When you are working on a construction project, you must have the appropriate quantity and kind of materials available to you to prevent obstacles that might extend the length of time it takes to finish the task. Although screed concrete may not have the same level of familiarity outside the construction industry as concrete, it is nevertheless a vital component of any structure. In this article, we will explain precisely what screed concrete is and how it benefits builders and contractors.
See also: Reinforced concrete: Meaning, types, design, and benefits
What is screed concrete?
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Screed is a thin layer of concrete, typically 25 mm to 75 mm in thickness, that is poured onto a concrete subfloor to create a smooth, level surface. It is commonly used in construction to provide a finish for concrete or to act as an underlayment for flooring. Screed is composed of a mixture of cement, sand, and water, and may include other additives depending on the specific type of screed being used.
It can be applied in a variety of ways, including traditional hand application, using a pump or mixer, or using a screeding machine. The thickness of the screed is determined by the specific application, with thicker screeds typically used in industrial or commercial settings, and thinner screeds used for domestic applications.
Screed concrete: Types
There are several types of screed concrete, including:
- Traditional screed: This is a sand and cement mix that is applied in a semi-dry state and levelled by hand. It is commonly used in residential and commercial flooring applications.
- Liquid screed: Also known as flowing screed, this type of screed is a self-levelling mix of cement, water, and additives that is poured onto a substrate and levelled by hand or machine. It is commonly used in large commercial or industrial flooring applications.
- Polymer-modified screed: This type of screed is a sand and cement mix that is modified with polymer additives to improve its strength and durability. It is commonly used in areas that are exposed to heavy traffic or extreme weather conditions.
- Fibre-reinforced screed: This type of screed contains fibres that are added to the mix to improve its strength and durability. It is commonly used in industrial and commercial flooring applications.
- Fast-drying screed: This type of screed is designed to dry quickly, often within 24 hours, making it ideal for projects that require a quick turnaround time. It is commonly used in residential and commercial flooring applications.
- Bonded screed: This type of screed is applied directly onto a base concrete slab using a bonding agent to ensure strong adhesion. It is commonly used in renovation projects where an existing concrete substrate is being covered with a new screed layer.
Screed concrete vs traditional concrete
- The primary difference between screed concrete and traditional concrete is the water content. Screed concrete typically contains less water than traditional concrete, which results in a drier mix. This is important because a drier mix is easier to work with when applied in thin layers, as it is less likely to flow or slump before it can be set.
- Another key difference is the composition of the concrete mix. Screed concrete is typically designed with a higher cement content than traditional concrete, which provides greater strength and durability.
- Screed concrete may be reinforced with fibres or wire mesh to improve its strength and resistance to cracking. This is particularly important in areas where the concrete will be exposed to heavy traffic, extreme weather conditions, or other sources of wear and tear.
- The application process for screed concrete is different from that of traditional concrete. It is typically applied in thin layers using specialised tools such as screed boards, trowels, and floats, and requires a skilled installer with experience working with thin-layer concrete applications.
Screed concrete: Characteristics
To be utilised for floor installation, the screed must exhibit certain technical and performance properties. The following are some characteristics of screed:
Clean
The screed surface must be spotless. Before flooring can be installed on top of the screed, all debris, including dust, dirt, rubble, disconnected sections, and other substances, must be removed. The adherence of the floor to the screed will be compromised by dirty surfaces.
Dry
The screed surface’s amount of residual humidity must be measured. This number should be consistent over the whole thickness of the screed and should not exceed the maximum allowed for the chosen flooring. This is done specifically when installing flooring that is susceptible to moisture damage. A residual humidity of less than 0.5% is required for anhydrite screeds. The level of residual humidity in a screed may be gauged using an electric or carbide hydrometer.
Flatness
For this purpose, a straight edge at least two metres in length is laid down on the screed in all directions to ensure uniform flatness. This straight edge has a maximum allowable deviation of 2 mm. Floor installation cannot proceed until the flatness is brought within tolerance, at which point the surface must be levelled with an appropriate product.
Sufficient thickness
The thickness of the screed is determined by many factors, including the kind of screed to be used, the thickness of the floor, and the expected volume of foot activity.
Smoothness
Which flooring is laid has a major impact on the surface’s appropriateness in terms of finish grade and roughness. It’s recommended that a skimming product intended for this purpose be used to achieve reflective finishing.
Mechanical resistance
A sufficient mechanical resistance must be acquired by the chosen screed to support the ultimate load (service load) and the load contribution from the kind of floor. If you’re using screed for a floor in your home, you should aim for at least 20MPa in compressive strength. Minimum strength of 30MPa is required for industrial use.
Compactness
A compact and uniform concrete screed is essential for the whole slab. There is a problem with the mechanical qualities if the screed has layers or sections of crumbles or reduced consistency. As a consequence of this flaw, the flooring will either crack or come loose.
Concrete screed curing and dimension
Before installing the floor, make sure the screed has been laid down evenly and has had enough time to dry. If there is any shrinking to be done, it may be finished during this curing process. Concrete screed is prone to hygrometric shrinkage during the curing cycles. The drying process or the evaporation of some of the mixing water might be to blame for this hygrometric shrinkage. Inevitably, screed may curl or fracture as a consequence of this shrinking. The floor might become detached from the subfloor or be damaged if these fissures appear soon after installation.
Crack-free screed
There are many potential causes for fractures in concrete screed. For example, there is the effect of humidity on the size of an object. Other causes include a high water content in the blend. Using fine aggregates or a mixture with an excessive amount of cement may also cause cracking. It’s recommended that every opening be completely sealed. Epoxy resins allow for very precise sealing. These steps are taken before the flooring is laid. Using the anti-fracture membrane may protect the screed’s surface from tiny fractures.
Screed concrete: Uses
Screed concrete is used in a variety of construction projects where a smooth and level surface is required. Some of the most common applications for screed concrete include:
- Flooring: Screed concrete is commonly used to create level and smooth flooring surfaces in residential, commercial, and industrial buildings.
- Underfloor heating: Screed concrete is often used as a base layer for underfloor heating systems, which can provide energy-efficient heating for a building.
- Pavements: Screed concrete can be used to create level and durable pavements for pedestrian walkways, bike paths, and other outdoor areas.
- Renovations: Screed concrete can be used to level and resurface existing concrete floors, making it a popular choice for renovation projects.
- Soundproofing: Screed concrete can be used as a soundproofing layer between floors in multi-story buildings.
- Drainage: Screed concrete can be used to create sloping surfaces that direct water towards drains, making it ideal for wet rooms, bathrooms, and other areas where water may be present.
- Industrial applications: Screed concrete can be used in a variety of industrial applications, such as warehouses, factories, and processing plants, where a durable and level surface is required.
FAQs
How is screed concrete different from traditional concrete?
Screed concrete contains less water and has a higher cement content than traditional concrete, making it easier to work with in thin layers and more durable for specific applications.
How is screed concrete installed?
Screed concrete is installed using specialised tools, such as screed boards, trowels, and floats, and requires a skilled installer with experience working with thin-layer concrete applications
How long does it take for screed concrete to dry?
The drying time for screed concrete can vary depending on the type of screed used but typically ranges from several days to several weeks.
Can screed concrete be applied over an existing concrete surface?
Yes, screed concrete can be applied over an existing concrete surface using a bonding agent to ensure strong adhesion.
Can screed concrete be polished or painted?
Yes, screed concrete can be polished or painted to provide a decorative finish for flooring and other applications.
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