A NON-DESTRUCTIVE TEST METHOD FOR ASSESSMENT OF CEMENT-SAND MORTAR QUALITY ON BLOCKWALLS FINISHES: A Short-Cut Method for achieving Acceptance Criteria

Abstract

Monitoring quality of cement-sand mortars used for plastering/rendering masonry surfaces has not been given utmost attention thereby adversely encouraging damp rising and other defects in walls. An attempt is made in this paper to propose a methodology for monitoring the quality of mortars using non-destructive testing method. It enables categorization of the quality of mortar mixes for making decision on acceptance criteria for short-term and long-term strengths of the composite mixture. Firstly, the Central Composite Design factorial experimental design (CCD) of the Response Surface Methodology was used, to design the mix for which compressive strengths at 28-day was obtained within the design domain considered. Secondly, a hardness test using the Mohs’ hardness scale was used on both the laboratory specimens and field tests on plastered walls of some selected housing estates. The method clearly exhibited defect patterns on the blockwall finishes which are closely related to the quality of the mix which also varied based on heights above ground level. The Mohs’ hardness test has proven to be a reliable non-destructive test method which can be used to reveal quality and categorization of cement mortar mix used on blockwall finishes. Consequently, the upper bound mix with ratio 1:4 cement to sand mortar remains a reliable mixture proportion based on the scale of hardness and strength performance both in the short-term and long-term values measured. This method would enable a reward system measurement/assessment on contractors and consultants on various building projects.