High-quality body painting begins long before a can of enamel enters the chamber. The foundation of an ideal paint coating is properly prepared surface and, what is critically important, properly diluted soil. It is on this stage that the adhesion (adhesion) of materials, the absence of shrinkage in the future and the visual smoothness of the finish depend. Many beginners make the mistake of relying on intuition when mixing ingredients, which often results in shagreen, craters, or even peeling paint.
The process of preparing the primer mixture requires the apothecary's precision and understanding of chemical processes. You need to take many factors into account: the temperature in the spray booth, air humidity, the type of solvent used and the technical characteristics of the paint itself. acrylic primer. Incorrect viscosity can ruin even the most expensive paint on top. In this article we will analyze all the nuances in detail so that you get a result indistinguishable from the factory one.
Selection of materials and necessary tools
Before you start mixing the ingredients, make sure you have everything you need on hand. Using unsuitable tools may result in mixture contamination or incorrect proportions. The basis of any high-quality primer is a two-component system consisting of the primer itself and a hardener. You will also need a solvent, the type of which depends on the ambient temperature.
To work you will need the following tools and materials:
- 🧪 Measuring containers with graduation for precise proportions.
- 🔧 Measuring ruler (scales) for weighing components.
- 🌡️ Viscometer (for example, Ford-4 funnel) to check viscosity.
- 🧼 Funnel filters for filtering the mixture before pouring into the tank.
- 🧤 Personal protective equipment: respirator, gloves, glasses.
Particular attention should be paid to the choice of solvent. For standard conditions (approx. +20°C), a solvent marked "Normal" is used. If the room is colder (+15°C and below), “Slow” is necessary so that the soil has time to spread. In hot weather (+25°C and above), use “Fast” to avoid boiling.
⚠️ Attention: Never use thinner 646 or acetone to thin quality automotive primers. They can cause a chemical reaction leading to material curling or loss of adhesion. Use only original solvents of the same system as the primer.
Mixing proportions of soil components
Compliance with proportions is not just a recommendation, but a strict requirement of polymerization chemistry. Each manufacturer indicates the ratio of components on the jar, and it may differ. The most common proportions are 4:1 (4 parts primer to 1 part hardener) or 2:1. Violation of these ratios leads to critical consequences: an excess of hardener will make the coating brittle, and a lack of it will not allow the material to dry completely.
The mixing process must take place in a clean, dry container. First, the primer is poured, then the hardener is added. Only after this, with constant stirring, is the solvent added until the desired viscosity is achieved. Usually this is 1-2 hours at a temperature of +20°C, after which the soil begins to thicken and becomes unsuitable for work.
For clarity, let’s consider the dependence of the number of components on the required volume of the finished mixture:
| Required volume of mixture | Primer (base), ml | Hardener, ml | Solvent (10-15%), ml |
|---|---|---|---|
| 500 ml | 350 ml | 90 ml | 60-80 ml |
| 1000 ml (1 l) | 700 ml | 180 ml | 120-150 ml |
| 1500 ml (1.5 l) | 1050 ml | 270 ml | 180-220 ml |
| 2000 ml (2 l) | 1400 ml | 360 ml | 240-300 ml |
When mixing, thoroughly mix the composition with a stick, removing from the bottom and walls so that no undissolved clots remain. Uniformity of the mass is the key to uniform application.
Viscosity control: working with a viscometer
Many masters neglect to use a viscometer, relying on experience (“it flows like milk”). However, to obtain a professional result, especially when working with a spray gun, instrumental control is necessary. The viscosity of the primer for initial application is usually 18-22 seconds on a Ford-4 funnel at a temperature of +20°C. For the secondary (filler) layer, the viscosity can be slightly increased to 22-24 seconds.
How to measure viscosity correctly? Fill the viscometer full, close the hole with your finger, immerse it in the mixture, and then lift it and start the stopwatch at the same time. Stop at the moment when the continuous stream is interrupted and the drop comes off. If the flow time is less than normal, the soil is too liquid, you need to add more base. If more, add a little solvent.
The temperature of the mixture itself also matters. Cold soil from a garage will have a different viscosity than soil warmed to room temperature. Always bring components to room temperature (approx. 20°C) before mixing and measuring.
Setting up the spray gun for the ground
After the mixture is ready, you need to adjust the sprayer. Primer is a thicker material than base paint, and therefore requires more pressure and often a larger nozzle diameter. The optimal nozzle size for acrylic primer is 1.7–2.0 mm. Using a 1.3 mm nozzle intended for the base will result in the torch “spitting” and the material becoming shagreen.
The pressure at the outlet of the gun (at the moment the trigger is pressed) should be 3.5–4.5 atmospheres. The torch is adjusted on a test surface (cardboard or an old door). Use the torch regulator to achieve a “dumbbell” shape or an elongated oval with clear boundaries. Use the material supply regulator to set the flow so that when the torch passes, a wet but not flowing layer remains.
- 🔧 Duza: 1.7 mm, 1.8 mm or 2.0 mm (for highly viscous soils).
- 💨 Pressure: 3.5 – 4.5 bar (check with the trigger pressed).
- 🌬️ Torch: wide, the maximum possible for this part.
Don't forget that settings may vary depending on the spray gun model (Hvlp, LVLP, RP). Read the technical data sheet of your instrument.
Technology of applying primer layers
Applying primer requires some skill. The first layer is always made thin, the so-called “sticky” or “foggy”. Its purpose is to ensure adhesion to metal or old coating. Hold the gun perpendicular to the surface at a distance of 15-20 cm. The speed of hand movement should be uniform, without jerking or stopping.
After applying the first layer, you need to let it “dry” (flash-off time). This usually takes 5-10 minutes at 20°C. The surface should become matte but sticky. If you apply a second coat directly onto a wet first coat, bubbles or craters may form. The second and third (if necessary) layers are applied more generously “on wet” in order to form a full thickness and hide risks from sanding.
☑️ Checklist before starting painting
⚠️ Attention: Don't try to pour a thick layer of soil right away to save time. This is guaranteed to lead to drips that will have to be sanded out for a long time and painfully, violating the geometry of the part. It's better to do 3 thin layers than 1 thick one.
Drying and eliminating defects
Complete polymerization of acrylic primer takes about 24 hours at room temperature. However, for grinding, forced drying with infrared lamps or in a chamber at 60°C for 30-40 minutes is often used. It is important not to overheat the surface so as not to “boil” the soil, which will make it porous.
After drying, the soil must be sanded. To do this, use abrasives P320-P400 for the base and P500-P600 for the metallic. If you find defects (craters, shagreen), they can be eliminated by local sanding and re-priming.
What to do if the soil bubbles?
If you see bubbles immediately after application, the technology is most likely broken (draft, dirt, incorrect solvent). Allow the primer to dry completely, grind the defective layer down to metal, thoroughly degrease and reapply, strictly observing the temperature regime.
Pay special attention to the ends and transitions. The primer should not have sharp steps (“antoshkas”) at the edges of the repair area, otherwise after painting they will be visible as stripes. Use P500-P600 abrasive to softly blend the edges.
Use a developing powder or spray in a contrasting color before sanding the primer. This will allow you to see which areas have already been treated and where there are still risks, ensuring a perfectly flat surface.
Frequently asked questions (FAQ)
Is it possible to dilute thickened soil if it has been left in an open jar?
If the soil has thickened due to solvent evaporation, you can try to restore it by adding fresh solvent of the same system and mixing thoroughly. However, if a hardener gets into the soil and the mixture begins to polymerize (turns into a gel), it is impossible to save it. Such material will have to be disposed of, as it will not dry correctly and will ruin the coating.
How many coats of primer should I apply to bare metal?
Bare metal or epoxy primer is usually coated with 2-3 coats of acrylic filler. The first layer is thin, for adhesion. The second and third are wet, to create thickness and fill in marks. The total amount depends on the condition of the surface and the required coating thickness.
How long after priming can I paint?
The time depends on the type of drying. With natural drying at +20°C, sanding can be done after 3-4 hours, and it is advisable to paint after complete drying (24 hours) or after thorough sanding. When drying in a chamber at 60°C, you can paint immediately after the part has cooled and sanded (after 40-60 minutes).
What is the best way to wash off soil from a spray gun?
For flushing, it is best to use the same solvent with which the primer was mixed (for example, 650 or 651 solvent). Acetone or 646 may be too aggressive for the rubber seals of the spray gun, although they dissolve the soil itself well. After rinsing with solvent, it is recommended to blow out the instrument.
The main secret of success is cleanliness. 90% of priming defects occur due to dirty dishes, unfiltered mixture or poorly prepared surface, and not due to the quality of the material itself.