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The impact of surface regularity

Garry Bateman elaborates on surface regularity and the impact it can have on fitting flooring as well as ongoing use.

CFJ asked me whether I’d be prepared to do a bi-monthly CFA president article with – on alternate months – a more technical article. So here we are with the first of, I hope, a series of bi-monthly technical based articles. I’ve chosen to talk about surface regularity and the impact it can have on fitting flooring as well as ongoing use.

Why is surface regularity important? British Standards refer to surface regularity and the need to ensure a floor is suitable for the use it is intended to perform. For example, an uneven, wavy surface floor will create problems for wheeled traffic and make fixtures and fitting more difficult to ‘sit level’ on the floor.

Even small localised variations can cause issues – a recent example of a well installed large format tiled floor (which had a standard 3mm layer or application of levelling compound) presented level challenges when positioning an antique non-adjustable leg cupboard.

Last year, the resilient flooring British Standard 8203:2017 added to the summary of the section on surface regularity as it was seen by the standard compilers to be a common marketplace issue that needed clarification. Section 6.2.3 in the standard has a useful commentary:

‘Surface irregularities can affect the overall visual appearance and wear life of the finished floor, resulting in premature wear, localised soiling problems, loss of bond with the installation of tile products, particularly large format tiles and geometric designs, and potential difficulties with the installation of sheet floor coverings where site-formed cove skirting details are used’
*Published by BSI Standards Limited 2017

So here we have the new British Standard providing some clear consequences of not having dealt sufficiently with surface level variances. These fall into two camps; those affecting the fitting and those affecting the appearance or use.

For the latter, premature wear will occur on the ‘high spots’ on uneven flooring as these areas are subject to heavier traffic. Such unevenness will cause issues when trying to clean, particularly with fixed rotary pad type machines, as they will tend to ‘float’ over the lower spots in the flooring as the ‘ride on’ the higher sections. Both will adversely affect the overall aesthetic of the floor initially and longer term.

For the installer, the comments on loss of tile bond owing to movement within the floor surface which can affect all types of tiles, resilient and textile, is particularly relevant in large installations and when dealing with geometric floor layouts such as herringbone pattern planks.

The problem is accentuated when unevenness is spasmodic throughout the installation leading to tiles running out of bond in all directions. I’ve seen large carpet tile installations where the tile bond progressively starts to run out by several millimetres over a few lineal metres – this creates extra work for the fitter in having to cut back tiles lines to insert a new ‘straight edge’ to work from.

The inclusion of sheet floorcoverings fitted with site formed coving is necessary to ensure consideration is given to check the levelness of the floor. However, with flooring material being coved up the wall, the straightness of the wall and consistency of the angle between the floor and wall are also factors to add in.

Sheet flooring, being a flat produced product, will quite happily bend two-dimensionally – so a flat floor and straight wall with a consistent angle makes for the perfect substrate on which to install. However, sheet products are not designed to bend three-dimensionally, so uneven subfloors and irregular walls can contribute to stressing the flooring leading to non-adhered sections, creases in the flooring or hollows behind the flooring and cove former.

Even minor unevenness in the subfloor can cause the extruded PVC cove former to move up and down when fixing (basically follows the floor profile) which in turn will cause the sheet material to have to try to bend in three dimensions – resulting in adhesion problems and the likelihood of failure long-term.

Of course, these subfloor deviations are often viewed by builders as normal and floors stated as fir-for-purpose. Not in my experience and they certainly can counter the stated recommendations in the British Standards. I remember a project where the subfloors varied over a two-metre length by up to 15mm in places, yet the builder stated they were OK as the screed installer had ‘guaranteed’ level finishes.

So, what does the British Standard say?

BS8203:2017 states:

The class of local surface regularity of a directly finished base or levelling screed, if used, should be selected in accordance with Annex C, Table C.1, according to the use of the floor. In making this
selection, account should be taken of the type and thickness of the wearing screed or flooring to be applied and the standard of surface regularity required of the finished floor. The highest standard (SR1) should be used where a thin flooring is to be applied and where the minimum irregularity is required of the finished floor, e.g. for a television studio.

NOTE: Conversely, the lowest standard (SR3) can be selected where a thicker type of wearing surface is applied and where the regularity of the finished floor is not a significant factor.
Annex C, Table C.1

Classification of surface regularity of direct finished base slab or levelling screed
Class    Maximum permissible departure from the underside of a 2 m straightedge resting in contact with the floor – measured in mm
SR1    3mm
SR2    5mm
SR3    10mm
*Published by BSI Standards Limited 2017

Measuring surface regularity is a straightforward process as surface regularity or flatness of screeds is generally measured as a deviation from a straightedge laid level on the screed surface.

In accordance with Annexe C (normative) of BS8204-1:2003 & A1:2009, the surface regularity of a screed for normal accuracy flooring is measured using a 2m long straightedge laid in contact with the floor surface ensuring it’s resting under its own weight.

The deviations of the floor surface from the underside of the straightedge are measured between the points which are in contact with the floor surface. This can be carried out by means of a slip gauge or other suitable accurate measuring device.

With this type of measurement, the various interested parties involved should come to an agreement at the design stage regarding the sampling rate for testing and the procedures to adopt if conformity isn’t achieved. From a practical standpoint, it’s prudent to include the number of positions where the straight edge will be placed to more thoroughly check conformity.

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