How to alleviate common issues when levelling over underfloor heating

The demand for underfloor heating is booming. Homeowners and property developers are moving away from traditional heating and turning towards underfloor heating and we can understand why.

The running costs are more affordable, there is a better distribution of heat making homes much more comfortable, zone heating allows people to heat rooms in their home differently and let’s not forget that by taking radiators out, we can create more space in our homes.

Before we get into the nitty gritty of underfloor heating, let’s take a look at the main types system available.

Although there are hundreds of systems available in the marketplace, the three main types we come across are:

  1. Inscreed. This is when hot water pipes are set within the screed itself.
  2. Retrofit warm water systems. This incorporates an insulated board system.
  3. Electric wire systems. This is when heat is generated by forcing electricity through the cables – a similar concept to a coil in a hairdryer.

When it comes to installing underfloor heating, we find that most installers come across the same type of issues. Here are our best tips to alleviate the most common issues when levelling over underfloor heating.

Tip 1: Ensure the subfloor is prepared correctly and the right materials are used. Most systems require subfloors to be perfectly flat before installing insulation boards. In many cases pre-smoothing is required but overlooked. Failing to pre-smooth will result in cracking adhesive and tile joints – an issue that will cause you no end of problems in the future.

Tip 2: When bonding the boards to different substrates, ensure to follow the manufacturer’s instructions. 100% coverage is always required when bonding the boards to the subfloor.

Tip 3: Part of the preparation for Inscreed systems is heat commissioning. This should be done prior to any product being applied to the substrate. It is at this point that any cracking or thermal expansion will occur. To heat commission effectively, you need to slowly increase the water temperature by 5°C per day, up to the systems maximum temperature. When you have reached this temperature, slowly decrease the system by 5°C  per day until it reaches equilibrium. This needs to be carried out on the manifold and not the room or boiler thermostat.

If you are using a Retrofit system, you need to pressure test the system at this stage to ensure there aren’t any leaks. You certainly don’t want to find a leaf after you’ve fitted your tiles!

Tip 4: Always ensure cables or pipes are secured to the floor. Use the appropriate clips and tapes to secure the cables before applying a smoothing compound. This will prevent cables from floating to the surface during the wet stage.

Tip 5: If you are working with insulation boards on either timber or concrete substrates, we would always recommend using an alkaline resistant scrim tape on the board joints. This will minimise any cracking that can occur due to micro movements on the edge of the board.

Alan’s Top Tip! Never use duct tape to stick your cables to the floor. The surface of duct tape is non-porous, therefore no cementitious product will adhere to the tape and you will end up with hollows.

Right that’s preparation done! Let’s take a look at product selection. Choosing the correct materials to go over underfloor heating can be tricky and is always dependent on the system and the substrate you are working with. Our number one tip would be to contact the adhesive and leveller manufacturer and seek technical advice before embarking on your project.

We are always happy to offer advice over the phone or in person. Don’t stand on site worrying about which product to use, just give us a ring and we will talk you through it.

Tip 6: Always apply a leveller over the underfloor heating system, prior to the adhesive, to encapsulate and protect the system. This will not only help shield the system from damage often caused during installation but will prevent the system being ripped up and replaced if your customer changes their flooring choice in the future.

Encapsulating the system will also improve thermal conductivity allowing heat to the distributed evenly across the floor eliminating cold and hot spots.

Tip 7: If you are going to be installing underfloor heating during the colder months, our advice would be to run the system at 15°C when you begin to fix the tiles. Heating the system up will give you a better substrate to tile to, eliminating cold spots and freezing adhesive.

Tip 8: When fixing tiles to an underfloor heating system, whether it be Inscreed or Retrofit, always use the back buttering method to ensure 100% coverage to eliminate air voids. Air voids result in delamination issues – a costly reason to go back to site!

Martin’s Top Tip! Once the tiling is complete and before your customer can enjoy their lovely warm house, you need to let the floor cure for 7 days. Don’t be tempted to turn the underfloor heating on before then – trust us, you will regret it! Turning the system on before 7 days will cause thermal shock and delamination.

After your 7 days us up, it is critical you heat commission the floor whether you have commissioned the slab or not. Read our earlier advice on how to do this correctly.

And that’s it! Follow our advice and you should have a problem-free installation every time!

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