Brush the surface and remove every remnant of waste from where the underlay will be installed in order to obtain an even and smoothed-out surface. The surface shall correspond to the following flatness criterias: ≥7 mm under a 2 m plank and it has to be ≤ 2 mm under a 20 cm plank. In certain cases, a levellling screed must be applied over the ducts to obtain an even surface.
Installation of the underlay
Place the insulFib 3+ while making sure that the white felt faces the ground. The insulFib 3+ strips must be laid side by side, with no space in-between. Remove the protective film from the flat overlap made of spunbond non-woven fabric (6 cm) and make sure to fully cover the parallel insuliFib 3+ strip. Use an edge strip made of PE-foam (Lfoam) or pull-up more or less 15 cm of insulFib 3+ along the walls. The vertical ducts have to be insulated (or covered) either with flexible sleeves or with handmade strips of insulFib 3+.
Making of the screed
Immediately after placing the underlay, pour a reinforced screed with a minimum thickness of 6 (allowed to be ≥4.5 cm locally). In case of underfloor heating, the thermal panels must be laid upon the underlay. When the screed and the floor covering have been successfully placed, cut the remaining insulFib 3+ or the remaining PE-foam circumferential strip. The plinth has to be placed slightly higher than the floor covering in order to avoid lateral acoustic transmissions. The last step would be to create a flexible joint under the plinth.
The screed and the slab made of hydraulic binders have to comply with the local regulation.