Ecomerchant Internal Wall Insulation System - Wood Fibre Board & Lime Plaster (IWI)

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The concept of this is similar to the External system, but as it does not need to be weather resistant it is very much simpler to specify and install. The system uses  Steico Therm   a lighter grade rigid woodfibre insulation board, insulated fixings for timber or masonry, a glass fibre mesh and Lime Green’s Solo one-coat lime plaster

Please view the individual elements by using this link, or see the main category Insulation/Ecomerchant IWI, or call for pricing and technical assitance.

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Ecomerchant  internal wall insulation system uses lime-based render on wood fibre boards chosen for their quality and durability and made from sustainably managed sources.

Introduction to Internal Wall Insulation (IWI)


Once in place, the plaster system ensures that walls are still able to ‘breathe', which means stone, brick and woodwork isn't damaged because no moisture remains trapped inside.

The system can be fitted to timber frame constructions or retro-fitted to masonry.

They are then covered with single coat of Lime Green Solo plaster incorporating a reinforcing mesh to give structural integrity to the wall surface. We recomend you use natural paints to give the colour you want. Click this link to view the information sheets on our complete range of Livos paints & finishes

To make sure you get the most from your internal wall insulation system, we offer an in-depth technical support service that covers all aspects of your build, from pre-planning right through to completion.

Most heat in old houses is lost through the walls, but successfully upgrading them with internal insulation is a challenge. Historic buildings were not designed or built to accept the retrofitting of plastic membranes, insulation or paints, and all too frequently the end result is trapped moisture in the walls which can eventually lead to rot, mould and expensive remedial work.

Ecomerchant have worked with Lime Green and Steico to create a wood fibre based  Internal wall insulation system which is designed and tested to allow solid walls to stay dry, while offering modern levels of insulation and ease of application. In addition, the system is safe and environmentally sustainable, using natural ingredients that will maintain a healthy internal climate.


Ecomerchant  Internal Wall Insulation System is suitable for solid-wall masonry buildings and some timber frames; however the following checks must be undertaken before starting:

  • External coatings and finishes – must be vapour-open. Synthetic masonry paint or waterproof cement render are not suitable for this system.
  • Pointing mortar – existing solid masonry pointing should be a breathable lime mortar and in good condition.
  • Damp walls - the system is not generally used beneath ground level, below DPC or on walls which are permanently damp – please ask Lime Green for written guidance before ordering.
  • High Humidity – in rooms with frequent high humidity (e.g. wet rooms, bathrooms and similar) a different specification is used. Please ask for written guidance before ordering.

If applied over a stud, there must be no cavities or air gaps behind the woodfibre insulation board we recommend the use of Steico Protect Dry board


  • Insulation board should only be fitted to damp free, dry walls.
  • Insulate only above DPC level and above ground level.
  • Services must be run beneath the insulation boards.
  • Do not cover with vapour-closed paints or wall coverings.

About wood fibre board

Wood fibre board is a rigid natural insulation material with either a tongue-and-groove or square edge profile, manufactured in accordance with EN13171. Wood fibre not only has good thermal conductivity properties in the range of 0.039 to 0.044 W/mK, but also its breathability helps regulate the internal climate of a building.

  • Excellent insulation properties, prevents thermal bridging
  • High heat protection during summer months
  • Water vapour open construction for healthy room environment
  • Fire class rating E (EN13501-1)
  • Easily cut and handled using traditional woodworking tools
  • CE marked and manufactured in accordance with ISO9001:2000
  • Non allergenic and durable
  • Environmentally sustainable – FSC certified
  • Certified by natureplus® - European quality mark
  • Fully recyclable
  • Helps fix CO2 - carbon is stored in the finished product

About Lime Green Solo one coat lime plaster

Lime green Solo one coat lime plaster is specially designed for breathable insulation boards such as wood fibre. When used together they produce a system with optimum levels of breathability. As houses become more air tight, avoidance of synthetic foams and resins becomes more important for a healthy indoor climate.

  • Ease of application – including same day finishing.
  • No need for undercoats.
  • High vapour exchange, maintains a healthy internal climate and a dry wall.
  • Free of cement and solvents, for safe and simple disposal.
  • Lime based, for durability, breathability and compatibility with historic buildings.
  • Natural binder
  • CE Marked

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 Installation Components




Thickness   / Dimensions

Typical   Requirements for 1 m² installed *

Plaster for levelling   walls underneath boards




Lime Green Duro 

Typically   12mm

(May   vary from 0 to 25mm+)

17kg @   10mm thick



Insulation Board






Wood fibre Square edge


1.3   boards





Wood fibre tongue and groove


2.2   boards










Insulated   hammer-in fixing





CSK - Fixing Screw

CSK Hinged Cap Washer

Insulating   washer & screw





Lime green glass fibre mesh 910 


1.10 m²

Plaster on boards



Lime green Solo one coat plaster 

Approx   8-12mm


Wall Preparation

  • Externally check the pointing, paint or render is in fair condition. If not repair with suitable breathable materials (e.g. Natural Hydraulic Lime render, lime putty, etc. Please ask us for advice specific to your application). Remove any masonry paints or materials which are sealing the wall or acting as a vapour barrier.
  • Internally, remove vinyl wall finishes and sealed plasters (e.g. gypsum)
  • Masonry must be flat, level and porous. Old lime plasters can be ripped open with a scouring float. Bare brick or stone must be plastered with lime green Duro to flatten the wall. For more information on using this product please consult the relevant data sheet.
  • Cables etc should be chased and run in the masonry or plaster before fitting the boards. 


Preparation and correct fixing of the board and profiles is vital. Time spent getting this right will help avoid problems later. The plaster should not be considered as a way to hide errors or defects in the application of the boards.

Fixing the boards

  • Only fix dry boards.
  • Cut the boards by hand or with a circular saw. Always cut out small pieces from a whole board.
  • The first board is placed at the base of the wall and fastened in the centre with the appropriate fixing for the background.
  • The number of fixings is dependent on the type of background. Typically 5 fixings per board are required on masonry, or 2 per stud on timber.
  • The boards are fixed in a lattice horizontally and pushed tightly together. They should alternate down corners. Vertical joints must be staggered.
  • Cut pieces must be at least 200 mm wide.
  • Services must be run beneath the boards.
  • Do not align board edges with the windows.
  • Always insulate reveals.
  • Make sure the boards have an air tight fit around windows and doors – use Compriband if necessary.

Fixing types

The special fixings keep the wall warm and prevent thermal bridges. Various types are available for different backgrounds; please see the data sheet below or call for details.


Before plastering, inspect the boards. Check they have been fixed according to section 3a. Steps in the boards must be dubbed out with lime green Solo one coat lime plaster and allowed to set before plastering. Gaps greater than 10mm between the board connections must be foam-filled or packed out. Consult product datasheets for the plaster before starting.  See below.


  • On older buildings corners may be formed traditionally with wooden rails.
  • Alternatively fix PVC or metal beads to the board before starting.

Plaster finish on boards

Apply Lime Green Solo One Coat lime plaster in 2 passes to a combined thickness of 8 to 12mm.

  • The first pass is applied approx 5-6mm thick – the 910 glass fibre mesh is pushed in to the plaster immediately while it is still tacky. Overlap joins in the mesh by 100mm
  • Lime green 910 glass fibre mesh is doubled up around windows and doors, with a diagonal layer applied. The diagonal piece should be at least 200mm x 400mm
  • The second pass is applied over the top usually within 4 hours to give a total thickness approx 8 to 12mm thick.
  • Level plaster with straight edge
  • Allow at least 2 weeks drying time, during which time the plaster should be protected from rapid or forced drying.
  • Do not over-work the surface as this may lead to “fire cracking”.
  • Apply in temperatures above 5°C and below 30°C. 

The system is vapour-open and functions by allowing moisture to pass freely. It is therefore important that only vapour-permeable paints are used for decoration. We recommend Livos natural paints.


Ecomerchant IWI System

Stud Wall

Insulated plasterboard system

Breathable walls?




Natural vapour control?




Low condensation risk?




Free of VOC’s?




Simple, safe disposal?




Single trade application?




Ease of application?




For more information see downloads

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