White primer for cars. Acrylic primer for cars. How to use acrylic primer

Priming is the basis for successful car painting. In this case, the soil acts as a kind of foundation, on which the remaining layers of the paintwork are laid. Almost all the mistakes made at the priming stage are not related to the lack of skills and knowledge of how to properly paint a car body part (the practical part is the easiest to master). Most of the problems come from the fact that today almost every well-known company that produces repair materials offers a wide range of primers that differ both in purpose and in the principle of operation. Therefore, it can be very difficult to choose the right primer for a car in a particular case.

What are the options

Given that today there are hundreds of brands and names of various primers on the market, they can be conditionally divided into two large groups:

• primers (primary);
• fillers (secondary).

The former are used to protect the metal from corrosion and further provide a strong adhesion of the paint coating to the painted surface. The purpose of the latter is to level out surface irregularities before painting and create a homogeneous base layer for enamel. Also today you can find universal primers that combine the properties of primers and fillers.

All automotive primers are divided into the following types:

• one-component (do not contain hardener and dry up to several days);
• two-component (they contain hardeners, so they dry out in a few hours);
• alcohol (due to the presence of alcohols in the composition, they dry out in a matter of minutes).

Primary soils

Primary primer (adhesive, etching) is designed to protect bare metal in places that are most susceptible to corrosion. Of this category, automotive primers with phosphating action are the most popular today. They are called so because the catalyst for the chemical reaction in them is a mixture based on phosphoric acid. Interacting with the metal surface, the primer forms a thin (up to 12 microns) and durable layer of sparingly soluble phosphates, which further protects the surface from corrosion. What is the best primer for cars? There are no special preferences here. Although, if possible, it is better to buy a high-quality, expensive primer, which precisely indicates the recommended application thickness and possible shrinkage upon drying.

Secondary soils

These include standard protective, passivating and other types of primers. They also protect the car body from moisture and corrosion, but their main purpose is to smooth out various irregularities, roughness and pores in the metal surface. After processing, the latter becomes absolutely even and uniform, which allows you to perform high-quality coloring.

Epoxy primers and insulating primers (sealers) can be placed in a separate category. The former are a good alternative to acid-containing primary primers, while the latter serve to isolate old coating layers, eliminating possible problems with their swelling and peeling.

Soil selection

When choosing which primer is best for a car, you need to give preference to trusted manufacturers. Here, as nowhere else, the rule that the miser pays twice is true. Repairing a car once, but with high quality, is much cheaper than saving money and then redoing all the work.

High-quality primers for cars at competitive prices can be found in the online store site in the appropriate section. The electronic catalog contains a huge range of primers and other materials. In addition, we have all related products for car repair and painting. Together with the primer, you can buy abrasives, car enamels, fillers, varnishes and all the tools necessary for the job.

A primer is a composition that is applied to the surface before any finishing material is applied to it. This is done in order, first of all, to increase the tenacity of the surface, but, in addition, the primer can improve frost resistance, level the absorbent surface. There are mixtures such as acrylic, acid, water-dispersion, latex, based on drying oil, alkyd or epoxy resins. The primer in spray cans is the most convenient in application.

The primer is sold in different types of packaging, most often found in jars or spray cans. Consider the main advantages of the latter option:

• The aerosol in the can is a one-component composition, i.e., immediately after purchase, it is ready for application and does not require additional preparation.
• Aerosol primer is more convenient to use and at the same time does not differ in its characteristics from the can version.
• Such a primer provides an even and smooth coating, and also allows you to achieve smoother transitions between surface areas with non-ubiquitous processing.

The only drawback and difference of such a primer is its density. After all, the composition must be well sprayed, so it is forced to have an appropriate fluidity.

Primer in spray cans will be an excellent option for applying to such coatings as:

• plastic;

• black metals;

• light alloys;

• aluminum parts;

• galvanized or chrome parts.

Primer for car

Autoprimer is used in auto repair to prepare metal surfaces for painting. Basically it is an epoxy primer. It is created from special resins and chemicals to create a protective film on the metal surface and prevent the development of corrosion processes.

Epoxy primer is available both in cans and in the form of a primer spray. For the repair of individual sections of the car, it would be better to use a spray primer.

Surface preparation before priming:

1. Wash and dry the area to be treated thoroughly.
2. Then degrease with white spirit.
3. Remove all signs of corrosion.
4. Sand the surface, but so that no irregularities remain on it.
5. Apply putty and fill in scratches, chips, etc.
6. Sand down.

After preparing the surface, you can apply an aerosol primer to the area of ​​\u200b\u200bthe car you need. It should be applied in two or three layers, while observing the intervals between applications. Read the instructions carefully, if you follow them, then you can not worry about the success of the work performed.

On the video: the advantages of epoxy primer in a can.

Application features

During construction, to prepare the surface for the application of finishing materials, it will also not be superfluous to use a primer in the form of a spray. Indeed, in this case, you can do without additional devices such as rollers, brushes, etc. There are mixtures designed not only for metals, but also for concrete, brick, plastics or wood. On average, one cylinder is enough to process an area from 2 to 6 square meters.

If you do not know on what basis to choose the composition, give preference to a universal primer.

Before applying an aerosol or any primer, you need to clean the surface well to avoid foam and other troubles. In general, the process remains unchanged: preparation of the processing area, drying, grinding. After that, you can use the aerosol primer in practice:

1. In addition to simple cleaning, you also need to degrease the surface, as the compounds may not adhere to it properly.
2. The correct choice of primer coating is a very important aspect, although the composition, for example, for wood, can also be applied to a concrete coating or metal, this will not improve adhesion, but, on the contrary, worsen the tenacity of the surface and finishing material.
3. Application. Shake the can well, then spray on the desired area at an angle of 90 degrees. In this case, the balloon should be at a distance of 25 to 30 centimeters from the treated area. Most often, the application occurs in 2-3 layers with a time interval of half an hour.

Spray the contents on every inch of the surface, but smoothly, do not linger on one of the areas longer than on others.

Some tips for working with spray primer

In construction or repair work, sometimes you have to deal with very rusty metal surfaces. But, few people know that it is not at all necessary to completely clean them, it is enough to remove fragile fragments of rusty scab with sandpaper, which may fall off during further work. After this step, it is allowed to apply the primer directly on the rust.

When you need to leave some areas of the surface untouched, stick masking tape or something similar on them.

It happens that when coating small objects, the mixture is overused, i.e., you can get by with a small stroke, and a volumetric jet escapes from the nozzle. In this case, you can simply extract a little liquid from the cylinder itself, just direct the jet so that it touches the inner wall of the jar, glass or any other small container.

After that, the priming liquid should be stirred so that excess gases come out of it. Now you can simply dip the brush and prime a small object with it without wasting a lot of material. It is important to remember that the temperature limits when working with an aerosol primer are not higher than +30 and not lower than +10 0 С.

Types of compositions and their description

It is not very difficult to choose the right option, it is enough to take into account several factors: the type of material being processed, the operating conditions of the structure and the weather conditions in your area. A primer from a can can be used to treat many metal alloys and more. For this, specialized types of soil are used, here are a few representatives of those:

• acrylic primer. It is used for a wide variety of surfaces, such as plastic, steel, aluminum parts, metal putty and so on. It is resistant to temperature extremes, moisture and harsh weather conditions. It has established itself as a reliable and high-quality composition.

• For different types of plastics. A single-component primer is applied to plastic decor elements, which is contained in a can, plus it consists in the absence of any additional mixing. Synthetic primer made to work with plastic, designed to cover small areas such as a rearview mirror or bumper.

• Anticorrosive primer. This tool is in the greatest demand at the moment. Spray mixtures are applied to metal parts, this provides good protection against corrosion, and also better adheres paint and surface.

• Firming. This composition is used in auto repair shops to repair dents, scratches or cracks on the car body. Several layers of this primer fill the damage, its hallmark is high adhesion.

• Epoxy primer in a can. The composition of the contents of the cylinder covers the car body with a thin film, improving adhesion, protecting it from corrosion and even mechanical damage. Enjoys great success with motorists and craftsmen.

• Etching or acid soil. This is a primer for metal, which means it should only be used on metal surfaces, its use on plastic or putty is strictly prohibited. After all, a feature of this composition is the erosion of a thin layer of metal to ensure reliable tenacity of the paint and combat the formation of corrosion.

It is worth noting that the aerosol primer based on epoxy resins dries for a long time. Thus, if you want a quick result, then you should use quick-drying products. The right choice of primer for a car or home renovation is based on the correct definition of the purpose, knowledge of the types of primer and their characteristics.

Aerosols in action (1 video)

If the foundation of the building is laid with high quality, then this can fully guarantee the durability of the structure. The same rule applies to the most ordinary cars, since the primer for the car is the base for the paintwork and protects the metal from corrosion. If you want to get a high-quality body coating, then you should not spare money for priming materials for cars.
This process is one of the important stages of body repair. Putty allows you to correct the shape of the part, and the primer helps in anti-corrosion treatment, and is also an intermediate layer between putty and paint. This is important, since paint cannot simply be applied to metal or putty.

When priming, several products are used. It is an epoxy car primer, leveler and sealer.

Epoxy primer is water resistant. It is used to protect the surface from oxidative processes. Before application, the mixture is mixed with a hardener in a certain proportion. The substance is applied with a spray gun in a couple of layers.

The primer can also be applied in this way: first filler, then several layers of soil. Then they are sanded, and then a sealant is applied.

Epoxy primer is excellent in that when using it, there is no need for grinding. Minor imperfections found during painting can be eliminated with fine sanding.

High-quality soil is quite expensive, but if you save money, then soon you will need to repeat the operation again.

Inexpensive primers shrink over time, and all defects become clearly visible. Obviously, their correction will require additional costs.

The primer on metal perfectly adheres to the surface and protects the metal from corrosion.

There are passivating primers that contain chromium compounds and make the surface water resistant. This material with inert additives is protected not chemically, but physically without passing water. It is used for small (local) works.

Primer tread compounds contain inclusions of metals that have a lower potential compared to iron. In the event of damage, this type of material will be the first to react with an aggressive environment, that is, it will protect the metal. Other types of car primers are also used: phosphating, rust modifier primers, one-component, two-component, alcohol.

The main types of soils used for car repair

There are primers of various colors that allow you to save paint. Acrylic types are used together with special acrylic thinners. It is important to remember that it is better to use solvents from well-known brands.

Remember to wear things like a respirator and gloves when doing body work to help minimize hazards.

How to apply?

Working with metal. With this type of work, care must be taken to protect against corrosion. Before painting, it is required to subject the metal to an acid primer, which will help protect the surface from rust. Then you need to treat with epoxy resins, and then with a primer against corrosion type 1K.

Acid primer. This type of priming is carried out using a product that consists of two components. It is good for twenty-four hours after stirring if its temperature is twenty degrees Celsius. The main work is carried out after the acid soil has dried, but this layer still has activity on the surface. Acidic soil is subjected to polishing with a sandpaper with grain P280-Z400. Different layers can be applied with a break of five minutes. You can apply the mixture in two or three layers. It dries from thirty to ninety minutes at twenty degrees Celsius.

This type of material should not be covered with polyester putty, as it can dissolve the primer. Only a mixture of type 2K can be used. A protective primer can be safely applied to a hard putty, since the putty will not have chemical activity.

It is very important according to the technology of work to wait for the complete drying of each of the layers.

Soil drying phases:

1. The state of drying when the dust no longer sticks to the treated surface. When pressed, deformation of the superimposed layer can occur.
2. Suitability of the machined part for assembly. In this case, surface deformation can be observed with a strong impact on the part.
3. Complete drying. The paint layer can be processed and polished.

Acrylic primer application and treatment

The filler is the basis for the paint. The paint can only be applied on the primer or the previous coat of paint.

Filler Functions:

1. creating the perfect surface;
2. masking layers of previous materials;
3. paint base.

You can not paint the putty itself or the primer if it is acidic. Otherwise, the quality of the final result may decrease, and inhomogeneities may appear on the machined surface.

Primer filler 2K includes acrylic in its base and is somewhat similar in properties to enamel paints.

The filling capacity depends on the content of the solid element and is divided into standard, medium (MS) and high (HS).

The filler is a layer or insulation. It is applied in several layers with an interval of five to ten minutes. After acquiring a solid state, the soil can be polished.

If the goal is to avoid different shades of the coating, then colored primers are used. They allow you to reduce the amount of paint used.

The type of filler depends on the work and the surface to be treated. If you manipulate the proportions of the composition, then you can achieve the desired properties of the substance. It is important to choose a hardener and solvent that depends on the air temperature.

Acrylic-based fillers retain their properties for one hour. Do not use more filler than necessary.

If you need to repair a large object, then the filler primer must be applied to the entire body. If there was no puttying, then it is pointless to use a filler. In this case, a primer against corrosion type 1K is used. If the surfaces are small, then the filler should completely cover the putty.

Acrylic primer is applied with a spray gun, and it is better to do this in a special chamber. If you use a special spray gun, you can achieve excellent quality coverage. The orifice of the remote control should be between 1.6 and 1.8 mm in size.

If the filler will be sanded, then several layers should be applied to eliminate irregularities.

After application, this layer must be subjected to diligent grinding. If this is not done, then defects will occur on the paint layer. The primer can only be sanded when it is dry. It is necessary to pay special attention to places where the thickness of the seams is increased. If the filler, which is not yet dry enough, is sanded, then there will be risks and the sanding paper will clog.

The drying time depends on what type of material was used and in what quantity. It can be dried from three to twelve hours at twenty degrees Celsius.

Grinding is carried out in two stages:

• rough grinding
• fine grinding.

With rough grinding, the surface of the filler is leveled. For this operation, sanding papers with increased grain size are used.

Fine grinding is carried out in order for the surface to acquire the desired structure and for the paint to adhere well to the surface and mask the traces of grinding. For this operation, sanding paper with a small grain size is used.

Proper grinding of soil and other materials is a stepwise process. It starts with a rough skin and ends with a thin one.

Final sanding. This operation directly depends on the number of layers of application of paints and varnishes. When painting in one layer, the film is thicker than when painting in two layers. If the painting is carried out in two layers, then the traces of grinding are masked by paint, not varnish. One-layer staining masks rough sanding marks. That is why preparing the surface for metallic painting is the most difficult.

Dry and wet grinding. In the first case, it is possible to achieve surface quality in a shorter time. Wet sanding is done without the aid of machinery and generates more waste. Dry grinding is carried out using special machines that suck up dust. Wet type allows the use of sandpaper for sanding with a smaller degree of grit.

Priming in car workshops

In upscale workshops, before painting a car, several layers of various primers are applied to the surface. First of all, an acid primer or phosphating primer is used, as it can provide a better level of adhesive performance. Primary primer is applied to the surface, free from dirt and grease. It is not necessary to grind the surface.

Then a couple of coats of a secondary primer are applied. Most often, a soft or hard soil of two components is used. Professionals use mixtures that do not need to be sanded. If the metal is very even, then in the second stage you can use the substance to create a glossy surface.

The choice and application of material

Before buying, it is important to make sure that the product has not expired. It is better to use products of the same brand in order to ensure the proper quality of work. It is also better to use proven brands of products.

It is important to observe the time for drying the primer. The surface can be leveled with sanding paper.

An automotive sealant should be used to prevent mixing of primer and paint layers. It gives uniformity to the layers and improves adhesion.

Every car owner wants to protect the paintwork of their car from corrosion. A reliable base, foundation for paint and protection of metal is a car primer. A large number of various products are presented on the modern market of auto products: from cheap to expensive, promoted and little-known brands. This means that the choice of autoprimer is not an easy task, but a responsible one. Let's figure out what you need to know about this tool and how to properly use its wonderful qualities?

Autoprimers calls a whole series of compounds intended for application to the surface of the body. A quality product is always expensive, but it is better to opt for it in order to avoid an unsatisfactory result and re-staining. There are several types of primers:

• Sealants: protect against the solvent properties of the paint, improve adhesion and make layers uniform.
• Resin-based epoxy waterproof primers: have a dense structure, protect against oxidation. Usually mixed with a hardener and applied in 2-3 coats. Does not require sanding after application.
• Primers (leveling primers): quick to apply, easy to sand, perform an adhesive and anti-corrosion function.

Compositions for priming the surface differ in the presence of various components. Based on this, they can be divided into:

• Alcohol: they dry very quickly, within an hour, they are used in places where it is impractical to work with conventional primers.
• One-component: rarely used, as they do not contain a hardener, and therefore the drying process takes a long time.
• Two-component: thanks to additional components (hardener cans), such primers dry out within a day, and therefore are used more and more often. There are two types: hard and soft. The former are more stable, but more difficult to grind, while the latter are easier to process, but at the same time they shrink and, consequently, the paintwork deteriorates over time.

Primers are also distinguished by the method of protective effect on the metal. What are the primers in this regard? Each of them is best searched for by a special letter marking. The following categories are distinguished:

• with phosphating action;
• passivating;
• tread;
• with inert particles;
• rust modifier.

Phosphating primer

The composition contains phosphoric acid, which forms sparingly soluble phosphates in combination with metal. The resulting layer, despite its thinness (only 8-12 microns), is strong and has good adhesion. The primer is able to penetrate the metal to a depth of 0.05 microns. After applying the first layer, you can immediately apply the second. Which of the primers has phosphating properties is easy to understand, they are marked with letters - VL.

Passivating primers

These products make the surface immune to moisture (that is, passive) due to the chromates of certain metals contained in their composition. Due to this property, an oxidation reaction will not occur.

To protect the wings and bottom of the car from corrosion, a lead-surface primer is often used. When choosing a composition, it is also best to focus on the letter marking - GF.

Protective means

Such a primer assumes the protection of the metal surface from the negative effects of the environment. The potential of the metal dust contained in its composition is lower than that of a car body. Thus, in relation to the car, such a primer acts as a tread. The letter designation EP and E refers to protective primers.

Compositions with inert particles

These primers mechanically protect the surface without interacting with other film-forming substances. These compounds are most often used during minor body repairs. Their marking, for example - FL-OZK, GF-21.

rust modifier

In fact, this primer is a converter of corrosion products. In cases where rust removal is impossible for some reason, the composition is applied directly to the damaged surface area, interacting with it. Corrosion elements are converted by the modifier into a durable protective film. The composition in cans can be applied by spraying or brushing, in two layers. A prerequisite for high-quality work with such a primer is the air temperature not lower than +15 C 0.

The car can be covered with soil in a car service or on your own. However, before that, you should take care of choosing a quality product. It is best to purchase products of the same brand in order to avoid their negative mutual influence on each other. Which company is preferable is a matter of taste, but before starting work, you should carefully study the composition of the primer, its shelf life and compatibility with other products. Do not neglect the implementation of the instructions and be sure to dry the layers thoroughly.

Priming in a car service

A car workshop will provide the owner of the car with a quick and high-quality result, but such work will not be cheap either. The fact is that a professional who respects the client and his work applies several types of soil to the car body. In the beginning, a phosphating or acidic composition is used to ensure the best adhesion. The first layer of primer is applied to the washed, degreased surface. It does not require subsequent sanding.

To avoid poisoning when working with chemical or phosphating compounds, it is necessary to ventilate the room well.

The second part of the work is the application of 2-3 layers of a two-component soft or hard primer. This tool is best to hide minor flaws and defects on the surface. The time interval between applying layers is 10-15 minutes. If the surface is flat, then usually use a primer that does not require grinding and, after it dries, proceed to paint the surface.

Do-it-yourself priming

Doing the work yourself, especially carefully approach the choice of primer. It is difficult to say which little-known manufacturer and its products guarantee good quality, and therefore it is better to focus on popular, well-established brands. It is also worth paying attention that the primer copes well with small irregularities, but larger defects are eliminated with putty.

Thoroughly prepare the vehicle surface before priming. After reading the instructions, proceed to the application of the composition. Let the layers dry well, and then, for leveling, process with sandpaper with different grain sizes. Applying a smoother of a thicker consistency will hide the shortcomings of grinding. Be sure to use an auto sealant to prevent mixing of paint and primer.

Priming a car with your own hands is much easier than doing it, because smudges on the ground are quite difficult to make. primer is so simple that anyone can master it. In order to qualitatively prime the car yourself, it is enough to familiarize yourself with the theory once.

Priming the machine is best done in a relatively clean, well-ventilated area that will have a minimum of dust. If we are talking about a local primer, then you should cover the parts that will not be primed with special paper (in extreme cases, newspapers) and masking tape. Before applying the primer, a tool such as a primer sprayer should be prepared in advance.

Primer basics

After gluing the machine, you can begin to dilute the soil. First of all, it must be thoroughly mixed in order to lift heavy components from the bottom of the can, and then diluted with a hardener (it is highly desirable to use only native) and a solvent (preferably native, but 646 is also possible). The proportions must be indicated on the bank. It is better not to breed by eye, but to use a special container where you can see grams.

It is desirable to filter the finished mixture through a branded filter or ordinary gauze folded 3-4 times. Usually it is enough to apply the primer in 2-3 layers. It is extremely important to adhere to drying between layers of 5-10 minutes. Otherwise, the soil may boil, which is highly undesirable.

On a note

The choice of soil color is of great importance. The paint should cover the ground so that it does not shine through from different angles. The universal color is grey.

There are also primers in black, white, red and other colors. With this palette, you can mix primers and get the desired color. It is important to remember that the mixed materials must be of the same company.

On a note

Before applying the primer, wipe the machine with an antistatic cloth, then degrease with anti-silicone or alcohol.

According to technology, the first layer must be filled normally. But, if the primer falls on the old paintwork, which in some places is wiped down to the old primer, then it is in these places that the new primer can be undermined. To prevent this, you need to spray the first layer and dry for about 10 minutes. The second and third layers can be poured, then allowed to dry for 24 hours.

You can process the soil both dry and with water. It should be remembered here that soils partially absorb water, which eventually leads to metal corrosion, therefore, it is better to process dry. A special grinder can help with this. For metallic, the body should be cleaned with R-600 and R-800 emery, but for ordinary acrylic, R-400 and R-500 will be enough.

New details need to be given extra attention, because they are covered with shipping primer (usually black). In order for the repair of the machine to be of high quality, the transport soil must be cleaned with R-240 emery to the metal. After this procedure, you can put 2-3 layers of soil.

After 10-15 minutes, it is necessary to show the primer with paint of a contrasting color. The next day you can start cleaning. During processing, the developer may show slight irregularities. In this case, it will be necessary to reprime the flaws or the entire part as a whole.

Do-it-yourself car primer is absolutely safe if you approach it correctly. The fact is that during any paint and varnish work, including the primer of the body, it is necessary to use personal protective equipment (respirator, gloves, suit). Primer fumes are very harmful, so be careful about your health.

Preparation of body parts under the ground

Putty surfaces must be well dried before priming. Residual moisture will not be sealed by the primer as it is not sealed (except epoxy) but can be absorbed by it. If you apply paint on wet ground, craters may occur.

The primer should be applied only when the putty is removed to such a state when its surface becomes smooth and uniform. Places where old paint remains should also be given enough attention. They must be sanded with grain of the same size.

The finished surface must be cleaned of dust. To do this, wipe it with a slightly damp cloth, after which they immediately pass dry. This procedure must be performed immediately before degreasing, after which they immediately proceed to applying the primer.

Degreasing before priming can be done with both solvent and anti-silicone. First, they are carried out with a swab dipped in a degreaser, and then they are walked with a dry cloth. This sequence is necessary so that no greasy film remains on the surface. A dry napkin must be constantly folded in order to work with a clean side.

Grout primed body

Each stage of car painting has its own purpose. The primer is an intermediate layer between paint and metal. If the part is puttied, then the soil falls on the putty. However, the ground layer itself needs to be polished, since it initially has some roughness.

Soil grouting can be done both manually and by machine. It is necessary to work with abrasives very carefully, since a thin layer of primer can be easily wiped off. If this happens, it is convenient to cover the wipes with epoxy primer in an aerosol can.

The primer at the finish is ground with 800 grit. This size is considered optimal for applying paint. If, as a result of grinding, the developing layer indicates defects, then it is necessary to eliminate them with a finishing putty, which then again will have to be primed, but this time pointwise. These places are then polished again, and so on, until the part becomes perfect.

Types of primers for car body

There are three main types of primers:

• acrylic;
• epoxy;
• acidic (phosphate, reactive).

Acrylic primer is used to fill the fine pores of putty and old paint layers and form an adhesive layer for the base paint. One of the undesirable properties of this soil is hygroscopicity. The moisture accumulated by it contributes to metal corrosion, so acrylic must be dried well.

Epoxy primers form an airtight film and are often used as an insulating layer. It can be used both for steel parts, and for non-ferrous metal, as well as for galvanic coatings. This is an excellent waterproofing agent that has high adhesion.

Acidic soils react with the metal, forming a film of oxides on it and deepening into its structure. Such primers are classified as rust converters and are actively used to coat old bodies, where surface grinding does not guarantee complete elimination of corrosion in the pores. Metal protected by acid soil becomes much more resistant to corrosion.