Before installing a floor, it’s absolutely critical to evaluate its foundation and prepare the subfloor per floor type and according to manufacturer’s specifications.

Nothing can quite compare to the beauty of a newly installed floor – a vital element of any project as it will be used on a daily basis and will remain a key visual element for several years to come. However, to achieve a successful flooring installation, the foundation on which it is to be installed has to be analysed, evaluated and thoroughly prepared, failing which unnecessary challenges may occur, resulting in pricey cost implications, delays and perhaps even permanent damage.

The substrate must be evaluated as it is the foundation of the entire flooring system and can therefore determine its long- and short-term success. The very first thing that any contractor should do is to evaluate the subfloor before installation to determine its conditions, paying special attention to the following:
•    Cracking and/or structural movement
•    Scaling concrete and/or loose, poorly bonded materials
•    Degree of tolerance to varying flat surfaces and levels
•    Surface contaminants that may interfere with the proper bonding of adhesives
•    Compressive strength
•    Smoothness
•    Structural integrity
•    Moisture intrusion and/or future exposure to moisture
•    pH/alkalinity – adhesive compatibility
•    Dusting/delamination
•    Protrusions

The proper evaluation of the substrate has to consider specific requirements of the flooring finishes. A contractor will therefore “match” substrate preparation requirements with the new flooring material. Typically some form of preparation is needed and the following are just a few preparation options available:
•    Skim coat or patch minor imperfections
•    Sanding of rough spots/areas
•    Grinding of “high spots”
•    Manual or mechanical removal of contaminants such as old mastics, adhesives, glues, etc.
•    Levelling or flattening of the surface using special polymer-modified cements
•    Moisture evaluation and various remediation methods
•    Sealing and removal of above-floor protrusions
•    Sweeping, cleaning and vacuuming

Evaluating and preparing a subfloor before installation is also dependent on the type of floor to be installed, and each has its own unique requirements and challenges. Below, each floor type’s needs will be identified and further explored to offer a comprehensive and realistic overview of the subfloor’s prominent role when it comes to flooring installations.

Resilient Flooring
Vinyl or rubber flooring is best laid on a smooth and level surface, which is achieved by making use of a self-levelling screed that is between 3 – 5mm thick (depending on the deviances of the substrate). It is also critical to follow manufacturer’s instructions with regard to water quantities and mixing instructions to ensure that the screed is solid, smooth and level.

The following three pointers are of paramount importance and should these not be monitored, the chances for failure dramatically increase. Firstly, moisture levels should not exceed 75% RH (some manufactures refer to 3,5% moisture); screeds should not be weak, crumbling or uneven; and temperature, both ambient and screed, should not be less than 5˚C or higher than 35˚C.

Due to the nature of these floors, after a few hot and cold cycles even the best floor products will start to take the shape of the subfloor and show all its imperfections. Unfortunately, it is at this point that the resilient floor is blamed for the end result, when in fact it is due to negligence – be it from ignoring manufacturer’s instructions or not taking the necessary action to evaluate and prepare a subfloor properly before installing a new floor.

As with any other finish, the better the preparation of the subfloor, the better the end result. This is why the correct tolerances and use of self-levelling screeds have to be specified in order to achieve a final floor that everyone can be proud of.

Wood, Laminate & Bamboo
When the floor is being glued directly to the screed, its mechanical strength has to be sufficient for the type of flooring (in this case, wood, laminate or bamboo) to be installed, and for the final use of the floor. The mechanical strength of a screed suitable for installing any type of flooring for domestic use must be at least 20MPa. The screed must also be compact and homogeneous both on the surface and through the whole thickness.

Before installing any type of flooring, it is absolutely essential that the screed be properly cured to ensure most of the shrinkage has occurred. With these types of floors, subfloor firmness remains a challenge, especially in the case of solid wood planks that might create tension by shrinking and swelling, which could damage weak subfloor surfaces.

High moisture content in concrete also causes cupping of wood floors and results in immense swelling forces that could damage the concrete by causing hollow spots and delamination.

Access Flooring
These floors require a decent levelled screed floor that enables smooth and rapid installation. There needs to be a proper construction programme that is implemented in the right manner in order to prevent a scenario where construction takes place on damp or wet screeds.

Specifiers also need to be aware of the product’s application requirements, along with an office’s IT needs. They need to ensure that the selected product has been tried and tested and that it has a long-standing track record in South Africa, and is backed by a minimum 10-year warranty.

Industry experts are of the opinion that the quality of a screed is all too often sacrificed due to a low MPa concrete mix ratio having been used to top the cast slabs, resulting in inferior screed strength. Cost saving and a complete lack of understanding of the subfloor/screed purpose are the main two culprits for these ongoing problems access flooring companies experience when installing on screed.

Ceramics, Porcelain & Stone
It is advised to first sweep the slab for dust and debris using a broom. Secondly, a wet mop should be used to remove any remaining dust from the cement floor which should then be allowed to dry for at least an hour. Lastly, any cracks in the concrete should be identified and filled.

Curing times are crucial, which is why new surfaces must be allowed to cure for the minimum periods detailed (new concrete requires six weeks and new screed four), to ensure that the tile installation is not compromised by drying shrinkage movement in the substrate.

The substrate must have a moisture content of 5% or less before tiling is commenced. In terms of floor levels, the tolerances of the substrate should be specified in relation to the finished floor surface. Where flooring is applied using an adhesive, very little correction can be made for variations in the substrate.

It can be very labour-intensive to achieve true levels when working with thicker beds of wet adhesive, and the higher adhesive consumption will have cost implications on the installation. Exceeding the maximum application thickness may result in an installation failure. It should also be noted that tile adhesives do not have the same compressive strengths as screed compounds and should not be used as such.

Exterior Flooring – Decking & Paving
Looking at the footing (the concrete base for the upright supports) is critical. The footing has to be prepared in order to spread the pressure of the load to prevent the deck from subsiding over time. The ground type and size and specification of the footing used are very important. Experts advise the industry to take into careful consideration the kind of substructure needed for the selected decking application and how ground conditions will impact the type of footing to be used.

With regard to paving, the supporting base has to be properly constructed. Drainage, subgrade and base-course are the primary base preparations for paving. A well-prepared, moist bedding course is the most important aspect of the installation of paving. Pavers will eventually fail if the bedding course was not sufficiently prepared.

Carpets & Carpet Tiles
A level and dry floor for carpeting is imperative. When specifying broadloom carpet it is important to specify a good quality underlay as it provides for greater underfoot comfort, improves acoustics and increases the lifespan of the carpet.

Cement substrate is considered an excellent subfloor along with a good quality screed that can also be applied to smooth and level the substrate if necessary. This is to ensure that any imperfections are removed, which could, in time, affect the performance of a newly fitted, soft floor. Other factors that should be considered are the difference in floor heights from one room to the next and the presence of a heating system – its type needs to be identified so that the correct underlay can be specified.

A quality installation hinges on three things: quality material; quality fitting; and a good subfloor. In discussing subfloor preparation and evaluation of each floor type, it becomes apparent that there are several overlapping preparations that need to be carried out not only to ensure a successful flooring installation, but to achieve a beautiful finish that performs according to specification and lasts for the duration of its intended use.