Instruction for installing and seasoning floor screeds with water-powered underfloor heating
Water – powered underfloor heating systems has become a very common element of up-to-date flooring projects. Although popular and widely met, contractors very often ask us about the ATLAS recommended procedure of its installation and seasoning. Our instruction should answer the mostly asked questions.
The screed layer above the heating pipes must be at least 35 mm thick. Heating systems where individual elements may heat up to over 40°C (CH or DHW systems) should not be placed within the screed layer. If it is not possible to avoid such installations, the elements must be insulated with thermal insulation materials (e.g. special insulation sleeves in case of pipes) to limit the transfer of heat to the screed. The screed must be “heated up” before the application of the top floor layer. The process of “heating up” can commence after 7 days since the screed application (in case of ATLAS POSTAR 10, POSTAR 20, POSTAR 40, POSTAR 80, POSTAR 100 or ATLAS SAM 500) or 24 days since the screed application (ATLAS SAM 150 or SAM 200).
Before the underfloor heating system is in full operation, one must rise the set temperature every 24 hours by maximum 2°C, up to the maximum operating value. Keep the maximum temperature for at least 1 day for every centimeter of the screed thickness, e.g. for a screed layer 6 cm thick, keep the maximum temperature for at least 6 days. Then, the set temperature must be reduced in the same way (every 24 hours by maximum 2°C) until the heating is turned off. During the process of “heating up”, the room with the screed should be ventilated. Avoid direct sunlight and draughts. Once the process is completed, the moisture content of the screed must be checked.
Maximum moisture content of the screed (measured with a CM method) before application of the top floor layer:
1) For anhydrite screeds (ATLAS SAM 150, SAM 200 or SAM 500):< 1.5%
Note. If impermeable or wood-based top layer is to be laid on the screed, one must follow the manufacturer of adhesives or carpets instructions.
2) For cement screeds (ATLAS POSTAR 10, POSTAR 20, POSTAR 40, POSTAR 80, POSTAR 100): < 3% – under ceramic tiles < 2% – under self-leveling compounds or vapour tight layers e.g. PVC.
Before installing water-powered underfloor heating, refer to the heating system manufacturer’s documentation and follow the instructions provided. Pipes in water-powered underfloor heating system must be protected from surfacing during work.
As for the maximum allowable moisture content in the screed and possibility of heating after application of the top finishes not covered by this instruction, one must follow the manufacturer’s instructions. Detailed information on ATLAS / AVAL screeds application technology can be found in the applicable product technical sheets and brochure “School of Flooring”.
