Steve Thornton discusses the different substrates fitters may come across when working on a renovation project, and how to select the best smoothing compound for the job.

BEFORE any renovation project can commence, a thorough understanding of the substrate you’ll be working with is crucial to choosing the best products.

In this article, I’ll outline some of the things to consider, the types of substrates you might come across, and how to effectively choose the best smoothing compound for the job.

Before selecting any product, the first thing to consider is the age of the building you’re working in to gauge the kinds of materials that were likely used. As an example, if the building dates back before the ‘70s, it’s likely there’ll be no base damp proof membrane.

Post-1970, the chances of having a base DPM are much higher, provided the building was designed to be habitable.

In every project, regardless of how it may look, moisture testing should be carried out to reveal the relative humidity (RH) of the subfloor. If it’s above 75%, the subfloor can be at a higher risk of failure if a DPM isn’t applied.

Thoroughly assess the subfloor, conduct a moisture test, and use a DPM if required to save costly rectifications further down the line. While existing floorcoverings should be removed, this isn’t always possible owing to the fast-paced nature of renovation projects.

Exceptions to this are flooring such as Granwood or magnesite, which cannot be left on any direct-to-earth (ie ground floor) areas. Resilient sheets or tile flooring, and cork should also be removed.
A solid terrazzo floor, quarry tiles and ceramics, however, can be good surfaces provided they’re cleaned up and a DPM is applied on a ground floor (or suitably primed on an upper floor) before the smoothing compound is applied.

Once these steps have been completed, you’ll likely have a greater understanding of the substrate you’re working with and can begin to assess which smoothing compound is right.

The right product for the job
When a DPM, also referred to as a moisture suppressant, is required, it’s important to assess the condition of the subfloor to avoid excessive use and ensure the product functions effectively.

On pitted, absorbent or undulating floors with voids and hollows, a moisture tolerant smoothing compound can be used to give a flat surface to enable you to apply the DPM at the desired coating.

On refurbishment projects, it’s common for old flooring to have been pulled up, and the residue of the adhesive used to lay it be left behind. In these instances, look for a low tension/high adhesion smoothing compound.

Typically supplied in a bag-and-bottle, these products are ideal for renovation work where residues of previous preparation methods have been left behind. They don’t require the intensive subfloor preparation that some other smoothing compounds do, which saves time on-site and can also save you money too.

When renovating in a property with underfloor heating installed, the cables will require encapsulation within the smoothing compound. Choose a fibre-reinforced option, as the fibres within will help prevent cracks as the floor’s temperature changes.

Fibre-reinforced smoothing compounds are also great for timber substrates, as the fibres help reduce the risk of cracking owing to slight movement or deflection.

If you’re renovating a space that’s likely to receive heavy traffic, such as a warehouse or garage, then opting for a heavy-duty smoothing compound will be your best choice.

These types of smoothing compound have a much higher compression strength and better resistance to abrasion and rolling loads, making them ideal for heavy usage areas.

An all-in-one solution
When working on a renovation project, it’s likely that within one site you’ll come across multiple subfloors which have all been subjected to different conditions. A great option is therefore an ‘all-in-one’, high-performance smoothing compound which can be used over many different substrates for full versatility.

These types of smoothing compounds, such as Bostik’s SL C955 ADVANCED, are perfect for renovation projects as they require less subfloor preparation, including no priming on certain subfloors, saving fitters time and money.

If you’re not sure which smoothing compound to choose, or if you’d like a second opinion on a subfloor before you begin the work, you should choose a manufacturer that provides excellent technical support.

Our expert team can visit the site to carry out an initial assessment of the subfloor and ensure you’re using the best products for the job.
www.bostik-profloor.co.uk
Steve Thornton is technical manager at Bostik