By Mark Prizeman, Technical Services Manager, Sika Flooring and Refurbishment.
A Health and Safety Executive study revealed around 1,300 work-related injuries were reported between 2015 and 2016 in the food and drink industries. Of these, it’s estimated at least 25% were caused by uneven surfaces. Level flooring is therefore essential in heavily-industrialised areas involving high-levels of footfall and machinery usage.
Without the need for rigorous effort, Sika’s self-levelling cementitious compounds can quickly even-out a large floor. Once the product is mixed with water according to its data sheet, it is simply poured over the floor’s uneven substrate. With a thinner consistency than other types of cement screed, the mixed compound will comfortably fill a surface’s uneven areas.
Sika underlayment offers a smooth, hard-wearing solution to a range of flooring substrates. The ease with which Sika’s self-levelling cementitious compound is mixed and applied enables wide-ranging surface coverage and a high-quality performance. Flat surfaces are comfortably achieved – even in thin layers – with little tension, stress and shrinkage during curing. A rapid-hardening version of the system is available. So, how is it applied?
Doing the groundwork
Firstly, it is important to remember that a levelled floor can never be stronger than its substrate. As such, a tensile test needs to be undertaken. This is achieved by adhering a steel dolly to the surface, isolating it and then pulling it off using a tensile tester, ensuring a minimum value of 1.5N/mm2. The compressive strength of a sub floor must have a value greater than 25N/mm2. The substrate’s dimensional stability must be secured and have permanent dryness in its lifetime.
Any weak areas on the substrate should be removed by sanding, scraping, grinding, milling, blasting or brushing. Also old, loose and weak underlayments should be removed mechanically. Surface defects such as cracks must be patched prior or during priming as there is the risk of the screed material flowing into them and producing air bubbles or reflective cracks in the surface in case of substrate movement.
Before applying subsequent floor coverings, cement screeds are required to display a residual moisture reading of ≤ 2.0 CM-% (heating screeds ≤ 1.8 CM-%); calcium sulphate screeds: ≤ 0.5 CM-% (heating screeds ≤ 0.3 CM-%).
Sikafloor primers can be used on a wide range of substrates before the application of Sikafloor self-levelling cementitious underlayment products. The primers can reduce the absorbency of the substrates and improve the adhesion between the underlayment and the substrate.
In some cases they are also used as a protection for the substrate against the moisture coming from the self-levelling cementitious underlayments. All Sikafloor primers are rated as low-emission and meet GEV-Emicode EC-1 plus.
With the substrate primed and ready for its self-levelling compound, the next step is to measure the total area to be levelled in m2. This will calculate the amount of material necessary to achieve the mixture’s desired level and performance requirements. It’s important to note: product data sheets exclude waste and practical considerations such as surface roughness.
Whether manually or pump-applied, the water added to the levelling compound should be clear, with the quality of potable water. It is prohibited to use contaminated or waste water. When it comes to applying the self-levelling compound, proper safety equipment should be worn and sufficient ventilation provided.
The amount of water required for the levelling compound varies from product-to-product – see relevant product data sheet. A suitable mechanical hand mixing or mixing pump is recommended for the stirring process. Never add water to the powder or add it in stages, as this alters the product’s properties.
The Sikafloor Primer and Sikafloor Level can be applied at substrate and ambient temperatures between +5°C and +30°C. Ensure all ventilation devices are switched-off during and after application for 24 hours. It’s also important to protect fresh surfaces from sunlight and direct sources of heat.
Applying for a Finish
After mixing, pour out the self-levelling compound onto the primed surface and spread using a notched trowel or adjustable pin-leveller (pinrake) to the required thickness. The compound is applied by walking along the front and keeping a ‘wet edge’; that is, always placing material onto previously placed material before it starts to set, dry (turn matt) and harden. The width of the front will be determined by the application conditions – the higher the substrate and ambient temperature, the narrower the front.
Ensure a continuous supply of mixed material and place it efficiently to allow maintaining a ‘wet edge’ which will reduce the differences between batches where the material is already starting to dry and set. Surface styling is affected by the choice of finishing tool. The use of a spike roller isn’t mandatory for every self-levelling compound, but can be recommended to remove troweling defects.
The spike rolling process should not be delayed for more than five minutes after placing, particularly at higher temperatures. A significant time-lapse could lead to roller marks, unevenness on the mortar surface or ‘waves’. Excessive rolling of the application could also cause an unsightly appearance. Depending on the thickness of the applied layer and the method of placing, the product’s ‘pot life’ and workability – usually limited to between 20 and 30 minutes at 23°C – should be decided.
Again, it’s important to reiterate that no flooring installation is the same. Mixture levels and application methods are product-dependent and likely to vary. Whatever the requirements, however, rest assured Sika offers the technical knowhow and support to ensure each self-levelling project runs as smoothly as the finished floor.