One of the most important things when constructing a new building of any sort is to ensure that the floor surface is flat and level before you affix the final flooring whatever that may be. This is especially the case when you are going to use tile or stone such as marble for the final flooring because it has to be affixed to the substrate with an adhesive. If that substrate is not level, then when people walk on the tiles they will crack. At that point, the only thing you could do is to remove all the tiles and start over again which would be very expensive.
In order to ensure a completely level and flat surface – well, as flat as you can get it – the concrete base layer needs to be covered with a layer of screed. Even this won’t be 100% flat but depending upon the type of screed that you use can achieve what is known as SR1 – Surface Regularity 1. This is a British Standards measurement and is calculated by laying a two-metre straightedge on the surface and measuring any dips or gaps using something such as a slip gauge.
SR1 means that the maximum gap at any point would be 3mm. SR2 allows for 5mm, while SR3 allows for 10mm. These are known as High Standard, Normal Standard, and Utility Standard respectively.
There are two main types of screeds in use today, one of which is the traditional sand and cement mix that has been in use for years. The other is one of the newer anhydrite screeds, or liquid screeds as they are also known, that has become more and more popular over the last 20 years because of the many benefits they provide vis-à-vis sand and cement.
As flooring screed contractors in Bristol, at UK Screeds we use only the best liquid anhydrite screeds. These use anhydrous, or dry, calcium sulphate as a binder in place of the cement.
One of the first benefits of liquid screeds is the speed of laying them. We deliver the screed premixed to the site and connect up a long hose and a pump to the delivery truck. This then simply pumps the screed into position where, being liquid, it levels itself out. This is why these screeds are also called self-levelling screeds. The only thing that then needs to be done is to run over the screed with a dappling bar in order to remove any air bubbles, and then leave it to dry.
Compare That To Sand And Cement
Compare that to a sand and cement screed which may be mixed on site in a cement mixer, or may also be delivered ready mixed, but is then barrowed on to the floor and then laid by a worker on hands and knees using a trowel. It takes forever! We can lay as much as 2,000 square metres of our liquid screed in a single day, which is up to 20 times as fast as laying a sand and cement screed.
The drying time of liquid screed is quick as well: you can walk on our screeds in 48 hours or less depending upon the weather. That means that other contractors on site are not going to be unduly held up.
Of course, the liquid screed cannot have the final flooring added until it is fully dried, and this can take around 50 days in perfect weather conditions of an average 20°C and 60% relative humidity throughout the drying period. This is based on a screed depth of 45mm which of itself is much less than that of a sand and cement screed. However, the drying time is likely to be longer than this because those weather conditions are unlikely to be obtained in the UK for that length of time.
There is an answer to this, and it is that with a liquid screed, force drying can be used. The screed does not curl and needs no reinforcement, and shrinkage is very low so large bays can be laid without fear of cracking.
Using the correct specialist drying equipment and controlling the environment can bring the total drying time of the liquid screed down to as little as 28 days. This is another considerable time saving when compared with sand and cement screeds.