Sand And Cement Screeds -V- Liquid Screeds: Which Is Best?

liquid screed

When constructing any sort of building, one of the (many) important things to take into account is the fact that the floors should be as flat as possible. This is for two reasons, one of which is that people have to walk on them, and the other is that the substrate has to be flat and level, because if it is not and you are going to lay, say, tiling as the final floor surface, those tiles will crack if there are dips and hollows underneath them. For this reason, it is usual to lay a floor screed in Reading, or anywhere else, on top of the substrate before laying the final flooring..

A floor screed will give a final coating on top of the substrate that will be, for all practical purposes, as level as it can be. It is particularly important to use a screed on modern precast concrete beam and block floors which have a noticeable camber which can cause serious problems when laying the finishing floor.

For many years, it has been standard practice to use a mixture of sand and cement in order to produce the screed, and traditionally this was done using a cement mixer on site and using a 1:3 or 1:4.5 ratio of cement to sharp sand. The mix would then be barrowed on to the substrate and then laid by a worker on hands and knees using a trowel in order to level it out as flat as possible. Using this method has certain problems:

  1. The sand and cement mix is not going to be exactly the same consistency in each barrow load. This is because the materials are going to be shovelled into the cement mixer by labourers with a shovel, and it is impossible to get exactly the same amounts of sand and cement in each load. For this reason, on larger sites today it is usual to have the screed pre-mixed and delivered to site by lorry.
  2. With the best will in the world, the screed will not be 100% flat. It is not being laid by a machine, but by a labourer, and a labourer is a human being. According to the British Standards Code of Practice, the surface regularity of screeds is measured using a 2-metre straightedge laid on the surface, and any deviations measured with a slip gauge. The results are recorded as Surface Regularity, and these are SR1, SR2, and SR3. SR1 allows for a maximum deviation of 3mm at any one point, SR2 is 5mm, and SR3 is 10mm. A worker laying a sand and cement screed by hand is very unlikely to achieve any better than SR3.
  3. Laying a screed by hand takes a very long time. So, you have the cost of the labour, but even more important is the amount of delay for other contractors who need to work on the site. There may be painters and decorators for instance who cannot start work until the screed has been laid and is dry enough to walk on.

Those Are Just Some Of The Issues

So those are just some of the issues when laying a traditional sand and cement screed. There are more, particularly when it comes to installing underfloor heating which is being done more often these days as the many benefits of it have come to be realised.

However, we are now well and truly in the 21st century, and over the last few years there is a new type of screed available which has become more and more popular as the many benefits of it, vis a vis sand and cement have been recognised. This is known by several different names, one of which is liquid screed – simply because it is laid in liquid format. However, it is also known as anhydrite screed because it uses anhydrous (dry) calcium sulphate in place of the cement, which becomes gypsum when mixed with water. That is why it is also called gypsum screed. Other names are self-levelling screed, calcium sulphate screed, and more.

Many Advantages Of Liquid Screed

There are many advantages to using a liquid screed in Reading, one of which is that it is so much faster to lay. The screed is delivered to site ready mixed and instead of barrowing it on to the substrate, a long hose with a pump is connected to the delivery truck and the screed is simply pumped into position on the flooring.

Since the screed is liquid, it levels itself out. This is exactly the same as pouring water into a glass, the surface of which will become flat and level after a minute or two and is also why the screed is called self-levelling. This is obviously far faster to lay than having a worker on hands and knees with a trowel. Indeed, suppliers and installers of liquid screeds claim that they can lay up to 2,000 square metres in a day which is around 20 times as fast as the older method. All that needs to be done once the screed has been poured is for a worker to go over it with a dappling bar in order to remove any air bubbles.

Liquid screed in Reading also dries a lot faster. Even though it is in liquid form when poured, it is dry enough to walk on within 24 – 48 hours.

That obviously has implications for other contractors who need to carry out work on the site, since the delay time is minimal. After all, time is money on any building contract.

The advantages of a liquid screed are even more obvious when it comes to the installation of underfloor heating. If you are installing a water-based heating system, which is preferable to an electric one for several reasons, the liquid screed will completely envelop the heating pipes leaving no voids or air pockets. When you use a traditional sand and cement screed it is almost impossible to achieve that, so there will be air pockets which will affect the transfer of heat into the room. With a liquid screed in Reading, the heat will be perfectly even across the whole of the flooring.



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