Sandberg can assist with screed testing, specification compliance and has extensive experience of assessing the quality of screed and in carrying out failure investigations. Techniques available include:
The adhesion can be examined qualitatively by tapping the surface with a rod or hammer.
When a quantitative answer is needed, the method given in BS EN 13892-8 for determination of bond strength of laboratory specimens is usually adopted.
As part of a site investigation, screed should be examined to determine that they have not lifted by a visible or measurable amount at joints or cracks that might lead to fracturing under loading. If the screed has cracked then site records of the crack pattern are important in assessing the cause and significance of the cracking.
In-situ Crushing Resistance
In-situ crushing resistance testing is carried out to assess compaction using the BRE Screed Tester Apparatus. The test method consists of subjecting the surface of the screed to four consecutive blows from a 4kg (or 2kg) weight dropped vertically through a height of 1m onto a foot 500mm² in area and then measuring the depth of indentation.
Slip resistance of the final floor finish is measured using the Pendulum Tester. The apparatus gives a slip resistance value by sweeping the test surface with a rubber slider on the end of a pendulum.
Abrasion (or wear) resistance can be measured in-situ using a machine with three hardened steel wheels rotating over a ring-shaped area for a fixed number of revolutions under a standard load. The depth of wear within the ring pattern is measured and used to indicate the wear of the floor. The test method was originally described in an appendix to BS 8204-2 but can now be found in BS EN 13892-4.
Screeds can take many months to dry out and it is extremely important to determine the moisture content of a screed accurately prior to the application of further floor finishes. Failure to determine that the screed has sufficiently dried prior to application of a damp proof membrane or a vinyl floor covering can lead to problems at a later stage. Sandberg can determine the moisture content of screed on-site using a probe to measure relative humidity at depth in the screed or using a hygrometer to measure the relative humidity of a pocket of air entrapped between an impervious thermally insulated housing and the surface of the screed. The latter test is the method detailed in BS 8203 for resilient floor coverings. Furthermore, samples can be removed from site and then the moisture determined in the laboratory.
Samples can be taken for a range of laboratory tests including moisture content, visual assessment of compaction and mixing and analysis to determine mix proportions. More information can be found on our Screed Analysis page.
General information about screed
Screed is defined in British Standards as ‘a layer of material laid in-situ, directly onto a base slab, bonded or unbonded, or onto an intermediate layer or insulation layer, for one or more of the following purposes:
- To obtain a defined level
- To carry a final flooring
- To provide a wearing surface
Two terms are used in connection with this:
Levelling Screed: this is used to form a flat level surface on which another flooring is laid.
Wearing Screed: this is known as ‘granolithic’ or ‘high strength concrete’ topping.
In the past ten years, several standards have been revised to accommodate the use of new materials and to align with European standards. The key standard is BS 8204 ‘Screeds, bases and in situ floorings’. This is actually a Code of Practice and as such provides guidance and recommendations – it does not specify requirements. Each Part has recommendations for testing, although, other than checks for level and surface regularity, other testing is normally only made when there are project specified requirements or the quality of the screed is in doubt.
For more information contact our in-house expert: