LEVELLING UP
When it’s necessary to raise the level of a subfloor before installing new floorcoverings, only levelling compounds especially formulated for this purpose are up to this task. F. Ball explains.
There is a wide range of levelling compounds on the market that can typically be applied up to a maximum thickness of 20mm ahead of the installation of floorcoverings. But what if you need to raise a floor more than a couple of centimetres? This is when problems can occur using a standard levelling compound.
The reason for this is that levelling compounds are primarily made up of cement and are often combined with water to create the mixture that is then applied over the substrate.
It is the water content in a levelling compound that allows it to flow easily but it can also lead 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, with the densest materials at the bottom and the least dense at the top. Some layers will be weaker than others and this can seriously compromise the strength of the levelling compound when dry.
Also, when cement reacts with water it results in an exothermic reaction. This heat can lead to thermal expansion of the product, which increases the risk of thermal cracking when the material subsequently contracts after the heat has dissipated, leaving you with unattractive and damaging cracks in the subfloor. An alternative is to apply multiple layers of levelling compound to build up the desired thickness, but this can be time consuming, requiring multiple drying times and priming between applications.
WHAT’S THE SOLUTION? Levelling compound manufacturers have developed products in response to this problem. For example, F. Ball’s Stopgap 600 Base provides contractors with a dimensionally stable product that can be applied at thicknesses between 5–50mm in one application, allowing contractors to raise floor levels quickly and easily.
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 levelling compound and minimise the separation of components when the compound is applied in a thick section.
Stopgap 600 Base also cures to chemically bind all the remaining water in the mixture. This means that flooring contractors are not forced to wait for all of the water to evaporate naturally as with other levelling compounds. Consequently, the drying time of Stopgap 600 is dramatically reduced and it sets in as little as three hours after application.
Once sufficiently set, these levelling compounds can be capped with another levelling compound to create a perfectly smooth surface ready to receive floorcoverings. However, only levelling compounds that will chemically bind all of the water into the mixture should be used. This is to minimise the risk of air bubbles in the subfloor, which can appear if there is moisture remaining in the compound. Usually, these bubbles
32 | SUBFLOOR PREPARATION
can be removed with a spike roller, but this is more difficult if the compound has been applied in a thick section.
Once the levelling compound has sufficiently dried, the flooring contractor can proceed to install floorcoverings.
A NOTE ON PRIMING It is almost always essential to prime a subfloor before the application of a levelling compound. Used over absorbent subfloors, including porous concrete and sand/cement screeds, primers promote adhesion and create a film to prevent the unacceptably rapid drying of a subsequently applied levelling compound. Priming also prevents ‘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 levelling compounds applied over it. This is particularly important for withstanding the increased stresses that thicker depths of levelling compound exert when drying.
Primers developed especially for use over non-absorbent surfaces, such as F. Ball’s Stopgap P141 have been specially formulated to create a textured finish to enhance bond performance between subfloor and levelling compound. The strong bond created when using Stopgap P141 makes it an ideal choice of primer when applying deep base levelling compounds at thicknesses greater than 20mm, such as when raising floor levels.
www.f-ball.com
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