Heated screeds
Preparation technique
Cover the newly laid screed with a waterproof sheet for seven days.This prevents the screed drying out too rapidly, which would cause shrinkage stress, and allows it to develop an inherent structural strength.
After this period, uncover the screed and allow it to air dry for a further three weeks (or longer depending on the ambient conditions of the installation).
For further information on drying times, please refer to BS 8204. As a general rule, if a screed is a thickness of more than 50mm, then it should be applied in layers up 50mm thick to ensure a compact substrate.
Before tiling, turn off any heating for a period of 24 hours and allow to cool down.
After the tiling and grouting is complete,wait for a period of 24 hours before turning the heating back on at increments of no more than 5°C every 24-hour period to stop cracking of the screed.
Do not use the heat to accelerate the drying process of the screed.
Adhesive application and Method
For underfloor heating use a polymer modified adhesive such as PCI’s Nanolight, applied with a notched trowel.
Ensure a minimum adhesive bed thickness of 3mm with no voids between the substrate and the tile.
Leave a joint width between each tile of between 4mm-5mm.
For internal angles, use proprietary expansion joint sealants or leave a joint width of 1.5 times the recommended grout width (so a joint width of 4mm would have a corner joint width of 10mm).Do not butt-joint corners of walls and floors.
Ensure that there is a perimeter expansion joint of 10mm in width.
Grouting
To allow some movement when the heating is turned on, use a flexible grout such as PCI’s Groutfast 20 Rapidflex.
Movement Joints
Please refer to Special Situations Bulletin 1 due to the complexity of this subject.
Electric Underfloor matting systems
An alternative system to the traditional method of heated water pipes laid into a screed is a thin matting system (just a few millimetres thick) which incorporates an electric heating element.This cost-effective system is thin enough to be used under ceramic floor tiles.
Preparation technique
The substrate onto which the matting system and tiles are to be laid, must be rigid in order to provide a solid background, such as a concrete or cement-based screed.
Refer to the ‘Tiling onto Concrete’ for further information on drying times and priming instructions.
If tiling onto wooden floors, improve its stability by overlaying with a suitable material such as a tile backer board such as PCI Pecidur (refer to Tiling on Wood section for further information on how to install these boards before installing the matting system and tiles.
Adhesive application and Method
For underfloor heating use a polymer modified adhesive such as PCI’s Nanolight applied with a notched trowel.
Ensure a minimum adhesive bed thickness of 3mm with no voids between the substrate and the tile.
Leave a joint width between each tile of between 4mm-5mm.
Ensure that there is a perimeter expansion joint of 10mm in width.
Grouting
Movement Joints
Please refer to Special Situations Bulletin 1 due to the complexity of this subject.
For more information, contact PCI’s Techincal Services Department on 0161 794 7411