What's the difference between screed and concrete?
Concrete and screed are common resources for the construction industry all around the world, and there are some similarities between them. At their core, they are both made using the same basic ingredients: cement, water and aggregate. The aggregate can be stone, gravel or sharp sand.
But there are some fundamental differences in terms of their applications for construction. In simple terms, screed is used to create a top later surface on a concrete subfloor, while concrete is used for structural tasks.
How do screed and concrete differ physically?
As mentioned, both screed and concrete consist of a mixture of cement, water and aggregate. Where they differ is in the type of aggregate that is added to the mix.
With concrete, more hard core aggregates like gravel are added. The stones involves are usually no more than 20mm in size, but they add strength and durability, as well as workability. These properties make the resulting material suitable for structural work, with a coarser mixture.
For screed, the aggregate used is not as coarse. It tends to involve sand and cement mixtures. With the addition of very fine, sharp sand, where the maximum grain size is around 4mm, the cement has a different texture. It is finer and more tightly packed, giving it a better finish when applied as a surface layer on top of a concrete floor.
Is there a visual difference between concrete and screed?
You can see the difference between concrete and screed. As mentioned, the texture of concrete is rougher due to its more coarse, hard core aggregates. Even the untrained eye will be able to see the larger pieces of gravel or stone in the cement mix.
Screed has an appearance more like mortar with its finer grains. This is why it is better suited to internal applications. The resulting surface will be smoother in appearance, and though it is rough the finish is fine once the hard-packed wet sand has set.
How thick should concrete or screed be?
Concrete is typically laid thicker than screed. The recommended thickness for domestic use is at least 100mm, and as much as double that for applications where there will be heavy use.
The thickness of screed usually ranges between 50mm to 100mm. The recommended thickness of a layer of screed varies depending on the type of screed used, the predicted footfall, the type of location and the required finish.
What are the advantages of concrete and screed?
The main advantages of concrete are:
High compressive strength
Superb durability
Versatility
Non-combustible properties
Economical
Ability to batch to certain specifications and volumes
The main advantages of screed are:
Its smooth, bump-free finish when applied
Durability
Strength under high footfall
Insulating properties
What are some typical applications for concrete and screed?
Concrete is an excellent construction material because it can have an extremely high compressive strength. It is highly-durable, economical and non-combustible. Add in superb versatility and its safety for use in an enormous range of applications and it is a very useful material.
Concrete is commonly used for:
Driveways
Walls
Foundations
Roads
Patios
Flooring
Screed is not applied for structural purposes, but creates an excellent top layer when applied to a concrete floor. It can be applied before adding final floor coverings like wood, resin, floor tiles or linoleum. It is durable and able to withstand high footfall, protecting the underlying floor whilst maintaining a level surface throughout. It also has outstanding insulating properties, making it perfect for underfloor heating.
Screed comes in three main forms:
Bonded screed
Unbonded screed
Reinforced screed, which contains a metal or glass mesh for added strength
How are concrete and screed made?
Volumetric mixers are used to create concrete and screeds in exacting quantities and to precise specifications. The mixer's separated hoppers are loaded with separated aggregates, using fine aggregates for screed and coarser aggregates for concrete. This enables precision control over the ratios of the raw materials to create high-quality batches of the desired concrete or screed.
Mix designs can be tailored to specific needs by adjusting ratios and introducing admixtures. This gives the resulting material different qualities for different purposes. For example, you can get a more lightweight product or one with a higher compressive strength.
How can you tell if concrete and screed are high-quality?
Both materials come with a BSI certification to show that the supplier meets the strict quality regulations. You should always choose a certified, quality-assured supplier over a cheaper alternative. You will receive a better standard of service and the materials will always be reliable and safe for your application.
