This water ingress damage could have been prevented with proper screed protection.
CRITICAL STEPS TO THE PERFECT SCREED: PART TWO
This concluding part of the two-part guide covers the key aspects of screed installation and testing to help you deliver the best subfloor for any floorcovering.
1. Laying and Compacting
When the slurry grouting method is used, ensure that the grout is wet before installing the screed. During the installation, the screed mix should be spread thicker and then compacted thoroughly to achieve the required thickness and soundness.
Extra compaction is recommended around corners and along bay edges. Screeds exceeding 50-60mm in thickness should be installed in two separate layers and compacted while still green. For screeds with thicknesses in excess of 75mm, layers of 50mm should be applied to the base, spread evenly over the whole area, compacted to achieve adequate soundness throughout the entire screed layer, and then raked to ensure proper adhesion of the subsequent layer.
2. Finishing
The surface of the screed should be finished according to the type of final floor. Wood floating and steel trowelling
10 | THE SCREED SCIENTIST
The guide to screeding supervision continues with advice regarding onsite activities. during building operations.
are two basic finishing techniques that can be used to enhance the resistance to wear of the screed and achieve a flat and smooth surface appropriate for most floor finishes.
3. Curing of screed
All standard cement sand screeds require polythene curing to prevent the formation of shrinkage cracks and curling and to develop maximum strength and resistance to abrasion and impact. Screeds must be covered closely with polythene sheets, right after the installation.
Check if curing is required for proprietary screed formulations. Since these screeds contain special admixtures that control the curing and drying process, most of them do not need polythene curing.
For traditional screeds, polythene sheets should be maintained for at least seven days. For proprietary screeds, curing conditions and times should be obtained from manufacturers.
When installing screeds under low temperature conditions, insulating quilts should be placed and kept in place for two or three days.
4. Screed Protection
Before laying the screed, assess potential traffic and loads expected
In all screeded areas, site traffic must be regulated to avoid screed failure due to premature traffic. For traditional screeds, light food traffic can usually commence after 48 hours from the installation. Advice should be sought from manufacturers for proprietary screeds.
Before light foot traffic is allowed, screed protection materials, for example corrugated plastic, reinforced paper, or cardboard, should be placed on top of screeds to protect them from direct impact and wear damage. These materials should be kept until the final floor finishes are installed.
5. Screed Testing
All screed surfaces should be checked for levelness and flatness issues. The measurements should be compared to the tolerance levels included in project specifications.
An in-situ crushing resistance test (BRE ISCR) should be conducted to assess the soundness of the screed and ensure that it is strong enough to withstand the traffic, loads, and environmental conditions expected.
For additional information about screed visit The Screed Scientist website or call our experts on 0845 500 4055.
www.cscscreeding.co.uk www.tomorrowscontractfloors.com
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