What type of screed should I be using and how thick?

What type of screed should I be using and how thick?

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Underfloor heating is becoming more popular in the uk, for both commercial and domestic properties. A big reason for this is the energy efficiency that a properly installed system can bring when heating a given space.

Each of the various underfloor heating systems (wet/dry, pipe/cable) work by an up-flow heating system which creates a radiant heat as opposed to convection heating which far less efficient. As the generated heat rises, it can be a benefit to the whole building too and not just the room where the system is installed.

Specialists London Flow Screed state “Screed thickness plays an important role in the efficiency of any underfloor heating system and it should be taken into account before work starts”.

Radiant heating systems and insulation

If an underfloor heating solution is going to be installed, it makes sense to make certain that it is installed to optimal efficiency. A correctly installed system should last for decades with little or no maintenance, adding to the value of the property and lowering energy bills in the process.

For maximum effectiveness, insulation should be sited under the system to make sure that the heat generated is not wasted by ‘leaking’ downwards through the floor and into the foundation.

Don’t just insulate the floor

Before UFH installation, it could be a good idea to take a good look at the insulation of the building as a whole. Windows, walls and attic spaces should also be well insulated in order to maximise the effectiveness of the underfloor heating system.

Semi-dry floor screed what is it and what thickness should be used?

Semi-dry floor screed is the most common screed and can be the more popular type, depending on the site itself.

This traditional screed is spread across the floor and is allowed to settle and ‘set’ around the pipes or cables of the underfloor heating system. Most installers will aim for 75mm of thickness and use fibres to strengthen the flooring. This allows for the best balance between efficiency and floor stability, fibres also help to reduce the risk of cracking.

Drying times

Semi-dry screed does need a certain amount of time to settle and dry and this is going to depend greatly on the environment and the property. Generally speaking however, at least 21 days should be given for the curing stage of the installation. UFH shouldn’t be turned on until at least a month after the screed is installed, although it can be walked on after 21 days.

Edge insulation strips are almost always used help with screed movement. This strip allows the screed to expand.

Liquid screed

Liquid screed is designed for larger projects, although it is perfectly happy in smaller projects too. This screed type is poured rather spread and it has the added benefit of being self-levelling. With liquid screed there is no risk of cracking and it can fully surround the pipes / cables, eliminating air pockets and improving efficiency.

Large coverage

Liquid screed is able to cover up to 1000 square meter in a single day, as opposed to 150 square meters that traditional screed can cover in the same time. Because this kind of screed is pumped, it will normally arrive on site in a mixing lorry and laid using a pumping pipe. It is best to consider the potential disruption this can cause if liquid screed is being considered.

Advantages of using a liquid screed

Liquid screed flooring is much more efficient, as well as stronger, than its more traditional counterpart and the layer doesn’t need to be as thick, with around a 20mm reduction to give a working depth of 55mm. This has the added effect of meaning that underfloor heating is more efficient since it takes a shorter time for the heat to radiate through the floor and warm the room.

Once laid, the underfloor heating system can actually be turned on to help with the drying process. This can be done because liquid screed is not prone to cracking, whereas traditional screed is.

Conclusion

You should now have a better idea of what type of screed is most suitable for your project. Liquid screed is more expensive, so that should be taken into account also, but if speed and heating efficiency are a concern then it is worth considering as a viable flooring option.

On the other hand, traditional screed is cheaper and can be a better option, depending on budget and project size. That said, it will take longer to dry and become ‘useful’ and there are higher associated costs such as labour and heating.

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