How to solve the problem of underbite in the coating

The reason for biting the bottom is generally that the paint layer is not dry to do the next layer, if there is baking, it is baked too fast, and sometimes the spraying is too thick and will bite the bottom.

How to solve it, see if the weight of the bite is heavy, the size of the area, if it is small, use about 800 sandpaper to polish it and spray it dry, not too thick. If it's big and severe, you have to grind it all off and respray it.

Paint construction bottoming refers to the phenomenon that the solvent in the topcoat easily softens or dissolves the underlying paint film and bites up. There are two main reasons for this:

1.Generally, some synthetic resin paint films modified by oil paint, alkyd paint and dry oil, before highly oxidizing and polymerizing into a film, once it meets with the strong solvent in the topcoat, the bottom paint film will be dissolved and bitten up, affecting the adhesion between the primer and the surface, such as alkyd paint contains stronger solvent than general oil paint, and the second layer must be painted after the first layer is fully dried, otherwise the first layer of paint film is easy to be bitten. However, the longer the primer dries, or the more the film is baked at high temperatures, this can be prevented.

2.The base and top coat are not matched. For example, the grease primer has a certain adhesion to the metal surface, but it cannot be matched with nitro paint, perchloroethylene paint, etc., because the primer cannot withstand the action of strong solvent after drying and produces bite.

In the selection of supporting must pay attention to their mutual tolerance, for nitro paint can be used iron red epoxy vinegar primer or iron red alkyd primer, for perchloroethylene paint can be used iron red alkyd primer, filling can not use oily putty, should be changed to perchloroethylene putty.

Causes: (1) The primer is applied before it is completely dry, and the solvent in the topcoat is very easy to dissolve and soften the primer, causing the bottom bite. (2) The operation is not fast when brushing the topcoat, and the phenomenon of biting the bottom will occur if the number of repeated brushing is too much.

3) For oil-based paint films and some synthetic resin paint films modified by dry oil, the primer paint film will be eroded once it meets with strong solvents before it is highly oxidized and polymerized to form a film. If phenolic paint is used for primer and nitro paint is used for topcoat, the solvent in the nitro paint will bite up the oily phenolic paint and separate it from the original adhesion base layer. (4) The amount of curing agent of the previous coating is insufficient, and the cross-linking is insufficient; (5) The front and back coatings are not matched.

The so-called "biting the bottom" of paint refers to the softening of the paint film, which affects the adhesion of the paint film and destroys the top paint film, and the front paint film cannot withstand the solvent erosion in the back paint. (1) Causes.

a. Mixing of two or more lacquer types;

b. Apply a piece of paint before the paint film dries;

c. Primer, topcoat and putty are not matched;

d Low operation skills, repeated painting in the same place. (2) Prevention methods:

a. Prevent the mixing of two paints;

b. Construction in strict accordance with the process;

c. Select matching paint species;

d. Improve technical skills.