The process of painting a car is not just about applying color, but a complex engineering task where every detail matters. Choosing the Right Size nozzles (nozzle) is one of the most critical points on which the quality of texture, speed of work and consumption of materials depend. A millimeter error can turn a perfect preparation into a defect requiring a complete repaint.
Many novice painters often get confused by the numbers stamped on the spray gun kit, not understanding the difference between applying filler primer and finishing varnish. HVLP and LVMP systems require an individual approach, since the physics of spraying is different. In this article we will look at why there is no universal answer “for all occasions” and how to choose the ideal tool for a specific task.
Modern paints and varnishes have different viscosity and pressure requirements. If you use a nozzle that is too large for the base, you will get overspray and smudges, and a nozzle that is too small for the varnish will result in a “shagreen” surface and poor flow. Understanding these nuances will allow you to avoid costly mistakes.
The physics of atomization and the role of nozzle diameter
The diameter of the spray gun outlet directly affects how the material is crushed into microscopic particles. The smaller the nozzle, the smaller the torch and the thinner the layer, but at the same time the higher the requirements for the preparation of the material. A large nozzle, on the contrary, allows the passage of more viscous compounds, but creates the risk of “orange peel” formation when working with liquid products.
The key parameter here is viscosity, measured in seconds by a viscometer DIN4. Each type of coating material has its own optimal viscosity range, which dictates the choice of equipment. For example, thick soil requires a larger hole so as not to create excess pressure in the system, which could disrupt the torch.
It is also worth considering the design of the spray gun needle. The needle must perfectly overlap the nozzle, and the gap between them determines the tightness and accuracy of the feed. Using a worn needle-nozzle pair will result in paint spitting and an uneven spray pattern, which is unacceptable when working on a body.
⚠️ Attention: Never try to force thick material through a fine nozzle (eg 1.3mm) by increasing the inlet pressure. This will lead to overheating of the material, a change in its properties and guaranteed defective coating.
Choosing a nozzle for applying acrylic primer
Priming is a step where performance and risk filling ability are important. Primary and secondary primers (acids and fillers) typically require the largest nozzles in a painter's arsenal. The standard size for most fillers is in the range from 1.6 to 1.8 mm, and for liquid primers for plastic - from 1.4 to 1.6 mm.
Using a 1.7-1.8 mm nozzle allows you to apply the primer in thick layers without the risk of shagreen formation, which is especially important when leveling the surface. However, if you are working with quick-drying soils in a hot room, it is better to choose a slightly smaller nozzle (1.6 mm) so that the material does not have time to dry on the fly, forming dry dust.
- 🛠️ 1.6 mm — universal size for most medium-viscosity acrylic primers-fillers.
- 🛠️ 1.7-1.8 mm — ideal for thick soils, working with large volumes and filling deep grooves.
- 🛠️ 2.0-2.5 mm - rarely used, mainly for applying liquid putty or very thick anti-corrosion compounds.
When working with soil, it is important not to skimp on diameter. Trying to save material by using a fine nozzle will result in you having to make more passes and spend more time drying and sanding. The soil should be laid down in a “wet” layer, which is only possible if the exit hole has a sufficient cross-section.
Optimal nozzle size for base enamel
Base enamel (metallic, mother-of-pearl, solid) is the most critical stage where the color and effect are formed. Here the requirements for nozzle diameter become stricter. For most modern water-soluble and solvent bases, the nozzle is considered the “gold standard” 1.3 mm.
Why 1.3? This size strikes the perfect balance: it is large enough to pass flakes without breaking them up, but small enough to create a fine mist. If you use a nozzle of 1.4 mm or more for the base, you may encounter a problem when large aluminum particles lie unevenly, creating spots (variation of tone).
On the other hand, the 1.2mm nozzle can be used for very liquid bases or when working in cold conditions, but it requires perfect filtration of the material. Any grain of sand or clot of paint will instantly clog such a hole, interrupting the painting process at the most inopportune moment.
The secret of working with mother of pearl
When working with three-layer pearlescent coatings (Candy, Chameleon), professionals often recommend using a 1.3 mm nozzle, but reducing the pressure by 0.2-0.3 atmospheres from the norm. This allows you to apply a thinner layer while maintaining transparency and depth of color without overlapping previous layers.
Applying varnish: requirements for the finishing coat
Clearcoat is the final shield of your car and requires great precision in its application. The most popular nozzle sizes here are 1.3 mm and 1.4 mm. The choice between them depends on the viscosity of the particular varnish and the desired speed of work.
A 1.3 mm nozzle is considered universal for varnishes. It gives excellent pouring and allows you to control the thickness of the layer, minimizing the risk of smudges on vertical surfaces. This is especially important when working with two-component varnishes, which have a limited life in the tank.
If you use high-viscosity varnishes (HS - High Solid) or work in a cool room where the material thickens, it makes sense to switch to a 1.4 mm or even 1.5 mm nozzle. This will ensure better flow and eliminate shagreen paint without having to over-thin the varnish with solvent, which could compromise its strength.
| Material type | Recommended nozzle (mm) | Pressure (Bar) | Nuances |
|---|---|---|---|
| Soil filler | 1.6 - 1.8 | 2.0 - 3.0 | Requires high performance |
| Base enamel | 1.2 - 1.3 | 1.8 - 2.2 | Torch accuracy is critical |
| Varnish (2K) | 1.3 - 1.4 | 1.5 - 2.0 | Filling and gloss are important |
| Liquid putty | 2.0 - 2.5 | 3.0 - 4.0 | Only for special pistols |
☑️ Preparing the nozzle for work
Specifics of water-soluble paints
Waterborne bases are becoming a standard in professional body shops due to their environmental friendliness. However, they require special attention to the choice of nozzle. Unlike solvent analogues, “water” is more sensitive to corrosion and requires the use of stainless steel.
For water-soluble materials, a nozzle is most often used 1.3 mm. Some paint manufacturers may recommend 1.2 mm for certain paint series to speed up water evaporation and reduce drying time. It is important to strictly follow the technical data sheet (TDS) of the specific paint manufacturer.
A feature of such paints is their low viscosity when wet. Using a nozzle that is too large (1.4 mm or higher) can cause the paint to flow over the body before it has time to “set”. Therefore, control of layer thickness is more important here than when working with traditional enamels.
Influence of temperature and viscosity on tool selection
Paint booth temperature is a hidden factor that is often overlooked. In a cold chamber (below +20°C), the viscosity of all materials increases. If you use a standard 1.3 mm nozzle in the cold, the varnish or base may be applied with dry shagreen, since the material will not have time to spread.
In such situations, experienced painters either heat the material (using special thermal covers on the tank) or temporarily switch to a larger diameter nozzle (for example, from 1.3 to 1.4 mm). This allows thicker material to pass through without increasing pressure, maintaining the quality of the torch.
The opposite situation is heat. In a very warm room (+25°C and above), the material becomes thinner and dries faster. Here, on the contrary, you can use a smaller nozzle or reduce the supply of material to avoid smudges and paint boiling on the surface.
Use a viscometer before each tank refill. Viscosity is not a constant value and depends on temperature. Even if you diluted the paint according to the proportion, it could thicken or become thinner due to the climate in the workshop.
Nozzle care and blockage prevention
Even the most expensive nozzle from Italy or Japan will fail if you do not take care of it. After each paint change, the system must be thoroughly flushed. Remains of varnish frozen inside the nozzle channel may break off in the form of hard crumbs during the next job and ruin the coating.
For cleaning, use the special brushes that come with the kit or soft brushes. Strictly prohibited use metal objects (needles, wire, paper clips) to clean the nozzle hole. You will inevitably scratch the polished surface inside, which will disrupt the geometry of the torch.
Check the condition of the needle O-rings regularly. If they are worn out, paint will leak into the back of the spray gun, dirtying the operator's hands and disrupting the balance of the tool. Timely replacement of the repair kit will extend the life of your equipment.
⚠️ Attention: When assembling the spray gun, do not tighten the nozzle head “all the way” with excessive force. Brass is a soft metal, and overtightening can lead to deformation of the thread or the nozzle itself, which will make it impossible to seal the needle tightly.
Frequent mistakes when choosing and using
One of the most common mistakes is trying to use one spray gun and one nozzle for all operations. There is no universal solution. Saving on the purchase of a second set of “head + nozzle” or a second spray gun often results in defective painting, the correction of which costs tens of times more.
Also, beginners often confuse the diameter of the nozzle with the diameter of the needle. Although they are related, they are different parameters. It is important that the needle matches the nozzle along the length of the cone. Using mismatched components (for example, a 1.3 needle in a 1.5 nozzle) will lead to incorrect operation of the supply valve.
You should not chase the cheapest Chinese analogues of nozzles. The quality of hole processing and needle polishing often leaves much to be desired. Irregularities at the outlet create turbulence, which spoils the torch. For professional work, it is better to choose proven brands, such as SATA, Iwata or DeVilbiss, or high-quality compatible kits.
A correctly selected nozzle is 50% of the success of painting. It ensures proper crushing of the material, which directly affects the gloss, color rendition and durability of the coating.
Is it possible to apply varnish with a 1.3 mm nozzle if the instructions say 1.4?
Yes, you can, but you have to be careful. A 1.3 mm nozzle will give a thinner layer and fine shagreen. It may be necessary to make an extra pass or slow down the arm speed slightly to ensure sufficient dispensing. However, for thick HS varnishes in a cold workshop, 1.3 mm may be too small.
Which nozzle is better for metallics: 1.2 or 1.3 mm?
For most modern metallics, 1.3mm is the standard. A 1.2mm nozzle will work for very thin bases or small details, but on larger surfaces it may not give the desired performance, and you will take longer to dry between coats, which risks causing variations in tone.
How often should the nozzle and needle be changed?
With careful use and proper cleaning, a high-quality nozzle will last for years. They need to be changed only if mechanical damage occurs (scratches inside the channel, chips at the end of the needle) or if there are irreparable problems with the torch that cannot be solved by cleaning.
Does needle length affect the choice of nozzle?
Yes, directly. The nozzle and the needle are paired elements. The needle cone should perfectly match the nozzle cone. You cannot use a 1.3 nozzle needle with a 1.5 head, as they will not hermetically block the flow of paint, which will lead to leakage and the inability to adjust the torch.