What is floor screed and what is its purpose?
Floor screed is indispensable for any construction project. It typically comprises a mixture of cement or anhydrite binder, sharp sand, and water, which can be bonded, unbonded or floating. The finer tolerance of a screed finish compared to concrete enables the laying of flooring above it. There are two primary standards for screeds: SR1 – the highest standard, and SR2 – medium standard. The tolerance for SR1 screed is up to 3mm, while for SR2 screed, it is up to 5mm. In this blog post, we look into what floor screeding is and how it can be effectively utilised.
THE DIFFERENCE BETWEEN SCREED & CONCRETE
Screed and concrete are both commonly used in construction, but what sets them apart? Both comprise cement, aggregates, and water; however, the type of aggregate used distinguishes them. Concrete comprises coarser particles for increased strength, whereas screed depends on finer grains to deliver a smooth surface for flooring installation. Moreover, screed is relatively more costly than concrete.
TYPES OF SCREEDS
Bonded Screed - A bonded screed is commonly utilised for thinner sections that will endure heavy loads, with a thickness ranging from 15mm to 50mm. This material can be bonded with cement slurry, SBR or an epoxy resin bonding agent.
Unbonded Screed - An unbonded screed isn't directly affixed to the base; instead, it's segregated with a damp-proof membrane or polythene sheet. Typically, these screeds perform better when employed with a thickness exceeding 50mm; however, certain adapted versions can be fitted at thinner depths. For further details on the minimum thickness requirements for an unbonded screed, it is recommended to refer to the data sheet of the relevant product.
Floating Screed - Floating screed is usually positioned above an insulating layer or on top of an underfloor heating system. Furthermore, a slip membrane should be installed between the insulation and screed to keep them apart.
THE THREE MAIN TYPES OF SCREED
Traditional Screed - Commonly referred to as sand and cement screed is a floor screed comprising sharp sand, cement and minimal water. It is the most prevalent type of screed, suitable for all applications such as bonded, unbonded and floating screed. Traditional screed necessitates the use of a straight edge to spread and level the screed to the specified level. Once levelled, the screed is then either hand trowelled or power floated to rectify any imperfections and enhance the density of the screed. This results in a smooth finish, preparing the screed for the final floor finish.
Liquid Screed - Also known as flowing screeds are primarily applied over underfloor heating systems due to their superior heat transference. Liquid screed is rapidly gaining popularity over traditional screed as it can be applied to large areas much more quickly. The application of liquid screed involves using a liquid screed pump. Once the liquid screed has been pumped, a dapple bar is employed to eliminate any air bubbles and provide a smoother finish.
Self-Levelling Compounds - Self-Levelling is commonly used to level substrates to achieve a finer tolerance for the installation of the widest variety of floor coverings. The self-levelling compound is typically mixed with water, which can be pumped or poured into place. Once the product has been poured, the next step is to spread it out, and the product will then begin to level itself out. Self-levelling compounds are usually applied in thinner sections than traditional and liquid screeds, ranging from 2mm to 40mm. Depending on the product, the surface can be foot trafficked within just 2-6 hours of installation.
CONCLUSION
In conclusion, floor screeding is a crucial step in attaining the perfect floor finish. It should only be undertaken by skilled professionals who have the requisite tools and equipment. Achieving a uniform and smooth screed finish requires expertise, precision, and skill.