Installation of ETICS Thermal Composite System up to 20 cm

ETICS is a tested and certified system. Each layer has a specific job, and all the layers should come from one manufacturer. A typical build-up looks like this:

• Adhesive mortar that holds the boards on the wall
• Insulation boards made of expanded polystyrene (EPS) or mineral wool
• Mechanical fixings, which are plastic anchors with a wide plate
• A reinforcing layer of base coat with glass-fibre mesh pressed into it
• A primer and the final thin-coat render

Base profiles, corner beads and window profiles are also part of the system. They are not decoration. They protect edges and joints, which is where render would otherwise crack. If you mix adhesive from one brand with render from another, the system is no longer certified, and the manufacturer will usually refuse any warranty.

In Europe, ETICS kits are covered by standards such as EN 13499 for EPS and EN 13500 for mineral wool, and by the manufacturer's technical assessment. When you choose a contractor, it is sensible to ask them to follow these standards and the manufacturer's installation guide.

The steps have to be done in this order, and the drying and curing times between them cannot be cut short. On site the work usually goes like this:

1. Prepare the substrate. The wall must be sound, dry and free of dust, moss and loose render. The installer taps old render to find hollow areas, knocks them off and repairs them. Larger unevenness has to be levelled first, because the adhesive can only make up for small differences. Absorbent surfaces get a primer.
2. Fit the base profile. It must be exactly level, because it sets the position of every row of boards above it.
3. Bond the boards. Adhesive goes in a strip around the edge of each board and in several dabs in the middle, so that it covers at least roughly 40% of the board. The boards are laid in a staggered pattern like bricks, with tight joints. Gaps wider than about 2 mm are filled with slivers of insulation or insulating foam, never with adhesive. Around windows the boards are cut into an L shape so that no joint runs out from the corner of the opening.
4. Anchor the boards. Anchoring starts once the adhesive has set, usually after one to three days depending on the manufacturer and the weather. The number and type of fixings follow a calculation based on the wall material, the height of the building and wind load. Corners and edges of the facade get more fixings.
5. Sand the polystyrene. Light sanding removes small steps between boards so they do not show through the render.
6. Apply the reinforcing layer. The mesh is pressed into the fresh base coat in the middle of the layer, without folds, with overlaps of at least about 10 cm. Before that, window corners are strengthened with diagonal strips of mesh.
7. Apply primer and render. The top coats go on only after the base coat has cured, which usually takes several days depending on the product and weather.

Throughout the work, both the air and the wall should be at roughly +5 °C or more. The facade should not be in strong direct sun, strong wind or rain.

For thicknesses up to 20 cm, two main materials are used. Each suits a different situation.

Facade EPS

White EPS is light, easy to cut and easy to handle. On a house with ordinary masonry walls it is the usual choice. Grey graphite EPS insulates slightly better, so you get the same effect with a thinner board. During installation it must be shaded from direct sun, otherwise the boards can overheat and warp. Polystyrene is combustible, so on taller buildings the design usually calls for non-combustible fire barriers of mineral wool, for example above windows or at each floor level.

Mineral wool

Stone wool does not burn, lets water vapour pass through and reduces noise better. It suits blocks of flats, buildings with stricter fire requirements and older masonry that needs to let moisture escape. It is heavier, needs more thorough anchoring and takes longer to install. Facades need boards or lamellas made specifically for ETICS, not the loft insulation sold in rolls.

Plinth and render

Standard EPS and mineral wool are not used on the plinth just above ground level. That area gets XPS or perimeter boards that tolerate moisture and knocks. Mineral wool should be finished with a vapour-open silicate or silicone render. With polystyrene the choice is wider. Silicone renders are often chosen for insulated facades because they repel water and stay clean for longer.

Two facades of the same size can mean very different amounts of work. The job is easier with:

• A flat, sound wall without old paint layers
• A simple building shape with few corners and openings
• Good access around the house and a low height where simple scaffolding is enough

Many windows, bays, balconies and recesses make the work longer. So do removing old render, treating damp or cracks, and moving downpipes, lightning conductors, outdoor lights or an air-conditioning unit. With insulation close to 20 cm, the details matter more. Window sills must be long enough, window reveals need thinner insulation, and on some houses the roof overhang has to be extended so the insulation is not left unprotected under the eaves.

Most insulation faults are not visible straight away. They appear after the first winter or a long spell of wet weather.

• Bonding onto a dusty, damp or crumbling surface, so the system gradually comes away from the wall
• Adhesive applied only in dabs without the edge strip, so boards bow and their outlines show on the facade
• Cross joints or wide gaps filled with adhesive, which create cold bridges
• Too few fixings, or fixings unsuitable for the wall material, especially at building corners
• Missing corner beads and diagonal mesh at windows, so cracks grow from the corners of openings
• Rendering in the cold, in full sun or just before rain, which leaves patches and hairline cracks
• Leaky junctions with windows and sills, letting water get behind the insulation

Insulating a facade changes how the building looks, and in many places it also affects fire safety and planning rules. Do not assume it needs no approval. Check your local building regulations and ask the local building authority before work begins, especially in conservation areas. In a block of flats the owners decide together, and the building management or owners' association handles the process. Taller buildings usually need a proper design, including fire safety. The work is done from scaffolding at height, so it is a job for a contractor, not for a DIY project.

At handover, walk round the facade in daylight and also look along the wall at a low angle. Check the following:

• The facade is flat, without bulges or visible board outlines
• No anchor plates show through the render as spots
• Corners and reveals have straight edges without cracks
• The render meets windows, doors and sills with a flexible seal
• The plinth is made of suitable material and the base profile is undamaged
• The render colour is even, with no patches or blotches after drying
• You have received documents for the system used, technical data sheets and warranty terms
• The site is tidy and downpipes, lights and other fittings are back in place