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. 

The foundation is key to a house’s stability and strength. The main types are strip footing and strap footing. Though they are similar, they have distinct differences, each designed for specific structural needs. Let us dive in and explore what each type is and its differences.

What is Strip Footing?

Strip footing is the most common foundation used for load-bearing walls. It consists of a continuous strip of concrete that runs under walls, which helps evenly distribute the building’s load to the ground.

Characteristics of Strip Footing:

• Continuous in nature: The foundation runs continuously in a strip under the walls.
• Supports load-bearing walls: This foundation is used primarily for walls that carry the weight of the building.
• Wide base: The base of the strip footing is normally wider than the wall it supports to help spread the load over a larger area.

Materials Used:

• Concrete: This is a very common material in strip footings. Its made from concrete and provides strength and durability through reinforcement.

Strip footings can provide uniform support in soils that are so stable and support the weight of the structure. They are also cost-effective and simpler to construct.

What is Strap Footing?

Strap footing is used when there are two or more columns that need to be supported but are too close to each other. In place of having individual footings for each column, a strap-a beam or concrete connection-joins the footings to transfer the load between them.

Characteristics of Strap Footing:

• Connected footings: The columns are connected at their footings via a strap beam.
• Used for uneven loading: The foundation can be useful in situations when there is uneven load distribution between columns.
• Prevents tilting: The strap beam equalizes the weight and prevents the tilting of the structure due to unequal load distribution.

Materials Used:

• Reinforced concrete: Like strip footings, strap footings are usually made of reinforced concrete.

Strap footing is used when the columns are close to property boundaries, where space does not allow independent footings for each column.

Differences Between Strip Footing and Strap Footing

When to Use Strip Footing?

Strip footing is suitable in areas where the soil can evenly support the weight of the structure. It is recommended for buildings with load-bearing walls, especially when the floor needs to be as simple and economical as possible. Since this is a continuous one, the load is dissipated over a large area, thereby reducing the intensity of stress on the soil.

When to Use Strap Footing?

Strap footing is typically used when columns are located near property boundaries and there isn’t enough room for independent footings. It is also useful when there’s uneven load distribution between columns, as the strap beam helps balance the weight. This footing type is more complex and expensive than strip footing but ensures better stability in specific conditions.

Advantages of Strip Footing

• Cost-effective: Strip footings are usually less expensive to build because they are less complicated in design.
• Even load distribution: The weight of the structure is distributed over a very large area, thus reducing the pressure upon the underlying soil.
• Easy construction: Since it is continuous, strip footings take less time in construct and are easier to build.

Disadvantages of Strip Footing

• Not suitable for unstable soil: If the soil is not strong enough, strip footing may not provide enough support.
• Requires more space: As strip footing runs continuously under the walls, it requires more space than other foundation types.

Advantages of Strap Footing

• Space-saving: Strap footings can be used when there’s limited space, such as near property boundaries.
• Prevents tilting: The strap beam helps balance uneven loads, preventing the structure from tilting.
• Supports multiple columns: Strap footings are ideal for structures with multiple columns that are close together.

Disadvantages of Strap Footing

• More expensive: Strap footings are more expensive to construct due to the additional materials and complexity.
• Complex construction: The connection between footings requires more planning and construction work, making it more complex than strip footing.

Conclusion:

Both strip and strap footings are vital in construction but serve different needs. Strip footings suit buildings with load-bearing walls on stable soil. Meanwhile, strap footings are for closely spaced columns or those near property lines. Knowing the differences helps builders choose the right foundation, ensuring safety and stability.

FAQs:

Think about it: every time you’re building something, like a tall tower of blocks, it’s important that everything sets in place so it doesn’t fall over. Well, the builders must face the same challenges when constructing real buildings. One of the major components of making the building safe and strong is something called a “strap footing.” Let’s find out what strap footings are, why they’re important, and how they work.

What is a Strap Footing?

Imagine building a tall tower of blocks. To prevent it from falling over, you need to ensure that the blocks on the bottom are spread out evenly. Similarly, strap Footing in construction ensures the building stands tall and doesn’t fall over.

What is a Footing?

Before trying to understand what strap footings are, let’s briefly understand what a footing is. A footing in construction is a particular type of supporting base that supports the very foundation of a building. Think of it like the foundation of a table. If the table’s legs are not sitting evenly on the floor, the table might wobble. Likewise, the footing helps make the building’s foundation sit even on the ground for stability and strength.

What Makes Strap Footings Special?

A strap footing refers to a type of footing that helps an individual distribute the weight of an entire structure over a large area. This especially will come in handy in cases where the ground one has decided to build on is quite weak or unevenly set.

Now, imagine trying to stand on a soft, sandy beach. If you just stand on one small spot, you may sink into the sand. But if you spread out by lying down, you will stay on top of the sand. That’s kind of what strap footings do for a building; they help spread the weight so the building doesn’t sink or settle unevenly.

Parts of a Strap Footing

Strap footings are made up of several parts:

1. Footing Slab: It’s a flat, thick layer of concrete slab that spreads out the weight of the building from the walls.
2. Strap: This is a beam or thick strip of concrete that connects two or more footings together. It helps distribute weight between different areas.
3. Foundation Walls: Sit on top of the footing and strap; they are the vertical pieces of the building that carry floors and the roof.

Why Use Strap Footings?

Here are some reasons why builders use strap footings:

1. Weak Soil: When building on unstable ground, strap footings help distribute the weight over a larger area of a building. This reduces the chances of the building sinking into the ground.
2. Uneven Ground: In cases of uneven ground, strap footings are used to hold the building steady since straps connect different parts of the footing for balanced weight distribution.
3. Heavy Loads: For heavy buildings, such as large warehouses or high-rise apartments, strap footings share the weight evenly so that there is no structural collapse of the building.

How are Strap Footings Built?

Building a strap footing involves several steps:

1. Planning: Planning is a step in the process whereby builders decide where footing and straps will sit. They use specific tools and plans to ensure everything is aligned just right.
2. Excavation: This process involves digging into the ground in which the footing will come into place – digging a large hole in readiness for the base of the building.
3. Setting Forms: Builders put wooden or metal forms into the holes. These forms mold the concrete as it is curing to shape.
4. Reinforcement: These are steel bars or mesh set inside the forms. This will give the concrete added strength and prevent it from cracking.
5. Pouring Concrete: A method in which concrete is poured into the forms. It is then allowed to cure for a few days. Just like you would let a cake cool down so you can take it out of the pan.
6. Removing Forms: With the hardening of concrete, the forms are removed, giving the site solid footings and straps.

Benefits of Strap Footings

Strap footings are important for several reasons:

1. Stability: They give buildings stability even on weak or uneven ground. It prevents the building from settling or tilting over time.
2. Durability: Strap footings distribute the weight of a building over a wide area, reducing the possibility of cracks and other structural damages that may result from unequal weight distribution.
3. Safety: While strap footing secures the building, it also keeps all the occupants of the building safe.

Examples of Where Strap Footings are Used

Strap footings are used in many types of buildings. Here are a few examples:

• Large Warehouses: These will carry heavy loads. Sometimes, the land where the warehouses are situated is not of total potency. The strap footings keep them firm and intact.
• High-Rise Buildings: High-rise buildings require highly strong footing structures if their weight is to be supported. Strap footings are useful in distributing the weight of a building evenly.
• Residential Homes: Strap footings are a very good solution to keep homes safe and strong in case the soil may not be strong or if the ground is uneven.

Conclusion

Strap footing supports usual building loads and distributes them in such a way as not to have concentrated binding forces. These types of footings, especially, will serve their purpose where lands contain weak or unevenly distributed soils and buildings that bear significant loads.

Spalling refers to the breaking off of pieces of concrete from a surface. Just think of walking on a sidewalk and noticing that sections have chipped away or crumbled. Visually, that is what concrete spalling might look like, and that could also happen to buildings, bridges, and other structures. But is it dangerous? Let’s find out.

What is Spalling in Concrete?

Concrete is a dense combination of cement, water, and other added ingredients, like sand or gravel. Over time, it may degrade due to improper care of the concrete. This is what they call spalling-when the breaking up of concrete is already obvious. First, tiny cracks or flakes may appear on the surface, and if this condition gets worse, it may result in the chipping off of substantial parts of concrete.

What are the causes of concrete spalling?

Some things might let concrete to spall:

1. Water: If water seeps into the concrete, it can rust the steel bars inside it. The expansion of these bars due to rust is responsible for causing the concrete to push outwards and thus results in the breaking of the concrete.
2. Cold Weather: In those places where the temperature falls considerably, water inside the concrete freezes and then thaws as it warms up. That kind of freezing and thawing causes cracking and spalling of concrete.
3. Poor Construction: Sometimes, concrete is mixed or poured inadequately. A mix applied with too much water or fails to dry out completely will eventually weaken and, after some time, spall.
4. Chemicals: Direct attack by strong chemicals, such as from ice-curing salts used on highways, can cause the concrete to deteriorate and spall.
5. Too Much Weight: When too much weight is applied to concrete that was not supposed to bear weight, it cracks and spalls.

Recognising the Signs of Concrete Spalling

• Flaking or Chipping: Visible signs of flaking or chipping on the surface of the concrete. Spalled areas often have a rough, uneven texture.
• Exposed Aggregate: When spalling occurs, it can expose the aggregate within the mix of concrete, therefore leaving a pitted look on the surface. 
• Cracks and Gaps in Concrete: The surface of the concrete should be checked for cracks and gaps within. Spalling is usually accompanied by the formation of cracks, which could deteriorate further or cause other hazards.
• Discolouration: Spalled areas can become discoloured, showing concrete that has weakened or been damaged.

Why is Concrete Spalling Hazardous?

Concrete spalling may not sound serious, per se, but workability can become hazardous for several reasons:

1. Weakening Structures: When spalling occurs in concrete, it tends to weaken the structure from which it is a part. What that means is the building, the bridge, or the structure must not be as strong, and that could be dangerous.
2. Falling Pieces: If large fragments fall off, they may hurt people or even damage anything that may be below them.
3. More Water Infiltration: Cracks and openings due to spalling can let more water in, exacerbating the problem and causing further damage.
4. Costly Repairs: The repairs that involve repairing spalled concrete are expensive, especially if the damage is extensive. Sometimes the costs accumulate when this is left unaddressed early in the process.
5. Unsightly Appearance: While less dangerous, spalling affects buildings and sidewalks by giving them the look of age and deterioration, which could be a worry to property or building owners.

How to Prevent Spalling of Concrete

There are ways to stop spalling of concrete or at least retard its pace:

1. Good Construction: Putting concretes properly mixed and correctly poured in the first place is the original step. The application of an appropriate quantity of water combined with the proper drying time can avoid spalling.
2. Regular Checks: Inspecting concrete surfaces regularly can help catch spalling early before it gets worse.
3. Keep Water Out: Sealers can prevent water from getting in and damaging the concrete with resultant spalling.
4. Utilise Superior Materials: Using materials that do not corrode or rust as easily can help maintain the strength of the concrete.
5. Allow for Movement: Putting in special joints at large areas of concrete allows the concrete to expand and contract without cracking.

How to Repair Concrete Spalling

It is important to then fix spalling that has already started to avoid bigger problems:

1. Patching: Small spalled areas can simply be patched up with new concrete. This is often limited to cleaning the area and refilling the same area with fresh material.
2. New Layer Addition: In the case of heavy-area spalling, the laying of a new concrete layer can be done over the damaged portion.
3. Epoxy Injection: If the spalling has caused cracks, epoxy can be injected to fill gaps and hold concrete together.
4. Treatment of Steel Bars: Potentially, spalling occurred because the steel bars rusted. In this respect, they may require either treatment or replacement to stop the damage.
5. Replacing Concrete: If the damage is too severe, the old concrete might need to be removed and replaced with new concrete.

Conclusion

Concrete spalling refers to the breaking of concrete apart, which becomes dangerous if not corrected. It may weaken buildings and other structures, cause pieces of concrete to fall, and can be so expensive to repair. On the other hand, good care in maintenance and repairs on time can reduce such damage to the concrete and keep structures safe and durable.

FAQs