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Commercial Flooring News

Being Flexible But Not At Full Stretch

Stuart Whiteley on flexible underlayments

THIS new series on the technical challenges of flooring installations begins with advice and information on flexible smoothing underlayments.

Some fibre-reinforced underlayments can ‘flex’ once cured to accommodate the likely movement of some substrates, including plywood.

Although not immediately obvious, there are several environments in which the flexibility of a new flooring installation needs careful consideration. In a factory, for example, an office area may sit on a mezzanine level with a steel substrate.

Alternatively, a call centre floor is likely to consist of raised access panels made of chipboard clad in steel. If a traditional smoothing underlayment were to be installed over either of these subfloors, classed as semi-flexible substrates, it may crack due to movement in the subfloor caused by changes in ambient temperature, moisture or traffic.

Cracking ultimately threatens the long-term integrity and aesthetic appearance of a finished floor, which can result in costly remedial work.

To avoid these issues, contractors should thoroughly prepare a subfloor, including moisture measurement and priming stages, before installing a suitable smoothing underlayment that has the ability to ‘flex’.

I Flexible properties: Flexible smoothing underlayments utilise the latest cement technology to withstand the potential movement within a semi-flexible subfloor, yet retain the strength required to prevent cracking occurring.
The products are able to ‘flex’ due to the high polymer to cement ratio in their formulation, and the use of acrylic fibres to reinforce the compound. These features suppor t a flexible smoothing underlayment, ensuring it remains a strong and stable base throughout the lifetime of a floorcovering.

I Preparing plywood overlays: During refurbishment projects, contractors may be asked, for example, to lay a new floorcovering over an existing wooden floor, resulting in the installation of a flooring-grade plywood overlay to create a smooth, sound surface.

In these instances the plywood should be a minimum of 6mm thick and screw fixed according to the guidelines outlined in BS 5325 and 8203.

As a wood composite, plywood is considered semi-flexible because it is particularly susceptible to movement caused by moisture, and so must be primed before a minimum of 3mm of a flexible smoothing underlayment

is installed.

I Other semi-flexible substrates: To create a sound surface, raised access panels should be securely fixed before the application of any flooring preparation products.

Steel subfloors need to be prepared by grit blasting to standard SA 21⁄2, or rotary disc / wire brushed to grade ST2, prior to the application of a suitable smoothing underlayment. In addition, the temperature of the steel subfloor must be maintained above 10degC throughout the application and dr ying of the

smoothing underlayment.

Contractors may work with steel subfloors when completing projects on marine vessels, commonly fitting new floorcovering onto decking. In these circumstances, it is important to note that products used during marine installations should meet the relevant standards, such as those set by the International Marine Organisation.
I Fast track solutions: Subfloor preparation product manufacturers, such as F Ball, understand that contractors are often under pressure to complete installations to strict deadlines.

Some flexible smoothing underlayments are ready to receive resilient floorcoverings in as little as three hours after an application, when applied at a thickness of 3mm over an absorbent plywood sur face.

To ensure the best floor finish when working on a project involving a semi-flexible substrate, such as plywood, select a specialist flexible smoothing underlayment that is formulated to cater for likely movement in

the subfloor.

Stuart Whiteley is section leader – cement technology at F Ball and Co

T: 01538 361633

This article has been reproduced from the Contract Flooring Journal website. You can find them at