Still wondering how to get the perfect screed? Consider compressive and flexural strength

January 2015

Bond to the right Screeding contractor for your project

In order to make sure that screeds will deliver appropriate support in different applications, screed manufacturers and screeding contractors are required to test not only the materials they use to formulate screeds, such as cements, aggregates, and admixtures, but also the final mixture. Why are compressive strength and flexural strength so important? Read on to find out.

Compressive strength (C)
Defined as the capacity of a structure or material to withstand loads that tend to reduce size, screed compressive strength is usually measured by breaking screed specimens in a compression-testing machine. The fractures that eventually occur during the test are considered the limit for the screed compressive load, indicating whether or not a certain type of screed is appropriate for particular applications.

Screed manufacturers are required to declare the compressive strength class for each type of screed they produce. The letter “C” from “compressive” is followed by a number in accordance with the British Standards code of practice. Compressive strength classes for screed materials range from C5, C7, C12, C16, C20, C25… to C80, the latter being appropriate for heavy duty applications.

Flexural strength (F)
Flexural strength, or bend strength, refers to the tensile strength of screeds and defines their ability to resist deformation under loads. In practice, flexural strength is measured by loading screed beams that are three times thicker than the layer of screed installed. However, the best measurements are done in laboratory settings, where technicians determine the highest stress that screeds can withstand without the risk of fracture.

As with compressive strength, manufacturers must communicate flexural strength classes for each type of screed produced. The flexural strength classes for screeds range from F1, F2, F3, F4, F5….to F50, the last one being typically recommended for heavy duty projects.

With over two decades of experience in floor screeding and under-floor heating, BuilderScreed experts offer a wide range of screeding services. They also work closely with numerous screed manufacturers to help independent builders keep abreast of the latest developments in the screeding industry. By visiting our BuilderScreed website, you will have the chance to browse through our extensive collection of articles, tutorials, and guides; by contacting us, you will receive answers to all of your queries along with free, no-obligation quotes upon your request.

BuilderScreed is a division of CSCScreeding Ltd.