Floor screed is essential for any construction project. It involves a blend of cement, sharp sand and water which can either be bonded, unbonded or floating. Due to the screed finish having a much smaller tolerance than concrete, it makes it possible to lay the flooring above. There are two main standards for screeds, SR1 – the highest standard & SR2 – medium standard. The tolerance for SR1 screed is up to 3mm, while the tolerance for SR2 screed is up to 5mm. In this blog post, we explain what floor screeding is and how it can be used effectively.
THE DIFFERENCE BETWEEN SCREED & CONCRETE
Screed and concrete are both popular in construction, but what is the difference? Both contain cement, aggregates, and water; however, the kind of aggregate used makes them distinct. Concrete utilizes rougher particles for added strength, while screed relies on finer grains to provide a smooth surface for flooring installation. Additionally, screed is more expensive than either concrete or mortar.
TYPES OF SCREEDS
A bonded screed is an excellent material for thin surfaces that will be bearing heavy weight, ranging in thickness from 15mm to 50mm. This material can be bonded with cement slurry, SBR or an epoxy resin bonding agent.
An unbonded screed is not adhered directly to the base, instead it is separated with a damp proof membrane or polyethylene sheet. Generally, these types of screeds are more successful when they are used with a thickness over 50mm; however, certain modified versions can be installed at thinner levels. For further information regarding minimum thickness requirements for an unbonded screed, it is suggested to look at the data sheet of the product in question.
Floating screed is generally laid above a layer of insulation or over an underfloor heating system. Additionally, a slip membrane should be placed between the insulation and screed to separate them.
THE THREE MAIN TYPES OF SCREEDS
Traditional Screed (typically known as Sand and Cement Screed) is a floor screed consisting of sharp sand, cement and minimal water. It is by far the most common type of screed which is suitable for all applications such as bonded, unbonded and floating screed. Traditional screed requires using a straight edge to spread and level the screed to the specific level. Once the area has been levelled, the screed then either gets hand or power trowelled to correct any imperfections and to improve the density of the screed. This will leave a smooth finish making it ready for the final floor finish.
Liquid Screeds (also known as flowing screeds) are most applied over underfloor heating systems due to the better heat transference. Liquid screed is quickly becoming a favourite over traditional screed since it can be applied to large areas at much faster rates. The application of liquid screed requires using a liquid screed pump, once the whole area has been pumped, a dapple bar will be used to eliminate any air bubbles and to give it a slightly smoother finish.
Self-Levelling is commonly used for levelling of pour substrates to achiever a finer tolerance for the installation of tiles, carpets etc. The self-levelling compound is mixed with water which can either be pumped or poured into place. Once the product has been placed, the next step is to spread it out and the product will then begin to level itself out. A great benefit of this is that it requires less hard work on the labour side, making it an efficient time-saver. Depending on the product, you can walk on it in just 3-24 hours of instalment.
SURFACE REGULARITY OF SCREED
The surface regularity of screed is a critical measurement as it determines whether the floor conforms to British Standards. There are two primary standards for screed: SR1 (allowing a tolerance of up to 3mm) and SR2 (allowing a tolerance of up to 5mm). Measuring your flooring’s deviation using SR can aid in determining its levelness. A smaller SR value indicates a smoother and flatter surface. The higher the value, the surface will appear wavier and less flat.
To sum up, floor screeding is a vital step for achieving the ideal floor finish. It should only be done by experienced professionals who possess the appropriate tools and equipment. Successful application of an even and smooth screed finish necessitates skill, expertise, and precision.