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Diathonite Thermactive applied over stone.
Diathonite Thermactive applied over stone.
An image of a product Diathonite Thermactive applied over stone.

Diasen Diathonite Thermactive

15kg Bag
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The calculation is based on spray applying the plaster to an even, level wall. For hand application with a trowel, add approx. 15% to the estimate below. The calculation is for guidance only and does not include material needed to level (dub out) the wall.
m2 of Diasen Diathonite Thermactive
mm thickness
  • Product Overview
  • Technical Details
  • Installation guide

Main purpose

Insulating the building and maintaining the breathability of the wall/ceiling. Protects from cold in winter and overheating summer. Also used as an insulated levelling coat prior to using Gutex Thermoroom or Calsitherm insulation boards.

Use it on

Internal solid stone or masonry walls and ceilings. Can also be applied to wood-based panels/sheathing, laths and plasterboard that have been primed with Diasen Aquabond Primer. 

Overview

Diathonite Thermactive .037 is a lime-based insulating plaster made from NHL5, cork, pumice, amorphous expanded silicate, perlite, natural fibres and diatomaceous earth.  Used internally on solid masonry walls and ceilings, it is highly breathable and helps walls in older buildings dry out thanks to its capillary active nature.  Diathonite Thermactive is compatible with a range of substrates, but is mostly applied to solid stone or brick (once any gypsum plaster has been removed) and provides significant thermal improvement to these walls.

Where to use it

Diathonite Thermactive can be used internally on any solid stone or masonry wall and is an ideal solution for the restoration and thermal insulation of older or Historic/Listed buildings.

What it does

Diathonite Thermactive is an insulating plaster that can help regulate moisture to manage humidity and damp in solid walls; especially within older buildings. It provides excellent thermal insulation in colder months and helps protect from overheating when temperatures rise outside. A more comfortable indoor climate can be achieved all year round and the energy demand for heating and cooling can be reduced.  

In a typical installation, application of 40-60mm of Diathonite Thermactive would improve the thermal performance of the wall by 3.5-4.5 times. This thickness is the most cost-effective way to provide a significant thermal improvement to the wall.

The clever combination of natural ingredients provides mechanical strength and elasticity to reduce the risk of micro-cracking and gives a long-lasting durable finish.

Diathonite Thermactive .037 is supplied in 15 kg bags.  There are 60 bags per pallet.

How it works

Diathonite Thermactive is capillary active and breathable. It actively transports moisture from the structure of the building away from the wall and allows vapour to pass through. It helps the wall dry out, regulates humidity and prevents condensation and mould growth. The natural materials and sustainable cork granules also provide excellent temperature buffering to prevent overheating in hot weather. 

Why we love it

The main ingredients are lime NHL5, cork, pumice, amorphous expanded silicate, perlite, natural fibres and diatomaceous earth. These are all-natural ingredients and compliment conservation requirements of historic or listed buildings and will contribute to LEED credits.

Thermactive dries much faster than a traditional lime plaster; usually it only takes one third of the time which works out at approximately 2mm per day.

Diathonite Thermactive .037 is malleable and flexible when being applied. This gives many beautiful aesthetic options for rounded window reveals and curved wall surfaces that follow the contours of the underlying stone or brick. This is especially relevant in stone cottage refurbishments.  Thermactive also allows a more modern style finished result when required.

Not only an excellent insulation system, Diathonite Thermactive .037 is also ideal for leveling uneven walls prior to using rigid insulating board systems like Gutex Thermoroom and Calsitherm.

It is also non-combustible so will not burn or emit smoke.

Features

  • The best thermal conductivity available in a plaster
  • Beautiful finish
  • Award-Winning
  • Breathable and Capillary active
  • Easy Application
  • High Elasticity
  • Easy thermal bridge solution
  • Excellent drying times
  • Fire Protection (A1 non-combustible)
  • Antibacterial Properties

Benefits

  • 50mm of Thermactive improves the thermal performance of a wall by approximately 4 times keeping walls warm in the winter and cool in summer.
  • Creates a sympathetic restoration and insulation which maintains the unique characteristic of existing walls allowing them to breathe and balance room humidity.
  • Winner of the Renewable Product Category at the RIAI Architects Choice Awards – 2018.
  • Dual function plaster can be used as insulation and a levelling coat on the wall.
  • Natural cork and lime offer breathability and thermal insulation to prevent condensation and mould.
  • Up to 10 times more elastic than traditional plasters reducing the risk of cracks.
  • Provides a simple and easy solution to thermal bridges.
  • Can be sprayed-on or applied by hand; experienced lime plasterers or DIY enthusiasts can install it without special training.
  • Dries much faster than traditional lime.
  • Euroclass A1 fire resistance, does not burn or smoke so improves fire safety of buildings.
  • Complies with Building Regulations.

Questions

Can this insulating plaster be finished with gypsum?

No, all our Diathonite insulating plasters require a lime-based finish to maintain breathability.  We recommend using Diasen Argacem HP.

Do you need to pre-prime bare brickwork or blockwork prior to applying the Diathonite range of plasters?

Typically, Diathonite plasters (Diathonite Thermactive and Diathonite Evolution) can be applied onto bare blockwork, brickwork or stone with no primer. A fine mist of moisture can sometimes assist with the initial key of Diathonite plasters onto the wall. For low-moisture absorptive surfaces such as timber, existing lime plaster etc., then Diasen Aquabond primer can be applied.

Are hydrophobic creams breathable? Do they prevent moisture from escaping from inside to outside?

Hydrophobic creams such as Diasen BKK Eco are water repellent and moisture vapour diffusion open. This has been tested for moisture vapour diffusion openness in accordance with EN7783. This means that the external face of the wall is protected from wind driven rain but any moisture inside the wall can harmlessly diffuse out of the building.

“Diathonite plasters are the best performing thermal plasters, but are very expensive!”

When compared with other thermal plasters, the overall applied cost of Diathonite Thermactive and Diathonite Evolution is extremely competitive. This is because each has an exceptionally low thermal conductivity, meaning they can attain a specific U value with a reduced thickness. Also, Diathonite plasters have excellent coverage rates of between 2.6kg/m2  and 4.1kg/m2 per 10mm thickness.

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Technical Details

Key Technical Data

Technical Datasheet

Material Safety Datasheet (MSDS)

Environmental Product Declaration (EPD)

Declaration of Performance (DOP)

Installation Guide

Brand/Manufacturer Brochure

Installation Guide

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The minimum application thickness of Diathonite plaster is 15mm, but a total thickness of 40-60mm is typical. Using 40-60mm improves the thermal performance of the wall by 3.5 - 4.5 times. Diathonite should be built up in 15-25mm layers to the required total thickness, typically one layer per day. 

For thicknesses of 60mm or more, Diasen Polites 140 reinforcing mesh must always be used. This should be applied when half the total thickness has been applied. So, for 70mm total thickness, you must apply 35mm of Diathonite, then Polites Mesh, then the remaining 35mm. On a ceiling, the typical application thickness is up to 30mm and a reinforcing mesh must always be used.

Drying Times

When applying multiple layers of Diathonite, each layer of plaster should be left for 24-48 hours before applying the next layer.  If you leave more than 24-48 hours between layers, a "spatter" coat can be applied and left for a few hours hours before you apply the next layer. 

A spatter coat is very small amounts of Diathonite (in tiny lumps) thrown or sprayed onto the wall to create a patchy texture of lumps on the surface. It creates a key of fresh Diathonite all over the surface; it is too lightweight to fall off and after a few hours it will provide an excellent key for the next normal layer to be applied over the top. 

In summary: if the previous layer is too dry, the Diathonite applied on top may peel away or "bounce off" the wall when it is applied (and will need a spatter coat). And if the previous layer is too wet, the Diathonite may slide off or slump towards the floor. In that situation, simply wait a few hours and try again. 

Once you have applied the final layer, the Diathonite must be allowed to fully dry before applying Diasen Argacem HP or Argatherm finishing plaster. At 20°C and 40% relative humidity, we estimate Diathonite will dry at a rate of approximately 2mm per day. So, 40mm of Diathonite, will usually dry in around 20 days. As the drying time does vary based on environmental conditions each day, it is best to look at the surface; if it looks light grey all over, with no darker areas, it is dry.

If the temperature is lower than 20°C or relative humidity is higher than 40%, drying time will be longer. In higher temperatures or lower humidity or if the diathonite is exposed to persistant winds or direct sunlight, the drying time will be less.

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How to Hand Apply Diathonite Plasters
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How Spray Apply Diathonite Plasters

When used internally, Diathonite Thermactive .037 should be finished with a layer of Argacem HP, a breathable lime-based finishing plaster. The wall should then be painted with Diasen D20+ breathable primer before finishing with a breathable paint like Auro. If the wall is only being insulated internally and the exterior is not rendered, we would recommend a breathable rain repellent like BKK ECO be applied on the outside to limit the amount of moisture absorbed by the wall externally.

A window reveal primed, and sealed for airtightness with pro clima Solido SL, ready to be plastered with Thermactive
Diathonite Thermactive being spray applied
Diathonite Thermactive being spray applied

For projects of 100 square meters or more, Diathonite Thermactive .037 can be spray applied using a spray pump machine. An experienced trained installer is recommended for larger projects and spray application.  Spraying is quicker than hand applying and uses approximately 10-15% less material because the plaster is not being compacted by a trowel.

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Hints and Tips

All coverage/yield figures quoted are based on application to a smooth level surface. They are for guidance only and do not include material required to level (dub out) the walls.  

Fixing items to Diathonite plasters

Diathonite thermal plasters are non-structural mortars. This means to fix items to walls, they must be fixed through the Diathonite directly into the masonry.  

Similar to most plasters, Diasen thermal plasters should not be relied upon as a means of fixing heavy items such as shelving, cabinets, sanitaryware etc. Lightweight items such as sockets, light switches etc. can be fixed using suitable wall plugs or dowels.

Example fixings for support of lightweight items secured into insulation (rather than masonry) can be seen in this PDF on pages 16-18. Always follow the fixing supplier's guidance precisely if the fixings described in this PDF are used.

Tiles may be applied to Diathonite thermal plasters following the tile adhesive's application instructions. A thickness of 30mm of Diathonite can support, up to 50kg of tiles per m². This is only possible if the bottom row of tiles rests on the floor in order to bear some of the weight.

Problematic walls

On walls with white salt deposits (efflorescence) or high moisture content, Diathonite Deumix+ can be used to speed up drying and act as a salt inhibiter. Diasen Regularisation could also be used as the first layer of plaster (underneath the Diathonite Evolution) on walls with severe salt issues when required.

Installation Guide

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