One essential thing home owners tend to overlook is that floor screed must be dry enough to develop adequate strength to undertake the expected loading and covering. To prevent deterioration due to high moisture content, screeders always let screeds dry for a prescribed length of time, before the floor finisher undertakes a moisture test.
For traditional screeds, the prescribed length of time means 1 day for each millimeter of screed up to 40mm and 2 days per mm thereafter. In ideal ambient weather conditions (20ºC and low relative humidity), a 75mm screed layer takes about 110 days to dry properly. Light-foot traffic can usually commence as early as 48 hours.
Although free-flowing anhydrite screeds provide identical drying rates (1mm per day up to 40mm) to the traditional screeds, they can be applied in thinner layers and force dried after a 7-day waiting period from the installation, which often results in shorter drying times.
However, these screeds are incompatible with standard cementitious adhesive compounds, which makes them inappropriate for tiled floors unless the screed surface has been sanded and primed. Then, the screed must be allowed to dry optimally; an appropriate adhesive should be used to achieve a strong bond between the substrate and tiled floor. Since free-flowing anhydrite screeds are also prone to rehydration, damp proof membranes (DPMs) should always be used underneath these screeds.
Although estimates indicate 80 days for anhydrite screeds with a thickness of 60mm to dry completely, the additional work needed to add insulation and apply a primer may require you to extend project timelines.
Fast-drying screeds, are the best choice for projects with tight deadlines. With drying times ranging from 3 to 21 days, these screeds allow light-foot traffic as early as 12 hours of installation.
During spring, autumn, and winter, when relative humidity increases due to the water-vapour content that accumulates in the atmosphere, screeds require more time to dry optimally.
Direct impact, friction, and excessive traffic can also deteriorate the screed and affect the way it performs over the long term. To prevent all these, you need temporary screed protection.
Although most screeds allow light-foot traffic to proceed after 12, 24, or 48 hours, screed protection is always needed until the final floor is installed. To protect screeds, contractors should take a series of steps, which range from installing plastic sheets to implementing certain measures for site traffic. For instance, furniture should not be transported across screeded areas before screeds develop the final strength (28 days irrespective of the type of screed applied). Screed protection measures are usually implemented as soon as the screed is installed.
Getting the perfect screed is not that difficult as long as you are aware of the factors that may impact its quality. To find out more about how to get a perfect screed for your floors, we invite you to download our “Essential guide to the perfectly screeded floor”. You can also contact us at HomeScreed, knowing that our unparalleled knowledge and experience combined with a rigorous quality control system allow us to achieve exceptional, consistent results every time.
HomeScreed is a division on CSC Screeding Ltd