Treatment of the underbody and arches of the car with coating type liquid raptor requires strict adherence to application technology, especially if you plan to use a pneumatic spray gun instead of the standard U-Pol kit. Unlike working with a brush or roller, where density is important, for spraying under pressure it is necessary to achieve ideal viscosity, otherwise the torch will “spit” or, conversely, produce excessive fog. Errors during the mixture preparation stage can lead to nozzle clogging, uneven texture distribution, or even peeling of the protective layer in the future.
The main question that faces the master is: what exactly and in what proportions should the two-component polyurethane composition be diluted? The standard kit often involves the use of a spray gun included in the kit, but for large volumes of work or to obtain a smoother surface, many resort to professional equipment. Liquid Raptor is a solvent sensitive material and the use of inappropriate chemistry may disrupt the polymerization process.
In this article we will analyze in detail the technical aspects of preparing the mixture, consider compatible solvents, calculate the exact proportions for different viscosities and provide a table of the dependence of the mixture's lifetime on temperature. You will learn how to avoid common mistakes that lead to defective painting, and what safety measures are critical when working with isocyanates.
Selecting the Right Solvent for Polyurethane Coating
The first and most important rule: Raptor is a polyurethane product, which means that it is chemically aggressive to many types of plastic and rubber, but requires specific solvents to change viscosity. The most common and recommended by the manufacturer U-Pol the substance is xylene. It is this that ensures proper spreading and does not conflict with the hardener, allowing the mixture to polymerize into a durable structure. The use of acetone or 646 thinner is acceptable in extreme cases, but may change drying time and final hardness of the layer.
Some craftsmen experiment with solvent or even Galosh gasoline, but such methods are a lottery. Solvent takes longer to dry, which can lead to material dripping from vertical surfaces if the viscosity is not correct. Gasoline, being highly volatile, can create a “boiling” effect or craters on the surface, since it evaporates faster than the curing reaction occurs. The optimal and safest choice for a guaranteed result is pure xylene or a specialized thinner for polyurethane varnishes.
If you try to dilute the base itself before adding the catalyst, you risk disrupting the stoichiometry of the reaction and the coating may remain tacky forever. The consistency should resemble thick milk or liquid sour cream, but not water. A mixture that is too liquid will lose its main function - creating a relief, shock-absorbing texture, turning into a regular, albeit thick, layer of paint.
⚠️ Attention: Never use water or alcohol as a thinner for Raptor. Water will react with isocyanates, causing the material to foam and completely lose adhesion, and alcohols can slow the curing process indefinitely.
Mixing proportions and viscosity calculation
Standard instructions for kits Raptor Tintable or Black states that for one bottle of base (750 ml) there is one bottle of hardener (250 ml). This gives us 1 liter of ready-to-use material in a basic configuration for a U-Pol gun. However, for a professional spray gun with a nozzle of 2.0–2.5 mm or even 3.0 mm (for highly textured surfaces), this mixture often needs to be further diluted. A typical recommendation is to add 5-10% solvent to the total volume of the mixture, but the exact amount depends on the desired texture.
If you want to get large shagreen (“orange peel”), then you can limit yourself to the minimal addition of xylene - about 30-50 ml per liter jar. To create a smoother, matte finish that is easier to clean, the amount of solvent is increased to 100-150 ml. The rule works here: more solvent means a smoother surface, but a thinner protective layer. Less solvent means higher relief and better sound insulation, but higher material consumption and the risk of “underfilling” in hard-to-reach places.
To calculate viscosity, it is convenient to use a viscometer (funnel) if you are working in large volumes. The optimal flow time for Raptor through a nozzle with a diameter of 4 mm should be about 18-22 seconds. If the mixture flows out faster, it is too thin and will leak; if slower, the torch will be torn. Don't be afraid to test paint on a piece of metal or cardboard before applying it to your car to visually assess the grain size.
Technical parameters and compatibility table
Understanding the chemical properties of components helps predict the behavior of a material under different conditions. The ambient temperature plays a huge role: the hotter it is, the faster the reaction occurs and the thinner the mixture becomes due to heating. During the cold season, the material thickens and a little more solvent may be required, but the main thing is to provide a warm drying environment. Below is a table showing the effect of solvent amount on coating performance.
| Mixture type | Volume of solvent (per 1 liter of mixture) | Recommended nozzle (mm) | Character of texture |
|---|---|---|---|
| Standard | 0 ml (base + hardener only) | Complete pistol | Large, pronounced shagreen |
| Working | 50-70 ml xylene | 2.0 - 2.5 | Medium grit, uniform |
| Liquid | 100-150 ml xylene | 2.5 - 3.0 | Small shagreen, closer to the mat |
| Extreme | more than 200 ml | > 3.0 | Risk of drips, loss of properties |
When working with professional equipment, it is important to consider the pressure at the outlet of the spray gun. For Raptor it is usually lower than for paints, and is about 3-4 atmospheres. High pressure will break up droplets of material, creating excess "fog" and overspray, as well as making the texture too fine. Air pressure and viscosity are two levers, balancing which you achieve the ideal torch.
Warm the base and hardener bottles to room temperature (20°C) before mixing. Cold material is thicker and you can make a mistake with the amount of solvent you add.
Instructions for preparing the mixture for spraying
The process of preparing the working mixture requires consistency and accuracy. First you need to shake the base, as the pigment and fillers will settle to the bottom. Then the hardener is added to the jar containing the base. Only after this, having thoroughly mixed the two components for 2-3 minutes, can you begin to introduce the solvent. Mixing should be vigorous to ensure uniformity throughout the entire volume, especially at the walls and bottom of the jar.
☑️ Preparation checklist
After adding xylene, the mixture is stirred again. A critical step that beginners often ignore is filtering. Even new material may contain clots or debris that will instantly clog the 2.5 mm nozzle. Use special painting funnels with a mesh or cup filters. If the mixture gets into the spray gun with lumps, you will have to disassemble and wash the tool during operation, which is unacceptable, since mixture lifetime limited.
The finished material should be processed for 60 minutes at a temperature of 20°C. After this time, active polymerization will begin in the jar, the material will begin to thicken and become unsuitable for spraying, although it will formally harden only after a few hours. Do not try to dilute a mixture that has already begun to thicken with additional solvent - the chemical reaction has already begun and the coating will be defective.
⚠️ Attention: Work only in a well-ventilated area or outdoors. Xylene and isocyanate fumes are toxic. Be sure to use a respirator with carbon filters (protection class A) and safety glasses.
Setting up the spray gun and application technique
For applying Raptor, HVLP (High Volume Low Pressure) or LVLP spray guns with a larger flow channel are best suited. The minimum nozzle diameter is 2.0 mm, but it is more comfortable to work with 2.5 mm or even 3.0 mm, if the design of the gun allows it. Using 1.3–1.5 mm nozzles intended for base enamels will lead to constant spitting and the inability to adjust the torch, since the filler particles are too large.
The application technique is not much different from painting with varnish, but adjusted for viscosity. Hold the gun perpendicular to the surface at a distance of 15-20 cm. Do not try to paint everything the first time - the first layer is made thin, “dust”, to ensure adhesion. The second and third coats are applied wet on wet at intervals of 30-60 minutes while the surface is still tacky. This ensures a monolithic coating without boundaries between layers.
What to do if it rains?
If you apply the first coat and it starts to rain, don't panic. Raptor is resistant to short-term exposure to moisture after initial setting (about 30-40 minutes). However, direct jets of water can leave craters. It is better to cover the car with film if there is a risk of precipitation in the first 2-3 hours.
It is important to control the angle of the gun. When working with thick compounds, the torch will fall off more often if you hold the gun at an angle. The movements must be uniform, with the same speed of movement. Lane overlap should be 50%. If you find that the material is laying down too smoothly, reduce the amount of solvent in the next batch or reduce the pressure.
Drying time and final treatment
After applying the final coat, the vehicle must dry for at least 12 hours at 20°C before first use. Complete polymerization and final hardness take about 7 days. During the first day, it is not recommended to wet the coating or subject it to mechanical stress. You can speed up the process by using IR drying or placing the car in a warm chamber (up to 60°C), which will reduce the drying time to 1-2 hours.
If you are not satisfied with the result (too large shagreen or streaks), Raptor can be sanded. However, due to its elasticity and viscous structure, ordinary sandpaper quickly becomes clogged. It makes sense to sand only a completely dry coating (after 24-48 hours) and always “dry”, using coarse grains (P80-P120) to smooth out defects. Fine sanding will turn the surface into mush.
The quality of the final coating depends 80% on the correct preparation of the mixture and filtration, and only 20% on the ability to hold the spray gun.
In conclusion, it is worth noting that experiments with proportions are best carried out on test samples. Liquid Raptor - forgiving material, it forgives some flaws, but fundamental errors in chemistry (wrong solvent, violation of the proportions of the hardener) cannot be corrected without a complete rework. By following the technology, you will receive a durable coating that will protect the car body for years.
Can Raptor of other colors be used to dilute the black?
Technically, you can mix different colors of Raptor with each other, since they have the same chemical base. However, if you add light Raptor to black to add volume, you will end up with a dark gray or dirty black hue rather than a deep black. For thinning, use only clear solvents (xylene), not colored bases.
What to do if the mixture in the jar begins to thicken after 40 minutes?
If 40-50 minutes have already passed since mixing with the hardener, the mixture has begun to polymerize. Adding a solvent at this moment will only liquefy the mass physically, but chemically the material is already “dying.” The applied layer may not dry completely or may peel off. It is better to prepare a new batch than to risk the quality of the entire car.
Do I need to prime the metal before applying Raptor?
Yes, surface preparation is critical. The metal must be free of rust, degreased and, preferably, treated with acid or epoxy primer. Although Raptor has high adhesion, applying it directly to bare metal without anti-corrosion preparation can cause the corrosion process to continue under a thick layer of polyurethane if there is any moisture or rust remaining.