Some Concepts of Dry Mortar

At present, the application of dry mortar is very wide. However, in the process of application, some production and use units are confused about some concepts and performance indicators of dry mortar. In this paper, we analyze these confused concepts as follows, and hope you can learn from them.

Viscosity and Strength

The higher the viscosity, the higher the strength. Strength usually refers to the physical property indicator of mortar after curing. Viscosity usually refers to the state of mortar after mixing and is an indicator of the construction process. Viscosity and strength are not necessarily related. There are more factors affecting the strength, and the viscosity is usually regulated by the viscosity of cellulose ether. The lowest viscosity of cellulose ether is in a few hundred, and the highest viscosity can reach 200,000. Cellulose ether is selected according to the different uses of the product, and the viscosity of cellulose is not necessarily related to the strength.

Bond Strength and Compressive Strength

Bond strength is the maximum bonding force of mortar acting on the substrate. Bond strength contains shear strength and tensile strength. Tensile strength is the ability of the mortar surface to resist the tensile force acting perpendicular to the surface; shear strength is the strength measured by applying a parallel force.

Compressive strength is the maximum value measured by applying pressure as the mortar is broken, which is generally the cohesive strength of the mortar. High bond strength does not necessarily mean high compressive strength, and low compressive strength does not necessarily mean low bond strength.

The two concepts are easily confused in two main aspects: one is the selection of admixtures. The test indicator of admixture (early strength agent, antifreeze, etc.) in concrete is compressive strength. For example, antifreeze is to test the loss rate of compressive strength of concrete at low temperature. The main test indicator of dry mortar products is bond strength. Some admixtures in mortar are selected with emphasis on bond strength. For example, the focus of the early strength agent for dry mortar is how much the early bond strength of the mortar increases, not how much the compressive strength increases, which is very critical. According to our experience, some concrete admixtures applied directly to the mortar will lead to a very large reduction in the bond strength of the mortar, which plays a negative role instead.

Second, wrongly judge the bond strength by compressive strength index. The standard of tile bonding mortar is not required for compressive strength indicator. And some people believe that the bond strength of tile bonding mortar with low compressive strength is low. This is because the bonding performance of the tile mortar is significantly improved after mixing with polymers such as re-dispersible emulsion powder, but it will reduce the compressive strength.

Waterproof and Water Resistant

The concept of waterproof and water resistance is mainly defined in putty products. Water resistance means that the performance of the material does not change significantly in water environment. Waterproof means that water cannot penetrate. Putty is only a leveling material before painting and does not and should not have the properties of a waterproof material.

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