If you are going to lay flooring in a building, and most people do (!), it obviously needs to be as flat as possible for people to walk on, perhaps push a push-chair over, or maybe you are building a skate park and people are going to skate on the final floor, but whatever, it needs to be flat.
Most buildings use concrete for the base flooring and that is because it is strong and can take a lot of punishment. However, unfortunately, the surface of concrete is never going to be as flat and level as you need in order to add the final floor surface. You might wonder why this is, and it is simply because in order to make concrete strong it has to have coarse aggregates added to it.
This makes it strong, but unfortunately means that it won’t be completely flat – even though, to the naked eye, it may appear so. This is because a few millimetres either way can make a very big difference when it comes to the final flooring, and equally importantly, the life of that flooring.
Now in order to achieve as level and flat a surface as possible, it is necessary to lay what is known as a screed over the top of the concrete. If you are in the building trade, you will know what a screed is, but if not, it is simply an additional layer of much smoother material that is laid over the top of the concrete in order to level out the dips and bumps.
A screed is a material that also uses sand but has much finer aggregates within it. For many years, a sand and cement screed has been used and this contains much the same ingredients as concrete – sand and cement and aggregates, but everything is much finer. Also, the grade of cement used is different.
In order to make the screed as level as possible, it is dumped on to the concrete flooring when it has been mixed (either by hand on site using a cement mixer, or being delivered ready mixed) and is then levelled out by a labourer using a trowel. In order to do this, he has to get down on hands and knees, obviously. It’s a messy and tiring job.
However, over the last 20 years a new type of screed has been introduced which is known by a variety of different names. This is made up with anhydrous calcium sulphate instead of cement. The word “anhydrous” is a chemical term which simply means “without water”. However, it has led to a bit of confusion because the same product is known as calcium sulphate screed, anhydrite screed, gypsum screed, self-levelling screed, flowing screed, and probably a few more terms.
What may also seem a little odd to the uninitiated is that the first thing that you are going to do to anhydrous calcium sulphate is add water to it which turns it into gypsum. Furthermore, it is mixed and poured into place as a liquid which is why it is called self-levelling screed because the surface levels out in the same way as water poured into a glass.
At UK Screeds, we call it anhydrite screed, and it has many advantages over sand and cement screed. An anhydrite screed in Reading is not only self-levelling – requiring simply a walk-through with a dappling bar in order to remove any bubbles or air pockets – but is also perfect for use in conjunction with underfloor heating. This is because it will completely surround and cover the heating pipes, which results in perfectly even transfer of the heat into the room. This is almost impossible to achieve with a sand and cement screed using a hand trowel.
Not only that, but anhydrite screed has a thermal conductivity rating that is almost twice that of sand and cement, which means less energy used to heat the room. In addition, our anhydrite screed can be laid a lot thinner than sand and cement – only 30 mm above the heating pipes, making a total of about 45 mm compared with 75 mm. This again saves money on the heating costs.
There are other benefits too, such as the screed is dry enough to walk on in 24 – 48 hours, so there is no hold-up to other contractors who need to work on-site.