Liquid floor screeds are being used more and more in the construction industry for several reasons. Not the least of these is the installation time. A cement and sand-based screed is laid by hand, whereas a liquid screed arrives on site in a truck and is pumped into the development. It is possible to cover as much as 2,000 square metres a day using liquid screed.
A liquid screed in London will have a more even surface than a traditional hand laid semi-dry screed. It flows into whatever shape is needed and is laser-levelled to an accuracy that is equal to or better than surface regularity SR2. Furthermore, it is denser, and this makes for better deadening of sound. It is also better at heat transfer which is important when underfloor heating is being laid. Liquid screed is laid very thinly compared to traditional screed and the thermal conductivity is almost twice that of cement and sand screed. In new build higher end homes, underfloor heating is becoming the norm in the 21st century.
Another very big advantage of liquid gypsum screed is that it does not shrink or curl and so minimises the risk of any cracking. There is also less weight, so there is no need for any reinforcement.
However, arguably the biggest advantage of a liquid screed is that it can be force dried safely and quickly. Screed drying times can be a big issue for contractors, with site running costs and penalty clauses for running over time that can run into hundreds of thousands of pounds. This can be a major headache for project managers who are trying to plan their work schedule.
The screed must be completely dry before you can lay tile or whatever other surface is being laid. When you look at data sheets for liquid gypsum floor screeds, they will usually tell you that the drying time is based on 1mm of thickness up to 40mm and half of that rate after that. This means that a typical 50mm deep screed will take 60 days to fully dry, the first 40mm taking 40 days and the other 10mm taking 20 days.
However, what they don't tell you is that those figures are based on a fixed environment of 20°C and an average humidity of 60%. The problem with that is that these figures are rarely, if ever, achieved naturally in the UK. So although a gypsum screed of 50mm is stated to take 60 days to dry, in practice, on a construction site it could quite easily take 90 days.
Force drying using the correct equipment can bring the drying time of 50mm depth liquid gypsum screed down to just 28 days – saving a whole two months which is a massive benefit for contractors and developers because it is a very considerable cost saving. Force drying does require the use of specialist equipment and complete control of the environment including both the temperature and the humidity, and also requires appropriate moisture testing. Done correctly, the heating and cooling process can be carried out with a very great degree of certainty. Another advantage of force drying is that it reduces the likelihood of the floor failing, with all the associated costs that would bring.
Underfloor heating is often thought to be only for higher end properties because of the expense of installation, so for affordable housing specifiers often use radiators. However, studies have shown that installing underfloor heating in conjunction with a liquid gypsum screed and combined with the use of force drying means that there is hardly any difference in the cost. If anything, installing underfloor heating in this way can often actually save money over the use of radiators when one takes into account the time saving involved on site as well. This means that specifiers can choose underfloor heating for any kind of property.
In addition, when one takes into consideration the thermal conductivity of liquid gypsum floors, underfloor heating is more economical to run than radiators and provides even heating of the room, which is not the case with a radiator, so there are ongoing environmental benefits.