Mortar Testing

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 practices in recent years in both residential and commercial properties. Several major brick wall collapses have also occurred leading to death and injury.

Badly eroded and soft mortar is not uncommon due to poor bricklaying and brick-cleaning practices.

Chemical analysis of Mortar is used to identify the mix proportions of a mortar and can be conducted both during the laying of brickwork and many years after completion. One of our oldest structures tested was a home built in the 1840's in Werribee. 

This test separates the Cement, Lime and Sand contents of the mortar, and identifies whether plasticizers or thickening agents have been used, the types of Cement and the Sand used. It also identifies contaminants such as excessive brick cleaning acid and the presence of waterproofing chemical additives.

The test confirms compliancy of masonry with the BCA/NCC (Building Code of Australia) and AS3700 (Masonry Code).

It also provides a check on the mix used by the bricklayer in cases of dispute where poor workmanship or unsatisfactory performance is suspected.

We often act in VCAT hearings or legal proceedings. Several major builders use this test for Quality Control purposes- ask your builder if they conduct QA/QC testing.

The results of testing are matched against acceptable criteria- for example a 1: 1 : 6 mix means 1 part Cement: 1 Part Lime and 6 parts Sand.

The greatest advantage of a chemical analysis is that it can be conducted during bricklaying on fresh mortar from the site. This allows any problems with the mix to be identified before completion of the brickwork. Changes to technique, materials, or mix rates can then be made immediately. 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- this allows faithful matching of the existing work.  

Non- Preferred Test: Scratch Test(Durability Test):

This is not our preferred test due to the limitations of the test and flaws in the methodology (in our opinion).

The scratch tester was not designed for use with uneven bricks which are frequently encountered on residential sites.

The scratch unit has not been designed for rolled or raked joints - Many bricklayers strike the final surface of the mortar which compresses the surface material and can give a firm surface, hiding soft mortar below. The scratch unit is designed primarily for flush joint mortar and flat faced brick or blockwork.

Low test results are often found which incorrectly Passes a mortar that should in fact fail.

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 anyway. 

Mortar with compositions as weak as 1:15 have been found to PASS the scratch test, yet this mix ratio is well outside any acceptable tolerances for any type of brickwork and could lead to collapse of the brickwork.

The scratch tester cannot be used until at least 7 days after construction and preferably 28 days after completion- this limits the application for use in quality control applications. By then it may be too late to rectify faulty workmanship.

AS 3700 states that tests conducted using this test after 12 months construction are to be considered as “guidance” value only and cannot be relied upon.

In some ideal circumstances it can be used to confirm or validate an analysis result- that is why we offer it as a back up to our major chemical testing processes 

Contact Information

Contact us today for all your chemical analysis and testing needs.

41 Greenaway Street
Bulleen
Fax: 03 9850 9733
Victoria 3105
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