What is Screed?
Screed is a thin, top layer of material laid over a concrete base. It is made from a combination of cement, water and sharp sand. Screed is used to make a surface smoother and more stable in preparation for the addition of a final floor layer.
While not as strong as the concrete subfloor it covers, it increases the floor’s durability and improves its appearance. It’s ideal for covering underfloor pipes and providing a level surface for various flooring, including laminates, tiling, vinyl, carpets, floorboards and stone.
What are the different types of Screed?
There are three main different types of screed: bonded, unbonded and floating. The type of screed you use depends on the type of concrete base and your requirements. Each type has its specialist uses, but you need a good foundation to get the most out of whatever type of screed you use.
In addition to the types of screed outlined below, reinforced and wearing screed are used for specific applications. Reinforced screed uses polypropylene, glass fibres or a metal mesh for extra strength. Wearing screed is the toughest type and can be used as a final top layer without having to add additional flooring like carpets or tiles. This type of screed is designed for maximum wear and tear and often requires additional aggregates to make it more durable. You can find wearing screed in industrial settings, such as warehouses and power stations, where there is a need for inexpensive, robust flooring.
Here are more details about the original three different types of screed.
Bonded Screed
Bonded screed is directly connected to the concrete subfloor (substrate) with an adhesive. It requires making the surface of the concrete rough and using a bonding agent. It is ideal for thinner applications where heavy loading is expected and comprises a thickness of 15mm to 50mm, but 25-40mm is optimum. Before bonding screed you need to prepare the area by thoroughly cleaning it.
Unbonded Screed
Unbonded screed is laid on top of a PVC/damp-proof membrane separating it from the concrete substrate. It’s an excellent choice in buildings where damp presents a serious problem. With unbonded screed, it’s important to monitor the drying process because if it dries too fast, the edges of the screed can warp. This type of screed is ideal for thickness that exceeds 50mm.
Floating Screed
Floating screeds are unbounded and generally added to an acoustic or thermal layer. Since it is unbounded, we recommend you add a membrane below or above the insulation layer, particularly if it has silver foil as a backing. Floating screed requires a minimum thickness of 65mm or up to 75mm for heavily loaded floors.
How is Screed Used?
Uneven floors can have problems with structural integrity when a top floor layer is installed, so laying screed helps to prevent these problems. Screed is used to protect the concrete subfloor, while withstanding the impact of constant use and heavy footfall. It also has excellent insulating capabilities, which make it a popular choice for floors with underfloor heating systems.
Screed is made from a 1:3 or 1:4.5 ratio of cement to sharp sand. A self-smoothing or ‘levelling’ screed is usually thinner in depth than a ‘wearing’ screed, which adds more to the structural performance of the floor. Before laying screed, prepare the area by clearing it of all debris. Once laid – and depending on the different types of screed – it takes between 16 hours and two days to cure and dry, but you should leave it as long as possible to achieve maximum durability.
The amount of screed you use depends on factors such as the measurements and unevenness of your floor and the purpose of your project. A screed calculator should help estimate how much you need.
What Projects Does Screed Work Best For?
Screed is most often found in commercial units, hospitals, schools, housing and airports, but it can be used in any setting with internal flooring. It is considered one of the best materials for underfloor heating systems. Screed is also good for sound-proofing residential properties between floors and and other buildings prone to noise transmission.
Screed can be used as the final layer of flooring for customers who want to achieve an industrial aesthetic. You can add a decorative finish by directly painting screed or stamping it with a pattern during the curing process.
What’s the Difference Between Screed & Concrete?
Concrete is coarser than screed because it uses larger aggregates and a different grade of cement. You can see bits of gravel and stone in a concrete mix, but screed has a finer more mortar-like appearance. The process of making concrete and screed is similar, but concrete aims to provide strength and stability while screed creates a smooth top layer. This is why concrete needs bigger, denser aggregates to achieve much higher levels of durability and longevity. Screed is usually optional, but its smooth consistency helps to correct uneven bases and improve their appearance. For more information on the differences between concrete and screed, read our blog post on ‘The Differences between Concrete and Screed Explained’.
Rely on Axtell for Screed Services
With more than 20 years of experience in the concrete industry, our team at Axtell are experts in mixing and applying screed. We create, supply and install the highest quality ready-made screed for a range of domestic and commercial customers across Surrey, West Sussex and Hampshire. Just use our screed calculator to estimate the amount of screed you require. We can provide flowing screed and self-levelling screed. Our concrete screed pumping service will place the screed exactly where you need it.
Visit our How To section for advice on laying liquid floor screed.
Explore our full range of screed services and find out how Axtell’s screed delivery services can meet your project requirements. Alternatively, contact us to speak to a member of our friendly team if you’d like more help understanding whether you need concrete or screed for your project.
