What Is Screed?

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  • Author Andy Guy
  • Published October 7, 2019
  • Word count 703

Many people who are not in the building trade are unaware of what screed is or what its' uses are. Put simply, screed is a layer of material that is laid over a concrete floor with the purpose of providing a flat and smooth surface for the final floor finishing materials to be placed upon. This could be tile, carpet, wood, linoleum, or any other desired flooring surface.

Traditionally, this is made from the same materials as concrete -cement, water, and aggregates (typically sharp sand) – but while the aggregates in concrete are coarse to provide great strength, those in screed are finer with the object of providing a smooth finish.

Traditional screed can be mixed on site or can be delivered ready mixed, but either way the method of application is by hand. This literally means getting down on hands and knees and distributing it evenly over the base concrete using hand tools.

This can be bonded, unbonded, or floating. A bonded screed is laid directly on to the concrete subfloor or substrate while an unbonded one is laid on to a layer of damp-proof membrane which is set upon the substrate first. It can also be floating, when it is laid on top of insulation materials as is often the case with a floor that is having underfloor heating installed. In the latter instance, there would be the concrete subfloor on top of which a damp-proof membrane would be laid, then a layer of insulation material, and the underfloor heating pipes would be laid on that. This would then be laid as the top coat.

The minimum thickness of the screed to be applied will depend upon the individual application. In general, the heavier the application, the thicker the screed will need to be. So for instance, in a warehouse where there are forklift trucks running about all day, the screed will need to be thicker than in a domestic situation. In a normal situation this will need to be 25mm thick, but this may increase to 50mm or even 65mm or more in a heavy traffic situation, or where this is going to be laid over underfloor heating pipes.

Of course, all this applies to traditional screed, but today more and more specifiers are using liquid screed which is somewhat different. This contains gypsum, and the screed is delivered to site ready mixed and then pumped on to the substrate, damp-proof membrane, or on to an insulating layer in the case of underfloor heating installation. There are several benefits to using liquid screeding in Derbyshire rather than traditional screeding.

Not the least of these is that a liquid screed can be installed very much faster than one where you are down on your hands and knees. A liquid screed can cover an area of 100 square metres in as little as 45 minutes, depending on the thickness required. It is possible to cover an area of up to 2,000 square metres in a day using liquid screed.

However, there are other benefits of using liquid screeding in Derbyshire and one of these is the thermal efficiency when underfloor heating is being installed. Liquid screeding is almost twice as efficient at heat transfer than is traditional screeding. What this means is that the energy required to run the underfloor heating will save anywhere between 25% and 40% of running the same heating using a traditional screed, so the benefits continue for as long as the building exists.

Liquid screed can also be laid more thinly than concrete and sand screed, so less weight is involved, and that also means that there is no need for reinforcement. Not only that, it does not curl and therefore minimises the risk of cracking, and it also almost eliminates any shrinkage.

Liquid screed can be walked upon after 24 – 48 hours and can be force dried after seven days. Traditional this can take anything up to 90 days to cure before the finishing floor can be laid on top of it. This can cause long delays on site and can result in financial penalties. Using force drying, liquid screed can be ready for commissioning in as little as 28 days from laying, cutting a whole two months off, with the resultant savings that can make.

Liquid Screeds Ltd can provide liquid screeding in Derbyshire for any project from a small home build to the creation of a complete industrial estate.

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