FEATURE SCREED DEPTH


This month the Screed Scientist discusses minimum screed thickness on traditional, fast-drying and anhydrite screed considering different applications.


One of the keys to laying a perfect floor is to install a good-quality screed, which must be solid, level, flat, and thick enough to bring the sub-floor to the pre-established height. Whilst standard screeds are typically laid at a minimum thickness of 75mm, a number of polymer modified screeds have been developed to deliver high performance at reduced depths.


Polymer modified formulations incorporate special additives that control the curing and drying process along with screed performance in service, which translates into lower moisture content. As a result, screeders are able to deliver thinner yet sound, durable, completely dry sub-floors within tight time frames.


TRADITIONAL SCREEDS Traditional sand-cement screeds are mixed in a 1:3, 1:4, or 1:5 ratio and installed semi dry, in situ, at a minimum thickness of 75mm for commercial floors. Since traditional screeds do not contain additives, they take approximately 110 days to dry thoroughly (one day per mm up to 40mm and two days per mm over 40mm). Besides levelling sub-floors and bringing them to the desired height, traditional floor screed formulations can be used to enhance the energy efficiency of underfloor heating systems. In underfloor heating, standard sand- cement screeds should be laid at a minimum thickness of 30mm over the heating elements. Traditional screeds are suitable for a wide variety of applications, ranging from residential to commercial projects.


FAST-DRYING SCREEDS Fast-drying floor screed formulations contain special additives and admixtures enable accelerated drying and hardening. Laid at a minimum depth of 15mm to 65 mm, depending on the application, these screeds allow light foot traffic to commence as early as 12 hours from the installation. Additionally, a 60mm layer of fast- drying screed can have a drying time


twitter.com/TomoFlooring Tracker insulation panel


Damp proof membrane Prepared concrete


Screed Floor finish


Underfloor heating screed construction


Edge strip board


of just 3 days, in ideal ambient conditions, facilitating early installation of decorative treatments. Fast-drying screeds are also characterised by a low shrinkage rate and stable performance in underfloor heating. To deliver a durable, efficient construction a minimum screed thickness of 25mm is required over the heating elements in underfloor heating applications.


ANHYDRITE SCREEDS Anhydrite screeds have a liquid consistency. Hence, they are easier to install in large areas and can be applied at reduced thicknesses. Anhydrite formulations also have a low shrinkage rate, which makes them suitable for use in conjunction with underfloor heating systems. Made from calcium sulphate, sand, and water,


these screeds are incompatible with cementitious adhesives and should not be used in areas subject to dampness. According to experts, the minimum application thickness for anhydrite screeds is between 25mm and 45mm, with 25mm above heating elements.


Correctly specifying the type and thickness of the floor screed during the earliest phase of the architectural design process is critical for project success. As each floor and flooring finish is different, we recommend that you consult a professional screeding company for your specific screed depth requirements.


For additional information about screeds and recommended thicknesses, visit the Screed Scientist website or call our experts on 0845 500 4055.


A Quick Guide to Minimum Screed Thicknesses** Traditional


Bonded


Unbonded Floating


Underfloor heating


Depth over pipes


20 mm 50 mm


65 mm residential 75 mm commercial


65 mm residential 75 mm commercial


30 mm


Fast Dry/Modified Screeds


15 mm 40 mm


65 mm 60 mm 25 mm


Anhydrite 25 mm


30 mm 35 mm


45 mm 25 mm


** Please note, this is a general guide only and you should seek professional advice. There are many proprietary products on the market that can have higher or lower thickness requirements depending on the application. For example screeds that will take heavy traffic generally require more in thickness. Please consult the relevant product data sheets.


19


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64