In the floor coating system, the middle coat is a coat between the primer and the top coat. Both the mortar layer and the putty layer belong to the middle coat and generally consist of multiple layers. On the one hand, the medium coating can level the base surface and carry out further processing on the base surface; on the other hand, it can increase the thickness of the coating film, improve the bearing capacity and the service life of the coating. If it is necessary to resist heavy pressure, reinforcement materials such as glass fiber cloth can be laid between the coats .
The general requirements for the mortar layer are: it cannot have adverse effects on the base surface and primer, such as undercutting, erosion, etc., and it cannot contain components that can penetrate into the top coat to cause ills; it has certain mechanical strength, such as compressive strength. , bending strength, tensile strength, etc.; it has good construction, drying and sanding properties. The paint used for the intermediate coating should match the primer and topcoat used, have good adhesion, and the durability should be compatible with the topcoat. If it is required that the coating can release the pressure of underground water vapor, the base coat, middle coat and surface coat must also have air permeability.
During the construction of the coating, the thickness of each coating should be controlled according to the construction thickness required by the customer and the drying performance of the product. When constructing solvent-based and water-based mortar layers, they should not be applied too thick together, otherwise the coating may become soft for a long time due to the difficulty of solvent volatilization, which not only delays the construction period, but also poor curing performance of the coating.
Scratch coating is a common construction method for mortar and putty layers. According to the viscosity of the mortar paint, magnesium coating can sometimes be used for construction. If the construction thickness of the mortar layer is required to be more than 3mm, solvent-free mortar is mostly used, constructed by sand pressing technology, and smoothed with a trowel. This process can be constructed up to 3-5mm at one time, eliminating the cumbersome process of multiple coatings .
Since the surface of the mortar layer is rough and has many pores, it is generally necessary to level it with putty to fill the gaps. After the intermediate coating is completed, the surface should be flat and free of pores, because the air in the pores may be replaced with the topcoat during the application of the topcoat, resulting in defects such as blistering and paint film collapse after the topcoat is applied.
If the base surface is relatively flat and does not need to withstand heavy pressure, the mortar layer may not be applied, but the putty layer may be directly applied to level the base surface, which will be more economical in cost, but the service life will be slightly shorter than that of the coating system with the mortar layer applied.
In order to obtain a surface layer with a good appearance effect, it is generally necessary to sand, vacuum, and then apply a top coat after the intermediate coating is completed.