Is Screed Testing Really Necessary?

April 2015
Taking a sample for a moisture test

Taking a sample for a moisture test

All screeds must be protected from direct traffic, impact, friction, and water ingress. Though some fast-drying screeds allow for light-foot traffic as early as 12 hours from the installation, they still need to be protected in order to stop direct impact and wear damage.

From polypropylene mesh and corrugated plastic to permeable sheeting, there are many forms of temporary screed protection that can be used to prevent damage to newly laid screeds. To choose the right type of temporary protection, specialists consider three main aspects: 1) site conditions; 2) traffic; 3) length of time a surface needs protection before the final floor finish is installed.

Selecting the right form of screed protection is very important. Choosing a product that is not fit for purpose may require screeders to replace the floor protection more frequently, which will result in higher overall costs and more time needed to complete the project. The wrong product may also affect the overall screed performance or damage the screed it was originally supposed to protect.

Once screeds have dried optimally, they should be tested. Why? Because there has always been – and we guess, there will always be – a need to test screeds to prevent flooring disasters. Whilst a good screeding contractor has several screed repair “aces” up his sleeve, repairs can be costly and time consuming, especially for a large construction company working on big, expensive projects.

To ensure that screeds comply with project specifications in relation to strength, flatness, levelness, and moisture before laying the final floor, screeders use the following testing methods:

Calcium Carbide Test

This method implies placing a sample of screed, crushed into a powder and mixed with calcium carbide, in a special cup provided with a lockable lid. The chemical reaction between the moisture in the screed and calcium carbide results in gaseous acetylene, whose pressure is measured with a pressure gauge. Moisture content in screeds can be calculated based on gauge readings.

moisture test result

Laser Level Surveying

The laser level is a tool utilised to measure departure from the datum level. The tool consists of a laser beam projector complemented with mirrors and prisms that collect the beam of light, pointing it in the direction chosen by the specialist. The beam of light projects a visual line, enabling specialists to measure the deviation of the screed surface from the agreed datum level. More advanced tools, such as rotary laser levels, can spin the beam of light 360 degrees, allowing for more accurate readings.

Surface Regularity Tool

Surface regularity (SR) testing is used to verify the flatness of screeds. The test consists of using a 2m long straight edge, laid directly on the floor. The gaps between the straight edge and screed surface can be measured by using a feeler gauge. Acceptable deviations are divided into three distinct surface regularity classes, such as SR1, with gaps that should not exceed 3mm in high standard floors; SR2, with gaps of maximum 5mm in normal standard floors; and SR3, with gaps up to 10mm in utility standard floors.

BRE Drop Hammer Test

The BRE Drop Hammer test is used to check the soundness of screeds and their future performance in service in relation to the stresses and loads expected. To perform the test, specialists use a 1m long, cylindrical guide rod attached to a case-hardened steel anvil, placed on the floor. An annular weight of 2kg or 4kg is then released, travelling along the rod and hitting the anvil, which transmits the impact to the screed. The weight is released 4 times consecutively; for accurate results, a total of 3 tests must be performed in every 20-25sq.m. The depth of indentation measured with a special gauge should not exceed 2.5mm in screeds meant to withstand light-foot traffic and 5mm in screeds that will be exposed to heavy traffic.

Drop hammer test result

Drop hammer test result

CSC Screeding is one of the few companies specialising in high-volume screed installation and testing. By training our staff, monitoring projects, and updating our equipment and technologies continuously, not only we have earned a reputation for providing the highest quality services to all our clients; we will also remain at the forefront of the screeding industry for many years to come.