When constructing any new building, there are many vital aspects that need to be considered and handled correctly if the building is to be a success. One of these is the flooring because that is what takes all the foot traffic – and in some buildings such as a warehouse, for example, motorised traffic, such as forklift trucks, as well.
The most important thing about the flooring is that it needs to be flat and level, and it needs to be firmly in position so that it causes no issues to the traffic that will use it. It also needs to be strong enough to last, and this is where things can go wrong if the subfloor on which the final flooring is laid is not fit for purpose. For example, when fitting tiles or stone flags the flooring upon which they are laid has to be flat and level because if it isn’t the tiles will not last for long as they will crack.
This is one of the main reasons for the use of a screed on the subfloor before the final flooring is fitted. It will provide a flat and level surface which you don’t get with concrete or precast concrete slabs.
For many years, screed has been made using sand and cement in a fairly strong 1:3 cement to sand ratio. Until recently, this was mixed on site but shovelling sand and cement into a cement mixer is very labour intensive and also inconsistent: it would probably be fair to say that every load will vary somewhat in the mix. For this reason, most larger building sites today use pre-mixed screeds delivered by truck and with added retardants so that they can remain workable all day.
However, in the last ten years or so we have seen the rise of a different kind of screed which is in liquid form and uses calcium sulphate as a binder instead of cement. When water is added to the dry, or anhydrous, calcium sulphate it becomes gypsum. This is known by a number of different names such as calcium sulphate screed, liquid screed, anhydrite screed, gypsum screed, and more, but it is all the same material.
As liquid screed contractors in Milton Keynes, and for that matter the rest of England and Wales, this is what we install at UK Screeds.
Old-fashioned sand and cement screed is fairly cheap to produce as it is prepared by unskilled labour and trowelled on by hand. Unfortunately, this process takes a considerable amount of time. However, in some places such as wet rooms with sloping floors, you obviously cannot use a liquid screed, so there is no alternative to the traditional screed. Sand and cement can be used with underfloor heating, but it is prone to having air pockets and voids which interfere with the heat transfer process. Using ready mix overcomes this, but unless it is applied by skilled labour the quality of finish can still be mediocre. Furthermore, sand and cement have a tendency to crack.
On the other hand, our liquid anhydrite screeds have several advantages. The material does cost more, but the speed of laying will offset this. We pump it into position, and we can lay it up to 20 times as fast as a sand and cement screed can be laid by hand, which saves a considerable amount on labour. We also use less material. Even with underfloor heating installed, the overall depth of the screed can be as little as 45mm compared with at least 75mm, and often more, for sand and cement.
Our liquid screeds are effectively self-levelling, and once poured only need dappling in two directions in order to remove any air bubbles and can then be left to dry. The screed can be walked on in as little as 24 – 48 hours, and it is far less likely to crack or shrink than sand and cement.
In addition, while a sand and cement screed aims to achieve Surface Regularity 3 (SR3) which allows for a 10mm variation over 2 metres, our liquid screed will always achieve SR2 (+/- 5mm) and usually SR1 (+/- 3mm). It is also ideal for underfloor heating as it totally envelops the heating pipes and leaves no voids.