Substrate preparation (by intended use)

Preparing the installation substrate for indoor cladding

Before cladding, the installation surface needs to be prepared. This depends on the substrate type, environmental conditions, traffic, the type of cladding, and tile size.

1. Horizontal cladding

The substrate for horizontal flooring is usually concrete, wood, particleboard, OSB, or old cladding.

A concrete substrate is prepared by applying a primer to even out absorption and pouring a base screed (bonded, floating, or unbonded), then a self-leveling screed if needed. The screed’s role is to level and even out the floor. Once the screed is dry, waterproofing is applied to its surface if the environment is damp. After waterproofing, the surface must be fixed, smooth, clean, and dry. Adhesive and stone tiles are then applied to this surface.

If the substrate is wood (or wood-based), it needs to be secured first. Flatness is then checked, and if differences are found, a self-leveling screed is poured locally. Then, 15-20 mm thick plywood panels are laid on the surface and screwed down. Cement board can also be used, with a joint between panels that’s glued to the substrate and then screwed down. Joints are covered with sealing tape. Then a primer is applied, followed by 1-2 waterproofing coats, and finally the tiles are installed.

For old cladding, it’s best to remove it entirely, since the substrate it provides for installation is rarely solid. If that’s not possible, the old cladding is secured as well as possible, and gaps left after removing tiles that can’t be fixed or were installed incorrectly are repaired. Gaps can either be filled with adhesive or patched with tiles of the same size. The surface (especially if polished) is then sanded to create a rough layer that improves adhesion. Alternatively, an acidic solution that etches the surface can be used.

For underfloor heating systems, installation is done with the system switched off. For sealing, 2 waterproofing coats are applied, followed by the tiles, using suitable adhesives and grouts.

2. Vertical cladding

Wall cladding depends on the type of wall being clad (masonry or drywall).

Masonry walls are plastered with a base coat for leveling, then a finishing coat. Before plastering, a primer is applied to the surface to increase adhesion. Finally, adhesive is applied and the tiles are installed. To even out masonry walls, a 9 mm particleboard sheet can also be applied, possibly mounted on wood battens. Particleboard can support up to 30 kg/sqm, so its use is limited by the weight of the stone tiles.

Drywall walls can support around 30 kg/sqm applied directly (adhesive + tile). This requires stone tiles no more than 10 mm thick. Adding the adhesive brings the maximum thickness to about 13 mm. Thicker tiles, typical of natural stone, aren’t supported by drywall. With a skim coat, the wall can only support 20 kg/sqm.

For flexible slate, which allows cladding on curved surfaces, the surface needs to be clean, solid, and dry.

3. Special cladding – steps, window sills, countertops

Step cladding is done on an existing substrate, most often concrete or brick. Steps can be made either directly by cutting a slab to the required size, or by cladding with smaller tiles. The substrate must be solid, smooth, clean, and dry. Substrate smoothness is essential, since otherwise the steps won’t be flat. After leveling the surface, tile cladding follows the same technique used for flooring.

Window sills, in turn, are cut directly from slabs and may have their edges processed. Their installation needs a flat, clean, solid substrate. The installation technique is similar to horizontal cladding.

Countertops are placed on concrete, brick, metal, or wood structures. These must provide flatness and strength, since stone countertops are heavy. Installing countertops on supports follows a technique specific to each type of support.

Surface preparation is essential to proper cladding; any mistake made at this stage will carry through and can compromise later steps, even though some defects can be compensated for.