An external wall insulation (EWI) render system is built up in layers on the outside of a wall: an adhesive that bonds the insulation board to the wall, the insulation board itself, a basecoat with a glass fibre mesh embedded in it, and a finish coat. Each layer has its own product, and the finish you see is only the last of them.
This guide walks through the four layers with the products sold in the EWI systems range at Sealants4All: Terraco Styrobond DP EWI Basecoat & Adhesive 25kg for the adhesive and basecoat layers, the decorative render, textured coating and stone-effect finishes, and fischer Insulation fixing FID 50 – 48213 for fixing lightweight items to the finished wall.
The figures that matter on site, from the water ratio of the basecoat to the thickness of the insulation board, come from each product’s data sheet and from the system specification for the building. This guide names the products and what each one does; it does not repeat those figures.
What an EWI Render System Is and What Each Layer Does
An EWI render system moves the insulation to the outside of the wall and protects it with a rendered or coated surface. Read from the wall outwards, the layers are:
- Adhesive: bonds the insulation board to the wall. The Styrobond DP product page describes the product as an adhesive “between mineral substrates and expanded polystyrene boards (EPS boards)”.
- Insulation board: the Styrobond DP page names EPS (expanded polystyrene), XPS (extruded polystyrene) and mineral wool panels as the boards it is applied over. The board type and thickness for a given wall come from the system specification, not from this guide.
- Basecoat with glass fibre mesh: a mortar coat applied over the boards with a glass fibre mesh embedded in it. The Styrobond DP page describes the product as “an embedding mortar applied over EPS (expanded polystyrene), XPS (extruded polystyrene) and mineral wool panels to embed the glass fibre mesh prior to application of finish coats”.
- Finish coat: the decorative render, textured coating or stone-effect coating that gives the wall its appearance. The EWI systems category at Sealants4All groups these as decorative renders, textured coatings and stone coatings.
EIFS and EWI: Two Names for One Build-Up
The Terraco product pages call the build-up the “EIFS Exterior Insulation Finishing System”. EIFS is the manufacturer’s term and EWI is the usual UK term; both describe the same sequence of adhesive, board, basecoat with mesh and finish coat. When a product page says a finish is “recommended for Terraco EIFS”, it means the finish is intended for this kind of system. The thermal performance of the finished wall depends on the board and the system specification and is not a property of any single product named here.
Adhesive and Basecoat: Bonding the Board and Embedding the Mesh
Terraco Styrobond DP EWI Basecoat & Adhesive 25kg does two jobs in the system. Its product page describes it as “a basecoat and adhesive for the Terraco EIFS Exterior Insulation Finishing System”, supplied in dry powder form and “easy to use by just adding water”. The page gives the manufacturer’s wording for its properties: water resistant, good flexural strength and good impact resistance.
Working as the Adhesive
Used as the adhesive, the mixed material is applied to the EPS board and the board is pressed into place using a level. The product page adds one instruction that governs the pace of the work: do not allow the adhesive to skin before the board is fixed in place. Mix only enough material for immediate use, so that no batch stands longer than the work in front of you.
Working as the Embedding Mortar
Used as the basecoat, the same product is the embedding mortar for the glass fibre mesh. The product page describes the sequence: apply a coat of the Styrobond DP mix to the board, embed the mesh using a trowel, then apply another coat of mix to the surface to ensure full cover of the mesh. The mesh must be covered on both sides by the basecoat, with no mesh showing through, before any finish coat goes on. Tools and equipment are cleaned with water after use.
The water ratio, mixing time, standing time, coat thickness, drying time and application temperature range for Styrobond DP are given in its product data sheet. Take them from there and from the system specification before mixing the first bag.
Choosing the Finish Coat: Decorative Render, Textured Coating or Stone-Effect Coating
Once the basecoat has cured, the finish coat decides how the wall looks and how it is applied. The EWI systems range at Sealants4All covers the three finish types with Terraco products; one example of each is described below in the wording of its product page.
Decorative Render
Terraco Terol Granule Cementitious Render 25kg is described on its page as “a trowel applied mineral based decorative render with a medium grain finish”, primarily used for EIFS systems, mixed on site and applied by steel trowel. It is polymer modified and vapour permeable. The colour comes from an overcoat: the page describes the render being overcoated with Terracoat Stain to the approved sample.
Textured Coating
Terraco Terracoat Sahara Textured Render 1-2mm is described on its page as “a trowel applied textured coating with a filled granular finish”, recommended as a finish for Terraco EIFS and available in two grain sizes. It is applied by steel trowel and finished with a plastic trowel, is water based and is described as vapour permeable, allowing the substrate to breathe. The page offers it in two grades, Pro (Acrylic) and Ultra (Silicone), and describes the coating itself being applied to the approved colour and texture sample.
Stone-Effect Coating
Terraco Terralite Granite Effect Wall Coating is described on its page as “a medium-high build spray applied granite effect coating suitable for general masonry and Terraco EIFS”, used to simulate natural granite and designed for interior and exterior use. It is water based and vapour permeable, and it is spray applied rather than trowelled.
How to Choose Between Them
Three questions separate the finishes. First, the look: a mineral granular render, a filled granular texture or a granite effect. Second, the application method: Terol Granule and Terracoat Sahara are trowel applied, Terralite Granite is spray applied, which changes the kit and the labour on the scaffold. Third, how the colour is achieved: Terol Granule is overcoated with Terracoat Stain, while Terracoat Sahara and Terralite Granite are applied in colour to the approved sample. Each product page also names the Terraco primer, and for Terralite Granite an undercoat, that goes on before the finish; follow the product data sheet for those coats rather than this guide. Confirm with the system supplier that the finish you choose is specified for the basecoat and board under it.
Fixing Lightweight Items to the Finished EWI Facade
Letter boxes, lamps and similar lightweight attachments are fixed into the insulation layer, not drilled through to the wall behind it. The fischer Insulation fixing FID 50 – 48213 product page describes the fixing as “a fixing for mounting lightweight components in plastered and un-plastered insulation panels made of polystyrene and polyurethane”, and states that “since the anchor is set exclusively in the insulation itself, fixtures can be installed without thermal bridges”. The page lists letter boxes, lamps and motion detectors as the kind of component it mounts, and names polystyrene, mineral wool, soft wood fibre and alternative ecological insulation boards as the facade insulation types it is used on (the page calls these ETICS facades, another name for EWI).
Setting the fixing is a hand operation: the page says the special spiral thread taps itself into the insulating board and that the fixing can be set either by hand or with a cordless screwdriver. Heavy or load-bearing items are outside this fixing’s use; the system specification says how they are fixed. The FID 50 page also notes that water ingress in the insulation can be prevented by sealing the plug collar with a suitable sealant after the fixing is positioned; the construction sealant guide explains the sealant types in detail, so this guide does not.
The Four Layers in Short
Adhesive and basecoat from one bag of Terraco Styrobond DP EWI Basecoat & Adhesive 25kg, the insulation board the system specification calls for, glass fibre mesh embedded in the basecoat, and a finish coat chosen from the decorative renders, textured coatings and stone coatings in the range. Fixings for lightweight items go into the insulation afterwards with fischer Insulation fixing FID 50 – 48213. See the EWI systems range at Sealants4All for the products in each layer.
