What factors affect bonding strength of mortars

Dry mixed mortar has been widely used at present. There is a bond strength index in dry powder mortar. From the point of view of physical phenomena, when an object wants to attach to another object, it needs its own viscosity. It is the same for mortars, Cement + Sand mixed with water to achieve initial bond strength, and then cured by additives and cement to finally achieve the desired bond strength of the mortar. So what are the factors that affect bond strength?

Effects of construction additives

Cellulose ether and redispersible polymer powder are indispensable additives in dry mixed bonding mortar. The RDP in mortars is generally water-soluble redispersible latex powder, which can be divided into rigid type and flexible type. The corresponding redispersible powder is used according to product needs; Its main function is to provide excellent adhesion and helps to improve the water resistance, heat resistance, plasticity and flexibility of the mortar.

The role of cellulose ether is mainly used to retain water in mortar and improve the workability of products; For example, when building houses in the past, many masters mixed cement and sand on the ground. After adding water and stirring, they often see the water running away, and when plastering the wall with this mortar, not only apply a thick layer, but also slowly apply a small amount. Another situation is to wipe it off. Improvements in these conditions were immediate. Water locks in the mortar and refuses to run off. When plastering the wall, it can be easily constructed like putty, and the thickness can be controlled and reduced; the biggest advantage is that the drying speed of the mortar can be effectively controlled, and the cement can be fully hydrated, which is beneficial to the overall improvement of the mortar strength.

Shrink

The shrinkage of the mortar can be said to be a complementary bond strength, which can affect the actual bond area, resulting in hollow cracks and direct loss of bond strength; therefore, we must have strict requirements on the grading of cement and sand in the mortar , which not only controls shrinkage but also contributes to the bond strength of the mortar. In addition, shrinkage reduction can also be mixed with active materials. Active material generally refers to a large amount of activated silica and activated alumina. Does not harden or hardens very slowly after adding water. Its finer particle size can replace part of the cement-filled mortar, thereby reducing the overall shrinkage of the mortar.

Waterproof and hydrophobic effects

In a sense, there is a contradiction between waterproofing and hydrophobicity with bond strength. For example, in the past, many people hoped to have waterproof performance in tile adhesive, which can reduce the construction process of kitchen and bathroom walls, but the feasibility is not high; First, if our mortar wants to achieve waterproof or hydrophobic effect, we must add hydrophobic agent. After the hydrophobic agent is mixed with the mortar, the surface will gradually form an impermeable film. In this way, when the tiles are pasted, water cannot effectively penetrate into the tiles, the wetting ability is reduced, and the natural adhesion cannot be improved during the subsequent maintenance of the mortar.

Bonding strength refers to the maximum bonding force of mortar acting on the bottom layer;

Tensile strength refers to the ability of the mortar surface to resist the tensile force acting perpendicular to the surface;

Shear strength means the strength determined by applying a parallel force;

The compressive strength refers to the maximum value at which the mortar breaks, determined by applying pressure.