EWI Install Guide

PLEASE NOTE: The following installation guide is to act as a reminder only to those with some experience in solid wall insulation. If you would like further information we recommend attending one of our training sessions where we will show you (and you will get to practise) each of the different parts of installing the system. During these training courses we also consider other elements out of scope of this install guide including how to insulate below the DPC, how to deal with downpipes, soffits and guttering as well as how to cap and finish the insulation off.

EWI-Pro Solid Wall Insulation Install Guide

EWI Pro has been designed to improve the thermal performance of UK properties and can be used either in the retrofit or new build market.

Our market leading insulation systems have been designed to maximise thermal comfort and significantly improve the look and durability of buildings old and new!

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Step 1 – Surface preparation:

As with every other job, preparation is extremely important. Before applying any insulation to the substrate (e.g. wall), the substrate needs to be examined and checked.

The substrate needs to be clean, dry and dust-free and if applicable it also needs to be cleaned of paint and other substances that might affect the way the EWI-220 EPS adhesive will perform.

One of the best ways to achieve a clean and ready surface is to use a high-pressure water-jet or prepare the wall mechanically (wire brush).

Step 2 – Substrate suitability check:

If the insulation is being attached directly to an existing render, a render test needs to be carried out to ensure that the render is suitable to support the insulation. In order to test its suitability a render pull test needs to be carried out. This involves producing 10 small pieces of EPS insulation (approximately 10cm x 10cm in size). These are then attached to the wall using EPS adhesive (EWI-220) in various places across the wall surface; these need to be left for approximately 72 hours to dry.

After 72 hours has elapsed and the EWI-220 has completely dried, the small pieces of EPS need to be pulled off the wall. The result we are after is the disintegration of the polystyrene, with part of each EPS sample still attached securely to the wall – this proves the underlying substrate is okay to support the insulation.

Pull test for solid wall

If when the samples are pulled, the EPS takes the underlying render with it, all the walls need to be striped completely of the existing render first before any insulation can be attached.

Step 3 – Surface-priming:

One the substrate has been prepared, it then needs to be primed before any EPS / adhesive are applied.

We recommend priming the substrate with EWI-301, which is a deep penetrating water based primer. The amount of priming (and therefore volume of primer required) will depend on how absorptive the underlying substrate is, but typically this can be anywhere from 50 – 300 ml / m2.

The EWI-301 primer will take approximately 4 hours to dry however additional coats maybe required depending on the absorptivity of the substrate. 24 hours should be left between primer coats.

Step 4 – Starter-track installation:

Once the walls are primed, starter track needs to be installed on the walls. The starter track is attached to the substrate above the DPC and not only provides a level surface for easy installation of the insulation; it also protects the bottom surface of the insulation against weather, damp and other damage.

We offer either a uPVC starter track or an aluminium starter track. The uPVC starter track is our premium product and helps minimise thermal bridging. Aluminium starter requires a uPVC starter track connector (this can be seen in the photo below) which provides a layer of mesh that helps tie the system together with the insulation when the reinforcement layer is added.

Starter Track

Both types of starter tracks are fixed to the substrate using rawlplugs, fixed at 300mm centres to ensure the starter track are held securely in place.

Step 5 – Applying the adhesive to EPS boards (ready to apply to substrate)

Once the starter track is in place you will need to start fixing the graphite EPS boards (EWI-110) to the substrate.

The EWI-110 graphite EPS insulation boards are attached to the substrate with EPS-220 adhesive.

The right preparation of EPS adhesive is absolutely crucial. EPS adhesive EWI- 220 should be mixed with clean water at a ratio of 4.8-5.3 litres/25kg bag. The compound should be mixed using heavy-duty power plaster mixer on a slow-rotating setting. Freshly mixed compound should be left for approximately 10-15 minutes and then re-mixed for a short period of time before use. Bucket life is approximately 1 hour.

adhesive on insulation board

We recommend applying the EPS adhesive (EWI-220) onto the EPS insulation using modified ‘Dot and Dab’ method. The EPS adhesive needs to be applied to the perimeter of the EPS board and 3 large dabs should be applied in the centre of the board.

With a trowel you need to apply adhesive evenly around the edges of polystyrene (3-4cm wide track) and inside that area Dot and Dab adhesive spots (approximately 4-7 of them). In general, EPS adhesive should cover no less than 40% of the surface of insulation sheet.

Step 6 – Applying the EPS to the substrate:

The insulation boards should be attached to the wall in a staggared formation as can be seen in the photo below. At the corners, it is important to interlink the insulation from the two sides – again this can be seen in the photo below.

EPS on wall

When installing EPS insulation around window and door openings it is important that the joints between boards are not in line with these openings. This will prevent cracks appearing in the future. For best result and ease of installation we recommend use of Lintel Mesh Corner as can be seen in the diagram below, which help strengthen this area.

EPS around Windows

Step 7 – Level control and filling gaps between EPS insulation boards:

It is important to ensure the EPS insulation boards (EWI-110) are aligned properly when attached to the substrate. These need to be aligned correctly both horizontally and vertically and this is best achieved using a spirit level.

Where the gaps between the EPS boards and these are larger than 2mm, these gaps need to be filled with polystyrene strips. The common mistake is to use EPS adhesive for filling these gaps, but this can lead to a formation of cold-bridges and cracks around the joints between the boards

Step 8 – Smoothing and levelling the façade:

The EPS insulation board’s surface must be smooth and level throughout the façade. All un-even areas should be made good prior to applying the reinforcement layer. For this job a polystyrene rasp needs to be used that will remove the outer surface of the graphite EPS boards. Smoothing of EPS boards should take at least 2-3 days after they have been installed to ensure the EPS adhesive has had sufficient time to go off.

Stage 9 – Mechanical fixings:

Mechanical fixings are used as an additional fixing mechanism to tie the EPS to the substrate. The mechanical fixings help to make for an even more secure installation. Drilling the holes for fixings should take place at least 2- 3 days after the EPS boards have been attached to the substrate with the EPS adhesive (EWI-220) and prior to adding the reinforcement fiberglass mesh layer.

Mechanical fixings

We recommend using 4 mechanical fixings in each of the corners of each EPS board as well as three further mechanical fixings in the middle of the boards. The mechanical fixings are hammered into place, although screws are available too.

The mechanical fixings used can be seen in the photo below. When 100mm of EPS is used, the fixings required are 140-170mm long.

mechanical fixings v2

Once the mechanical fixings have been hammered into place, dowel caps are then used; this is another way of minimising thermal bridging. These are held in place using the EWI-220 and mean that once the system is dry, you will not be able to see any hint of the mechanical fixings.


Stage 10 – Preparation and application of reinforcement mesh layer:

For the reinforcement layer please use the EPS adhesive EWI-220. The preparation of EWI-220 is covered in Step 5.


The adhesive is applied with a notched trowel to the top of the now secured EPS insulation boards. The mesh is then placed on to the adhesive and embedded into the adhesive. Fiberglass mesh should overlap another section by approximately 10-15cm. A layer of 3-5mm thick adhesive should be applied to the wall prior to sinking the mesh within it (if a double layer of reinforcement mesh is added this has to be 5mm).

Stage 11 – Priming the wall before the final render layer:

Once the reinforcement layer has dried for a period of 48-72 hours, it needs to primed with either the acrylic / mineral render primer or the silicone silicate primer (EWI-330 or EWI-333) depending on the final render being used – this is simply painted on top of the reinforcement layer.

This primer needs to be left 24-72 hours to dry prior to adding the final layer of render.

Stage 12 – Rendering the wall:

Using a trowel, apply the silicone silicate render from a bucket onto the wall and smooth it out. Take out the excess of product. Then with a PVC float by round/circular movements of hand, spread and ‘texture’ the render. Although at first complicated, the application procedure is in fact easy and straightforward. We recommend practicing on a smaller area at first. Remember to have enough tradesmen on site especially if coloured render is being used. Otherwise you might be able to see separate layers visible once dry. A whole section of wall needs to be done at the same time.

Rendering v2

If you are using the mineral render then the render needs to be mixed with water prior to applying to the substrate.

This render then needs to be painted with a topcoat once dry – we recommend using EWI-005 Silicone Paint.


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