Screed in the construction industry has a major role in leveling the surface with a smooth finish. Eventually, the screed acts as the top, like the concrete slab or any base to finish the final flooring. A thin layer is prepared to level the surface and create a smooth base. It serves as a base for other materials, including tiles, hardwoods, and carpets.
What is Screed in Construction?
A slim layer known as the screed is typically obtained from a mixture of cement sand and water. When applied over a concrete base, it serves as a base helping enhance the strength and workability with the inclusion of additives. When undergoing reinforcement with a screed, popularly used materials are fibers or mesh. It helps improve durability and strength. Based on the application, the thickness of the screed can very commonly range from 25 mm to 100 mm. Demanding modern advancement has forced the incorporation of screed with advanced materials to meet contemporary construction requirements.
The purpose of the screed is to provide even flooring by avoiding irregularities and protecting the underlying structure. Extending the lifespan of the flooring by the process also contributes to distributing the load, which prevents a localized stress point.
What are the Different Types of Screed?
There are three primary types of screed, each suited for specific applications based on the type of base being used. These include:
Bonded Screed
The bonded screed is directly applied to the concrete substrate. It creates a strong bond between the screed and the base layer. It is normally made from cement, sand, and water. They are ideal solutions for areas with heavy loads or high traffic. Bonded screeds include traditional sand-cement screeds and modified screeds. When added with additives, it helps enhance the performance. They often utilize bonding agents or primers, improving adhesion. Frequently, it requires regular maintenance to ensure longevity. They are generally more cost-effective with reduced material usage. Often considered less flexible than unbonded screeds, bonded screed offers superior strength and precision, guaranteeing consistent thickness and levelness. Its application includes warehouses, industrial floors, and car parks, providing good thermal conductivity for underfloor heating.
Additionally, specialized training is required for optimal use, and bonded screeds are considered eco-friendly, especially when low-emission bonding agents are utilized. They operate quietly compared to mechanical screeds, are easy to transport due to their lightweight nature, and require minimal storage space. Proper handling reduces the risk of injury, making bonded screeds a safe choice for indoor and outdoor applications.
Unbonded Screed
Unbonded screed is indirectly bonded, unlike bonded screed to the substrate. Instead, the concrete undersurface is separated by a membrane. Generally, it is composed of a mix of cement, water, and sand. Unbonded screeds are ideal for places with movement or where seismic activity is seen. It includes traditional sand-cement screeds and modified screeds with additives for enhanced performance. A polythene slip membrane is generally used to separate the screed from the substrate. It is generally thicker than bonded screeds, with a minimum thickness of 40 mm. An unbonded screed provides good strength, but its performance relies on its thickness and reinforcement. It also faces the problem of curling.
Floating Screed
A floating screed is laid over an insulation layer, allowing it to “float”. It is ideal for areas where enhanced acoustic or thermal performance is required. It includes traditional cement screeds and modified screeds with additives for improved performance.
The screed typically requires a minimum thickness of 65mm, which can increase to 75mm for heavily loaded floors. Floating screed offers good strength and durability, making it suitable for various applications, although it requires regular maintenance to ensure longevity.
Additionally, it is generally more cost-effective due to the reduced need for bonding agents, although its thicker application makes it heavier. The design also allows for flexibility, enabling the screed to move independently of the substrate.
Types of Screed Tools
Hand Screeds
A hand screed is a tool known for its versatility, designed for smoothing and leveling the concrete. They are most commonly used for projects like residential driveways, slabs, etc. Made from materials like aluminum, magnesium, or wood, these tools consist of a straight edge manually applied across the concrete surface. It is known to be a suitable and ideal solution for small projects and areas with difficulties in reaching the power creed.
The length of the hand screed can range from 3 feet to 20 feet in length and often requires physical effort to pull across the concrete. Although hand screed operates significantly slowly, it has an impact on the quality of the finish by achieving a flat surface level. The wooden screed remains a popular choice due to its low cost
Some hand screeds with vibration features help enhance the settling of concrete, which contributes to a smooth surface finish, giving a final touch. It is quite easy to operate and has a less environmental impact, creating a lower risk of injury due to the absence of any moving parts. This makes it a go-to choice due to its cost-effective solution for achieving a smooth concrete surface.
Vibratory Screed
A vibratory screed is an essential tool for leveling and smoothing the process of screed application, which uses vibration. Known for its light weight and durability, it is typically made from aluminum or magnesium. It uses a mechanism consisting of a vibrating unit attached to the screed bar.
Common types of vibratory screeds are
- Truss screed
- Handheld screed
- Roller screed
Using the vibration mechanism helps settle the concrete by removing air bubbles. The usual length of the vibratory screen ranges from 4 feet to 20 feet in length. The major power sources are mostly gasoline, diesel, or electric motors to produce the vibration. It has a frequency range from 3000 to 5000 vibrations per minute, which ensures consistency and is suitable for larger and open areas.
Laser Screed
A laser screed is categorized as a high-tech tool used to level and smooth freshly port concrete. Laser technology is applied in this process, which consists of a laser transmitter, receiver, and a laser screed head. It serves as an ideal solution for large-scale projects that require higher precision and flatness.
The major types of laser screeds are:
- Walk behind screeds
- Ride on screeds
- Boom screeds
By utilizing a laser transmitter and receiver, precise leveling is always obtained. The typical length of this type of screed ranges from 10 feet to over 20 feet in length. It is majorly designed to withstand heavy use and harsh conditions. Compared with manual screeds, these are heavier and require support for transportation. However ,physical effort and manual labour are reduced by using this, making it more suitable in more open areas and large spaces.
Roller screed
Roller screed uses a spinning tube to obtain the final level and smooth surface. Its basic design consists of a power source under a rotating table that enables the smoothing process of the concrete. Aluminium or steel are the most common materials used. It increases durability, making it ideal for low-slump and pervious concrete applications.
Major types of roller screed are:
- Hydraulic screed
- Electric screed
- Gas screed
- Battery powered screed
Roller screeds are generally powered by electric, hydraulic means, and gas. Though it is best for heavy-duty industrial applications, it is also suitable for indoor uses. It stands out significantly due to no emissions. Proper handling is required to reduce the risk of injury as it is machine-oriented. It also releases some noise due to the motor. It is efficient for large-scale projects and requires significant storage space. It produces minimal vibration and reduces operation fatigue. The major applications are commercial floors, large slabs, and parking lots.
Conclusion
Screed is an indispensable element in the construction process. It provides structural benefits and contributes to the overall performance of flooring systems. Understanding the importance of screed is essential in improving stability. The selection of the appropriate type for specific applications. It can enhance building functionality, sustainability, etc. As the construction industry continues to evolve, the innovation and development of screeding techniques play a key role.