CEBA has done extensive research and conducted many laboratory tests to aid in the development of an ideal mortar recipe. The importance of the mortaring system used must not be overlooked. Attentiveness and all care must be taken to ensure the maximum desired outcome is achieved through-out the build.
The most important functional properties of mortar are its consistency, its durability and its ability to bond with the masonry units. All of these can be significantly affected by workmanship and site practices.
AS 3700 requires that mortar provide adequate workability, appropriate durability and the ability to impart to the masonry the required compressive and tensile strengths. The standards are based on an expectation that all masonry will have a characteristic flexural tensile strength of not less than 0.2 MPa.
Mortar for our Earth Masonry Units
The amount of water to be added for workability is best left to the bricklayer. It is difficult to use a mortar that is too wet or too dry and, apart from the possible adverse effects of admixtures the most suitable mortar for the bricklayer will usually impart the best properties to the masonry.
During all stages of testing it was found that lime is not compatible with the clay colloids of our soil and so should only be used in certain proportion with cement, if at all. We have discovered that lime based mortars have an adverse effect to the tensile bond between the bricks and mortar and actually this bond decreased when higher proportions of lime were added to the point of no measurable bond at all.
Use of the same soil to make the bricks in the mortar has shown an increase in the bond between the two due to the harmonious chemical bond. Soil also increases workability, reduces the amount of cement needed, increases water retentivity during curing and aids in the appearance due to the similar color. CEBA supplies this soil screened down to 4mm.
Due to the high suction nature of earth bricks, wetting of the bricks prior to application is crucial for the tensile bond strength. Wet the surface of the brick with a renderer’s wetting brush and allow for the water to be absorbed completely before adhering the mortar. Applying the mortar whilst water is pooled on the bricks has also shown to decrease the bond.
Studies have shown a decrease in bond strength up to 50% for ever minute once the mortar has been placed on the wall before setting the brick. Good practice and workmanship is to lay the bricks immediately once the mortar is applied. Studies have also shown if a laid bricks bond is broken after the initial setting is complete (just a few minutes) then the bond is permanently compromised and must be removed and reapplied.