For people unfamiliar with the technical terms of the construction industry, concrete and screed might appear to be the same. But as we delve deeper into the nitty-gritty of their characteristic we observe some core differences. The overview of the comparison will be helpful for people who are confused about the material to choose when laying a terrace, building a foundation, or are just curious about the building materials that are used in a certain project. Before we continue discussing the differences between the two, there is one main similarity. The core ingredients of ready-mix concrete and screed are the same; cement, water, and aggregates. The differences arise in the percentage composition of the resultant products, the texture and the area of application.
Composition, Mix Proportions, and Physical Properties
Both the products are made of cement, water, and aggregates, but the mix proportions are varied to obtain either concrete or concrete screed.
Concrete is ideally composed of one part cement, two parts sand, and three parts coarse aggregates like ballast or gravel. Several variations and admixtures can also be added to the basic mix to increase the strength or comply with the weather conditions. The coarse aggregates are usually of 20mm diameter or less in size. This is important for durability, workability, and is suitable for structural work.
Screed, on the other hand, is a thin layer of cement paste mixed with finer sand or aggregates. They follow a mix proportion of one part cement and three to five parts of sand of size which is 1-4 mm washed sharp for leveling screed. When talking about concrete screed which needs to be heavy-duty, 25% of the 1-4 mm sand is replaced with 6-10 mm single sized aggregate to facilitate trowelling and increasing the density of the said screed.
Ready-mix concrete can be used as an ideal building material as it has the caliber to reach very high compressive strength. It is quite long-lasting and economical as well when used for small and large scale projects. Quality-assured concrete is known to be highly versatile and can be used to lay foundations, driveways, small home renovations like patios, walls as well as long-term projects like roads, pilings, drainage layers as well as car parks. Adding admixtures can enhance bonding and hydration which will lead to presenting a myriad of applications for concrete.
Whereas, concrete screed is not generally used in structural projects but rather as a top layer for a concrete floor. It is also durable and is considered to withstand the impact of heavy footfall and constant use. The main idea is to define screed by its function which is to improve the appearance of a pre-existing concrete floor, provide an even base for further applications like tiling, parquet, linoleum, or vinyl flooring. The last and most important function of a concrete screed is the complete addition of underfloor heating. The heating tubes are encased in screed concrete so that they are hidden and screed also acts as a conductor of heat.
Ready-mix concrete, as we all know, is distributed through line or boom pumps or through direct discharge from the ready-mix trucks. The coarse structure of concrete mandates specialist equipment for mixing as well as a skilled individual to complete the job with safety and precautions.
Screed has a fine quality that lacks aggregates and therefore can be applied easily and evenly using a trowel. Some other methods that are considered useful for the distribution of the cementitious screed are pneumatic pump or forced action mixer whereas anhydrous screed is distributed through a worm or grouting pump.
Summary of the Differences Between Concrete and Screed
So far, it is clear that the basic chemistry for both the products is the same while having minor differences in physical appearance, composition, and texture. They have completely different applications where ready mix concrete is used for structural integrity and screed is used as a layer for even and smooth finish. The screed can be of different types like concrete screed, pre-mix screed, or anhydrous screed and is selected depending on the job at hand. Also, there is a difference in the mode of application of concrete and concrete screed which is a significant factor. Both have individualistic properties which can be modified using admixtures like silica in concrete and a synthetic resin or mastic asphalt in the screed. These conclude the major differentiating factors between the two materials.