For many years now it has been usual to add a screed to the substrate when constructing a building so that the final flooring has a flat and level surface on which to be laid. This is especially important in the case of a floor such as tile or stone because if the surface is not flat it is very likely that the tiles or stone will crack when walked upon, and restoring such a surface would be very expensive.
Traditionally, the screed is made up of sand and cement in the ratio of 1 part cement to 3 parts of sharp sand. This is often mixed in a cement mixer on site, but that can obviously lead to inconsistencies in the mix, and for this reason many larger sites now have the screed delivered by lorry ready mixed.
The screed is then barrowed on to the substrate and is laid by a worker on hands and knees using a hand trowel. Naturally, both the preparation, when using an on-site mix, and the laying and levelling take a considerable amount of time and are very labour-intensive.
When underfloor heating is being installed at the same time there is another issue. This is that it is very difficult to ensure that the heating pipes are fully covered. So, there are often air pockets or voids which will affect the even transfer of heat into the room.
Drying Time
Another consideration is the drying time. This is calculated on the basis that the screed will dry at a rate of 1mm of depth per day up to 40mm and 1/2 mm per day thereafter. It also assumes that the average temperature is 20°C and the relative humidity 65%. It is unlikely that these figures would be achieved over the whole drying period, and so that can make the drying time much longer.
All of these things have led to a considerable upswing in the use of liquid flowing screeds over the last 20 years or so. These are made using anhydrous (dry) calcium sulphate as the binder instead of cement. When water is added, the calcium sulphate becomes gypsum.
At UK Screeds we deliver the gypsum screed to site ready mixed. We then connect a pump and a long hose to the delivery lorry and simply pump the screed into position. This type of floor preparation service in Henley-on-Thames is far faster than laying a screed by hand. Indeed, we can cover a whole house in a morning, and as much as 2,000 square metres in a day. Compare that with laying by hand where a worker will probably not be able to cover more than 100 square metres in a day.
Our gypsum screed is dry enough to walk in within 24 – 48 hours, which means that there is no delay to other contractors who need to work on the site. Because it is in liquid format, it also flows all over any heating pipes that are installed with the result that heat transfer into the room is even.
