SCREED SCIENTIST WHY TIME MATTERS
This month the Screed Scientist clears up some of the confusion over walk on, drying and curing times, what they are and why they are important.
Cure times, Dry time, walk on times, final strength times. There seems to be a lot of waiting around when it comes to screed. But as our poll shows, many of you may be waiting too long to start the next phase of your projects whilst some of you are not waiting long enough and may be damaging your screed.
Poll When do you believe it is ok to walk
on a freshly screeded floor, ie light foot traffic?
24 - 48 hours (49%, 606 Votes) 48 - 96 hours (25%, 306 Votes) 12 hours (15%, 183 Votes) 96 - 196 hours (6%, 79 Votes) > 196 hours (5%, 66 Votes)
Total Voters: 1,245
LIGHT FOOT TRAFFIC Walk on time/light foot traffic: Light foot traffic implies the movement of people on the screeded area. The earliest that light foot traffic can proceed is 12 hours for some modified screeds and 24-48 hours for traditional screeds. However, the screed will need further time to dry before being strong enough to take general site traffic.
Dry Times Cure Times Walk on time
Final Strength time Screed Protection required
GENERAL SITE TRAFFIC: General site traffic includes the normal activities that can be resumed on a newly screeded surface. A minimum of 5 – 7 days is generally required before general site traffic can proceed on a freshly screeded floor. Screed protec- tion is required to remove the direct contact with the screed surface. How- ever, special care should still be taken before loading heavy weights.
CURING SCREED Traditional screeds generally dry from the top down. Curing screed allows it to gain strength and helps to reduce curling by preventing the top layer from drying too quickly before the bottom layers. A polythene layer is laid on top of freshly laid screed for a minimum of seven days. This will control the rate of moisture evaporation during this period and reduce cracking and curling. Some proprietary screed systems have a controlled drying process and do not require a polythene cure.
SCREED DRYING TIMES Screed Drying Time is the time required for a newly laid screed to be dry enough to take on the final floor covering, car- pets, tiles, vinyl and so on. Depending on the type of screed formulation selected, the drying period may range from several days to several months. Whilst 75mm screeds mixed in a 1:4 or 1:5 cement- to-sand ratio take around 110 days to dry, in ideal ambient weather conditions,
Time required after laying screed Traditional Screeds (75mm)
110 days 7 days
24-48 hours 28 days
Yes
60mm free-flowing anhydrite screeds require 80 days. Additionally, fast- drying screeds take between 3 and 21 days for complete drying.
It is extremely important to carry out the moisture test to ensure that the screed has dried out to the required level as premature installation of the final floor covering can adversely affect the quality of the entire flooring.
FINAL STRENGTH. Irrespective of the type of screed used, most screeded surfaces reach their maximum strength at 28 days. For example, even a screed with a drying time of 7 days will gain its final strength only after 28 days of installation. There are some premium priced products that can reach higher strength gains sooner but again, the final strength is reached only after 28 days. It is ideal to wait until the screed has reached its final strength to resume major activity levels on the screeded surface.
Paying attention to the differences in cure, walk on and dry times as well as protecting your screed can go a long way in helping you hand over the screed to the final finishing contractor in per- fect condition and in achieving the best possible results.
Visit the Screed Scientist website for more information on screeding and un- derfloor heating.
Fast Drying and Modified screeds
Will vary according to manufacturer but can be up to 80 days
Will vary
Will vary according to manufacturer but can be as little as 12 hours
28 days Yes
BRE Drop Hammer
Do you have a flooring conundrum to put to the Screed Scientist? Email
sarah@opusbm.co.uk or tweet us @TomoFlooring, to have your questions answered by the experts!
twitter.com/TomoFlooring 15 Testing Available Calcium Carbide
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