Base coat

Base coat : solutions pour l'isolation par l'extérieur

The base coat, or undercoat, is the layer that covers the insulation boards and encases the reinforcement mesh. It provides the external thermal insulation system with its strength and impact resistance, and prepares the surface for the final finish. Centrale ITE offers cement and lime-based adhesive renders suitable for EPS, rock wool and wood fibre, at trade prices for both private individuals and professionals.

Réf. KB13

KB13 417 – White organic lime undercoat, 25 kg

KB13 417 is a white, lime-based organic undercoat designed for use as a base coat on external thermal insulation systems (ETIS). It offers excellent adhesion, good water vapour permeability and provides a high-quality substrate prior to the application of façade finishes.

6,14 € TTC

5,12 € HT - TVA 20,00%

External thermal insulation base coat: definition, function and composition

The layer that gives your insulation its strength

The base coat of an external thermal insulation system (ETIS) is a mortar applied directly to the insulation, into which a fibreglass mesh is embedded. Together, they form the reinforced base layer which protects the insulation from impact, accommodates thermal expansion and serves as a substrate for the finishing render. At Centrale ITE, the product of choice is Fassa’s A 96 adhesive-plaster. This is a mortar made from white Portland cement and limestone sand, which is used both to bond the panels and to plaster them. It is designed for:

expanded or extruded polystyrene;
mineral wool;
concrete.

Its performance characteristics (EN 998-1, GP-CSIV-W2):

particle size < 1.4 mm;
compressive strength ≥ 7 N/mm²;
flexural strength ≥ 3 N/mm²;
vapour resistance factor µ 25.

For more mineral-based substrates and insulation materials, Centrale ITE offers two alternatives to lime:

the BIO KB13 417 undercoat;
the lightweight Eco-Light 950 adhesive and base coat, containing natural hydraulic lime (NHL 3.5).

All are suitable for use within the certified insulation system (Technical Approval or DTA).

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Applying the base coat: thickness, coverage and drying time

A precisely controlled thickness, a crack-free façade

The base coat is applied in two coats, with the mesh embedded between them, to achieve a thickness of at least 4.5 mm once dry. This is a requirement of the Fassatherm Technical Approval.

Mix each 25 kg bag of A 96 with approximately 6.5 litres of water using a mixer.
Apply the first coat using a notched trowel.
Press the mesh into the render using a stainless steel trowel, ensuring at least 10 cm of overlap between the strips.
Apply a second coat to completely encase the reinforcement.

The A 96 data sheet recommends 5 to 6 mm on polystyrene and mineral wool, compared with 2 to 3 mm on concrete. The coverage is approximately 1.5 kg/m² per mm of thickness. In practice, allow:

approximately 4 kg/m² on expanded polystyrene (EPS);
approximately 6.3 kg/m² on rock wool (4.2 + 2.1 kg/m² according to the Fassatherm Plus MW Technical Data Sheet).

Application conditions:

apply at temperatures between +5 °C and +30 °C, away from direct sunlight and strong winds;
do not expose to frost for the following 24 hours;
allow to dry completely – several days in cold and damp weather – before applying the primer and top coat.

Comment choisir son isolant extérieur ?

Étapes d'une ITE

Quelle fixation pour quel support ?

External thermal insulation base coat: definition, function and composition

Getting your base coat right first time

The test results, including the fixing depth, must be at least 4.5 mm. This is a requirement specified in the technical specifications. For polystyrene and plasterboard, Technical Data Sheet A 96 specifies a thickness of 5–6 mm, in two layers, with a reinforcing mesh positioned between them; the wire must not be visible at any point.

Please use a spray bottle and a brush, for example, A 96, which is suitable for both types of application: For local repairs and patchwork, apply at a rate of 3–4 kg/m²; for the base coat over a polystyrene foam (PSE) substrate, approximately 4 kg/m² for the base coat, and even more on concrete surfaces. Always follow the instructions for your specific certified system.

In accordance with the technical guidelines, there must be an interval of at least 24 hours between doses. However, it is necessary to allow the coating to set completely before applying the first and final coats, which usually takes several days, or even longer in cold or damp weather. The glaze must be hard, smooth and of a uniform colour.