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THE SCREED SCIENTIST


hold, and does not crumble (too dry) or drip water (too wet).


6. Laying and Compacting • If using a bonding slurry grout, ensure that the screed mix is laid on the base while the grout is still wet, and see to it that the screed mix is consolidated thoroughly to achieve the expected level and maximum compaction.


• Pay special attention to bay edges and corners. Ensure that thicknesses of over 50-60mm are compacted in two separate layers, with minimal time delay between laying of the layers. For thickness greater than 75mm, make sure layers of 50mm are rolled and raked, applying fresh on fresh screed to achieve thorough compaction throughout the full depth.


• If using reinforcement, check that it is laid at approximately mid-depth of the screed.


• Ensure that the polythene sheets are kept in place for a minimum of seven days. Follow manufacturer’s advice for proprietary screeds.


• Under conditions of extremely low temperature, ensure that the screed is protected with insulating quilts for two to three days.


9. Screed Protection • Ensure that site traffic is regulated, and the proceeding of light foot traffic is allowed only after 48 hours of traditional screeds. Follow manufacturer’s advice for proprietary screeds.


• Even if light traffic is allowed to proceed, make sure the screed is protected from direct impact by protecting the screed using materials such as corrugated plastic, cardboard or reinforced paper. This should be retained until the screed is fully dry and ready for the final floor finish.


• Make an assessment of expected traffic and loadings in advance during building operations.


(which complies to BS12) mixed with three to five parts of sand, which complies to grading limit C or M of BS882 (where not more than 10% should pass through 150mm sieve), and should be mixed with water of potable quality. Make sure the screed mix proportions are checked against the data sheet for specialist proprietary screeds.


5. Batching and Mixing • Where screed pumps are used, check the suitability of screed mix for pumping. Cement content, water content and aggregate grading can affect the pumpability of screeds.


• When using ready mix screeds, check the screed supplied is in accordance with BS4721: 1981. Batching should ideally be done in compliance with BS EN 13139. This is a new standard applying solely to pre-manufactured ready-mixed screeds delivered to site. Check the workability of the screed using the ‘snowball test’ by squeezing a handful of screed mix with a gloved hand. The right workability is when the screed forms a moist ball on releasing the


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7. Finishing • Check that the finishing technique is appropriate for the final floor finish that will be used. Wood floating followed by steel trowelling can produce a smooth surface, which is found to be satisfactory for most floor finishes.


8. Curing of screed • For proprietary screeds, check whether curing is necessary to prevent premature drying. Many proprietary screeds do not require curing.


• For traditional screeds that require polythene curing, ensure that the screeds are closely covered with polythene sheets immediately after installation.


10. Screed Testing • Check the completed screed surfaces with a straightedge to make sure it complies with the specified tolerance levels.


• Ensure the screed is sound enough to take on the expected traffic using the In-situ Crushing Resistance Test (BRE ISCR).


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Why you need to implement screed protection measures


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