When you are engaged in the construction industry, creating new buildings from scratch, you have to get everything right – and there are a lot of things to cover. One of these is getting the floor perfectly level, because if not it can lead to all sorts of issues – especially when the final floor is something such as tiling or stone. This is especially the case when the sub-floor is of the modern pre-cast beam and block floors which have a definite camber that can cause problems when you come to lay the final floor surface.
This is the reason that we use screeds in order to level out the floor before the final flooring is laid, whatever it may be. For very many years, a screed has been made out of sand and cement, but this does have certain issues. Shovelling sand and cement into a concrete mixer is labour intensive and prone to producing a screed which can vary considerably in consistency. One way to overcome this is to use ready-mixed screeds delivered by a truck.
However, these are more expensive, and they have to have retardants added to them so that they can be worked on all day. Then there is the actual process of laying, which is carried out by hand by a man using a trowel. That again can lead to issues, especially because it takes a long time, and it is not best suited to underfloor heating.
Nonetheless, sand and cement screeds are fairly cheap and do not require much preparation. They can also be used in place such as wet rooms with sloping floors where you cannot use the modern liquid screeds. The finish can be patchy, though, and sand and cement is subject to curling and cracking. For this reason, it is often laid in bays of 5m in length with anti-crack fibres or mesh added to it.
Over the last few years, there has been a development in the production of screeds resulting in the liquid screed that we install at UK Screeds. These are made using anhydrous (dry) calcium sulphate which becomes gypsum when it has water added to it. The terminology can be a little difficult because they are called anhydrite screeds, gypsum screeds, flowing screeds, self-levelling screeds, and calcium sulphate screeds, and the terms are all used interchangeably.
Anhydrite screeds cost about half as much again as sand and cement screeds, but this is offset by the speed of laying. If you are looking for liquid screed suppliers in Newbury, for instance, we can lay as much as 2,000 square metres in a single day. This is because the screed is liquid.
When the screed arrives on site, we attach a long hose and a pump to the delivery truck and we simply pump the screed into position. So we can lay our screed as much as 20 times faster as a sand and cement screed can be laid by hand. We then run over it with a dappling bar in two directions and the job is done. Obviously, this represents a huge saving on labour costs.
The next advantage of our liquid screed is that it dries very quickly and will be ready to walk on in 24 – 48 hours. That means that there is a minimal delay to other contractors who need to work on the site. Furthermore, our liquid screed can be laid considerably thinner than a sand and cement screed, so there is a further cost-saving on material and it also helps with the drying time.
As far as levelling is concerned, a sand and cement screed aims to achieve measurement SR3 which allows for a difference of 10mm over a 2m distance. With our screed, we aim for SR1 which is as good as you can get, but it will always achieve SR2 with a difference of + or – 5mm.
But perhaps one of the biggest advantages is that our screeds are perfect for use with underfloor heating because they totally envelop the heating pipes. With a sand and cement screed, you always get voids and pockets of air which affect the transfer of heat into the room. Our liquid screeds leave no voids whatsoever.