When you are in the process of constructing a building, one of the things that it will have is flooring upon which people can walk, or in the case of a warehouse or factory, on which vehicles such as a forklift truck may be driven. Either way, you want the final floor surface to be as flat and smooth as possible, and the way to achieve that is to lay a screed on top of the substrate.
Furthermore, if you are installing underfloor heating, a screed will be essential in order to cover the heating wires or in the case of water-based systems, the heating pipes, so that the final flooring can be laid on top.
The screed can be made of different materials and maybe either bonded or unbonded. For many years now, it has been the case that a sand and cement screed in Herefordshire – or anywhere else for that matter, has been used, but over the last few years, the use of a calcium sulphate screed has been gathering momentum because of the many benefits that it has over sand and cement.
Whichever type of screed material is used, if it is to be bonded it is laid straight on the substrate so that the two bonds together. If the screed is to be unbonded, a dampproof membrane is laid onto the substrate and the screed is laid on top of that. If insulation boarding is being used as well, that is laid directly onto the substrate, and a dampproof membrane is laid on top of it, and in this case, the screed is referred to as a floating screed. This method is perfect for use in conjunction with a water-based underfloor heating pipe system.
If a sand and cement screed is being used, it can be mixed on-site and will be laid by a worker on hands and knees using a trowel. However, many people prefer to use a ready-mixed screed that is delivered to the site because there will be a more consistent mix of the material.
In the case of a calcium sulphate screed, this is also delivered to site ready mixed but is in liquid form and is poured into position using a pump and a long hose. These types of screeds are also known by several other names such as anhydrite screeds, gypsum screeds, floating screeds, self-levelling screeds, but they are all the same things.
One of the big benefits of anhydrite screeds is that they are far quicker to lay than the traditional sand and cement screeds because they are poured into position. At UK Screeds, we can lay 100 square metres in 45 minutes and up to 2,000 square metres in a day. In fact, this is anything up to 20 times as fast as laying a sand and cement screed by hand which is a huge difference on a building site where time is of the essence.
It is also far more efficient because when you are installing underfloor heating pipes the screed needs to completely envelop them. Obviously, as the screed is liquid, it will do just that. Laying sand and cement by hand means that it is almost impossible to achieve this and so there will be gaps where the screed does not meet the heating pipe and therefore the heat transfer into the room will not be even.
Just as importantly, the thermal conductivity of anhydrite screed is almost twice that of sand and cement, so that means that less energy is required to heat the room, which in turn means that the heating bills are less. Yet another benefit of anhydrite screeds over sand and cement is that they can be laid much thinner, and again that means that less energy is needed to heat the room to the required temperature. Using less material also means that there is a weight saving as well.
Yet another advantage of anhydrite screeds is the drying time. Because they are laid thinner, they dry faster, and they can also be force dried and/or the underfloor heating used to help to dry, because the screed does not curl, and any shrinkage is absolutely minimal.