This section provides a brief overview of floor layers, presenting the most commonly used floor finishes, paving and ceiling linings. The layers of flat roofs as terminal floor assemblies along with the available surface-covering options were discussed in detail in Course 3, Module 2. Similarly, in Course 1, Part 3, we covered the waterproofing of ground-bearing slabs although did not examine their floor layers.
I. Subfloor for floor finishes
Floor finishes or coverings are rarely applied directly onto the slab or the floor slab. Firstly, a solid, even-surfaced (flat and smooth) subfloor is prepared on the structure to provide a suitable base for the floor covering. The subfloor may consist of in-situ concrete, a reinforced concrete subfloor, a screed of mortar-like material or a dry floor system made of thermal insulation and building boards.
Between the subfloor and the slab / floor slab, there may be several additional layers to ensure proper technological construction. One example is the waterproofing layer on the foundation slab; in this configuration, the floor is classified as an unbonded screed.
Another example is the thermal insulation layer, which, when applied, results in a floating floor. The built-in thermal insulation layer can serve multiple functions simultaneously:
-
For intermediate floors, it provides impact sound insulation.
-
For floors on grade, the thermal insulation function is more important, and the layer thickness is designed accordingly.
In addition, other layers may be present in floor structural layers such as waterproofing against service water in facilities, separating membranes, or sheet drains that function as a drainage system.
Subfloor Construction
The subfloor concrete is a 5–7 centimetre thick monolithic reinforced concrete layer, which must be dilated every 40 square metres to prevent cracking.
Here are the steps to construct a floating floor concrete subfloor:
-
Install a 1-centimetre-thick edge insulation strip along walls to accommodate thermal expansion and prevent stress-induced deformations.
-
Install expansion joints to divide the subfloor into smaller sections if any surface length exceeds 8 metres, or if the area is larger than 25–40 square metres, or if the side ratio exceeds 3:1.
-
Lay expanded thermal insulation boards for impact sound insulation in a staggered pattern.
-
Install a polyethylene (PE) foil as a separating layer to protect the insulation, sealing the overlaps with adhesive tape.
-
Establish the top level of the concrete or reinforced concrete subfloor, measuring from the pre-levelled and marked reference line positioned exactly 1 metre above the finished floor level.
-
Install reinforcement mesh. For lighter loads, reinforcement may be omitted.
-
Prepare fresh concrete of minimum C12 strength, either through on-site mixing or by using dry concrete mix.
-
Using straightedges, form 15–20 centimetre-wide guide strips spaced 1.5–2 metres apart, ensuring they are level.
-
Fill spaces between the guide strips with concrete, levelling the surface to match the top of the guide strips.
-
Keep the finished concrete surface moist to prevent cracking.
Construction of other subfloors:
-
The procedure is similar when constructing a cement screed. The main difference is that the fresh mix is prepared on-site using a mechanical mixer and applied with a pump. The typical layer thickness in this case is 2–5 centimetres.
-
For a heated subfloor concrete, a 6–8 centimetre minimum concrete or smooth cement screed will ensure that the heating pipes covered by at least 3–4 centimetres of concrete above. A special PE foil, laminated with a reflective heat barrier, is laid beneath the concrete layer to reduce heat loss.
-
A dry subfloor can be constructed using either factory-produced building boards combined with thermal insulation or separate insulation boards and building boards. The building boards may be made of gypsum fibre, OSB, MDF, or plasterboard. They are laid as two layers on top of the thermal insulation surface.
The surface of a finished subfloor may not always be perfectly even. In such cases, a self-levelling compound can be used to create a completely flat and uniform screed suitable enough for covering. The flowing, fine-grained self-levelling layer typically has a thickness of 2 to 10 millimetres, up to a maximum of 20 millimetres. First, a primer must be applied with a roller; when it has dried, the levelling compound is poured onto the surface and then spread evenly using a trowel or spiked roller.
