Rob Russell explains why mechanical surface prep is the difference between floor success and failure
PART of my daily routine is to inspect substrates and recommend the best course of action to achieve the best results. The first and most important recommendation is that surface preparation should be undertaken to provide a solid, sound, and smooth base.
This is achieved by using appropriate mechanical surface preparation equipment to remove any weak surface layers – such as plaster, residues from other trades, dust, dirt, curing agents, resinous coatings, shiny or power-floated surfaces, loose or friable material, or any other contamination likely to impair adhesion. Doing so creates a surface that allows subsequent products to perform as intended.
The ‘why’
In short, to avoid system failure. Some materials react with other materials and chemicals, and some substrates react when covered and therefore can’t breathe. If a weak layer isn’t removed, the overall strength of the installation will only ever be as strong as its weakest point.
While some smoothing compounds in the UK can be applied directly over certain well-bonded adhesive residues, in Europe a more thorough approach is often considered best practice. This typically involves removing more of the existing subfloor before applying new preparation materials.
Surface preparation is often regarded as the most critical stage in the whole process. The overall failure rate can be very high when floor preparation isn’t completed correctly.
To deliver the best outcome every time, we now have greater knowledge than ever before – along with tools that make the process quicker and more economical. The UK flooring industry has evolved significantly in recent years, driven by technological advancements, changing consumer preferences, construction moisture challenges, underfloor heating systems, and growing environmental awareness. All of this underscores the importance of detailed floor preparation.
The ‘how’
When preparing an existing substrate, there are various mechanical methods available. Even newly applied substrates often have some contamination due to the nature of the construction process.
When assessing the type of surface to be removed and what will be applied afterwards, factors such as site restrictions, availability of electrical power, noise limitations, and dust and debris control should all be considered. These will help determine the best machine and method to use.
From handheld tools powered by a bit of elbow grease to durable shot blasters and multi-head grinders and polishers, there’s a wide range of surface preparation machines on the market. Let’s look at some of the main processes and tools available:
Scrapers or strippers: The oscillating blade movement mechanically removes floor coverings and adhesive residues. They’re also very effective at removing rubber, felt, and fleece-backed carpets quickly.
Shotblasting: Steel shot is propelled at high velocity onto the concrete surface. The residue is extracted into a filtration unit or vacuum, and the shot is separated and reclaimed. This leaves an open-textured, profiled surface with the previous layers removed. The speed and size of the shot, as well as the type of material being removed, determine the effectiveness of the process. Shotblasting isn’t suitable for materials exceeding 2-3 mm in thickness or for surfaces that are uneven, soft, or wet.
Grinding: Single or multiple diamond heads rotate to level, clean, and smooth the substrate. Diamond grinding is used to remove high spots or uneven joints up to around 3 mm.
Scarifying: Uses cutting elements to aggressively remove, groove, texture, and level the substrate. Within the rotating drum, the type and size of the cutting elements determine the depth and profile of the cut.
Sanding: While the above processes mainly apply to cementitious bases, for timber-based substrates sanding or planing is the appropriate method. The goal is again to remove contaminants and leave a clean surface ready for bonding.
Once the main work is complete, removal and disposal follow. Industrial vacuum extraction is a very important step to minimise dust and debris – not just for the operatives, but also for the surrounding environment. Many machines now feature on-tool dust extraction.
When the substrate is properly prepared, it allows subsequent layers to perform to their full potential. Failing to remove contaminants can affect how materials react and increase the risk of failure.
Next steps
Primers: These improve adhesion and prevent issues such as pinholes or dusting. They seal the subfloor and enhance the bond between the subfloor and the new flooring or smoothing compound.
Damp proof membranes and vapour barriers: These prevent moisture from affecting the smoothing compound, adhesive, and floorcovering. Contamination can otherwise prevent proper adhesion to the substrate.
Old adhesive residues: These are often too soft to support additional layers and can cause chemical incompatibility.
Once the substrate has been assessed, the appropriate level of preparation can be determined. Today’s ‘advanced’ smoothing compounds can be applied over old bitumen residues, as well as firmly bonded unglazed ceramic, terrazzo, and non-polished quarry tiles – though cleaning and removal of contaminants still apply.
Some moisture-tolerant smoothing compounds don’t require a primer thanks to their high adhesion and low shrinkage properties. However, when applying to porous substrates, priming absorbent surfaces is beneficial.
It reduces preferential absorption, minimises pinholing, extends working time, and helps achieve the ideal surface finish.
Ultimately, careful assessment provides the foundation for the best decision – helping to mitigate risk and deliver a properly prepared substrate that supports the floor covering throughout its lifespan.
rob.russell@bostik.com
www.bostik-profloor.co.uk
Rob Russell is technical consultant, Bostik UK