Screed – It Is Not Just A Long Article
Martin Cummins on ‘smoothing compound’ or ‘screed’?
IN technical support roles I find that I deal with a vast array of customer types. This can include architects, quantity surveyors, counter staff, other manufacturers and joe public among the ranks.
Then there is, of course, the flooring contractors themselves. This diversity is something which can make the day a lot more interesting and a lot more challenging. The understanding of flooring in general among the aforementioned group varies tremendously. This is most often realised when the discussion turns to screeds!!….or is that what they really mean?
I would like to take this opportunity to clarify what my understanding of screeds, levellers, underlayments and smoothing compounds are. This is not based on any technical research but purely on experience.
NOTE: I am putting this get-out clause in as I am fully aware of the European Standards for Screed materials (BS EN 13813:2002 for example) and there is no apparent differentiation within.
Again to limit confusion I am only referring to cementitous generic materials as they are still far and away the most common materials used by flooring contractors. Other screeds do exist.
So when the phone call comes through with the question ‘What screed do you recommend for going over particular substrate?’ my immediate response is to clarify from the customer what they really mean;
is needed to make the floor ready to receive floorcoverings. Don’t look for a dictionary definition for the word ‘screed’ as this may well describe it as, I quote, ‘A long monotonous speech or piece of writing’.
To me a screed is part of the internal fabric of the building. It is not something which contributes to the load bearing capabilities of the structure itself, but sits within the walls of the structure. The screed on any particular floor level only has to be concerned with the loadings of that floor level and not the overall building above.
Partitions etc can be built on them provided the overall compressive strength of the screed, plus any insulation, can withstand the loads. The screeds themselves have some depth to them, typically 30mm minimum if bonded and 50mm minimum if unbounded (i.e. on polythene).
So having clarified that it is preparation of the existing floor slab, existing screed, previous levelling compound, old adhesive etc that the customer really wants advice about, we can enter into further discussions as to what the requirements might be.
If you look at any manufacturer’s product listing, you will see a range of preparation materials classed as underlayments, smoothing compounds or levelling compounds.
They are effectively all one of the same in that they are materials applied to an existing floor to provide the underlayment before a floorcovering is bonded or laid. They can be applied to give a smooth surface, or where required, a level surface. So what is the difference between this family of products and screeds? During my years in flooring, the screeds have been installed by screeding contractors, whilst the other materials have been applied by the flooring contractor (ie. those fitting the finished flooring). This is gradually changing with cross- skilling being more prevalent these days.
There are levelling-type products capable of being used in the same application as screeds when used in thicker sections, but generally the underlayment family of products is used from 1mm or so up to 10mm. They are formulated products and should have enhanced flow characteristics and adhesion capabilities which are not necessarily required with screeds.
They will have drying profiles that enable you to continue the flooring programme in a short space of time, unlike screeds which need to be left, typically, for a minimum 21 days before testing for moisture (and where necessar y taking appropriate measures to suppress moisture).
Most importantly they will be capable of giving the finished surface you require to install the decorative floorcovering required to give a long term fully functional floor. The finished sur face is something I will discuss fur ther next month.
Martin Cummins is Ultra Floor technical sales manager
T: 01827 871871
This article has been reproduced from the Contract Flooring Journal website. You can find them at www.contractflooringjournal.co.uk.