Substrate Advice

Concrete screeds are typically made up of sand and cement, they can often be referred to as traditional screeds.

In line with applicable regulations, concrete screeds should have a minimum cure time of 28 days - always be led by your professional installer. Prior to installing the tiles, it is important that the underfloor heating has been commissioned and the screed is fully cured - this can only be determined by a moisture test. Substrates must comply with BS 5385, parts 1-5, be stable and non-deformable, without cracks and have already completed the curing period for hygrometric shrinkage; must be free from dust, oil and grease, free from any rising damp, with no loose, flaky material.

Subject to meeting the above conditions, the screed should be primed using Kerakoll Eco A - full application advice can be found on the Kerakoll Eco A product page.

In the instance of an uneven surface, a levelling compound such as Keratech Eco R10 can be used (suitable for thicknesses between 1-10mm) - full application advice can be found on the Keratech Eco R10 product page.

Heated floors are subject to thermal expansion and require an anti-fracture mat.

Calcium Sulphate, Anhydrite & Gypsum screeds can often be referred to as self-levelling screeds. These screeds have become increasingly popular due to their reduced installation time (compared to sand & cement). It is important to note that the curing times for these screeds are longer than sand & cement screeds, due to their high water content.

We strongly advise you to follow your manufacturer's recommendations on curing times, however as a guideline, the curing time for Anhydrite screeds is approximately 1mm per day up to 40mm in ideal conditions. Where the screed is thicker, or with poor drying conditions drying times can be significantly increased. During the curing process, it is necessary to remove the laitance layer as soon as possible (as advised from screed manufacturer) which forms on top of the screed, this layer is too weak to tile on to and can increase drying times.

Laitance should be removed by using a suitable machine i.e. a rotary floor scarifier. All excess dust should be removed completely with a vacuum cleaner. Your screed manufacturer will be able to advise further on this.

Prior to installing the tiles, it is important to be sure that the screed is fully cured - this can only be determined by testing the moisture content within the screed. The RH must be below 75%.

As cement based adhesives will not bond directly to anhydrite screeds it is essential to isolate the screed by using a suitable primer such as Kerakoll Eco A - full application advice can be found on the Kerakoll Eco A product page. Anhydrite screeds are not suitable for use in damp conditions or where wetting can occur.

Heated floors are subject to thermal expansion and require an anti-fracture mat.

Floating Floors/Wooden substrates are affected by both moisture and deflection. It is important to eliminate both of these elements prior to installation.

Overboarding with Tile Backer Boards

Tile backer boards are usually made from re-enforced cement which provide a flat surface to tile upon. Tile backer boards can be used to add rigidity and over floating floors.
Please refer to the manufacturer's guidelines on suitability and installation as they can vary from board to board.

British Standards (BS 5385-1: 2018) currently advises not to tile directly onto plywood.

Bitumen or Asphalt is a sticky, black, and highly viscous liquid or semi-solid form of petroleum. Typically, Bituminous paint is found on floors in older properties, used as a damp-proof membrane or where parquet flooring has been used. We strongly recommend employing the services of a professional installer who has experience with problematic substrates such as Bitument/Asphalt.

Prior to installation, it is important to idenitfy that it is flooring grade Bitumen/Asphalt, and that it has been installed for a sufficient amount of time - your installer will be able to guide you. Substrates must comply with BS 5385, parts 1-5, be stable and non-deformable, without cracks and have already completed the curing period for hygrometric shrinkage; must be free from dust, oil and grease, free from any rising damp, with no loose, flaky material.

The majority of installation products such as levellers and adhesives can not adhere to Bitument/Asphalt, which can cause the tiles to debond and crack, therefore it is imperative to prime the Bitumen/Asphalt prior to installing the tiles. The recommended primer is Kerakoll Keragrip Eco - full application advice can be found on the Kerakoll Keragrip Eco product page.

Please note the maximum period allowed for tiling is 24 hours. Once this period has elapsed, a new, complete application of Keragrip Eco will have to be carried out directly over the existing application.

Limecrete substrates are commonly used in period properties whereby the building needs to breathe to avoid damp associated issues.

The key to installing on top of limecrete is to use breathable materials. This means that anti-fracture matting cannot be used with a limecrete floor.

Natural stone tiles should be used as they enable mositure to pass above the substrate. Always make sure the natural stone chosen is not moisture sensitive - this is stated on the product page.

A breathable adhesive such as Kerakoll H40 Gel (standard set) must be used alongside a breathable grout, such as Kerakoll Fugabella Colour. In addition, it is advisable to allow for slightly wider grout joints to aid the evaporation of the moisture.

The stone must also remain unsealed, therefore it's best to adopt a maintain approach only.

In most instances, plaster skim is not suitable to bear the weight of wall tiles. We recommend a backerboard which can accomodate a minimum 50KG/M2 to bear the load of 15mm stone. It is advisable to provide support to the tiles whilst the adhesive sets. Below are some approximate figures on load bearing capabilities - we recommend contacting the manufacturer directly.

Gypsum Plaster - 20KG/M2

Gypsum Plasterboard (direct with no skim) - 32KG/M2

Fibre Cement Backerboard (Hardiebacker) - 200KG/M2

Cement Backerboard (No More Ply) - 100KG/M2

If you are tiling on to walls in wet areas, we recommend you fully tank (waterproof) the walls with a specific tanking system.

The subbase must be made up of a well compacted layer of MOT type 1 to a minimum depth of 100mm. This should be compacted at 50mm intervals which will ensure maximum solidity and aid with achieving an even level. Following this a thin layer of washed sharp sand can be compacted to the surface of the compacted MOT type 1. Ensure a fall of 1:60 has been accurately set within the subbase to allow for adequate drainage away from the building.

The pavers must be installed onto a full bed of mortar made from 5 parts washed sharp sand and 1 part cement, mixed to a workable consistency. Prior to laying onto the mortar we advise coating the back of the paver with an SBR slurry mix made from 5 parts cement, 1 part SBR and 1 part water which will improve the
bond strength to the mortar.

It is best practice to gauge out the mortar bed and manoeuvre the paver into position rather than strike heavily with a mallet as this can lead to breakages, should there be any natural weak points. Pavers must be installed onto a full bed of mortar as per BS7533 – under no circumstances should they be spot or ribbon fixed. During the laying process it is advisable to clean away any spots of mortar or slurry as soon as possible as they can be difficult to clean when dry. After the pavers have been laid the area must not be walked on
for at least 36 hours

Ensure a fall of 1:60 has been accurately set within the substrate to allow for adequate drainage away from the building. If installing onto a solid cement substrate the minimum curing time is 28 days before installation can commence. Please note this timeframe will vary depending on site conditions and thickness of concrete.

The method for laying exterior pavers onto a concrete subbase is very similar to installing tiles internally. First the substrate must be clean and dust free as this can impair the bond strength and could lead to failure. Please note the installation must be carried out in dry conditions.

Pavers should be back buttered with a thin coat of exterior grade flexible white adhesive and laid onto a full bed of trowelled adhesive using a 10mm notched spreader. Ensure the paver is pushed into place to collapse the ridges from the notched trowel, this will provide full coverage beneath the paver and allow maximum strength for the finished patio. Under no circumstances should any of the pavers be spot fixed. Please note uncalibrated pavers should be graded prior to install and will require more adhesive in some areas.