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Commercial Flooring News

Handle Your Screeds With Care

Today we will talk about the importance of handling anhydrite or calcium screeds with care in terms of the fact they become more and more popular, especially in the past two decades. As they are self-levelling and pumpable, they are very suitable for heated London flooring as they provide lower thickness. However, despite the pros of calcium sulphate screeds, London flooring experts warn that there are many potential problems that may arise in front of floor installers and tile fixers which may lead to unexpected delays. But what is the difference between these and the traditional screeds? Let our flooring professionals in London explain:

  • Calcium sulphate screeds contain anhydrous calcium sulphate – it is dry. This sulphate forms alpha hemi-hydrate calcium sulphate when water is added – it is a harder crystalline form. This is known more commonly as gypsum (or di-hydrated calcium sulphate). The reaction with the water stops typically after 3-7 days and the water that remains eventually evaporates through the surface of the screed.
  • London flooring specialists point out that the moisture content is of utmost importance. The drying time that is considered normal for calcium sulphate screed is about 1mm per day up to 40mm provided with perfect drying conditions. The estimation is based on conditions of relative humidity no greater than 65% and air temperature of 20 degrees Celsius. One of the main reasons of eventual failures is that when screeds are exposed to poor drying conditions the time increases drastically. This is why London flooring professionals recommend checking the conditions in advance so no delays occur due to bad estimation. If the conditions are poor, installers should consider external heaters or dehumidifiers.
  • Another way to aid in removing excessive moisture is remove the laitance mechanically after about 5 days of the installation of the screed. Flooring contractors in London point out that this is one of the most common reasons for surface covering problems as laitance must be removed completely and effectively. But what is laitance actually? It is a weak layer (intermediary) consisting of fine waste particles that are generated during the drying time. London flooring professionals explain that this layer is too thin and it must be removed so a strong bond between the screed, adhesive and the primer is reduced. A very important aspect to note is that the foot traffic should be kept off until the screed has hardened in accordance with the instructions of the manufacturer, otherwise you risk achieving mediocre results. You should also protect it from damage and contamination and then you can apply the final flooring finish. If you fail to do that, the screed will require additional remedial work soon after.
  • What to do when you are about to install the tiles? London flooring experts recommend applying a primer to the screed surface before installing tiles. This is so as a chemical reaction is provoked if the primer applied is not suitable for the certain conditions. We recommend using acrylic primer. Don`t forget that a lot of other factors must be taken into account such as the grout, adhesive and tile type. For example, if you are installing marble you should use an uncoupling matting. You should also consider what would be the following maintenance and cleaning regime so you choose the right products. If the London flooring will be subject to significant thermal changes, tiles should be divided into areas no bigger than 40square metres.

To conclude we would say that you better seek professional help and guidance before you decide to take up such project. Don`t forget that you must ensure that not only the flooring will look neat but also that it will last for the years to come!

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