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Choosing the right specification floor screed

Screed is not the most expensive component in a flooring system, but it certainly is one of the most important. In order to avoid costly mistakes there are two major questions that need to be answered:


  1. Which screed should I install?

  2. How should it be installed?


Traditionally, the options for a floor screed were limited with sand cement screeds of varying strength being the only options, however now we have a different screed for practically every scenario and an installation technique to match.


This article will deal with how to choose the appropriate floor screed. Our follow up article will discuss the various installation techniques.


How to choose the appropriate screed


The screed selections can be driven by the following questions:


1. Is the intended floor covering tile & stone or resilient such as vinyl, epoxy, carpet or timber?


For tile and stone a traditional sand cement screed such as ScreedMax Commercial is appropriate, but if the floor covering is a resilient product then an engineered screed from the ScreedMax Pro range must be used.


Resilient floor coverings require a higher compressive strength and flexural strength in order to be able to cope with point loading and different stresses that come from resilient products.


2. How quickly does the floor covering need to be installed?


Often the decision on which floor screed is required is made not because of strength characteristics but because of time constraints. If the floor covering needs to be installed within hours or days, then the rapid curing capabilities of an engineered screed are required.


3. What is the condition of the substrate?


If the substrate is in a poor condition or compressible, then this tends to recommend an engineered screed. Engineered screeds have higher flexural strength which makes them more resistive to cracking even if the substrate is of poor quality or has high degrees of movement.


4. Is underfloor heating being installed


For underfloor heating installations, we strongly recommend that an engineered screed is always selected. The water pipes in underfloor heating system create a weak, compressible point and an appropriate engineered screed should always be used in such cases


5. Is the screed being installed over compressible foam insulation


If the screed is being installed over foam insulation, then an engineered screed should always be used. Sand cement screeds do not have the flexural strength to be able to withstand the movement that comes from the compression of the foam insulation boards. Even "industrial grade" insulation boards have a degree of compressibility and it is quite common to see a couple of millimeters of compression in the floor after installation of the screed over foam boards.


6. What is the thinest part of the screed?

Sometimes it is the minimum thickness of the screed that determines whether a traditional or engineered screed can be installed. Sand cement screeds typically should not be installed at thicknesses less than 15mm as they have an increased risk of cracking. Engineered screeds however can be installed down to 10mm due to their higher compressive and flexural strengths.


Conclusion


We are increasingly seeing builders, architects and tilers move to engineered screeds as it takes the guess work out of choosing the right screed for the circumstances. However, through asking the appropriate questions, it is possible to make the correct choice whether it is a traditional screed or an engineered screed.


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