One of the most important considerations when planning the construction of a building, or buildings, is the timing of the work on site. All of the various trades need to work on the site in the right order and at the right times, so one needs to follow another as quickly as possible in order to keep costs to a minimum and ensure that the project is not delayed. If you have labour hanging around idle, those people still need to be paid, and that means that somebody, somewhere along the line, is going to have to do the paying. Time is of the essence.
When it comes to laying a floor screed, this is just one of the benefits of the liquid screeds that we install at UK Screeds. Traditionally, a screed has always been made of sand and cement and aggregates, and has been laid by hand by a labourer using a hand trowel. This is obviously a time-consuming process.
By contrast, the liquid screeds that we install can be laid almost in the blink of an eye. Well, perhaps not quite, but certainly far faster than sand and cement. It has been calculated that pouring a liquid screed, as we do, is up to 20 times faster than laying sand and cement. Certainly, our expert teams can lay as much as 2,000 square metres in a day.
The process is very straightforward. Our screed is delivered to site ready mixed and all we have to do is connect a pump and a hose and we are good to go. We can pour 100 square metres in well under an hour. All we need to do when the screed is poured is run over it with a dappling bar in two directions in order to remove any air bubbles.
There is another huge advantage when laying liquid screed, as far as speed is concerned, and that is the drying time. As a rapid cure screed company in Oxfordshire, we do not need to lay a liquid screed as thickly as a sand and cement screed.
The average sand and cement screed is laid to a depth of 75mm or more when being used to cover underfloor heating. By contrast, our liquid anhydrite screed only needs to cover the heating pipes to a depth of 30mm, making perhaps 45mm overall. Not only does this save on material costs, but it also obviously has an advantage on drying time as well. It is calculated that the overall curing time is at a rate of 1mm per day to a depth of 40mm and 1/2mm per day for anything deeper. So, to fully cure a liquid anhydrite screed to the point where the final flooring can be laid would take just 50 days. This is based on the air temperature being 20°C and the relative humidity not greater than 65%. The actual drying time could be a little more or a little less depending upon the actual conditions.
With that said, after the screed has been poured it will actually be dry enough to walk on and take light traffic within 24 – 48 hours, so there is virtually no delay to other trades on the site whatsoever.
If underfloor heating is being installed, then the drying time can be accelerated further. After 7 days the heating can be brought into commission and can then be increased by 5°C per day until the maximum working temperature is achieved according to the manufacturer’s instructions. This is often 29°C, and it can be left at this level for at least a week before being gradually reduced again to around 15 – 20°C. Another way of speeding up the curing process is by the use of dehumidifiers in addition.
There is one other job which needs to be carried out before laying the final flooring, however. When a liquid anhydrite screed dries it produces a layer of fine particles on the surface which are known as laitance, and this must be removed before laying the final flooring.
At UK Screeds we remove the laitance by sanding the screed between 7 and 10 days after pouring. Any longer than this can delay the drying process, and also make the laitance harder to remove.