When constructing any type of building, one of the most important factors is the floor. Certainly, the walls and roof are of vital importance, but equally important is the floor because that is going to take all the traffic, whether it is foot traffic, which it will be in most buildings, but can also be heavier, such as forklift trucks in a warehouse.
The floor obviously needs to be as flat and level as possible, but when you are laying concrete, that is easier said than done. The surface of a floor is measured in what is known as Surface Regularity, which is often described as the “waviness” of the surface, the top-quality smoothness being SR1. There are also measurements SR2 and SR3.
The level of a floor is measured using a straight edge over a distance of two metres. The straight edge is laid flat on the floor and any deviations are measured between the points at which the straightedge is in contact with the surface. This is done by using a slip gauge or other suitable device for measurement.
British Standards Code of Practice define SR1 as having no more than 3 mm deviation at any point. SR2, which is defined as normal standard, can have up to 5 mm, while SR3 – utility standard – can be up to 10 mm.
Now with a concrete substrate it is very difficult to achieve even SR3 as there will be bumps and dips, and the concrete also uses large aggregates in order to provide strength. For this reason, a screed is laid over the top of the concrete in order to provide as level a surface as possible upon which to lay the final flooring, whatever that may be.
A screed can be made of a number of different materials, and the traditional material for years has been sand and cement. This will use finer sand than that used for the substrate, and is mixed on site in a cement mixer, or today may be delivered ready mixed. The latter will produce a more consistent material. Whichever way the screed is mixed, it is laid by a labourer on hands and knees using a trowel to smooth it out.
However, at UK Screeds we do not use sand and cement, but rather we provide an anhydrite screed which uses calcium sulphate instead of cement. When water is added to calcium sulphate it becomes gypsum, and these screeds are also known as gypsum screeds.
The screed that we produce is delivered to site ready mixed, but it is in liquid form, so we pump it into position using a pump and a hose. For this reason, our screed is also known as flowing screed, self-levelling screed, levelling compound, and so on.
Using a levelling compound in Reading, or anywhere else, has many advantages, one of which is that it is going to be more level than sand and cement, always reaching SR2 and usually SR1. This makes it ideal for any type of final flooring to be laid, including tile.
Fairly obviously, tiling needs to be laid upon as level a surface as possible, since if the screed is not level it will be easy for the tiles to begin to crack when they take traffic.
Our levelling compounds can take foot traffic after 24 – 48 hours, but before laying tiling, must be fully dry. The standard measurement of drying time is 1 mm per day up to a depth of 40 mm and ½ mm per day thereafter. Our screeds do have a big advantage in that they can be laid thinner than sand and cement: even when laid over underfloor heating, they only have to have a thickness of 25 mm above the heating pipes producing a total depth of perhaps 40 mm – 45 mm, so the drying times will be less than for a thicker sand and cement screed. The drying times are measured assuming that the temperature is 20°C and the relative humidity no greater than 65% which is difficult to achieve for any length of time in the UK, so drying times may be longer, but will still be considerably less than a sand and cement screed.