If you are building a new home, actually applying the floor screed can be an exciting moment because it is the point at which parts of your building start to look like a finished room. OK, once you have the floor covering down you won’t see the screed, but there are advantages to using one type of floor screed over another.
The two main types of floor screed today are a mix of sand and cement and what are known as anhydrite screeds which are a mix of sand and anhydrous (dry) calcium sulphate. The latter are also known as gypsum screeds which is what calcium sulphate becomes when mixed with water. In addition, being in a liquid format when they are applied, they are known as liquid screeds, flowing screeds, and more.
The traditional type of screed is sand and cement which is mixed in a consistency of 1:3 cement to sharp sand, and this used to be done on site, and still is in some cases, by shovelling it into a cement mixer. This is very labour intensive, obviously, and also leads to inconsistencies in the mix which is why today on larger sites the mix is delivered ready mixed with suitable retardants so that the set is delayed, and the mix can be worked all day.
The mix is then barrowed into position and is laid on the sub floor by a man with a trowel on hands and knees. Again, a lot of labour is involved, and if underfloor heating is laid it can be extremely difficult for even an experienced worker to ensure that the heating pipes are completely covered. The result of that is that there will almost certainly be air pockets left around some of the piping and this will affect the transfer of heat into the room.
By contrast, an anhydrite screed is delivered to the site ready mixed, and as we have seen is in liquid format. As skilled flooring screeding contractors in Reading, at UK Screeds we simply connect a hose and a pump to the delivery vehicle and pump the screed into place. Compared with laying a screed by hand, this is unbelievably quick. In fact, we can lay a 100 square metres in around 45 minutes, and up to 2,000 square metres in a single day. This is around 20 times as fast as a worker using a trowel can lay a sand and cement screed.
Our Screed Is Self-Levelling
Not only that, because our screed is in liquid form it is self-levelling. It is just like pouring a glass of water. When you leave the glass alone for a couple of minutes the surface will be flat. The same thing happens with our liquid screed. All we need to do once the screed has been poured is to run over it with a dappling bar just in order to remove any air bubbles, and then it can be left to dry.
There is another very big advantage when laying a liquid screed on top of underfloor heating and that is that because it is in liquid form, the heating pipes will be totally covered with the screed, so there will be no voids or air pockets. The result is that the heat transfer into the room will be even across the whole floor.
Furthermore, a liquid anhydrite screed has very nearly twice the thermal conductivity properties of sand and cement, the result of which is that it takes less energy to heat the room to the same temperature. There is a further saving as well, because a liquid screed can be laid more thinly than a sand and cement screed. It only needs to be 30mm over the top of the heating pipes, making about 45mm in all. If you use a sand and cement screed it needs to be 75mm overall as a minimum and can often be more. So, again, there is a saving on the amount of energy to heat the room.
Because our screed is liquid it always achieves what is known as SR2 level of regularity, and usually SR1 which is as flat as you can get. With a sand and cement screed, it is unlikely to be any better than SR3.