When restoring the geometry of the body after an accident or eliminating deep scratches, it is the soil-filler that becomes the very layer that hides the risks from abrasive and equalizes micronervities before painting. This material has a high hardness after polymerization and is able to fill the risks up to 100 microns deep, making it an indispensable final stage of preparation of the metal for enamel. Unlike primary soils, which work for adhesion and anticorrosion protection, filler It solves only the problems of mechanical surface alignment. Incorrect choice of layer thickness or violation of the temperature regime of drying often leads to material drawdown, when a month after painting on the body appear the contours of the putty or risks.
The main task of this product is to create a perfectly smooth, non-porous surface, on which the base paint will then lie. Modern two-component systems based on acrylic resins allow you to obtain a coating with minimal shrinkage, which is critical for maintaining the quality of repairs in the long term. HS products High Solids contain more dry residue, so they give less shrinkage compared to traditional materials, but require more accurate compliance with the mixing proportions with the hardener.
The application process requires strict adherence to the technology, as this material is not decorative and does not protect the metal from corrosion directly without the use of insulating layers. If you skip the preparation stage or apply the composition to a greasy surface, the entire structure will begin to peel off along with the finish enamel. Therefore, understanding of chemical nature corn-soil And their interaction with other materials of body repair is a basic skill for a painter.
Chemical composition and principle of action of acrylic fillers
Most modern fillers are based on acrylic polymers, which, when interacting with the hardener, trigger a polymerization reaction. Two-component system provides the creation of a strong grid of polymer bonds, which after drying becomes chemically inert and solid. Unlike single-component aerosols, which dry due to the evaporation of the solvent and sit strongly, professional products in banks create a layer that can withstand temperature changes and mechanical stress.
The most important component is the filler - usually it is talc, microtalc or special fibers, which create the volume, filling the voids. The concentration of particulate matter determines how deep a material can “tighten” the risk. High-density soils They contain more solids, allowing them to be applied to thicker layers without the risk of bubbles or craters.
The solvent in the mixture performs the function of a regulator of viscosity, allowing the material to spread out and form a smooth surface. Depending on the temperature in the paint chamber and the area of the painted part, the masters choose a solvent with different evaporation rates: fast, standard or slow. Choosing the Right Solvent It directly affects whether the material will have time to spread before polymerization or, conversely, whether it will not flow on vertical surfaces.
⚠️ Warning: Never mix the filler soil with nitrosolvents or solvents for base enamels, as this will cause a chemical structure to break down and the coating to swell.
Key differences from epoxy and primary soils
A common mistake of beginners is confusion between filler, epoxy soil and rust primer. epoxy creates an impermeable film that blocks the access of oxygen and moisture to the metal, and has excellent adhesion, but is poorly polished and has a low filling capacity. The filler, on the contrary, is perfectly grindable, but hygroscopic and requires metal insulation, especially if we are talking about ferrous metals that are subject to corrosion.
Primary soils (acid or phosphate) are designed for chemical etching of metal and creating roughness for the adhesion of subsequent layers. They have no scope and cannot hide the risks. Acrylic filler It is applied on top of these layers or on pure non-fat metal (if the product specification permits), performing the function of the coating body.
Below is a table that helps you quickly navigate the appointment of various types of soils during body repair:
| Type of soil | Substantive function | Grindability | Corrosion protection |
|---|---|---|---|
| Acid (phosphate) | Chemical adhesion | Low (thin layer) | High (passivation) |
| epoxy | Barrier protection | Medium (scores abrasive) | Very high. |
| Acrylic filler | Alignment | Great. | Low (requires isolation) |
| Sealer sealant | Isolation and adhesion | Not grinding. | Medium |
2K Technology
Why two components?: Two-component (2K) systems involve mixing the base with a hardener immediately before use. After mixing, an irreversible chemical reaction begins, so the material has a limited lifespan, usually from 30 minutes to 2 hours. Unlike 1K materials, 2K soils do not require air to dry and polymerize even in a confined space, forming a stronger coating.
Technology of preparation of the working mixture and selection of solvent
The quality of the final result depends on the correct preparation of the mixture by 80%. The mixing proportions are indicated on the manufacturer’s bank and can vary, for example, 4:1, 3:1 or 2:1 by volume. Dosage accuracy hardener is critical: its excess will make the coating fragile and prone to cracking, and the lack will not allow the material to gain full hardness, which will lead to prolonged drying and poor grindability.
The solvent is added to already mixed components to bring the viscosity to the working. The amount of solvent is usually 10-20% of the volume of the mixture, but the exact percentage depends on the ambient temperature and diameter of the spray gun. For work in hot weather or in a large chamber slow-motionTo avoid "drying" of the torch and shaking, and in the cold - fast to accelerate evaporation and prevent leaks.
After adding all the components, the mixture must be thoroughly mixed, lifting the material from the bottom of the jar, where heavy fractions of the filler settle. The solution is then filtered through a funnel with a mesh (usually 125-190 microns) to prevent the insoluble particles from entering the spray gun. Filtration - a mandatory step, since even a small motley can spoil the entire layer, creating a crater or scratch when grinding.
- 🧪 Use measuring glasses with calibration to accurately observe the proportions of the base and hardener.
- 🌡️ Choose the evaporation rate of the solvent in strict accordance with the temperature in the shop (T° air + 10-15° C for metal).
- ⏳ Consider the “viability” of the mixture: cook as much soil as you can use in 40-60 minutes.
- 🌀 Stir the composition for at least 2-3 minutes, paying attention to the bottom and walls of the container.
⚠️ Note: The finished mixture cannot be stored "for later". After the expiration of the life life, the material begins to thicken and loses its adhesive properties, even if it appears to be liquid.
Rules for application and formation of layers
The application of the soil-filler is carried out with a spray gun with a duse diameter from 1.6 to 2.0 mm, depending on the viscosity of the product and the manufacturer's recommendations. The pressure at the exit of the nozzle is usually 2.5-3.5 atmosphere. Before starting work, you need to configure the spray torch and check the uniformity of the material supply on the test surface. First layer It is always applied in a thin, "dust" way to ensure adhesion to the surface and avoid dissolving old coatings or putty.
After short exposure (usually 5-10 minutes, the so-called "cushion"), the main wet layers are applied. Their job is to shape the thickness and fill the risks. The number of layers varies from 2 to 4, depending on the thickness and type of product required. It is important to give each layer time to evaporate the solvent (interlayer drying), otherwise the effect of "boiling" or the formation of bubbles in the future is possible.
When working with vertical surfaces, you should be especially careful with the thickness of the wet layer to avoid ducts. Thyxotropic properties Modern soils allow them to keep their shape, but exceeding the thickness of the layer will inevitably lead to the drainage of the material. The movements of the gun must be smooth, with a 50% overlap of the torch for even distribution.
☑️ Soil application control
Drying, grinding and preparation for painting
Complete polymerization of acrylic filler can take from 12 to 24 hours under natural drying at a temperature of +20 ° C. However, in a car service environment, time is often shortened by infrared drying or forced drying in a chamber at 60°C for 30-40 minutes. Heat treatment Not only does it speed up the process, but it also promotes more complete polymerization, making the material harder and easier to grind.
Grinding is performed only after the material is completely dry. If you start grinding the undried soil, the abrasive will instantly clog, and deep furrows will remain on the surface, which will appear after painting. For grinding, paper gradations from P320 to P600 under enamel and to P800-P1000 under metallic are used. Machine grinding is preferable to manual, as it provides a flatter surface.
After grinding, the surface must be thoroughly cleaned of dust with compressed air and degreased. If between grinding and painting passes a long time, or if the soil was polished "dry" and managed to dust, it is recommended to apply a layer. sealant (sealer). It canned the surface, leveled absorbency and will provide the perfect adhesion of the base paint.
Typical errors and defects when working with filler
One of the most common problems is subsidence, when after painting, the outlines of the putty or risks become visible. This is due to the application of too thick layers, insufficient interlayer exposure or the use of a cheap material with a high solvent content. Shrinkage It can last for weeks, so saving on a quality product often comes off sideways.
Another frequent defect is “boiling” or pore formation. This is a consequence of applying the next layer to the undried previous one, when the solvent is locked inside and when heated (from the sun or drying) tries to evaporate, tearing the film. Also, defects result in the wrong selection of solvent: too fast in a cold shop will not allow the material to spread, leaving a shaking, and slow in the heat will provoke leaks.
Peeling off the soil from metal or putty is most often caused by poor degreasing, the presence of silicone contaminants or moisture on the surface. Sometimes masters forget that some types of putty (especially polyester) require mandatory priming with epoxy before acrylic, as they can be hygroscopic. Violation of compatibility Materials are the right way to marriage.
The ideal result is only a comprehensive approach: clean surface + the right product + compliance with drying time intervals. Missing any stage leads to a defect.
Can I apply the soil-filler directly on the bare metal?
Technically, acrylic soil will lie on the metal, but this is not recommended for long-term repairs. Acrylic is porous and lets moisture through, which will lead to corrosion of the metal under the paint layer. On bare metal, it is better to first apply an epoxy soil or an acid primer, and already on top - an acrylic filler.
How much does the filler dry before painting?
At a temperature of +20 ° C and normal humidity, the drying time "on the stick" is 30-40 minutes, but the material gains full polymerization for grinding in 12-24 hours. When using an IR dryer or camera, the time is reduced to 30-40 minutes at 60°C.
What abrasive to use for grinding under the base?
Under solid (solid colors) usually use the abrasive P400-P500. Under metallic and pearl surface should be smoother, so use the P500-P600, and sometimes P800, so that the risks do not shine through the thin layer of the base.
What to do if the ground has flowed?
If the leak is detected immediately, you can carefully remove its excess with a soft brush or a finger in a glove, without rubbing. If the material has already begun to grasp, you need to let it dry completely, then grind the influx of abrasive P320-P400 and locally subtract this area.