BRE Drop Hammer Test

Overview

The BRE Drop Hammer test is done to identify areas of a screed that may not be strong enough to withstand the expected load or traffic.  The test is increasingly being used by screeding contractors as a routine procedure for ensuring the quality of the screed mix, and as a precautionary quality check to detect any inadequacies in mix proportions, mixing or compaction of the screed.
It is also used in the investigation of screed collapse – to determine the extent of weakness of the screed.
How it’s performed
An annular weight (4kg for category A and Band C screeds – bonded and unbonded, and 2kg for category C – floating screeds under 75mm) is dropped from a distance of 1m down a rod, to strike the collar of an anvil – the face of which is in contact with the screed surface.  The area of contact is 500 sq.mm. After four consecutive drops of the weight in the same position, the depth of the resulting indentation is measured to determine the ability of the screed to carry traffic. Measurements are made to the nearest 0.1mm using a depth gauge.
A minimum of three tests is recommended for areas of 20 sq.m or less, whereas for areas greater than 20 sq.m the recommendation is to go for a minimum of three tests per 20-25 sq.m. The tests are to be carried out at an interval 3-5 m in corridors. But the test positions are to be kept random, but including vulnerable areas adjacent to bay joints, cracks and in doorways.
Acceptance Limits:

Category Description Maximum depth of indentation (mm)
Bonded and Unbonded Screeds Floating Screeds
Category A Screeds subjected to heavy traffic 3 3
Category B Screeds subjected to heavy traffic – e.g.) Trolleys in public areas 4 4
Category C Screed for light foot traffic – e.g.) Domestic use 5 2.5 ( use 2kg weight only)

When is it done?
It is advisable to carry out a BRE Drop Hammer Test in case of any suspicions of inaccuracies regarding the amount of water in the screed mix or inaccuracies in mixing and compaction of the screed – as all these can affect the sound ness of the screed. Other signs to look out for are:

  • Crumbling/friability of screed
  • Poor screed colour
  • Patches of broken down screed below vinyl

The BRE Drop Hammer Test can is also used as a precautionary quality check to ensure the set and hardened screed will be strong enough for its intended use.
The test is done when the screed is at least 14 days old. However, as the screed continues to gain strength up to 28 days, it is best to carry out the test after 28 days of installation.