When you are constructing a building, it stands to reason that you want the floors to be as level as they possibly can. You can, of course, install flooring of many different types such as wood, tile, stone, carpet, vinyl, lino over wood, laminate, concrete, and more.
However, whichever final flooring surface is going to be used, it needs to be laid on a surface which is also as flat as possible. This is especially true in the case of something such as tile or stone because if the underfloor surface is not even then the tiles or stone can break when walked upon.
This means that you need to lay a screed on top of the concrete substrate in order to achieve as level a surface as you can.
The levelness, or evenness, of a surface is measured by taking a two-metre straightedge and laying it on the floor and then measuring any gaps underneath it by using something such as a slip gauge. The deviations are measured between the points on the straightedge which are in contact with the floor.
The British Standards Codes of Practice allow for a maximum gap of 3mm to achieve what is known as SR1 – Surface Regularity 1. Gaps up to 5mm result in SR2, while gaps up to 10mm are SR3. SR1 is known as High Standard, SR2 is Normal Standard, while SR3 is Utility Standard. Ideally, all surfaces should achieve SR1, but this is far from the case, and it will depend upon the type of floor screed that you use.
If you are going to use a floor screed in Newbury there are basically two different types of screed from which you can choose. For many years now, the traditional screed has been made from a mix of sand and cement. It has the advantage of being quite cheap and it can be prepared on site using cheap labour. It also requires minimal preparation other than taping joints between insulation boards. In addition, it has a big advantage over the other type of screeds, which are in liquid format, and that is that it can be used on sloping floors in wet rooms.
However, sand and cement mixes can result in a patchy quality and an uneven finish. Sand and cement screed also has a habit of developing cracks as it dries and can curl. In addition, although it can be used in conjunction with underfloor heating, it has to be laid quite thickly, typically 75mm depth or more, and it is also very difficult to fully cover heating pipes. The result is that there will usually be some voids or air pockets, and these can interfere with the transfer of heat into the room.
The other type of screed is the one that we use at UK Screeds and is a liquid screed which is delivered to site ready mixed. It does cost about twice as much as sand and cement, but you don’t need so much of it. When used directly on to a substrate it can be laid as thinly as 35mm depth. When using it over heating pipes you usually need to cover them with 30mm of liquid screed, making a total of 45mm overall.
Another very big advantage is the speed of laying the screed. We deliver the liquid screed to site ready mixed, and simply connect a hose and pump to the delivery vehicle and pump the screed into place. Laying screed this way means that our teams can lay up to 2,000 square metres in a day which is about 20 times as much as a worker using a hand trowel can lay sand and cement, so there is also a huge saving on labour costs.
In addition, our liquid screed does not curl or crack, and is not likely to shrink. On top of that, there is a further saving of time because it will be ready to walk on within 24 – 48 hours. What that means is that where other contractors need to work on the site there are minimal delays.
Certainly, there is one disadvantage (there had to be one!) which is that as the screed dries it produces a layer of laitance – fine particles – on the surface and this must be removed. However, we do this by sanding it between 7 and 10 days after pouring.