If the advice below is not followed then any warranties on our flooring and guarantees will be invalid. Please see our terms and conditions for more information.

Resin, polished concrete floors and underfloor heating technical document

This article has been produced after extensive research and more importantly our own experience in fitting poured resin or polished concrete flooring over underfloor heating (UFH). All of our poured resin or polished concrete flooring is suitable for any type of UFH. There is a very interesting article from Brain Sensecall at the end of this publication that gives an independent view of poured resin or polished concrete flooring with UFH. As carpets are an insulating material they are not as effective with UFH.

The following are the basic steps when you are considering choosing UFH with a resin or polished concrete floor. Poured resin or polished concrete is a great choice for UFH as it is natural, warm to the touch.

It would be highly recommended that a certificate is obtained from the company that fitted the UFH system to ensure that it is fully operational with controlled temperatures so that the surface temperature does not exceed 27°C/26°C degrees centigrade depending on floor finish used. The only way to control the surface temperature of the screed is with flow control vales and not thermostats.

  • If no certification is available from the installer. Before the floor is fitted the under floor heating system should be calibrated back to the boiler to ensure the surface temperatures of the sub floor is correct.
  • If there is no certification it may well invalidate any guarantees that apply to our floor coverings and you should look at UFH problems.

Choice of System

Your choice of a UFH system will depend on your current sub floors, height restrictions and what you want the system to do for you. A good source of information can be found on this web site http://www.uhma.org.uk/ Electric carbon film and mat systems are acceptable for background heat and many are now getting more effective but hot water system are generally more efficient and when our floor systems are installed directly to the heated screed you get the best floor with the warmest touch.

There are a large number of systems available but we always advise our clients to choose carefully and ensure that whoever fits the system is qualified and follows the manufactures requirements and advice. A lot of hot water systems do not control the boiler temperature properly which can lead to hot spots and other issue affecting whatever you lay on the floor. A typical boiler will heat water to about 82 degrees which is much too hot for pipes in an underfloor heating system.

Any system you install must have the pipe temperature controlled by valves and not thermostats. In the TerraTherma underfloor heating systems the hot water pumped from the boiler goes to a pump rack, where it is mixed to approximately 50 degrees centigrade and is then distributed via a manifold to the heating circuits.

The surface temperature of the screed for our floor coverings must never exceed 27°C/26°C degrees centigrade depending on floor finish used.

Water Based Systems taken from http://terratherma.co.uk/

Concrete and Anhydrite Screeds

There’s been much discussion amongst flooring contractors in recent months about the thorny subject of anhydrite screeds. Many installations are failing, seemingly because of the highly specific requirements needed to ensure success. So much so, that the Contract Flooring Association has published a technical paper on the generic installation of floor coverings onto these calcium sulfate-based screeds, see more information here: http://www.contractflooringjournal.co.uk/archive/helpfeb01_2011.html

Anhydrite screeds are a mixture of screeding sand and binder and are more porous than concrete screeds; these WILL require sufficient drying and extra priming with a DPM before installing in the case of a resin or polished concrete overlay because as Anhydrite screeds are gypsum based any moisture kept in the screed will break down its structure.

We always prefer clients to have a concrete screed which should confirm with building regulations. General cement and Anhydrite screeds dry out at the rate of 1mm per day under normal drying conditions.

We always feel that a normal concrete screed is best for UFH see more information from a specialist company here http://www.ocscreeding.co.uk/Choosing-Screed-for-Under-Floor-Heating.html

Installation of UFH

This should be left to qualified installers recommended by the manufacturer of the UFH system and you must have “flow” control valves to ensure that the temperature never exceeds 27°C/26°C degrees centigrade depending on floor finish used where our floor covering meets the screed or underlay. You cannot achieve this with thermostats.

There are so many UFH systems on the market today which means we cannot cover all aspects of UFH installation here. There are some relevant links and the main points to watch out for are:

  • Hot water pipes must be at least 65mm below the top surface of the screed to ensure you get an even heat distribution and no “hot spots”
  • There must be sufficient insulation below the UFH and also a good DPM to prevent heat loss and moisture being drawn up through the screed
  • Ensure that you meet all building regulations and terms and condition of the UFH system manufacturer, do not take short cuts to save money as the longer term costs could be enormous.
  • NEVER dry the screed out by using the underfloor heating system you will destroy the integrity of the cement screed.

If you have reduced the underfloor heating pipe spacing on perimeter areas, for example where there are a lot of windows it is advisable to leave additional spacing around the perimeter,

Commissioning an UFH system before installing a floor covering. You must never install a floor covering before commissioning the system as set out below.

  • To gain the best performance from your heating system and the finished floor it is important to have all components working together.
  • Hot water radiant underfloor heating system must be installed in conjunction with the manufacturer’s guidelines and commissioned and run for 21 days to ensure that the system is fully operational*.
  • The screed must have a moisture content less than 1.8% before the underfloor heating system is started up.
  • If the screed is 75mm then in normal weather conditions this will take at least 75 days to cure and dry out.
  • Set the water temperature in the pipes to 20 degrees Celsius on the first day, and then gradually increase by a maximum of 5 degrees Celsius every 24 hours, up to a max. 45 degrees Celsius. This maximum temperature must then be maintained for approx. 8 days. This is controlled by flow valves and not thermostats.
  • Then reduce the water temperature in the pipes in the reverse order over 8 days. The total procedure to take 21 days.
  • During this procedure ensure that there is good ventilation in the room so that any moisture that is there will be released and can be correctly discharged.
  • After commissioning, the installer should provide documentary evidence of commissioning; particularly the temperatures achieved at the finished sub floor, and these should be available to the trades that follow. This documentation should fully explain how the surface temperature of the screed is controlled by the flow valves.
  • CRITICAL: The surface temperature must never exceed 27°C/26°C degrees centigrade depending on floor finish used..Timescale: Run heating for 21 days

* Unless a fast track screed is used such as Ardex A38, in which case following the installation guidelines is recommended.

Flow Temperature Controls.

Unless a condensing boiler with a low temperature control is being installed then a mixing valve is used to reduce the temperature of a normal boiler which is 82 degrees down to about 50 degrees which will give a surface temperature on the screed of about 25 agrees depending on the pipe spacing. This is the safe way to control the system.

In more advanced controllers, called weather compensators, use an external sensor (thermistor) and programmer to adjust flow and temperature to compensate for outside conditions. It is vital to have a device to control the boiler and pump to prevent flow temperatures exceeding safety limits.

CRITICAL: The surface temperature of the screed must never exceed 27°C/26°C degrees centigrade depending on floor finish used.

Ongoing maintenance and use of the floor and UFH system

Generally the temperatures should not vary drastically and in a perfect world the UFH should never be turned off just kept at a very low temperature. Always try to avoid taking the floor from one extreme of heat and humidity to another within a very short timescale. Ideally the room temperature should be 20 degrees Celsius and not lower than 18 degrees Celsius. The air relative humidity should be between 35% & 60%.

If you do turn off the system and the floor gets cold as it can in Summer then you must turn the system back on in a controlled fashion as you would when commissioning the system after installing the floor. If you turn it back on to full heat this will “shock” the flooring.

The maximum temperature of the floor should never exceed 27°C/26°C degrees centigrade depending on floor finish used to avoid excessive drying-out problems, which can cause stresses in the applied overlayment.

You must also use the recommended maintenance kit to clean and look after your floor and follow any guidance given.

Pre-Installation Measures

It is required that prior to any installation the underfloor heating system is fully commissioned in accordance with the manufacturers guidelines once the screed/substrate is ready and dry. For a wet underfloor heating system this will comprise of a gradual increase in temperature of 5°C per day up to the maximum flow temperature which will usually take 4-5 days. Once this temperature is reached, the setting should be held for a further three days before slowly lowering the temperature by 5°C per day to the lowest setting and turning off. However, please note that this is a general rule. Full guidance can be sought from your system installers.

Finally, installing a remote thermostatic sensor device below floors will limit temperature and associated humidity, thus safeguarding the client’s interests.

How to avoid Potential Problems with Floors and Underfloor Heating

Most of the problems associated with Resin or Polished Concrete floors and UFH come from the following conditions:

  • Dramatic changes in the surface temperature
  • Hot spots
  • Lack of heat distribution
  • High humidity in the room
  • Operating the heating above a surface temperature of 27°C/26°C degrees centigrade depending on floor finish used.

If any of the above applies you can get the following flooring reactions:

  • cracks or hairline fractures
  • delamiation
  • Lack of effective heat transference through the flooring

How to ensure you do not get problems:

  • Always use a professional UFH installer
  • Ensure you have the right system to achieve what you want see some tips here
  • If you want an electric system then you must follow the manufacturer’s installation requirements and make sure you do not get hot spots, some cheap systems will cause this
  • Hot Spots occur where there is no effective reflector plates that spread the heat or where the screed is too thin
  • Always leave a water based UFH system on and do not increase or decrease the temperature excessively
  • You must clean the floor with the appropriate maintenance kits and in accordance with any instructions. For our flooring always use the recommended maintenance recommendations if you do not then all our warranties and guarantees are invalid.

Please see more details about UFH by clicking this link http://www.uhma.org.uk/

Hot Water Under Floor Heating System Pipe Centre’s and heating dissipation Basic Technical Information

UFH System Basics

The majority of modern UFH systems are warm water systems, which integrate high tech plastic pipes either within or just below the floor.

Normally, water at a temperature of 47-62°C is circulated through this pipe and this warms the floor to a surface temperature of 25-28°C, about the same temperature as the palm of your hand.

The heat generated by radiators is transferred from a small surface area far hotter than the space it is heating. By comparison, UFH transfers heat from a very large surface area, which is only slightly warmer than the room.

Modern UFH systems are economical to run, virtually maintenance free and utilise effective controls. They provide the most comfortable all round warmth of any heating system.

In concrete floors, it is usual to set out the heating pipe or cable on top of insulation before the screed covers the pipe and completes the floor construction.

The table below shows the surface temperature of the screed according to the water temperature in the pipes.

Max Heat Output Achievable by Flow Temperature Settings (Watts W/m²)

Room Temp (°C)Pipe Centres (mm)Flow Temp 47°CFloor Temp (°C)Flow Temp 50°CFloor Temp (°C)Flow Temp 55°CFloor Temp (°C)
1810092261042712329
182007525842610027
201008528862811530
20200692676279328
221007729893010832
22200632872288730

Notes: Based on 8°C temperature drop between flow and return

Screed thickness 45mm above pipe crown

Typical thermal resistance = 0.10