The final stage of restoring a body element or completely repainting a car is the application of a protective coating, which in the professional environment is simply called “varnish”. It is this transparent layer that is responsible not only for the depth of color and saturation of the shade, but also serves as the main barrier against the aggressive external environment. Acrylic varnish takes on the impact of small stones, the effects of acid rain, ultraviolet radiation and chemical reagents used to treat roads in winter.
Many novice painters mistakenly believe that the quality of the result depends solely on a good base, but without the right choice and application of the finishing layer, all the work can go down the drain. Incorrectly selected chemicals can become cloudy in a month, crack, or lose their gloss after the first wash. In this article we will look in detail at how to choose HS-varnish or MS-varnish, how to avoid shagreen and streaks, and what to do if the surface has lost its original appearance.
Understanding the physical and chemical processes that occur during polymerization will allow you to avoid fatal mistakes. The temperature in the cell or garage must be strictly no lower than 20°C, otherwise the varnish may not spread and remain matte. Let's look at all aspects of working with two-component systems so that your car sparkles like new even after years of use.
Classification of varnish materials: MS, HS and UHS
The first thing a craftsman encounters when purchasing materials in a store is the abbreviations indicating the dry matter content. MS varnish (Medium Solid) refers to materials with medium dry matter content. It is more liquid, contains more solvent and requires 2-3 layers to obtain full thickness and gloss. Its main advantage is its low cost and ease of use for beginners, since it is less prone to the formation of shagreen with minor violations of the technology.
However, professionals increasingly prefer HS varnish (High Solid). It contains significantly fewer solvents and more solids, which allows you to obtain a thick, saturated layer after 1.5-2 passes. This material has superior spreadability, creating the effect of “liquid glass”, and dries faster. But there is also a downside: HS-compositions are more capricious in temperature, gain viscosity faster when diluted and require a highly qualified painter.
There is also UHS varnish (Ultra High Solid), which represents the pinnacle of the evolution of paints and varnishes. It is more environmentally friendly, as it emits a minimum of volatile organic compounds, and allows you to create ultra-thick coatings with minimal shrinkage. For vintage cars or projects where maximum color depth is required, the use of UHS products is the quality standard.
The choice between these types should be based on the conditions under which the painting will be done. Unless you have a perfectly heated chamber with air filtration, HS varnish can be more trouble than it's worth due to its rapid drying time and the risk of dust ingress. At the same time, MS options are more forgiving of mistakes, but require more time for drying and polishing to achieve an ideal result.
System components: varnish, hardener and solvent
Two-component car varnish is never sold in a ready-to-use form. This is always a set of two cans: the main composition and hardener. A hardener is a catalyst for a chemical reaction, without which the varnish will remain sticky forever. It is important to strictly adhere to the mixing proportions indicated on the can by the manufacturer, usually 2:1 or 4:1 by volume. The use of a hardener from another manufacturer or with a different reaction rate is strictly prohibited.
The third essential component is solvent. It is needed not only to bring the viscosity to working level, but also for proper spreading of the material. Solvents are divided by evaporation rate: fast, medium and slow. The choice depends on the ambient temperature. If you use a fast solvent in hot weather, the varnish will “boil” and become covered with craters. If you apply a slow one in the cold, it will flow and dry for days.
Mixing the components should take place in a clean container using measuring cups. Failure to keep the utensils clean may result in curdling of the material. After adding the hardener you have a limited time, the so-called "pot life", usually 2-4 hours. After this time, the varnish in the jar will thicken and become unsuitable for application, even if visually it seems normal.
If you bought varnish Mobihel, then it is better to take both the hardener and the solvent of the same brand. Experiments with “mixes” often result in the appearance of matte spots that cannot be removed by polishing and require complete repainting of the element.
Required tools and surface preparation
The quality of varnish application depends 80% on preparation. The surface of the base must be completely matte, dry and grease-free. If you plan to varnish a fresh base, you need to wait a technological pause (usually 15-30 minutes after the last layer of base) so that the solvent has time to evaporate. Applying varnish to an under-dried base will cause boiling and loss of gloss.
To work, you will need a spray gun with a nozzle of 1.3-1.5 mm. A smaller diameter will not allow material to spill, while a larger diameter will create excessive consumption and the risk of drips. The compressor must provide stable pressure, and the air filtration system must have a moisture-oil separator. Even a drop of oil in the varnish will ruin the entire element, creating a fisheye that will have to be cut out and painted over.
Degreasing is a critical stage. Use special degreasers or anti-silicone, wiping the surface with a lint-free cloth. Immediately after this, just before going out with the spray gun, go over the part sticky napkin. It will remove the smallest dust that has settled on the base while you were fiddling with solvents. Ignoring this step will ensure that every speck of dust will become a visible defect under the varnish layer.
⚠️ Attention: Never use gasoline, acetone or aggressive solvents (646, 647) for degreasing before varnish. They can dissolve the bottom layer of the base or leave a greasy film, which will lead to peeling of the varnish. Use only specialized automotive degreasers.
Application technology: from the first layer to the finish
The varnishing process requires rhythm and constant control of the position of the torch. The first layer is applied thin, the so-called “dust layer”. Its task is to create adhesion (coupling) with the base and bind possible residual dust. Do not try to fill the part the first time, this will lead to drips. Let this layer dry for 10-15 minutes (intercoat drying time).
The second layer is the main one. It is applied with a wet, generous pour. Hold the torch perpendicular to the surface, covering the previous pass by 50-70%. It is at this moment that the varnish should spread, turning into a glossy mirror surface. Movements should be smooth, at the same speed. Stopping the hand in place instantly creates a rush of material.
If HS varnish is used, one and a half coats is often sufficient (the first thin, the second full, and at the end of the second pass, when the material in the tank runs out, a light pass is made to level it out). The third layer may be required for MS varnishes or when painting large surfaces (hood, roof), where it is necessary to ensure the absence of shagreen.
It is important to maintain a distance to the surface - usually 15-20 cm. If you hold the gun too close, drips will occur; too far - the varnish will dry in flight, leaving a dry “grain” that cannot be polished. Constantly monitor the pressure at the outlet of the gun; it should be stable (usually 2.0-2.5 atm).
Drying time and temperature conditions
Drying polish isn't just about waiting for it to stop sticking. This is a complex chemical polymerization process. There are several stages: drying from dust (30-60 minutes), when nothing sticks to the surface, but it is still soft; and complete polymerization, which takes from 7 to 24 hours depending on the type of hardener. Only after complete polymerization can you begin to wash the car or install parts.
To speed up the process and increase the durability of the coating, infrared drying is often used or the car is placed in a chamber at a temperature of 60°C for 40-60 minutes. However, haste is dangerous: if you start polishing a varnish that is not sufficiently dry, it will become “greasy,” heat up from friction, and tear rather than polish.
| Hardener type | Drying time "from dust" | Time before polishing (20°C) | Accelerated drying (60°C) |
|---|---|---|---|
| Normal | 45-60 min | 16-24 hours | 45-60 min |
| Accelerated (Fast) | 20-30 min | 4-6 hours | 25-30 min |
| Slow | 60-90 min | 24+ hours | 60-80 min |
Temperature conditions are critical. If you dry your varnish at temperatures below 15°C without special additives, it may never reach its final hardness and will remain matte. Conversely, heating fresh varnish too quickly can cause the solvent inside the layer to boil and cause bubbles to appear.
Varnishing defects and methods for their elimination
Even experienced craftsmen have defects. The most common one is shagreen (orange peel). It occurs due to too viscous varnish, incorrect pressure or fast solvent. Light shagreen is removed by polishing with P1500-P2000 abrasive. Heavy shagreen has to be sanded off and varnished again.
Streaks (sagging) are the result of the master’s greed. You can try to “pull out” a small drip with a needle or blade while drying, but more often it has to be sanded off after drying. If the drip is deep, the varnish is cut off all the way to the base, dried and reapplied locally or to the entire element.
Haze (clouding) is often caused by high humidity in the room or water entering the spray gun. Moisture condenses in the cooling layer of varnish, making it whitish. Light clouding can sometimes be saved by polishing, but most often repainting is required. Dullness can also occur if you apply varnish to a cold part - the solvent will cool and condensation from the air will settle on the surface.
⚠️ Attention: When sanding defects, use only water with added soap or special lubricant. Dry sanding will clog the abrasive and leave deep scratches that cannot be removed by polishing.
Polishing: the final touch
Polishing is necessary to remove fine shagreen and give the varnish a perfect gloss. The process begins with assessing the hardness of the varnish. Soft varnishes (often found in Japanese manufacturers or in cheap materials) polish easily, but heat up quickly. Hard European varnishes require a powerful machine and aggressive abrasives.
The first stage is abrasive polishing with a paste with a grain size corresponding to the grinding (if the grinding was P2000, then an appropriate paste is needed, or we immediately move on to the finishing one if there are no shagreens). We use a polishing machine with a medium-hard wheel. Cross movements, without strong pressure, so as not to rub the varnish to the base, especially on the edges and corners.
The second stage is final polishing to remove holograms and add depth. Here a soft circle and fine abrasive paste or anti-hologram are used. After polishing, it is necessary to apply a protective layer (wax, ceramic coating or liquid glass), which will close the pores of the varnish and prolong its life.
How long does car paint dry before polishing?
The time depends on the type of hardener and temperature. For a normal hardener at 20°C, it is better to wait at least 12-16 hours, and ideally a day. Accelerated hardeners allow you to start working in 4-6 hours. Polishing underheated varnish will cause it to smear and lose its shine.
Is it possible to apply varnish to old paint without a base?
Yes, if the old coating (original varnish) is in good condition: there are no chips to the metal, deep scratches or peeling. The surface must be matted with P800-P1000 abrasive, degreased and applied 2-3 layers of varnish. This is called “zero varnishing” or gloss restoration.
Why did the varnish become cloudy after painting?
The main reasons: high humidity in the room, a cold part, the use of a quick solvent in cold weather, or water getting into the spray gun. Moisture condenses inside the layer, creating a whitish fog. Mild cases are treated by polishing, severe cases by repainting.
Do I need to sand the base before varnishing?
No, modern base enamel (metallic, mother-of-pearl) cannot be sanded before varnishing. It should remain naturally matte once dry. Sanding the base will cause streaking and a change in color tone. Only the old varnish or primer is sanded.
What is the varnish consumption per part?
On average, about 300-400 ml of ready-made diluted varnish is used on one side of the body (for example, a door or fender). A standard 0.85 liter can (varnish + hardener) is usually enough for 2 medium elements or 1.5 large ones when applied in 2 full layers.