John elaborates on solutions for situations where floor levels need raising quickly and easily.
THERE’s a wide range of smoothing compounds on the market that can typically be applied up to a maximum thickness of 20mm ahead of the installation of floorcoverings. However, sometimes flooring contractors need to raise the level of a subfloor by more than a couple of centimetres before new floorcoverings can be installed – after removing thick ceramic tiles and adhesives, for example, where underfloor heating needs to be encased, or simply for aesthetic reasons.
The challenge
This is when problems can occur using standard smoothing compounds, which are primarily made up of cement and are often combined with water, allowing them to flow easily but potentially leading to a separation of the components in the compound (e.g. sand, aggregate and cement) when applied thickly. This separation can lead to layers forming, some weaker than others, with the densest materials at the bottom, compromising the strength of the smoothing compound when dry.
Also, when cement reacts with water it results in an exothermic reaction, which can lead to a build-up of heat and thermal expansion of the product when applied at thicker depths, increasing the risk of thermal cracking when the heat dissipates and the material contracts.
The solution
For situations where floors need raising by more than 20mm, smoothing compound manufacturers have developed deep section base compounds, such as F Ball’s Stopgap 600, which can be applied at thicknesses between 5-50mm in one application.
To minimise the capacity for thermal expansion, the amount of cement in these products has been reduced. As decreasing the amount of cement would weaken the material, the water content in the mix is also reduced. This helps to limit the flow of the smoothing compound and minimise the separation of components when the compound is applied in a thick section.
Stopgap 600 is also formulated to chemically bind all the remaining water in the mixture when it cures so that flooring contractors are not forced to wait an extended amount of time for all of the water to evaporate naturally as they would if applying a regular smoothing compound.
Consequently, the drying time of Stopgap 600 is dramatically reduced, and it sets in as little as three hours after application, meaning it’s a much quicker option that multiple applications of a standard smoothing compound. It can also be pump applied over large areas to save further time.
When sufficiently set, these base compounds can, if required, be capped with another smoothing compound to create a perfectly smooth surface ready to receive floorcoverings. However, only smoothing compounds that will chemically bind all of the water into the mixture should be used.
Underfloor heating
When working over electrical wired or water-fed underfloor heating systems that are increasingly installed over subfloors as part of new build or refurbishment projects, it is advisable to allow at least 15mm of a specialist smoothing compound above the pipes to avoid hotspots and ensure its structural integrity.
F Ball’s Stopgap 1600 is a fast-drying, fibre-reinforced smoothing compound that is formulated especially to be applied between 3-40mm thick to encapsulate underfloor heating and cooling systems installed over internal subfloors in both domestic and commercial environments.
The product is suitable for use over a wide range of absorbent and non-absorbent subfloors, including sand/cement screed, tile backer boards, concrete, plywood, granolithic, terrazzo, epoxy and polyurethane resins, ceramic and quarry tiles, as well as Stopgap waterproof surface membranes. It is walk-on hard from three hours after application and ready to receive floorcoverings in as little as 12 hours.
A note on priming
It is almost always essential to prime a subfloor before the application of a smoothing compound. Used over absorbent subfloors, including porous concrete and sand/cement screeds, primers create a film to prevent the unacceptably rapid drying of a smoothing compound, which helps to develop both the overall strength performance and open time.
Priming also reduces the formation of ‘pinholing’ caused by the slow escape of air from absorbent surfaces.
When used on non-absorbent surfaces, such as waterproof surface membranes, terrazzo or ceramic tiles, primers serve the important role of promoting adhesion between the subfloor and smoothing compounds applied over it.
This is particularly desirable where smoothing compounds are applied at thicknesses greater than 20mm, where the bond line is subject to increased stress as the smoothing compound dries. F Ball’s Stopgap P141 primer has been specially formulated to create a textured finish and enhance bond performance between subfloor and smoothing compound, making it an ideal choice in these situations.
Final steps
Once the smoothing compound has sufficiently dried, a flooring contractor can proceed to install chosen floorcoverings with a compatible adhesive.
www.f-ball.co.uk
John Green is technical service officer, F Ball and Co
