Stages of an EWI Installation

Lots of customers hear about our external wall insulation systems by witnessing their neighbours installations, but often the stages and process of the installation are not very clear. Here at EWI Store, we set out to make sure that our customers are fully informed about our systems, including how they are installed and why we install them in certain ways. So keep reading to learn about the EWI installation process!

Wall Preparation

Before any works can begin, the external walls will need to be prepared. The preparation required tends to vary depending upon the condition of the building. In most cases, a simple rub-down will do, although sometimes we may need to remove your existing wall coating. If you are installing EWI onto a smooth surface, then you will need to use our EWI-310 Universal Primer (read about it here in our primer guide) to allow for the adhesive to stick to the walls. If the wall isn’t completely straight, then the EWI-260 Levelling Mortar must be used to dub the wall. Fungicidal wash should be used to remove any organic growth.

Addition of Starter Tracks to the wall

The correct starter tracks should be applied to the walls above the DPC. The starter tracks not only allow for the easy installation of insulation to the walls but also protects the bottom surface of the insulation against weather, damp and other damage. Clip on profile should be attached to aluminium starter tracks to create a neat finish between the starter track and the insulation.

Applying insulation to the walls

At EWI Store our basecoat can be used as an adhesive. The basecoat should be applied to the insulation using our modified dot and dab method (three dots in the middle and all around the perimeter). A notched trowel should be used to evenly spread the basecoat on the back of the insulation board. The basecoat should be about 4-5cm thick. When placed on the wall, mechanical fixings should be used to add some additional security to the insulation (6 fixings per square metre of insulation). Allow 2-3 days for the basecoat to set before installing the mechanical fixings.

Addition of Beading and Verge Trims

Before the addition of the basecoat, all beading must be applied. Beading is used to reinforce weak or impact-prone areas within the system, helping to prevent damage and reinforce the structural integrity. Each beading has its own special function and area of application:

Corner beads: Corner beads have mesh and sink into the basecoat. Corner beads reinforce the external corners of the EWI or render-only system.

Movement Beads: used inside corners in thermal insulation systems to create a permanent and weather-proof sealant of vertical movement joints.

Bellcast Beads: designed to provide a clean, natural stop to the render just above the damp proof course. The bellcast bead also drives water away from the wall.

Render Movement Beads: Should be used where there is a large expanse of render area. The render movement bead is used vertically and is designed to prevent cracking within the render through thermal expansion and compression.

Basecoat and mesh layer

After 2-3 days, another layer of the basecoat should be applied with a notched trowel over the top of the insulation boards at a thickness of 5-6mm. Fibreglass mesh is then embedded into the basecoat in vertical strips using the flat edge of a notched trowel. Each vertical strip of fibreglass mesh should overlap its neighbouring vertical strip by approximately 10-15cm. We use fibreglass mesh because it increases the tensile strength of the system and goes an extra step further in preventing cracks and impact damage.

Render Primer

Render primer tends to be an optional step, however for best practice and for increased durability and adhesion you should apply a render primer to the basecoat. The render primer that you use will depend upon the render itself; if you’re using our Silicone Silicate render, then the SiSi Render Primer is the most appropriate. For our Acrylic render, the Mineral & Acrylic Primer is the most ideal, and so on. This should be painted on and then left to dry for 12 hours – check out our blog all about our primer range for a complete guide.


Once your final basecoat layer is dry, your render of choice is then installed over the top. When we talk about thin coat renders, we are referring to our Silicone, Silicone Silicate, Acrylic or Mineral renders. All of which can be mixed into any shade using our specialist colour tinting equipment.

There you have it! This is a very basic installation guide which should be used purely as an overview of an EWI install for informative purposes. Every installation is different, so if you have any further questions about installing EWI on your property then call our technical team who are always happy to answer questions!

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