While placing screed on a concrete floor is not compulsory, it is absolutely recommended in order to level uneven floor surfaces and steer clear of bumpy floors.

What is Screed? What is it used for?

Screed and Concrete

Everyone knows what concrete is. Being one of the most common and abundant construction materials, it is used to construct almost every other structure, from foundations to walls and driveways to patios. Its affordability and availability make it the preferred choice for construction projects of all sizes. Screed, however, is more specific, and few people know about it.

What is Screed?

Common people have seldom heard of screed. Those who have heard the name often confuse it with concrete, and they are not to be blamed because it is a thin layer used to form a coating over any base floor. Just like concrete, it is made from different aggregates and materials, such as cement and sharp sand. The purpose of the coating is to create a smooth finish, but it also has other properties, such as high insulation. The preparation of both screed and concrete are very much similar, but there are a few differences, including:

  • The aggregate size may be different.
  • A different grade of cement is used.
  • The consistency of the mix is different.
  • The finish quality is different.
  • They are both used for different purposes.

What’s the Difference between Screed and Concrete?

Concrete has a coarser mixture and appearance compared to screed. Larger and harder aggregates are used to prepare concrete with high longevity and durability. A much smaller volume of aggregates is used when preparing screed, which is why it is smoother. Screed does not have the same durability as concrete because that is not the primary purpose of screed. It gives a finishing touch to concrete slabs used in residential and commercial flooring to create a smooth surface so that tiles, carpet, resign coatings or wood flooring can be installed. Harder and more reliable screed is used for high-traffic areas such as restaurants and universities. It is also used for covering thermal and heating insulation systems such as underfloor heating.

Types of Screed

Screed is highly versatile and adaptable. It can be prepared for meeting specific requirements but is typically ready in floor variations:

  • Underfloor Screed

Underfloor screed is the most common type used in residential and commercial properties. It can be liquid as well as solid. Liquid screed is highly effective when it comes to insulating underfloor heating systems.

  • Floating Screed

Floating screed is also primarily used for covering insulations. They are often used along with damp-proof agents to create a layer between the screed and the insulation.

  • Bonded Screed

Screed can also be installed by bonding with concrete. The bonding is achieved with the help of a primer or bonding agent.

  • Unbonded Screed

Unbonded screed is used to separate the concrete base and the screed later with a damp-proof membrane in between.

Should You Screed Your Floor?

If your floor is uneven or rough and you want to install ceramic tiles, wooden flooring, or a carpet, it is best to apply screed on your floor first. This will smooth the rough surface and create a uniform layer which will improve the appearance of your flooring material and also prevent it from damage. You can also use screed to cover underfloor heating and improve your heating efficiency.

The Process

For screed to provide its benefits, it should be given sufficient time to dry. The drying time depends on several factors, such as the surface it is applied on and how thick the screed layer is. It usually takes two days to completely dry and become usable. At times, additives are used to reduce the drying time, which can go as low as 16 hours. If the location where the screed is applied will be experiencing high traffic, it is highly recommended that the drying time be increased to one week. It should be noted that any heavy pressure before allowing the screed to dry can seriously affect your floor. It should also be noted that the total time screed will take to reach its peak durability is one month.

  • Adding Final Flooring to Screed

All cementitious mixtures, such as screed, shrink during the curing stage. Therefore, whatever flooring you wish to install, the installation process should start after the screed has completely dried. The best time period is one month. Early application may result in damage or cracks in the top floor layer.

  • Levelling Screed

It is essential to level the screed properly before installing any flooring. Construction workers often use a wooden float to create a uniform layer. Self-levelling floor screeds are also available in the market that you can select. This option yields quick results with the same consistency and uniformity.

  • Using Screed as a Final Flooring Finish

People often choose screed as the top layer of their flooring. This type of application can often be seen in commercial areas, including shop floors, restaurants, and universities. When appropriately applied, screed will look elegant and aesthetic.

Site-Mixed or Ready-Mix Screed?

When using screed, builders and contractors face the question of choosing between ready-mix or site-mixed screed. Screed failure has become a common issue in the recent past, so contractors should be extra cautious. Let us look at some of the features of both ready mix and site mixed screed.

Ready-mix Screed

  • Convenience: It is more convenient as the required volume and the specifications can be easily prepared in batches.
  • Quality Control: Ready mix screed must comply with BS EN Standards BS EN13813, and strict quality measures must be ensured for compliance.
  • Price: They cost more than other screed types.
  • Lack of Flexibility: Retardants are often added to ready mix screed to prevent it from getting hard during transit. Longer delays can make your screed useless. If there are any errors, they cannot be reversed.
  • Workmanship: Screed specialists often prefer site mixing as ready-mix screed does not offer flexibility. Due to their cost and restrictions, they are used mainly by beginners, reducing the application’s quality.

Site-Mixed Screed

    • Flexibility: Site mixed screed allows considerable freedom to choose and change specifications as they are mixed on the site. Additives and accelerators can also be added to reduce drying time, something absent from ready mix screed.
    • Pricing: Site mixed screed is available at highly competitive pricing and is less expensive than ready-mix concrete.
    • Skilled workmanship: It is used mainly by screed experts because of its freedom. The experts, therefore, give a much better show of workmanship.
    • Quality: Maintaining quality in site mixed screed can be challenging as there is no controlled environment.

Liquid Screed and Its Benefits

Liquid screed is one of the most underrated types of screed. It has many benefits, which are discussed below:

  • Easy to install

Liquid screed application is many times faster than other types of screed applications. It also requires much less labour.

  • Greater insulation

Liquid screed offers excellent insulation than other methods. Only a thin layer of liquid screed is enough, giving you more room to install thicker insulation. The thicker the insulation, the lower the heat loss, and the more energy costs you save.

  • Quick to dry and cure

The thinner application implies that the drying time is considerably less than other screed applications. Therefore, liquid screed application is highly suitable for projects that need to be finished quickly. After just one day, you can walk on your screed application without fear.

  • Improves the efficiency of underfloor heating

Underfloor heating uses hot water pipes or electric cables to heat your floors. The space between the pipes/cables and all other voids will cause heat loss if not properly insulated. Dry screed will fill up more space, and you will have less space for insulation. However, liquid screed application will allow you to use thicker insulation which will improve the efficiency of your underfloor heating system.

  • No shrinkage

Liquid screed does not shrink and therefore does not cause any cracks. It results in a much smoother and more reliable finish.