THE application of a suitable floor levelling compound helps to ensure a perfectly smooth subfloor surface for the receipt of new floorcoverings and safeguard the appearance of an installation for years to come. While general-purpose levelling compounds are available, there are many situations when it is advisable to use a product with specialist properties. Here I’ll talk through selecting the optimum one for a particular project.
F. Ball recommends the application of a levelling compound as part of any flooring installation to create a smooth base to prevent subfloor imperfections affecting the appearance of the finished result, as well as optimising the bond between the flooring adhesive and the subfloor.
While general-purpose levelling compounds, such as F. Ball’s Stopgap Green Bag, are ideal for many situations, there are also scenarios when it is advantageous, or even highly recommended, to use a levelling compound with specialist features. Such products have been developed to provide a long-lasting, professional flooring finish, as well as to optimise the installation process when working over specific subfloor types and where floorcoverings will be exposed to certain environmental factors, including damp and humid conditions and extremes of temperature.
Many recent innovations in levelling compounds have also been intended to help meet increasing pressures to work to shorter timescales.
With multiple products often suitable for a given situation, whether it be in a clinical or biologically sensitive environment, such as a hospital, or a factory subjected to heavy-duty traffic, the final choice will often depend on the particulars of a specific project and the unique benefits of appropriate levelling compounds. Contractors may also need to undertake preliminary work, for which specialist repair and finishing compounds may be necessary.
First things first
Before a levelling compound is applied, the subfloor must be checked to ensure that it is suitably sound, smooth and dry enough for the receipt of subfloor preparation products and floorcoverings. This should include the removal of any surface contaminants and old adhesive residues (when not using a levelling compound designed to be applied directly over old adhesive residues). There are also situations where additional preparations will be required to achieve a perfectly smooth base; for example, where sand/cement screeds are mechanically damaged or when working over a plywood base.
Excess subfloor moisture should also be checked: whether residual construction moisture or rising damp, it can attack adhesives and floorcoverings, causing carpet underlays to rot, wooden floors to warp, and resilient floorcoverings to blister, ruining the finished appearance of an installation. It continues to be the leading cause of floor failure, resulting in major inconvenience and remedial work.
Therefore, it is recommended that contractors undertake a moisture test to determine subfloor moisture levels. Where relative humidity (RH) levels within the subfloor are above 75% (65% if installing wood floorcoverings), the application of a waterproof surface membrane will be required to prevent excess subfloor moisture attacking adhesives and floorcoverings, potentially leading to floor failure.
The application of a primer is also required in almost all circumstances to promote adhesion of subsequently applied subfloor preparation products and stop the rapid drying of levelling compounds when applied over absorbent subfloors. It also prevents pinholing, caused by tiny bubbles resulting from the slow escape of air from the subfloor, which burst on reaching the surface, leaving small pinholes or craters as the levelling compound cures.
Where subfloors are made up of panels, as in the case of raised access floors, for example, it will be necessary to fill the gaps between them so that they do not transfer to imperfections in the appearance of the finished installation. This is no more important than when working with thin resilient floorcoverings, such as LVTs.
For when working over metal raised access panels, cement-based primers, including F. Ball’s Stopgap Fill and Prime, are available that fill the gaps between flooring panels whilst simultaneously priming the subfloor, saving valuable time. They have a thixotropic consistency, meaning that they flow freely when stirred but set to a gel-like consistency on standing, enabling the joints to remain filled. They are also suitable for use over well-bonded, waterproof adhesive residues prior to the application of the recommended levelling compound.
When working over plywood panels, the holes caused by screws used to affix them to the substrate, as well as gaps at joins between them, should be filled.
For this purpose, floor finishing compounds are available, such as F. Ball’s Stopgap Micro Rapid, a new ultra-smooth, flexible, rapid-drying floor finishing compound for creating a flawless subfloor finish. The product can be applied to a seamless micro feathered edge to fill indentations formed by screws used to secure plywood and hardboard sheets and gaps at joints. It can also be used to repair minor surface defects in a wide range of other absorbent surfaces, including sand/cement and calcium sulphate screeds.
This latest addition to F. Ball’s range of floor finishing and repair compounds utilises the same advanced cement technology as the company’s fast-track levelling compounds. It is walk-on hard and ready to receive new floorcoverings from just 20 minutes after application, and priming is not required prior to use, making it perfect for when working to tight time constraints and deadlines.
In the case that a contractor finds that the subfloor has dormant, non-structural cracks or holes in it, which may be the case where sand/cement screeds have been mechanically damaged, a suitable repair compound should be used to fill in the gaps. F. Ball’s Stopgap 400 Repair is a fast-setting, rapid-drying repair compound that can be applied in thicknesses between 2-50mm to repair internal floors in light to heavy duty areas. The product can also be used to fill gaps in tiled areas where individual ceramic tiles are missing.
Time is one of the most common challenges when completing a flooring installation, particularly for projects in retail, hospitality, education and healthcare, where areas often need to be reopened as quickly as possible. Fortunately, recent innovations have proven fruitful in speeding up the subfloor preparation process to help meet the ever-increasing pressure to work to shorter timescales, without compromising on finished results.
The fastest-drying levelling compound on the market, F. Ball’s Stopgap Fast-Track 30 is walk-on hard from just 30 minutes and ready to receive floorcoverings in as little as 45 minutes after application. It is suitable for use over a wide range of subfloor types, including sand/cement screeds, concrete and waterproof surface membranes.
For refurbishments where old adhesive residues are present, F. Ball’s Stopgap 1200 Pro can be applied directly over the top, avoiding the need to mechanically remove them. Further, the levelling compound can be used without having to prime beforehand, saving further time and expense. It is therefore ideal for situations where newly installed subfloors and areas with old adhesive residues are next to each other. Stopgap 1200 Pro will accept foot traffic about one hour after application and is ready to receive new floorcoverings from three hours later.
Wood and metal subfloors
When working over plywood or steel subfloors, the application of a levelling compound that is designed to accommodate movements in the subfloor, such as F. Ball’s Stopgap 700 Superflex, is recommended.
The product is reinforced with tiny fibres that maintain the integrity of the levelling compound, preventing cracks from forming as a result of minor subfloor movement caused by foot traffic or temperature fluctuations. It is also suitable for application over concrete and sand/cement screeds.
The high compressive strength of heavy duty levelling compounds, including F. Ball’s Stopgap 300 HD, create a durable surface for where floors will be subject to heavy loads or high levels of foot traffic. As a result, they are a popular choice for preparing subfloors in retail settings, schools and hospitals.
The excellent self-levelling properties of such heavy-duty levelling compounds ensure a completely smooth and even base, making them optimal for the installation of designer flooring.
Raising floor levels
While most levelling compounds can be applied up to a maximum thickness of 20mm, floor levels sometimes need raising by more than a couple of centimetres. In these situations, several layers of an appropriate floor levelling compound or a concrete or sand/cement screed can be used to build up floor levels. However, multiple levelling compound applications and subsequent drying times can cause considerable delay to projects; concrete and sand/cement screeds can take weeks, or even months, to dry naturally to a level sufficient to install new floorcoverings. It can also be a very expensive method to raise floor levels.
For this reason, deep section compounds, such as F. Ball’s Stopgap 600 Base, have been developed. Stopgap 600 Base can be applied in thicknesses between 5-50mm in a single application and cures to chemically bind all the remaining water in the mixture, meaning flooring contractors are not forced to wait for all of the water to evaporate naturally as with other levelling compounds.
Consequently, the drying time of Stopgap 600 Base is dramatically reduced compared to other levelling compounds when applied at these thicknesses, and it sets in as little as three hours after application. Once sufficiently set, these deep section compounds can be capped with another levelling compound to create a perfectly smooth surface ready to receive floorcoverings.
Exterior levelling compounds
When installing floorcoverings outside, a levelling compound required to create a level surface also needs to be weatherproof and able to withstand extremes of temperature.
Stopgap 850 Exterior is F. Ball’s levelling compound for external use. It is suitable for smoothing and levelling rough concrete and sand/cement screeds prior to the application of a non-slip coating or artificial grass in light to medium duty applications. This makes it ideal for preparing balconies, patios, garages and walkways. It can also be left as a stand-alone exterior wear surface and when fully cured, it is resistant to frost and rain.
If external floors need repairing, F. Ball’s Stopgap 460 Exterior Repair should be used prior to the application of a levelling compound. It has been specifically designed for use in damp conditions and has excellent freeze and thaw resistance when used in external environments.
Stopgap 460 can be used for the non-structural repair of lower strength concrete elements such as floor screeds, concrete paving slabs, balcony edges, stair treads and riser. It is also suitable for producing gradients for ramps.
Where excess subfloor moisture is detected and repairs to the subfloor are required in indoor environments, contractors can apply Stopgap 460 rapid repair mortar prior to the application of a waterproof surface membrane.
Ready to go
To recap, once all of the subfloor checks have been carried out and any necessary preparatory works have been undertaken, namely: the removal of surface contaminants, repairs and checking for excess subfloor moisture and actioning it if present, contractors can proceed with installing a levelling compound, remembering to prime beforehand.
Once the levelling compound has cured, the subfloor is ready to receive new floorcoverings. It is always recommended to check the compatibility of the chosen floorcovering with the selected adhesive. Like levelling compounds, there are many specialist adhesives which offer unique benefits to the job and floorcovering in-hand.
For this purpose, F. Ball produces its industry-leading recommended adhesives guide (RAG®), which contains over 6,000 adhesive recommendations for floorcoverings from over 200 international manufacturers. The latest version of the guide is now available as a printed booklet and features more recommendations than ever before, each the result of stringent testing and endorsed by the individual floorcovering manufacturer. A continuously updated version of the RAG® is available as a free app and on the F. Ball website. Alternatively, F. Ball’s technical service department can be contacted from 8.30am – 5.00pm, Monday to Friday, for advice on adhesive compatibility. Otherwise, manufacturer’s instructions should always be consulted.