The situation when the spray gun streaks is familiar to every master who has encountered painting work. Instead of an even, uniform layer of paint, greasy stripes, drops, or areas with different color saturation appear on the surface. This defect not only spoils the appearance of the product, but also requires additional time and materials for repainting. Most often, the problem lies in an imbalance between the supply of air and material, but the reasons can be much deeper.
Many beginners immediately blame poor-quality paint or a malfunction of the tool itself, starting to frantically disassemble spray head. However, haste here does not lead to anything good. It is necessary to consistently check the viscosity of the material, the pressure in the system and the cleanliness of the channels. Only a systematic approach will allow us to identify the true cause of the defect and eliminate it the first time, returning the tool to factory efficiency.
In this article we will analyze in detail all the possible reasons why the spray gun spits and leaves marks. You will learn how to properly set up a torch, select a solvent and carry out equipment maintenance. Understanding the physics of the spraying process will help you avoid common mistakes in the future and get professional results even in difficult conditions.
Problems with viscosity and paint preparation
The most common reason why a spray gun starts streaking is because the paint was not prepared correctly. If the material is too thick, it does not have time to disperse into small particles under the influence of air flow. As a result, large drops fall on the surface and merge into unsightly paths. Viscosity - this is a key parameter that must be monitored before each tank refill.
To measure this indicator, a special instrument is used - a viscometer, which is often a funnel with a calibrated hole. The flow time of a certain volume of liquid indicates its suitability for working with a specific diameter. nozzles. If the flow time exceeds the rate specified by the paint manufacturer, it is necessary to add solvent. It is important to use exactly the type of solvent that is recommended for this group of materials, so as not to violate the chemical formula.
⚠️ Attention: Never try to compensate for high viscosity by increasing the pressure at the spray gun inlet. This will lead to the formation of fog and waste of material, but will not provide high-quality spraying.
In addition, it is worth considering the ambient temperature. In a cold room, the viscosity of any liquid naturally increases. If you are working in an unheated garage in the winter, the paint may thicken even if the mixing ratios are correct. In such cases, it is recommended to preheat the material to room temperature, but this must be done carefully, using a water bath rather than an open fire.
Use a measuring cup with a strainer when pouring paint into the reservoir. This will trap any stray debris and clumps that can clog the channels and cause uneven spraying.
Poor mixing of the components also leads to the appearance of streaks. If you are using two-component enamels, it is important to thoroughly mix the base and hardener and wait the exposure time. An uneven consistency of the mixture will result in the sprayer throwing out a thinner fraction at one moment and a thicker one at another, creating a “zebra” effect on the surface.
Malfunctions and blockages of the spray head
The second most important factor influencing the quality of the torch is the condition spray head and needles. Even a microscopic particle of dried paint or dust that gets onto the end of the needle or inside the air channels can completely change the spray geometry. The spray gun begins to “spit”, throwing out material in uneven portions.
When inspecting the head, pay attention to the integrity of the hole nozzles. If it is deformed as a result of falling or mechanical cleaning with metal objects, it will no longer be possible to obtain a perfect torch. In this case, only replacing the worn part will help. Also check that the needle is firmly seated on the seat. Gaps are unacceptable here, as they violate the tightness of the system and lead to paint leakage.
- 🔍 Visually inspect the head for adhered particles of old material.
- 💧 Soak the removable parts in a special solution for cleaning spray guns.
- 🚫 Never pick the nozzle hole with metal brushes or needles.
- 🔩 Check the tightness of the head - it should be fixed tightly, but without tightening.
Cleaning should be carried out immediately after completion of work, without waiting for the remaining paint inside the channels to dry. Solvent pressure washing helps remove contaminants from hard-to-reach areas. If the problem persists after cleaning, the O-rings may be damaged or the metal structure itself may have become corroded due to the use of harsh chemicals.
☑️ Daily maintenance of the spray gun
The influence of air pressure on the quality of the torch
Air pressure is the force that breaks a stream of paint into tiny particles. If the pressure is not enough, the material is not sprayed, but simply flows out of the nozzle, forming drips and streaks. On the contrary, excess pressure leads to the formation of a dry, rough layer and increased fog formation. The optimal value depends on the type of paint and diameter nozzles.
It is important to distinguish between the pressure at the outlet of the compressor and the pressure directly at the inlet of the spray gun. Due to the resistance of the air hose, these values may vary. For precise adjustment, it is recommended to use a gearbox with a pressure gauge, which is installed directly on the tool handle. This allows you to see the actual operating pressure at the moment the trigger is pulled.
Pressure instability can also cause defects. If the compressor does not have time to pump air or the receiver is too small, the pressure will jump. When the pressure drops, the spray gun will begin to streak. Check the performance of the compressor: it should exceed the consumption of the spray gun by at least 20-30%.
| Material type | Nozzle diameter (mm) | Recommended pressure (bar) | Torch type |
|---|---|---|---|
| Base enamel | 1.3 - 1.4 | 2.0 - 2.5 | Soft, wide |
| Varnish / Acrylic | 1.4 - 1.6 | 2.5 - 3.0 | Medium |
| Soil | 1.6 - 2.0 | 3.0 - 4.0 | Concentrated |
| Liquid putty | 2.0 - 3.0 | 4.0 - 6.0 | Wide |
When adjusting, always start with the minimum pressure and gradually increase it while testing the spray on a test surface. As soon as the torch becomes homogeneous and no longer leaves streaks, no further increase in pressure is required. Remember that working at the minimum required pressure saves material and reduces the risk of dust getting onto the surface to be painted.
Adjusting the paint supply and torch shape
Adjustment of the torch shape and material supply is carried out using screws located on the body of the spray gun. The screw responsible for the shape of the torch (usually the top one) controls the air supply through the side horns of the head. If it is completely closed, the torch will be round, which is good for local work, but bad for large planes. An oval, flattened spray pattern is required for uniform coverage.
The ink feed screw (often located at the back or top) limits the needle stroke. Beginners often turn it up to maximum, believing that this will speed up the work. However, excessive supply leads to the fact that the air flow does not have time to process the entire volume of paint, and it lies in stripes. It is necessary to find a balance when the material is supplied exactly as much as a given air flow can efficiently spray.
Application technique also plays a role. The spray gun must be held strictly perpendicular to the surface. The tilt of the tool leads to a change in the distance from the nozzle to the surface at different points of the torch, which causes unevenness of the layer. Movements should be smooth, overlapping the previous lane by 50-70%.
⚠️ Attention: Do not allow your hand to stop moving while pressing the trigger. This is guaranteed to lead to the formation of a local sag, which will have to be removed by grinding.
To check the setting, make a few test passes on cardboard or metal. Evaluate the width of the torch and the uniformity of droplet distribution. If the edges of the plume are more saturated than the center (or vice versa), then the air channels require cleaning or adjustment. An ideal print should look like a uniform oval without breaks or thickening.
Surface defects and external factors
Sometimes the reason that the spray gun streaks lies not in the tool, but in the operating conditions or the condition of the surface. Strong drafts can blow away the paint flare, bending its trajectory and creating streaks. Dust in the air settles on a fresh layer, creating roughness that is visually perceived as unevenness.
Surface temperature also matters. If you are painting hot metal (such as engine parts or bodywork in the sun), the solvent may evaporate too quickly. This leads to the effect of “dry paint”, when the material lays down in stripes without having time to spread. In such cases, it is necessary to either cool the part or use a slower drying solvent.
The quality of foundation preparation is the foundation of a good result. Oily stains, silicone or wax on the surface can cause paint to repel, creating so-called “craters” or breaks in the layer, which can easily be confused with a spray defect. Thorough degreasing and the use of anti-silicone wipes are required before starting work.
The secret of professionals
Temperature: The ideal temperature for painting is 20°C. At lower temperatures, increase the proportion of slow-drying solvent; at high temperatures, use fast-drying solvent to avoid boiling of the paint.
Comprehensive diagnostics and fault table
If none of the above methods help, an in-depth diagnosis is required. Disassemble the spray gun completely and check each connection. Sometimes the problem lies in a crack in the tank, through which excess air is sucked in, disrupting the vacuum and stability of the supply. Or the gasket between the head and the body has worn out.
Organize your observations. The nature of the stripes can tell you where exactly to look for the problem. For example, vertical stripes often indicate a blockage in one of the side channels of the head, while horizontal stripes often indicate a problem with the central channel or needle. Occasional spitting may indicate air bubbles in the hose or reservoir.
Below is a summary table to quickly diagnose the most common problems:
| Symptom | Probable Cause | Solution |
|---|---|---|
| The torch is divided into two parts | Side horns clogged | Clean the air supply channels |
| Large drops in the center | Low pressure or thick paint | Dilute material, add pressure |
| Uneven stripes along the edges | Damage to the needle seal | Replace Teflon bushing or ring |
| Paint flows by gravity | Valve not closed or needle worn | Tighten the adjustment, replace the needle |
Regular maintenance will extend the life of the tool. After each shift, lubricate moving parts with special oil for spray guns. This will prevent the mechanisms from souring and ensure smooth movement of the trigger. Careful attitude towards nozzle and the needle is a guarantee that you will not often have to wonder why the tool began to work worse.
90% of streaking and blemish problems can be solved by properly adjusting the paint viscosity and cleaning the spray head. Don't rush into buying a new tool until you rule out these factors.
Is it possible to use gasoline for cleaning a spray gun?
The use of gasoline is strictly not recommended. It is too aggressive for rubber seals and plastic parts of the tool, causing them to swell and break. In addition, gasoline is a fire hazard and leaves a greasy residue. Use only specialized solvents (646, 647, 650) or special cleaners for spray guns.
What nozzle diameter should I choose for my first spray gun?
For universal use, including painting the car body (base, varnish, acrylic), the best choice would be a set with nozzles 1.3 mm, 1.4 mm and 1.6 mm. The most universal size is considered to be 1.4 mm, which allows you to work with most types of enamels and varnishes with the correct viscosity settings.
Why does the spray gun spit when the trigger is pressed?
This often happens because the air supply opens first, and then the needle begins to move. If there is some paint left in the channel, the air pushes it out in large drops. To avoid this, train yourself to first lightly press the trigger to purge, and then smoothly open the feed of material, or use the “idle” pressing technique before approaching the part.
How to store the spray gun between uses?
After thorough washing and drying, it is recommended to leave a small layer of oil in the reservoir on the instrument and blow it through the system. This will create a protective film and prevent corrosion of the internal channels. It is better to store the instrument disassembled (with the head removed) in a special case to prevent accidental impacts and deformation of the needle.