Applying primer is one of the most critical stages of body repair, on which paint adhesion, corrosion resistance and the final appearance of the coating depend. However, even experienced craftsmen often argue about what nozzle to apply primer with?to avoid shagreen, smudges or insufficient layers. The choice of nozzle diameter, type of sprayer and air pressure directly affect the quality of work - and mistakes here are expensive: from excessive consumption of materials to complete rework.

In this article we will analyze technical nuances selection of nozzles for different types of primers (epoxy, acrylic, acid), consider the optimal settings of the paint gun and typical problems associated with improper spraying. We will pay special attention practical recommendations for beginners and professionals - from preparing equipment to controlling layers on complex surfaces (edges, corners, plastic).

Why nozzle size is critical for soil

The nozzle (nozzle) of the spray gun determines material consumption, the shape of the torch and the degree of atomization. Primer, unlike paint or varnish, requires a larger nozzle due to the high viscosity of the composition and the need to create a thick layer (usually 80-120 microns). Too small a nozzle will lead to:

  • 🔹 Nozzle clogging - soil will not pass through a narrow hole, frequent cleaning will be required.
  • 🔹 Uneven coverage — the torch will be “torn”, with bald spots.
  • 🔹 High blood pressure - this is fraught with the formation of a “crater” (the “orange peel” effect).

On the other hand, an overly large nozzle will result in excessive material consumption, smudges and difficulties in controlling the layer thickness. For example, nozzle 2.0 mm suitable for liquid soils, but will be useless for thick two-component compositions.

📊 What type of soil do you use most often?
Acrylic
Epoxy
Acidic (phosphating)
Polyurethane
I don't know

Optimal nozzle diameters for different soils

The choice of nozzle diameter depends on soil viscosity, its type and manufacturer's recommendations. Below is a table with exact values for popular formulations:

Soil type Recommended nozzle diameter (mm) Inlet pressure (bar) Features
Acrylic (1K, 2K) 1.6–1.8 2.0–2.5 A universal option for most jobs. Suitable for beginners.
Epoxy 1.8–2.2 2.2–2.8 More viscous, requires a larger nozzle. Often used for anti-corrosion protection.
Acidic (phosphating) 1.4–1.6 1.8–2.2 Apply a thin layer, the nozzle should be smaller than for acrylic.
Polyurethane 2.0–2.5 2.5–3.0 The most viscous, requires high pressure and a large nozzle.

Critical error: using a 1.3–1.4 mm nozzle for two-component primers will lead to clogging of the nozzle and uneven spraying after only 5–10 minutes of operation. Manufacturers (eg SATA, Iwata, DeVilbiss) always indicate the recommended diameter on the soil packaging - this data cannot be ignored.

💡

Before work, check the viscosity of the soil with a viscometer (for example, DIN-4). The optimal value for most formulations is 18–22 seconds at 20°C.

Nozzle types: materials and design

In addition to the diameter, it is important to consider nozzle material and its shape. Modern nozzles are made from:

  • 🔧 Stainless steel - durable, resistant to aggressive compounds, but more expensive.
  • 🔧 Teflon coated aluminum - lightweight, but less wear-resistant.
  • 🔧 Ceramics - used in premium pistols (for example, SATAjet 5000), provide a perfect torch.

By design, nozzles are divided into:

  • 🔄 Removable — allow you to quickly change the diameter (convenient for workshops).
  • 🔄 Integrated — built into the pistol body, found in budget models.

Optimal for professional use ceramic or steel removable nozzles - they retain the hole geometry longer and are less susceptible to wear from abrasive particles in the soil.

What happens if you use a brass nozzle for acidic soil?

Brass reacts chemically with acidic compounds, which leads to oxidation of the nozzle, changes in the shape of the hole and deterioration in spray quality. After 2-3 uses the nozzle may become unusable.

Setting up a primer spray gun

Even a correctly selected nozzle does not guarantee a high-quality result without the correct settings of the gun. Key parameters:

  1. Air pressure:
    • For HVLP-pistols: 2.0–2.5 bar (at inlet).
    • For LVLP: 1.5–2.0 bar.
    • For conventional (obsolete): 3.0–4.0 bar.
  • Torch shape: for soil usually used round torch (the setting on the gun is "O"), not flat ("/").
  • Material consumption: Adjustable with a screw on the housing. For soil, open 1.5–2 turns from the fully closed position.

    • Check spray uniformity on a test surface (eg cardboard). The torch should be symmetrical, without “tails” or bald spots. If the edges of the torch are blurred, increase the pressure or check the cleanliness of the air channels.

    Rinse the tank and channels with a solvent (for example, 646th)

    Install a nozzle of the recommended diameter

    Adjust the pressure using the compressor pressure gauge

    Check the connections for tightness (no air leaks)

    Do a test spray on a test surface -->

    Common mistakes and how to avoid them

    Even experienced painters encounter defects when priming. Let's look at the most common problems and their causes:

    ⚠️ Attention: If shagreen (fine texture) appears after applying the primer, this is a signal that the pressure is too high or the viscosity of the composition is incorrect. Reduce the pressure by 0.2–0.3 bar and add 5–10% solvent to the soil.
    Defect Probable Cause Solution
    Smudges The nozzle is too large, the pressure is low, the gun moves slowly. Reduce the nozzle diameter, increase the speed of passage, hold the gun at a distance of 20–25 cm.
    Craters ("fish eyes") Surface contamination (silicon, oil) or too liquid soil. Clean surface antisilicon, increase the viscosity of the soil.
    Uneven layer Incorrect gun angle (should be 90° to the surface). Control perpendicularity and use guide beacons.

    Another common mistake is non-compliance with interlayer drying. For example, when applying epoxy primer in 2 layers, the second is applied after 10–15 minutes (depending on temperature). If this interval is violated, adhesion will deteriorate and the paint may peel off.

    💡

    The ideal speed of movement of the gun when priming is 30–40 cm/sec. Moving too slowly leads to smudges, too fast - to a thin layer.

    Features of priming complex surfaces

    Smooth panels are easy. It is much more difficult to properly apply primer to:

    • 🔺 Ribs and edges — here the soil accumulates in a thick layer. Solution: reduce material feed by 30% and walk faster.
    • 🔺 Corners and joints - use angle attachment for a pistol or apply primer in two approaches at different angles.
    • 🔺 Plastic parts - require special soils (for example, Plastic Primer) and nozzles 1.5–1.7 mm for a thin layer.

    For hard-to-reach places (for example, internal cavities of thresholds), use mini pistols with nozzle 1.0–1.3 mm or aerosol primers in cans. Important: before applying to plastic, be sure to treat the surface antistaticto avoid ground repulsion.

    Nozzle maintenance: cleaning and storage

    Primers, especially two-component ones, quickly polymerize and clog the nozzle. To extend the life of the nozzle:

    1. Wash the gun immediately after use special cleaner (for example, Gun Wash).
    2. To remove dried soil, use metal needle (included with the gun) or an ultrasonic bath.
    3. Store nozzles in airtight container with silica gel to avoid corrosion.
    ⚠️ Attention: Never use to clean nozzles. sandpaper or abrasive pastes - this disrupts the geometry of the hole and leads to uneven spraying. To remove stubborn deposits, use chemical cleaners based on dimethylformamide.

    The average service life of a high-quality nozzle with proper care is 2–3 years of active use. Cheap nozzles made of soft alloys can wear out after just a few months.

    FAQ: Frequently asked questions about ground nozzles

    Is it possible to apply primer with a 1.3 mm nozzle if there is no other?

    Technically possible, but only for liquid one-component soils (for example, acidic). For two-component formulations, this will lead to clogged nozzles and uneven coverage. As a last resort, dilute the primer 10-15% more than recommended and reduce the pressure to 1.8 bar.

    Which gun is better for priming: HVLP or LVLP?

    HVLP (High Volume Low Pressure) is suitable for beginners - it produces less fog and is easier to set up. LVLP (Low Volume Low Pressure) is more economical in terms of air and material consumption, but requires experience. Optimal for soil HVLP with nozzle 1.6–1.8 mm.

    What to do if the soil is “dusty” (does not lie on the surface)? summary>

    The reason is usually static electricity (especially on plastic) or too dry air. Solutions:

    • Use antistatic for the surface.
    • Increase indoor humidity to 50–60%.
    • Add 2–3% to the soil slow solvent to improve spreadability.
    Do I need to change the nozzle when switching from primer to paint?

    Yes, definitely! Remaining primer in the nozzle can get into the paint and ruin the finish. If the nozzle is visually clean, use a separate paint nozzle (usually 1.3–1.4 mm).

    How to check that the nozzle is worn out and it’s time to replace it?

    Signs of wear:

    • The torch becomes asymmetrical even after cleaning.
    • The test spray shows "streaks" or uneven spots.
    • Even with the correct settings, shagreen appears.

    Check the nozzle under a magnifying glass - if the edges of the hole are rounded or jagged, it needs to be replaced.