MORTAR TECHNICAL BULLETIN - CHEMICAL TESTING VS SCRATCH TESTING -THE FACTS
Recommended test - Chemical Testing
Please note that Sharp & Howells is the only NATA accredited testing authority for both chemical and physical testing of mortar to AS3700.
There has been a spate of serious defects associated with poor bricklaying and brick cleaning practices in recent years in both residential and commercial properties. Several major brick wall collapses have also occurred leading to death and injury.
The greatest advantage of a chemical analysis is that it can be conducted during bricklaying on fresh mortar from the site. This is a great quality control tool for the building industry.
This test also identifies whether the bricklayer, the brick-cleaner or the raw materials are responsible for a “faulty” brickwork job.
We also conduct heritage-based testing of mortar and render for restoration work.
Scratch Test (Durability Test):
This test has serious limitations and flaws (in our opinion). Uneven bricks and rolled or raked joints. The scratch test is designed primarily for flush joint mortar and flat faced brick or blockwork.
The scratch unit is extremely operator dependent.
The Scratch test does not provide any material information about the mortar or what has gone wrong in cases where the mix performs poorly. Chemical testing is then required to identify this.
Very weak Mortar has been found to PASS the scratch test, this test cannot be used for upfront quality control testing. The test is best used as a back-up to chemical testing only.