09-Tiling On Under


Heating elements should be embedded in screed which has a minimum thickness of 7,5 mm.

Do not tile onto new screed. Leave screed for at least 6 weeks before substrate repairing, surface smoothening and tiling. Duration may extend in lower temperatures and/or high humidity conditions. The screed should be wetted each day during curing to prevent formation of cracks caused by shrinkage, in dry and hot ambient conditions.

The deepest point of the application surface in 2 m long gauge should not exceed 7 mm. For larger deviations, the surface should be smoothened with flooring products (CERMIFLOOR 3-10 is recommended).

The substrate must be clean in order to ensure the adhesive bonds properly. Surfaces should be clean and free from dust, dirt, grease or any other contaminating barrier. Subsequently hardened or polished surfaces and laitance (concrete and etc.) must be removed by scabbling. Ensure that substrate is mature, sound, stable and smooth, and not too dry or wet. It is recommended to clean up the surface with pressurized water.

Surface should have been heated (to the desired temperature) for minimum 3 days before application, and then the surface temperature should be allowed to reduce down to ambient temperature. Purpose of this operation is to determine deformations and cracks which may form on floor screed due to heating.


Floor and porcelain tiles of any format and size as recommended by the manufacturers.




For tiling on under heated floors, compatible products should be selected for corresponding to the movements (expansions and shrinks on floor) caused by thermal and mechanical effects.

High porosity substrates should be primed with CERMIFILM before fixing. Priming will balance the water absorptivity of the surface and enhance bonding adherence. Wait for at least 3 hours for the primer to dry and then continue to next application.

After tonality and calibration controls of the tiles, fixing may commence. For fixing tiles (<30x60 cm) select CERMIPLUS.

Gradually add clean water to powder (in quantities as stated in technical legends of products), and mix to a smooth and homogenous paste. It is recommended to use a low cycled electrical drill-mixer for mixing.

The paste should be in a consistence such that it does not flow when handled with a trowel.

The paste should rest for 5 minutes prior to application and should be applied after remixing.

Apply the adhesive on the substrate (for tile sizes >33x33 cm, adhesive should be buttered onto the tile back as well) with a suitable notched trowel to achieve the required bed thickness. Glass tiles, natural stones and marbles should be fixed with double buttering method.

The tiles must be fixed within the open time of adhesive and pressed on with a twisting and sliding action to achieve a good contact. The tile should be gently hammered with a rubber hammer in order to provide the stability of bonding and the adhesive to spread and fully cover the tile back. Lift an occasional tile after fixing to verify that the required contact is being achieved.

Excess adhesive must be cleaned off from the tiles and joints with a damp cloth or sponge before it hardens.

In fixing transparent and light colored tiles and natural stones, a sample application should be carried to observe the possibility of the formation of stain and shades. In case, white coloured adhesive should be used.

To improve the technical performance of the adhesive, it is recommended to add CERMILATEX into the mixing water in the ratio 1:3 (As for the mixing water; instead of 3 scales of water, 2 scales of water and 1 scale of CERMILATEX). With additive added, CERMIPLUS can fix tiles in sizes up to 60x60 cm.

Grouting should start after the adhesive has set and dried. Grouting material’s colour may taint due to adhesive’s cement content and colour.

For grouting application select CERMIJOINT 3-10 FLEX.

While applying cement based grouts, carefully follow the rules and instructions on product packaging and technical legends of the products. Do not add more water into the mixture or re-wet once the mixture is prepared. This will cause the set grout to be weak. It may also cause discrete holes and grains on grout surface, and surface discolouration and variation which will be more noticable with darker grouting colours.

For an easier application and to ensure full final product performance, the grout should be applied at an ambient temperature range of +10 °C - +25 °C.

To improve the technical performance of the grouting material, it is recommended to add CERMILATEX into the mixing water in the ratio 1:3 (As for the mixing water; instead of 3 scales of water, 2 scales of water and 1 scale of CERMILATEX). With additive added, CERMIJOINT 3-10 FLEX has improved elasticity and durability.

Grouted surfaces must be protected for at least 24 hours from direct sunlight, frost and rain.

If any stains and residues remain after grouting, wait for 10 days and treat the tile with CERMINET tile cleaning material to loosen and remove these residues.

Expansion joints should be incorporated to allow for slight movements due to changes in temperature, humidity and thermal and mechanical loads formed on the surface and substrate. Expansion joints should be provided considering heat transmitting systems and insulation applications, floors exposed to heavy traffic and pedestrian loads, wideness of the area, where tiling meets other materials, along all internal corners, existing movement joints or changes in background material. As described above expansion joints absorbs the stresses formed between different movement capacities of overlapping materials. Thus, it prevents the deformations that may arise in the flooring and covering. Expansion joints should be insulated by using proper profiles or mastics. Cementitous grouting materials are not appropriate for expansion joints.

No coatings or coverings should be applied on the existing dilatation zones and structural expansion joints in buildings. These zones should be insulated by using proper profiles or mastics.

If there exist any expansion joints on the floor, artificial expansion joints should be created. Before laying the covering, cold joints should be formed on the screed within rectangular areas of minimum 4 m x 4 m (for large sized tiles up to 8 m x 8 m) with minimum depth of 1 cm. Spiral or concrete cutting machines can be used for forming the joints. If the area is smaller than 4 m x 4 m, expansion joints should be incorporated in the shape (+) on the area. If this is not possible, expansion joints should be laid within columns. These artificial joints will eliminate the stress formed by the structural movements of the building.

Expansion joints should have minimum width of 6-10 mm along internal corners (wall and floor intersections) this rule should be followed, and skirting should be fixed upon to the completion of tiling.

CERMITHANE mastic can be used to fill expansion joints.

The heating system should be heated with daily increments of 5 °C till the desired temperature.

Heating temperature of the system should not exceed +30 °C.

Please consult the technical service for more detailed information.