When choosing and installing new flooring, it is important to consider the subfloor as well as the uppermost layer. If the subfloor is inadequately prepared, then no matter how good the quality of the upper flooring, it will not have optimum performance levels. In order to get a good return on your investment, it is important to address the subfloor. 

What is meant by the subfloor?

The subfloor is sometimes confused with the underlay, but they are not the same thing. Underlay is placed beneath the carpet or vinyl to provide extra cushioning and insulation. It isn’t crucial, but it makes the flooring more comfortable to walk on, improves the visual appeal, softens noise, minimises wear and tear, and helps to retain warmth. 

The subfloor is the actual surface that covers the foundations or joists in the building. Ground or basement floors tend to have concrete or cement subfloors, while upper floors will usually have softwood, plywood, or particle board floors. 

How does the subfloor impact on flooring installation?

The subfloor can dictate the installation method to some extent, because the flooring cannot be nailed to a concrete or cement base. Instead, it must be bonded with an adhesive. If the subfloor is solid plywood, then the carpet or laminate flooring can be nailed or stapled down. However, some types of engineered wood are not suitable for this method.

In this case, the flooring may be bonded with glue to the subfloor, or installed as a floating floor. This means that the flooring is not secured, but held together in a locking system by means of weight dispersal, and an expansion joint is fitted around fixed objects. Floating flooring can be installed over most types of subfloor, even if it has existing tiles.

However, flooring that requires glueing or nailing needs extra subfloor preparation. The subfloor needs to be completely flat and smooth, with no dents or bumps. This is because over time, the flooring will wear against the uneven surface, causing visible raised edges that are prone to tearing.

This means that the flooring will not last as long as it should, and it also creates a surface that is unsightly and hazardous to walk on. In commercial spaces, this not only looks unprofessional but could lead to breaches of health and safety regulations. 

If the uneven flooring was to cause an accident or injury, the business would be liable to be sued for damages.

How is a subfloor prepared?

A concrete or cement subfloor that is unlevel or in poor condition may need to be levelled with a screed. This is a semi-liquid compound that is poured over the concrete subfloor and fills in any gaps and holes. It solidifies to provide a smooth flat surface.

An uneven wooden subfloor may need to be covered with a layer of plywood to provide a stable and level surface for the flooring. Unless you have previous experience of this type of work, it’s best to discuss it with a flooring specialist.