Preparation of paint and varnish material is the foundation for high-quality car body repairs. Many amateur craftsmen underestimate the importance of cleaning enamel from foreign matter, relying on factory quality or thorough mixing. However, even a microscopic speck that gets into the spray gun nozzle can ruin the entire coating process and create defects, the elimination of which will require many hours of grinding.
The question of what to strain spray paint through is especially acute when working with expensive materials such as metallics and mother of pearl. Undissolved pigments, hardener clots or dust particles that get into the container during tinting will inevitably lead to clogging of the torch. This causes uneven spraying, the appearance of “spitting” and the formation of shagreen, which is critical for body repairs where visual perfection is important.
Using the correct filter element is not just a recommendation, but a mandatory step in the technological process. Modern painting systems require high purity of the material, since nozzle diameters in professional HVLP sprayers can be only 1.3–1.4 mm. Any lump exceeding this size will cause work to stop and require disassembly and cleaning of the instrument with solvent.
The need for filtration of paints and varnishes
Paint filtration is necessary to remove solid particles that could compromise the integrity of the applied layer. Even if you work in an ideal spray booth, the likelihood of dust getting into the bucket with diluted enamel remains high. In addition, if stored for a long time or improperly mixed, paint components can form micro-clumps that cannot be broken up with regular stirring.
Soils and putties liquid consistency require filtration even more often than finishing enamels. They often contain larger fractions of filler, which, when settled, can precipitate and clump. If you skip this step, the risk of clogging the nozzle increases many times over, which is especially dangerous when using gravity spray guns with top feed material.
⚠️ Attention: Never ignore the filtration step, even if the paint looks uniform. Microscopic inclusions become visible only after the layer has dried, when the defect can be corrected only by completely repainting the part.
Particular attention should be paid to materials containing metallized pigments. Aluminum powder is prone to the formation of agglomerates, which, when released into the torch, create characteristic stripes and stains. Straining through a mesh with the correct mesh size allows you to even out the distribution of metal particles, ensuring uniform shine and color over the entire area of the part.
Filter types: meshes, funnels and cups
There are several main types of filter elements on the market, each of which has its own application characteristics. The choice of a specific type depends on the amount of work, the viscosity of the material and the design of the sprayer used. The most common option is disposable nylon mesh filters that fit over the neck of the measuring cup.
The second popular option is ready-made funnel filters. They are a plastic structure with a built-in mesh that is inserted directly into the spray gun tank. This solution is most convenient for quick work, as it eliminates hand contact with chemicals and minimizes material loss during transfusion.
For professional painting jobs, there are also reusable metal filters. They are made of stainless steel and require careful cleaning solvent after each use. Although they have a higher initial cost, they can be more cost effective in the long run for larger painting volumes, but the risk of residual contamination from poor cleaning remains high.
- 🎨 Nylon mesh: disposable, cheap, suitable for all types of paints, varnishes and primers, easily disposed of after use.
- 🛠️ Plastic funnels: convenient design, minimize spillage, often included with spray guns, but less universal in volume.
- ⚙️ Metal filters: durable, require perfect cleaning, risk of corrosion when using aggressive solvents, suitable for large volumes.
Selecting the cell size depending on the material
The key parameter when choosing a filter is the mesh size, which is measured in microns (µm) or mesh (number of holes per inch). An incorrect choice of mesh density can lead to either rapid clogging of the filter or the passage of particles dangerous to the nozzle. Different types of paints and varnishes have their own filtration standards.
For base enamels and metallic paints typically use meshes with a mesh size of 125 to 190 microns (approximately 80–120 mesh). This allows you to retain large particles of pigment, but allow aluminum powder to pass through without hindrance. Using a mesh that is too fine in this case may disrupt the orientation of the flakes (metal flakes) in the torch.
Understanding the conversion of units of measurement helps to more accurately select consumables, especially when ordering filters from foreign catalogs, where the dimension can only be indicated in Mesh.
For soils and fillers that have a coarser fraction of solids, meshes with a cell size of 190–250 microns (60–80 mesh) are used. Denser filters are not recommended here, since viscous material will have difficulty passing through them, creating a vacuum in the tank and disrupting the stability of the torch. Varnishes, on the contrary, require maximum cleaning, so meshes up to 125 microns and finer are often used for them.
| Material type | Recommended mesh size (µm) | Mesh Size | Features |
|---|---|---|---|
| Soils (Primer) | 190 – 250 | 60 – 80 | Passes heavy filler fractions |
| Basecoat | 125 – 190 | 80 – 120 | Maintains metallic structure |
| Varnish (Clearcoat) | 125 – 150 | 100 – 120 | Maximum purity for gloss |
| Liquid putty | 250 – 300 | 50 – 60 | Only for removing large lumps |
Correct straining technology
The filtration process begins with preparing the workplace and personal protective equipment. You will need a clean measuring cup, a funnel or mesh holder, and the filter cartridge itself. It is important to work in a well-ventilated area as solvent fumes can be toxic and the use of a respirator is mandatory.
First, mix the paint thoroughly. If you are using two-component material, make sure that hardener fully integrated into the base. Then install the filter on the container. If using a mesh stocking, pull it over the neck of the glass, avoiding too much tension, which could tear the material. When pouring paint, try to pour it into the center of the filter, without raising the liquid level above the edges of the funnel.
☑️ Checklist for preparing for filtration
If you see a significant amount of sediment remaining on the mesh, do not try to push it out with a stick. It is better to replace the filter with a new one to avoid the breakthrough of contaminants into a clean container. After completing the transfer, carefully remove the filter, being careful not to splash any remaining paint, and dispose of it according to the rules for handling chemical waste.
⚠️ Attention: It is strictly forbidden to use the same filter for different types of materials (for example, first for primer, then for varnish) without intermediate rinsing, if the filter is reusable. Disposable nets cannot be reused.
Features of working with metallic paints
Metallized enamels require a special approach to filtration due to the presence of aluminum powder in the composition. The main task here is not to filter the pigment itself, but to remove only foreign inclusions and stuck together lumps. Filtration that is too aggressive can change the visual effect of the finish, making it appear dull or patchy.
When working with metallics, it is critical to prevent the formation of air bubbles during the pouring process through the filter. Air bubbles entering the spray gun will come out along with the paint, creating craters on the surface of the part. Therefore, paint should be poured in a thin stream along the filter wall or use funnels of a special design that dampen turbulence.
This will help the metal particles to correctly orient themselves in the paint layer until the solvent evaporates.
It is also worth considering that some types of pearlescent pigments have a different fraction than standard aluminum. Before purchasing filters, be sure to check the Technical Data Sheet (TDS) for the specific product. The manufacturer often indicates the recommended filter mesh size in the “Preparation for Use” section.
Common errors and ways to resolve them
One of the most common mistakes is the use of inappropriate means at hand, such as old nylon tights or gauze. These materials may have unpredictable mesh sizes, fade when exposed to solvent, or leave lint in the paint. Villi tissue caught in the nozzle causes the same problems as solid particles and often dissolves into the varnish, becoming noticeable defects.
Another mistake is filtering paint that has already been diluted and mixed with hardener, which has begun to thicken. The viability of the material is limited, and if you take your time, the paint may begin to polymerize right in the filter, clogging it tightly. In such cases, you have to throw away not only the filter, but also some of the expensive material stuck in it.
Don't forget to check the integrity of the mesh before starting work. A microscopic tear, invisible to the eye, will allow a large speck to pass through, which will ruin the entire work. If you use reusable metal filters, inspect them for corrosion and cell deformation after each wash.
The cost of the mesh is negligible compared to the cost of repairing the sprayer or repainting the part.
Questions and answers (FAQ)
Can the nylon filter be washed and reused?
Theoretically, this is possible if you wash it with a large amount of solvent immediately after use, before the paint dries. However, in practice, this is a labor-intensive process that rarely gives an ideal result. Remaining paint in the cells can dissolve in the new material and spoil the color. Considering the low cost of nylon mesh, it is more advisable to use them once.
What to do if the paint is too thick and does not pass through the filter?
Don't try to force it through. Most likely, the viscosity of the material is too high for the selected mesh size or temperature. Add the solvent recommended by the manufacturer, mix thoroughly and let sit for a few minutes. If the problem persists, you may need a larger mesh filter appropriate for the type of material (eg soil).
Is a paint filter suitable if I am working with water-soluble varnish?
Yes, most modern nylon filters are chemically inert and are suitable for both solvent (based on organic solvents) and water-soluble materials. The main thing is to make sure that the material of the mesh and plastic holder is resistant to water and alcohols if they are used as a base or thinner.
How to dispose of used filters with leftover paint?
Dried filters with paint residues are classified as hazardous waste. They should not be thrown into regular household waste. Collect them in a sealed bag or container and take them to a special chemical waste collection point or hazardous waste collection point, if available in your region.