Underfloor heating

The following is best practice advice for the installation of Weber flooring screeds in flooring systems which feature underfloor heating. 

Preparation

Substrate preparation - depending on substrate:

  • Cleaning
  • Rough levelling of the substrate for installing the system plates or optional additional installation layer EPS-plates.

The surface in general has to be dry and free from surface contamination and other impurities. All dust and debris should be vacuumed from the surface. Smaller holes and floor irregularities, such as prefabricated elements and height differences, can be smoothed out with bagged sand to ensure the stable application of the heating plates.

Optional installation layer 

This optional layer can be used for sewers, water pipes, electrical installations or any other requirement for an intermediate layer.

Small installation needs are conveniently dealt with using a 30-50mm layer of EPS boards into which 'omega shaped' grooves are cut with a heat cutter.

Where there are several pipes, it is more convenient to make a complete duct and to tie down the group of pipes. The gap is filled with thick flowing mortar or screed to form a uniform support for the system plates.

Pipes can also be drilled down through intermediate slabs and be led in the suspended ceiling below or through self-bearing base floors.

Heating pipes

Heating pipes made of PEX or composite materials are common. To achieve a high efficiency at the windows, start the heat circuits at the perimeter walls. The areas close to the central heating and at pipe joints should be fixed to corner plates.

The ingoing water is usually ≈ 23-30°C and the returning water cools down approx. 1-4°C. The heating designer calculates these temperatures and the ingoing water temperature is usually adjusted with an outdoor thermostat, whereas the circulation per room is regulated by room thermostats.

The length of the pipe circuits, the pump's pressure, the room area and the used floor covering material also affect these temperatures. Therefore, the heating design is carried out by professional heating designers.

Dividing layer 

Geotextile separates the fresh screed from the heating system below and stops the screed flowing in between the insulation boards. Geotextile is carefully selected for its resistance to leaks and its workability guaranteeing a rapid and secure final result. The Geotextile is rolled out on to the plates. Connecting parts are taped and the dividing layer is applied to all vertical construction elements. This ensures that materials added subsequently cannot run behind them.

Surface slab

As a load and heat distribution layer, three different self levelling screeds can be used within the Comfort Floor Concept:

  • weberfloor 4310 fibre flow or weberfloor 4320 fibre flow rapid  - A fibre reinforced, flexible cementitious screed with high polymer content. The minimum thickness should be 15mm over the top of the heating pipes up to a maximum thickness of 50mm. 
     
  • weberfloor 4360 base flow rapid - An economical fibre reinforced cementitious base screed, designed for floating floors. The minimum thickness should be 25mm over the top of the heating pipes up to a maximum thickness of 80mm. 

Please note: If the final floor covering is PVC or linoleum, a finishing layer of weberfloor 4150 fine flow or weberfloor 4160 fine flow rapid is required prior to application of the floor covering.

 

All materials are pumped directly on to the Geotextile in the recommended thickness and are levelled by wobbling the fresh screed.

Please note: Pure Portland cement-based screeds or concrete are not suitable for the Weber Comfort Floor, due to the aluminium reacting (vaporizing) with the high pH of the humid concrete.

Further recommendations

The floor covering may be applied once the drying conditions are suitable. The indications referring to the readiness for covering apply to a dry substrate, a room air temperature of 20°C and a relative humidity of 50%. Air dehumidifiers, draughts and too high temperatures must be avoided.

Normal apartments can usually be done without any joints. In the case of unfavourable geometry (narrow long corridors or big areas where the uniform slab is "cut" by partitions), we recommend creating a "dummy joint" by cutting the slab approximately 5mm deep at such critical places. If the slab is to crack, it will crack in a controlled manner at these places but it will still be held together by the glassfibre mesh. If the floor covering requires a joint, and a crack-free floor is required, these dummy joints can be injected as soon as the shrinkage stresses have ceased, i.e. when the screed material has dried out completely!

As the heating pipes are completely below the screed slab, the risk of damaging these when cutting the dummy joints is very small. Also, the heat pipes will not suffer from the screed slab having any joints as they are not embedded in the screed.

Expansion joints do not have to be used as the surface slab floats completely freely, independently of the building. On the contrary, we can offer seamless floating screed floors which also enable the tiling of large areas without joints and cracks.

After 14 days the underfloor heating can turned on at a maximum of 15°C, and then increased by 5°C every day until the required temperature is reached. This is to avoid thermal shock in the screed.

Please note: Small hair cracks may occur due to the building shape or the substrate. These are purely optical flaws and have no influence on the floor's adhesion or loading capacity.

Contact us

If you have any questions or would like assistance, please contact our technical team:

Our technical team is available Monday to Friday, 8:30am until 5.00pm.

Click Compare to help you choose the right product for your project, if you need further assistance please email technical@netweber.co.uk

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