Sooner or later, every car owner faces the need for body repair, whether it is the elimination of chips, combating corrosion or a complete repainting of the part. In the chain of preparatory work acidic It occupies one of the central places, being the foundation of durability of paintwork. Many beginners confuse it with a regular acrylic filler, not understanding the chemical difference, which often leads to the peeling of the paint and the reappearance of rust after a short time.
This material is also known as wash primer phosphate soil, performs a unique function of chemical protection of metal. Unlike insulating compounds, it does not just create a film, but reacts with the surface, providing unprecedented adhesion. Understanding the principles of this product will allow you to avoid costly mistakes and make body repairs truly professional.
In this article, we will discuss in detail the composition, application technology and typical misconceptions associated with the use of acid primers. You'll find out why. The acid soil layer should not exceed 10 micronsWhat happens if you break this technological parameter? We will also discuss compatibility with different types of enamels and putty.
Chemical composition and principle of operation
The basis of any acid soil is polyvinylbutylenewhich serves as a binding substance. It creates an elastic and durable base, able to withstand the vibrations and temperature expansions of the metal. However, the key component that gave the name to the product is orthophosphoric acid. It plays the role of an active agent that converts iron oxides into stable compounds.
When in contact with the metal surface, the acid reacts, creating a thin layer of phosphates. This process is called metal passivation. Phosphate film reliably blocks the access of oxygen and moisture to unprotected areas, stopping the development of corrosion even in microscopic pores. Without this stage, any subsequent painting will only be held mechanically, not chemically.
It is important to understand that acid soil is not a filler. It is not able to hide scratches, risks from sandpaper or minor irregularities. Its thickness after drying is only a few microns, making it transparent or semi-transparent. Other materials, such as acrylic filler soils or putty plates, must be used to level the surface.
Can I paint directly on acid soil?
No, you can't. Acid soil is hygroscopic and requires mandatory overlapping with an insulating layer (acrylic soil or epoxy primer-surfacer), otherwise moisture from the air will destroy the coating.
When it is necessary to use acid soil
The use of phosphate primer is justified not in every case of body repair. The main scope of its application is work with βbareβ metal, especially if there are corrosion foci on the surface that cannot be completely removed mechanically. It is also indispensable when working with non-ferrous metals such as aluminum, zinc and stainless steel, where the adhesion of conventional soils may be insufficient.
If you are doing local repairs and cleaning the metal to the base, applying an acid layer will be your insurance against film corrosion in the future. However, there are situations where its use is strictly prohibited or does not make sense. For example, you can not apply acid soil over old paint coatings, putty or epoxy compositions.
Letβs consider the main use cases in more detail:
- π Corrosion repair: After removing loose rust mechanically, the acid soil finishes the residues of oxides chemically, stopping the process.
- π‘οΈ Weld protection: When replacing body elements, welded joints are extremely vulnerable, and their processing with a phosphate primer significantly prolongs the life of the body.
- π© Work with aluminum: Aluminum parts (hoods, discs, suspension elements) require special training, which is provided by this type of soil.
Acid soil is a first-strike anti-corrosion weapon, not a finishing coating to level the surface.
Types of acid soils
In the modern market of autochemistry there are several formats of phosphate soil release, each of which has its own application features. The choice of a specific product depends on the scope of work, the equipment available and the conditions in which the repair is planned. The wrong choice of format can complicate the process or reduce the quality of the result.
The most common option is two-pound. They come bundled with a separate hardener bank. Before use, the components are mixed in a certain proportion specified by the manufacturer. This format provides maximum reliability and predictable results, since the chemical reaction is triggered at the time of mixing.
The second popular option is aerosol cans. They are convenient for small local repairs or hard-to-reach places where it is difficult to climb with a spray gun. However, aerosols often use less aggressive compositions, and it is more difficult to control the thickness of the layer in them. In addition, the cost of a liter of soil in aerosol is much higher than in banks.
There are also single-component soils that do not require mixing, but their use is limited. They are less resistant to external influences and are more often used as temporary protection or in specific industrial conditions. For high-quality body repair in the garage or service, preference should be given to proven two-component systems from well-known brands, such as: Reoflex, Novol or Motip.
Application technology: step-by-step instructions
The process of applying acid soil requires strict adherence to the technology, since we are talking about working with aggressive chemicals. Mistakes at this stage could nullify all further efforts. Surface preparation is 80% of the success of the whole event. The metal must be thoroughly cleaned of oils, silicones and dust.
For degreasing, it is best to use special antisilicone solvents. After degreasing, the surface must be dried. If two-component soil is used, it should be mixed with the hardener in the proportion indicated on the package (usually 1:1 or 1:4, depending on the brand). The mixture retains viability for a limited time, usually from 30 minutes to 2 hours.
You can apply the soil with a spray gun or brush (for hard-to-reach places). It is important not to overdo it: the layer should be thin, βwetβ, but not current. Excess material can lead to the fact that the soil does not dry out inside and lose its protective properties.
βοΈ Checklist for preparation and application
After application, it is necessary to wait for the time of technological drying. It is usually 15-20 minutes at a temperature of +20 Β° C. After this time, the surface is ready to be covered with an acrylic filler or epoxy soil. The acid soil is usually not needed to be polished unless it has dried for too long (over 24 hours) β in this case, a light refurbishment is required to improve the adgsia of the next layer.
Characteristics comparison table
To better navigate the properties of different types of soils and understand the place of acid composition in the general scheme of work, it is useful to refer to comparative data. Below is a table showing the key differences between phosphate soil and its main competitors.
| Parameter | Acid (Wash Primer) | epoxy | Acrylic |
|---|---|---|---|
| Metal adhesion | Chemical (maximum) | Mechanical + chemical | Mechanical |
| Anti-corrosion protection | High (passivation) | High (barrier) | Medium |
| Thickness of layer | Up to 10 ΞΌm (very thin) | Up to 50-100 ΞΌm | Up to 200 ΞΌm (filler) |
| Grindability | Not grinding (usually) | grinding | Easy to grind. |
| Time to dry | 15.30 minutes. | 1 hour to day | 30-60 minutes. |
The table shows that acidic It gains in drying speed and depth of penetration, but loses in the ability to form a thick layer. Epoxy compounds, on the other hand, create powerful insulation, but take longer. Acrylic soils serve mainly for leveling. The ideal scheme often includes a combination of: acid for protection, epoxide for insulation, acrylic for alignment.
Material compatibility and precautions
One of the most critical aspects of working with acid soils is their compatibility with other materials. The chemical activity of orthophosphoric acid can come into conflict with certain types of putty and paint. In particular, it is strictly forbidden to apply polyester putty directly to an undried or improperly prepared acid layer.
β οΈ Attention: Never apply a putty directly to the acid soil without first overlapping with an insulating layer (epoxy or acrylic soil). The acid can react with the components of the putty, causing swelling or absence of adhesion.
You should also be careful when working in poorly ventilated areas. Solvent vapors and acid vapors are harmful to the respiratory system. The use of high-quality respirator and gloves is a mandatory safety requirement. Do not allow soil to get into the open areas of the skin or eyes.
If you use products from different manufacturers, always run a compatibility test on a small, unobtrusive area. Chemical formulas can vary, and reactions between components of different brands can sometimes be unpredictable. Better to be safe than to redo the work.
If you accidentally overexpose acid soil in the air for more than 24 hours before overlapping, be sure to walk a little over it with the abrasive P600-P800 and degrease the surface again.
Typical errors in work
Even experienced craftsmen sometimes make mistakes that can cost the customer the quality of the coverage. The most common of these is applying a layer of acid soil too thick in the hope of improving protection. As we have already found out, this leads to the opposite effect: the upper part of the layer is polymerized, locking the solvent and acid inside, which eventually causes detachment.
The second mistake is to ignore the time of interlayer drying. Attempting to speed up the process with heating (dryer or IR drying) immediately after application can lead to boiling of the solvent and the formation of pores. Acid soils should dry naturally or at a moderate temperature indicated in the technical map.
The third mistake is to keep an open can with diluted soil. The viability of the mixture is limited. Trying to use the residues the next day will lead to the fact that the soil will lose its properties and will not provide the necessary adhesion. Dilute as much material as you can produce in 30-40 minutes.
β οΈ Attention: Do not try to resuscitate thickened or partially dried soil with the addition of a solvent. This will disrupt the chemical balance and the coating will lose its anti-corrosion properties.
Compliance with technology, the use of quality materials and attention to detail will allow you to get a result that will please the eye and protect the car for years. Acid soil is a powerful tool in the hands of a professional, but it requires respect for chemical processes.
Can I apply acid soil to rust?
Yes, you can and should, but with reservations. Acid soil is designed to work with residual, tightly sitting rust after mechanical cleaning. It converts the oxides into a stable layer. However, it is useless to apply it to a thick layer of loose, flaking rust ("red mud") - first it is necessary to mechanically remove all unstable formations.
Do I need to grind the acid soil before painting?
In most cases, it is not necessary to grind the acid soil if no more than 24 hours have passed since it was applied (the maximum interlayer exposure time specified by the manufacturer). If more time has passed, the surface may become dusty or oxidized, then light refurbishment with fine abrasive (P600) and degreasing are required.
What is the difference between acid soil and epoxy?
Acid soil (wash primer) penetrates the metal and chemically binds to it, creating a thin film, but it is hygroscopic and requires overlap. Epoxy soil creates a thick, waterproof barrier film that insulates the metal from the medium, but it does not have the same penetrating ability and adhesion to oxides as acidic.
How much acid soil dries?
The drying time "on the stick" is usually 10-15 minutes at a temperature of +20 Β° C. Complete drying and readiness to overlap with other materials occurs in 20-30 minutes. Always check the exact time in the specific manufacturerβs technical documentation (TDS), as the compositions may vary.