So much time is spent on choosing finishes and flooring that subfloor preparation is often an issue that is pushed onto the backburner. A subfloor can be broadly defined as the base upon which a floorcovering is placed and this subfloor needs to be prepared before a floorcovering can be placed on top of it.

Various steps need to be followed before a new floor can be installed. Here is a breakdown of the five crucial steps needed:

1. Rectify any defects
A subfloor that has broken concrete, damaged wooden boards, loose nails or cracks needs to be repaired. The subfloor needs to be 100% defect free before any type of new flooring can be installed.

2. Level the subfloor
Any type of level variation needs to be evened out. Check the entire surface area for low spots. During this step, you must make sure that the subfloor is structurally solid and capable of supporting the load of the floor.

There is a general perception that a 3mm – 4mm self-levelling screed will effectively level the floor. This is incorrect. “Self-levelling” doesn’t mean that the product will level a floor regardless of the variances found on site.

Many floor variances may exceed 4mm. It stands to reason that a 4mm self-levelling system can flow into the ‘low’ areas of the floor, but a variation greater than 4mm between high and low spots in the system will only improve the levels by an average of 4mm. If the client requires a perfectly flat floor, this needs to be communicated to the main contactor responsible for the application of the slab or builders screed, as they will need to ensure that the slab or screed is poured with as much accuracy as possible before the ‘self-levelling’ screed is applied.

Most self-levelling screed suppliers offer products with cure strengths ranging from approximately 10MPa to 50MPa. A 30MPa should be used for commercial spaces. Whilst residential screeds are less costly, they also have a lower cure strength and using these in a commercial space can lead to the screed cracking or breaking up under heavy traffic. It is crucial to specify the depth as well as the hardness of the screed that you want installed.

3. Ensure the substrate is clean and dry
The substrate must be completely clean and dry. All curing agents, dust, debris, surface contaminants, laitance and curing agents need to be removed because contamination on the surface can have a negative impact on the bond between an underlayment and the substrate. Moisture tests may also need to be done in certain circumstances. However, the minimum moisture level may vary for different flooring types, so be sure to check the product manufacturer’s guidelines. If the moisture levels are not low enough, then a barrier coat may need to be applied. This coat will prevent water vapour from passing through to your floorcovering.

4. Consider priming systems
The type, and finish, of subfloor you are working on and the kind of floorcovering you are installing may necessitate a priming system to achieve a good bond onto the substrate.

5. Follow best practices per floor type
In a previous feature on subfloor preparation (, FLOORS in Africa magazine approached various flooring manufacturers to find out their subfloor preparation best practices per floor type. Readers are encouraged to review the article sections that apply to their flooring project, but some of the best practice tips can be summarised as follows:
• Resilient flooring: Vinyl or rubber flooring is best laid on a smooth and level surface. The most effective way to achieve this is to use a self-levelling screed at least 4 mm thick. Moisture levels that are above 75% RH will disqualify a subfloor for installation of resilient flooring.
• Wood, laminate & bamboo flooring: If the floor is being glued directly to the screed, then its mechanical strength must be sufficient for the type of flooring being installed and for the final use of the floor. The screed must also be compact and homogeneous on the surface and through the whole thickness. The subfloor has to be prepared with a suitable moisture barrier, by grinding or sanding, priming, levelling compounds or de-coupling systems and cast resins.
• Access flooring: One should have a suitably levelled screed floor that enables smooth and rapid installation. In addition, a levelled smooth subfloor is potentially an asset for future changes in the building.
• Decking & paving: Considering the footing (the concrete base for the upright supports) is critical. For example, a deck being built on a beach will require a specific dimension of footing. Product selection and specification for the sub-framework is crucial, because there could be severe implications if the substructure fails.
• Ceramics, porcelain & stone: A concrete floor should be level and free of cracks or abrasions. Self-levelling screed can be applied to the concrete floor prior to tiling.
• Carpets & carpet tiles: Cement substrate is the best subfloor preparation. Good-quality screed can also be applied to smooth the substrate if necessary. The reason for this is to ensure that any imperfection that in time could affect the performance of a newly fitted, soft flooring is removed.

Specialised tip: A subfloor needs to be 100% defect free before any type of new flooring is installed.

Thanks and acknowledgement are given to,,,, and for some of the information contained in this article.

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