Smooth start, perfect finish

From Peter Wilson, Setcrete Brand Manager

Specifying beautiful floorcoverings for a new property can transform the appearance of a room dramatically. Today there are so many options from traditional carpet to wood, ceramic and porcelain floor tiles and, increasingly, luxury vinyl tiles, offering a plethora of styles and designs.

But optimising the aesthetic appearance of floorcoverings to reflect their ‘perfect world’ showroom settings demands that the subfloor is properly prepared using a floor levelling compound that creates a super smooth and level base; eliminating any sign of imperfections, dips, indents or undulations in the screed showing through to the finished floor finish.

The issue is exacerbated with thin vinyl floorcoverings, but an ill-prepared subfloor will compromise the look of any high end floorcovering.

Even more important in modern homes, where open plan design sees floorcoverings run throughout a ground floor and even to outside spaces, creating a consistent, even and level subfloor base across a home’s footprint is essential.

Moisture check

However, before a levelling compound is applied, a crucial check needs to be made on the subfloor to ensure its moisture content is below a maximum level. Measured in terms of relative humidity (RH), moisture content of a subfloor must be below 75% RH or below 65% if wood flooring is being installed.

This is because excess moisture in the screed will rise to the surface and then become trapped under the floorcovering that has been installed. With nowhere to go, the moisture will attack the adhesive used to adhere the floorcovering to the floor, resulting in vinyl floors blistering or tiles lifting, wood floors warping and carpets rotting. It can also lead to bacterial growth, presenting a health hazard for occupants. Excess moisture is the most common cause of flooring failures.

In older homes, the cause of moisture may be rising damp or water ingress. In new homes it is likely to be residual construction moisture in the screed (a sand/cement subfloor dries at an approximate rate of 1mm per day).

Excess moisture cannot be determined visually or by touch or smell. The only sure way of measuring the RH of a floor is by using a calibrated digital hygrometer, which requires taping securely to the floor slab in various locations across a room and leaving overnight until an equilibrium reading is obtained.

If excess moisture is detected, the application of a single-coat, epoxy resin damp proof membrane will provide protection up to 98% RH. If moisture levels are below 75% (65% for wood floors) a levelling compound can be applied directly to the subfloor.

Smoothly does it

For most applications general purpose levelling compounds – often referred to as ‘latex’ – are available that are normally applied over the subfloor (or DPM) at between 3mm to 10mm thick. Modern day formulations, developed by leading manufacturers, exhibit excellent flow properties and will naturally settle to achieve a smooth finish, requiring only minimal work with a smoothing trowel.

These levelling compounds will normally be ‘walk on hard’ 2-3 hours after application and be ready to receive a floor covering the following day.

Where time constraints are an issue, the introduction of advanced, rapid-drying levelling compounds that are ‘walk on’ hard just 30 minutes after application and ready to receive a floor covering in as little as two hours offer a faster option. These water-mix products rely on the latest cement technology, which sees the water retained in the mixture as it cures, rather than waiting for it to evaporate. As well as truncating the build programme, these fast-track solutions are excellent for minimising the time that areas are out of commission if following trades need to gain access to an area.

Levelling up

When it comes to levelling up adjacent floor areas where the screed levels are markedly different or if a wall has been removed between adjacent rooms leaving a trench in the floor, a conventional levelling compound won’t be suitable. These can normally applied up to a maximum of 10mm or 15mm in thickness. Multiple layers could be used to build up the level, but it is expensive and time consuming.

The practical option is to use a specialist ‘deep base’ compound, which is formulated to be applied up to 50 mm thick. Furthermore, such compounds demonstrate impressively fast drying times, being walk on hard from as little as 90 minutes after application and ready for ceramic or textile floorcoverings to be installed after six hours (depending on the ambient temperature) and resilient floorcoverings the following day. 

Flexible floors

Another application area where conventional levelling compounds are not suitable is the levelling of flexible subfloors, such as plywood. The slight movement of these floors as they are walked on will, over time, result in a conventional levelling compound cracking under repeated loading and unloading until it eventually fails completely. 

Fortunately, high performance, fibre-reinforced levelling compounds have been developed for this very purpose. The tiny fibres in the mix work in a similar way to steel rods in reinforced concrete, holding the cured compound together as it is subject to slight movements in the subfloor. 

Again, the levelling compound can be applied over a variety of subfloor types, including sand/cement and concrete, as well as non-absorbent subfloors such as quarry tiles, epoxy and polyurethane resins. This adaptability means that adjacent floor types can be levelled in one go using a single levelling compound to ensure a consistent and uniform finish. 

Outside chic 

All of these levelling compounds are designed to be used inside. Over the last few years, however, there has been a trend to create higher specification exterior areas. In particular, there has been a growing trend to create an uninterrupted run of flooring from the inside of a home, through bifold doors, to an adjacent outside terrace or barbeque area.

Typically, this has been achieved through the use of porcelain tiles – practical for both the inside and exterior.

To achieve a high quality finish when installing tiles externally demands the same level of subfloor preparation that is required for interior installations. Specifically, the subfloor based needs to be as smooth possible and, crucially, level with the internal floor (accommodating a suitable fall where necessary to drain rainwater away from the building).

Providing all the benefits of their internal cousins, specially formulated exterior grade floor levelling compounds offer a quick and easy way to create a high quality, smooth and level finish that will withstand anything from the rain and frost of a harsh winter to summer temperatures in the 30s.

Today’s floor levelling compounds have been developed to be quick and easy to use, minimising drying times to avoid hold ups to a build programme. Furthermore, options that will accommodate flexible substrates, deep section fills and even outside applications ensure that floor coverings will always look their best – and not only on the day they are installed, but for many years to come.