Choosing the right materials is one of the most important parts of planning an External Wall Insulation (EWI) project. An EWI system is not simply a layer of insulation fixed to a wall. It is a combination of components that work together, from the insulation boards and fixings through to the reinforcing layer, primer and final render.
Selecting materials individually without considering the complete system can create compatibility issues. For this reason, it is important to understand what each component does and how it fits into the overall EWI build-up.
At Infinity PM, we supply a range of EWI materials including insulation boards, basecoats, reinforcing mesh, mechanical fixings, profiles, primers and render products for UK trade projects.
What Materials Are Used in an EWI System?
A typical External Wall Insulation system can include several key components:
- Insulation boards
- Adhesive or bonding mortar
- Mechanical fixings
- Basecoat or reinforcing layer
- Fibreglass reinforcing mesh
- Primer
- Final render
- Façade profiles and other detailing products
The exact combination depends on the building, insulation type, system specification and the manufacturer's requirements. ATLAS identifies these components as part of its external wall insulation systems and provides different system arrangements for EPS, XPS and mineral wool.
1. Start With the Insulation Material
The insulation board is one of the most important decisions in an EWI project.
Common options can include:
EPS Insulation
Expanded polystyrene (EPS) boards are widely used in external insulation systems. ATLAS systems include both standard and elastified EPS options, with systems designed for different building requirements.
Graphite EPS
Graphite EPS is another option used within suitable EWI systems. The exact board specification should be selected according to the project requirements and the system manufacturer's documentation.
Mineral Wool
Mineral wool insulation boards are used in specific EWI systems where their properties and the overall system specification make them suitable. ATLAS provides dedicated mineral wool systems, including ATLAS ROKER.
XPS
Extruded polystyrene (XPS) can be used for particular areas where its properties are appropriate. ATLAS identifies XPS systems for applications including plinths, foundation and cellar walls, subject to the relevant system specification.
The important point is that insulation should not be selected based on thickness or price alone. The substrate, building requirements and complete system specification all need to be considered.
2. Choose the Correct Adhesive or Basecoat
The adhesive or mortar has a specific role within the EWI build-up.
Depending on the system, an adhesive may be used to fix insulation boards to the substrate, while another compatible product may be used to create the reinforced basecoat layer.
Some products can perform more than one function. For example, ATLAS GRAWIS U is specified for polystyrene and mesh embedding, while ATLAS HOTER U is designed for EPS and XPS and for mesh embedding.
Always check the manufacturer's technical information before selecting a product for a particular application.
3. Select the Right Mechanical Fixings
Mechanical fixings can form part of the EWI system alongside adhesive.
The required fixing type, length and fixing pattern depend on factors such as the insulation thickness, substrate and system specification.
ATLAS design guidance includes dedicated arrangements for mechanical fixings with different insulation systems, including EPS, XPS and mineral wool.
This means fixings should be selected as part of the overall system rather than simply choosing a fixing based on the insulation board.
4. Don't Overlook Reinforcing Mesh
Reinforcing mesh is incorporated into the basecoat layer and is an important component of many EWI systems.
Glass fibre reinforcing mesh is designed to provide reinforcement within the basecoat. ATLAS describes its reinforcing mesh as alkali-resistant, durable and flexible, and specifies its use with both polystyrene and mineral wool insulation systems.
The mesh should be compatible with the basecoat and the wider EWI system. Correct installation, including appropriate overlaps and detailing around openings and corners, is also important.
5. Consider the Façade Profiles
Profiles are used to deal with specific areas of an EWI installation.
Depending on the system, these can include:
- Corner profiles
- Stop profiles
- Window profiles
- Expansion joint profiles
- Sill profiles
- Other edge and detailing products
Profiles can help form clean edges and provide reinforcement around particular areas. ATLAS façade profiles, for example, can incorporate reinforcing mesh and are designed for applications including external corners and expansion joints. Atlas
These smaller components are easy to overlook when preparing a materials list, but they can be important for completing the system correctly.
6. Choose a Compatible Primer
Primer sits between the reinforced basecoat and the finishing render where the system requires it.
The correct primer depends on the render being used. ATLAS technical guidance lists products such as ATLAS CERPLAST as priming masses for render systems.
Using the correct primer helps prepare the substrate for the selected finishing coat, so it is important to check the manufacturer's recommendations rather than choosing a primer independently.
7. Select the Final Render
The final render provides the visible finish of the EWI system.
There are different render types available, including:
- Silicone render
- Silicone-silicate render
- Acrylic render
- Mineral render
- Other system-specific finishing options
Different renders have different characteristics, so the choice should consider the building, desired finish and requirements of the complete EWI system.
ATLAS currently lists silicone, silicone-silicate and acrylic render products within its external wall insulation range. Atlas
Why System Compatibility Matters
One of the most important considerations when choosing EWI materials is compatibility.
An EWI system is made up of multiple layers, and the products are designed to work together. ATLAS states that its complete insulation systems provide compatibility between the components, which is particularly important for the long-term operation of the system. Atlas
This is why simply choosing the cheapest insulation, adhesive, mesh, primer and render separately may not be the best approach.
Instead, consider the complete system from the beginning.
What Should You Check Before Ordering EWI Materials?
Before placing an order, it is useful to establish:
- What type of wall or substrate is being insulated?
- Which insulation material is specified?
- What insulation thickness is required?
- Which adhesive or basecoat is compatible?
- What type of mechanical fixings are required?
- Which reinforcing mesh is specified?
- Are additional profiles required?
- Which primer is compatible with the selected render?
- What final render finish is required?
- Are there specific requirements around windows, doors, corners or joints?
Having this information available can make it easier to prepare an accurate materials list and reduce the risk of selecting incompatible products.
Choosing EWI Materials for Your Project
An EWI project should be approached as a complete system rather than a collection of individual products. Insulation, adhesive, fixings, reinforcing mesh, profiles, primer and render all have a role within the overall build-up.
At Infinity PM, we supply a range of EWI materials, EPS insulation boards, reinforcing mesh, basecoats, insulation fixings, profiles, primers and render products, including ATLAS products for external wall insulation and render applications.
If you are preparing an EWI project, explore the available materials and make sure the products selected are suitable for the intended system and application.
Explore EWI materials at Infinity PM and build your project materials list around the correct system components.