Do I need to clean the primer before painting the car. Grinding methods
Content
It is recommended to sand large areas with a grinder to save time, but it is not applicable in all areas. Bottlenecks, proximity to decorative elements that can be damaged in the process - you have to wield manually there.
To sand the primer before painting or not - this question is asked by many motorists who carry out body repairs on their own. To answer it, we will deal with the rules for preparing the surface for painting.
Whether to clean the primer before painting the car
Most car painters agree that sanding the primer is necessary to make the surface to be treated smooth. The ground is a protective layer that has bulges and craters that will be visible after painting.
When applying paint and varnish, sags and smudges form at the location of the irregularities, which subsequently cannot be polished. It is necessary to carefully clean the primer before painting the car, since a thin layer can be damaged, leaving “bald spots”. It is recommended to do this with a grinder using a fine abrasive. If in some places the coating has worn off to the metal, the defect can be eliminated with a can of primer in aerosol form.
It is recommended to clean the primer with a grinder
In case of detection of other shortcomings (detected by the developer), it is recommended to putty the problem areas and cover them with a primer for better adhesion.
Grinding methods
There are 2 main options for precoat sanding:
- using water;
- without her.
In the dry
This method does not involve the use of water and is characterized by the formation of a large amount of dust, which is not liked by painters.
Features
The dry method is the most common in professional paint shops not only in Russia, but also in the West:
- it is considered environmentally friendly (dirty water with flush products does not enter the sewer);
- and more efficient in terms of time costs.
Dry sanding
Since it is impossible for water to penetrate into the putty layer or to the metal, the likelihood of re-corrosion and cracking of thick putty layers is reduced.
How to grind
It is recommended to sand large areas with a grinder to save time, but it is not applicable in all areas. Bottlenecks, proximity to decorative elements that can be damaged in the process - you have to wield manually there.
Как
It is recommended to sand the primer before painting the car, following the sequence of actions:
- After applying the primer layer, the body part is left for a day until completely dry.
- Grinding is carried out with a grinder with a small stroke of the moving part and a soft abrasive element so as not to change the given surface shape.
- The work is completed by applying the developer - it highlights problem areas.
The painter applies a uniform force on all planes to avoid the formation of craters. Movements should be diagonal, with a change in direction - so that there are no “risks” visible to the eye.
Grinding the surface with a hand sander
Use of powder and dust developer is allowed. The composition for detecting defects must be applied after the primer has completely dried in order to avoid deterioration of its structure.
Advantages and disadvantages
Advantages:
- there is no possibility to damage the treated surface with moisture - the metal does not corrode, the putty does not change the structure;
- high grinding speed.
Wet
Most often, this method involves manual labor - sandpaper and water are used, which wets the surface to be treated. It is used in small workshops that are not equipped with additional premises and specialized equipment.
Features
The surface can only be sanded with waterproof sandpaper. Pure water is used for processing - it reduces dust formation and smoothes the resulting defects.
How to grind
Equipment for the wet method is not used, all work is carried out manually with special sandpaper.
Как
Procedure:
- The surface to be treated is pre-moistened with water, constantly monitoring its amount - the rule “the less, the safer” works (penetrating into irregularities, it can reach the metal, subsequently causing corrosion and cracks in the putty structure).
- The soil is cleaned with diagonal movements, with a bar around which the abrasive element is wrapped.
- After rough sanding, they are polished again with their hands, trying to press the paper evenly.
Wet sanding
Advantages and disadvantages
Advantages:
- low consumption of sanding paper;
- dust is not generated during processing, so additional ventilation and respirators are not required.
Disadvantages:
- manual physically hard work;
- low grinding speed.
It is also possible to damage the coating, causing the appearance of secondary rust.
What sandpaper to grind the primer before painting a car
With the dry method, the thickness of the nozzle on the grinder is selected depending on how many layers of soil are applied. Universal size - P320. Rougher types are also used - P280 or P240 for places with thickenings.
After the preliminary stage, it will be necessary to carry out processing with fine sandpaper to remove subtle defects. Finishing grinding of the primer before painting is carried out with a grain of up to P600. Smaller sizes contribute to the deterioration of the adhesion of the treated surface to the paint (enamel).
For wet processing, an abrasive with a finer grain is used compared to the previous method. Large defects can be cleaned with P600 paper, subsequently moving 200 units lower. There is a limit on the size of the abrasive less than P1000, otherwise the paint will fall worse and eventually come off.
