no unsightly ridge or step at the cornice.


  • Capillary Active and Breathable 
  • Made from lime and sand
  • Natural mould inhibitor
  • Ideal internal insulator for Listed or historic buildings
  • Ideal internal insulator for commercial and domestic refurbishments
  • Excellent natural thermal insulation
  • Non-combustible (A1 Fire rating)
  • Lightweight, easy to cut, shape and install


  • Ideal for preventing structural damage from raising damp and wind driven rain by absorbing moisture and regulating dampness in walls.
  • Allows moisture to actively move through the wall and rapidly evaporate helping it dry out faster and more easily.
  • Twice as breathable as lime plaster, it is ideal for use on existing breathable walls and materials.
  • Contains lime which is toxic to mould.
  • Helps improve indoor air quality creating a healthy living environment for respiratory disease sufferers by eliminating mould.
  • Significantly improves thermal performance of the wall; 30mm of climate board can reduce heat loss by 50%.
  • Provides exceptional thermal insulation to reduce energy costs without changing the external appearance of the building.
  • Extensively used on historic buildings throughout Ireland, UK and Europe including the Rijksmuseum in Amsterdam.
  • Being lime based, the Calsitherm System is fully compatible with traditional materials used in heritage buildings.
  • Non-combustible insulation provides the highest level of fire safety for the building to meet all fire regulations. 
  • Ideal solution for thermal bridges at windows, doors and between joists within a separating floor.


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Technical Details

Key Technical Data

Technical Datasheet

Material Safety Datasheet (MSDS)

Environmental Product Declaration (EPD)

Declaration of Performance (DOP)

System Brochure

Installation Guide

How to Install

Calsitherm Climate Board should be installed on to a level surface where all gypsum plaster has been removed. Any firmly attached cement or lime based plaster may remain in place. All non-breathable paint and wallpaper must be removed prior to application.  If the wall is uneven, use a lime based plaster or Diathonite (for additional insulation) to level it before installing Calsitherm. Any mould on the stone/brick should be cleaned off before applying the levelling coat.

Calsitherm Climate Board installed onto a wall levelled with Diathonite Thermal Plaster
Calsitherm Climate Board installed onto a wall levelled with Diathonite Thermal Plaster
Calsitherm Adhesive applied with serrated trowel
Calsitherm Adhesive applied with a comb/serrated trowel

Apply Calsitherm Adhesive Mortar to the wall with a 5-8mm comb/serrated trowel then apply the boards tightly together in staggered rows. For optimum performance, the board must be completely bonded to the wall with no air pockets behind.  Adhesive mortar is not required between the edges of boards when they are installed without gaps (butt-jointed).

Calsitherm Climate Boards should be finished with a layer of Calsitherm Finishing Plaster (KP Kalkglaette), then Reinforcing Mesh, then a second coat of Finishing Plaster. In corners, mesh must be used and it must overlap each adjacent wall.  In order to optimise the performance of the Climate Board, the final top layer should be a breathable paint such as  Auro natural paint. If you wish to use ceramic tiles on the wall, at least one third of the area insulated with Climate Boards must be left un-tiled so the system can continue to work effectively. Wallpaper is not suitable for use over Calsitherm Climate Boards.

Layered view of Calsitherm finishing plaster with embedded fibreglass mesh
Layered view of Calsitherm finishing plaster with embedded fibreglass mesh
Pro Clima Fiden gap filling expanding tape perfectly seals an uneven gap where the Calsitherm boards meet the floor.
Pro Clima Fiden gap filling expanding tape perfectly seals an uneven gap where the insulation boards meet the floor.

Where the climate board meets a concrete or wooden floor, windows or any area that may be exposed to structural movement, Pro Clima Fiden flexible joint strip should be installed between the climate board and the other surface, prior to applying the board.

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