Problems on refurbishments can be avoided by doing a thorough and intrusive assessment of the subfloor, says Adam Jones.

As most people reading this article will know only too well, flooring can be low down on the list of priorities in the eyes of some main contractors and end-users, despite the aesthetic and performance requirements that make it an essential part of every building. This is most true when it comes to refurbishment projects.

Over my years of working in technical support for Bostik, I’ve lost count of the amount of times I have walked into an old building to see everything stripped out, of course aside from the old flooring, which is hanging on for dear life and now has an all-new interior fit-out sitting on top of it.

In this article, I’ll highlight some of the more problematic scenarios and substrates when it comes to refurbishment jobs and what you should do when you encounter them.

Consider the age of the building
Asbestos concerns: If the building is pre-2000, it needs to be established whether there is asbestos in the floor make-up before conducting an intrusive assessment of the existing floors. Asbestos was used in some types of floorcoverings, such as some thermoplastic tiles and linoleum, some old adhesives, and can also be in magnesite, which is an old type of floor substrate I’ll discuss later.

Moisture concerns: If the original construction date of the building commenced prior to 1965, it must be assumed there’s no structural damp-proof membrane incorporated and so a surface applied moisture control system must be utilised for any moisture sensitive coverings. To enable this to take place would require that existing material that cannot tolerate moisture must be removed.

A common misconception is to only apply moisture control systems in refurbishment projects if relative humidity (RH) readings are above 75%. This isn’t the case. Some of the old floorcoverings could be allowing the floor to breathe efficiently, meaning it’s unlikely elevated readings will be detected until impervious coverings block the passage of moisture and cause it to build up over time.

Common problematic substrates
Asphalt: This is a black, tar-like substrate, typically 15-25mm in thickness. If found in perfect condition, dealing with asphalt can be relatively straight forward, however this is rarely the case. It will usually have some cracks and damage which would require an asphalt specialist to repair (or completely remove).

Asphalt is a very effective moisture barrier and so cracks and damage left untreated will become a passageway for rising damp. Asphalt floors are also very sensitive to being covered with smoothing compound, so the application should be limited to a 5mm maximum depth with a low-mid strength product. It’s very surprising how a smoothing compound can pull up an asphalt floor. If an existing layer of smoothing compound is already present, it should be removed if a new coat is required.

Magnesite: Magnesite floors are sometimes found in buildings constructed between 1920-1960. They’re typically 10-25mm (can be much thicker) and a creamy-yellow or red colour. It’s a material that was used when other, more stable materials were at a shortage. Wood flour, sawdust, and sometimes asbestos were used as a filler, which results in magnesite being sensitive to moisture. Magnesite will require removal to enable the installation of modern floor coverings as it needs to breathe to perform successfully.

Wood blocks/Granwood: The most obvious thing to consider with timber-based substrates is moisture. It is well understood that timber will not tolerate rising damp and so must not be covered by resilient floor coverings. This is also the case for Granwood (a composite flooring material which uses sawdust as a filler), which is commonly found in old schools and commercial buildings.

Timber substrates of a certain age will be adhered with Bitumen (may contain asbestos), so consider that these residues will also require removing as well as the timber itself. Granwood will generally be bonded with a thin sand/cement slurry bed or tile adhesive.

Thermoplastic tiles: Often referred to as crunchy tiles or Marley (the original manufacturer) tiles, these are a very robust type of floor covering that were widely used between 1960 and 1990. Both the tile itself and the bitumen adhesive used to stick them down have the potential to contain asbestos. As they are commonly found in domestic environments, it can be impractical or not possible to utilise the machinery required to effectively remove the adhesive. Due to this, some fitters prefer to leave them in situ and encapsulate with a low tension/high adhesion smoothing compound. The draw backs to this method are that the level of moisture control being provided by the bitumen is adequate for the thermoplastic tiles but may not be suitable for subsequently applied modern coverings; the integrity of the new flooring will rely heavily on the adhesion of the old bitumen; and, finally, these types of compounds are generally low strength and can be dented or marked by furniture and dynamic loads.

So, plenty to think about when taking on a refurb project. The above are just some of the factors that can lead to problems on refurbishments, so it is always worth doing a thorough and intrusive assessment of the subfloor. You never know what might be hiding under 3mm of someone else’s compound, so it always pays to check right the way down to the base.
Most preparation material suppliers such as Bostik have technical representatives that are more than happy to assist with onsite product and installation guidance, so, if in doubt, get the manufacturer out.
www.bostik-profloor.co.uk
Adam Jones is technical consultant at Bostik UK