Here, Bostik discusses the importance of controlling the drying rate of smoothing compounds during winter months.

When it comes to applying subfloor preparation products there are many factors that can prevent or indeed encourage them to dry out.

Smoothing compounds both dry and cure and the reactivity of the binders will be affected by the temperature and humidity on site, along with how the products have been stored since manufacture.

So what needs to be considered when working with smoothing compounds during the colder winter months to ensure they dry and cure properly?

SITE CONDITIONS The site conditions have an important role to play. Standard smoothing compounds have a controlled, two-part cure. The first is reactivity of the cements / binders and the second is evaporation of the excess moisture used to make the smoothing compound flow. It is worth remembering that cold, damp conditions with poor airflow will delay this curing profile.

For standard smoothing compounds, the delay in drying and curing times due to cold, damp sites can be significant and mean waiting days before you can continue flooring works. If you can’t afford to wait, then, where appropriate, look to use a fast setting option, such as Bostik’s Screedmaster Speed 30.

Formulated from the latest advances in cement technology, Bostik Screedmaster Speed 30 will smooth sound, uneven surfaces prior to the laying of decorative floorcoverings in as little as three hours, with a loose lay time of 45 minutes. Consisting of a 20kg powder bag and four litres of polymer liquid, the two- part product is suitable for use with underfloor heating systems and will cover up to 5m² at 3mm thickness.

Rapid curing smoothing compounds are generally designed for fast turnaround projects allowing flooring to be done in a day. The chemistry of the products differs, enabling the moisture levels to reduce much more quickly and for the strength build up to be much faster. The right products will give you the advantage in cooler conditions of still being ready for flooring the following day, which helps to minimise time on site.

One thing worth remembering though is that fast setting options will also be slower than their stated drying time if temperatures are low. In all instances, a temperature of below 5°C will be a serious problem, as it will affect the curing of the binders and may result in long-term issues. Cold, damp storage conditions will slow things down too.

If you are relying on the fast setting nature of a product for a work time programme, 34 | LEVELLING COMPOUNDS

then make sure you store your bags and bottles in a warm environment (at least 24 hours for single bags and several days for pallets) before you plan to use them.

APPLICATION THICKNESS Another factor affecting the drying rate is the thickness that the product is applied. Drying times are often based on a 3mm thickness, but if you’re applying thicker than 3mm there is more moisture to escape, so you may need to factor in more time.

It is very difficult to tell if a smoothing compound has dried sufficiently and most contractors use their instinct based on how it looks, however the colour change can often be misleading and more of a surface effect. A pin meter is a good way of assessing if the compound is anywhere near dry. A reading up in the red or a surface very easily compressed by the pins shows it is not cured or dry enough to lay on.

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