If youare installing underfloor heating in a building in Marlow, whether it is a new build or retrospective, you will need to install a floor screed in order to cover the heating pipes and to provide a flat and level surface upon which to lay the final flooring.

When installing into an existing building you have to take into account the fact that you will lose a certain amount of height in the room. There are two main types of screed that can be used, either the sand and cement screed which has been used for years, or the fast-growing in popularity liquid anhydrite screed.

Liquid anhydrite screeds are known by a number of different names apart from liquid screed. They are also called gypsum screeds because they contain anhydrous (dry) calcium carbonate in place of cement which becomes gypsum when water is added to it. Because they are laid in liquid form they are also known as flowing screeds and self-levelling screeds: since they are liquid they level out after they have been pumped into position.

There are several advantages to using a flowing screed in Marlow in combination with underfloor heating, especially in a retrofit project. You need to cover the heating pipes whichever screed you use, but with a flowing screed it can be laid much thinner than sand and cement. It needs to cover the pipes by 30mm, making a total depth of 45mm. If you use sand and cement it will be at least 75mm overall, and often in excess of 100mm. This has clear benefits when it is a retrofit because you won’t lose as much height in the room.

Several More Benefits

There are several other benefits too. When you use a sand and cement screed it is laid be a worker on hands and knees using a trowel. It is almost impossible to totally cover the heating pipes, and this means that there will be certain gaps or voids in the screed. This in turn will interfere with the transfer of heat into the room above. However, when you use a flowing liquid screed it will completely cover the heating pipes and cannot leave any gaps, so the heat transfer into the room is totally even.

Because a flowing screed is laid thinner than sand and cement, it takes less energy to heat up the room to the desired level because there is less screed to heat first. This also gives a better response/controllability. So, there is an ongoing cost saving on heating energy bills that will last as long as the building does.

Another advantage of flowing screeds is that they do not curl and they are far less prone to shrinking than sand and cement.

If there is a downside to flowing screeds it is that, as they dry, they produce a layer of fine particles on the surface known as laitance. This needs to be removed by sanding between 7 – 10 days after the screed is poured so that the final floor fixing is not jeopardised in any way.