A mat (4) is provided between the mortar layer (3) and foundation (2) whereby the mortar is fixed to the mat. The mat can have a steam-permeable fleece which is impermeable for the mortar. The fleece is made of plastics fibres or glass fibres. The mat is provided with a mesh grid on the side facing the mortar layer. The grid may also be made of plastics and/or glass fibres and is connected to the mat in some areas by adhesive spots.
