Primer for plastic for car painting: how to use, rating of the best

MesterulManole June 14, 2017Specialization: many years of experience in finishing works of residential and office premises, dachas, country cottages, etc. Hobby: cycling in all its forms

Assortment of aerosol primers and paints for garage painting work

Products made of polymer materials are not easy to paint, since most paints and varnishes on such surfaces are poorly retained. An effective solution to the problem is a plastic primer. I will tell you what primers are used to prepare plastic for painting. After reading the recommendations in this review, you can paint plastic without fear of the coating peeling off or blistering.

Is it easy to paint plastic?

The first requirement for a paint layer applied to a plastic surface is high adhesion to this surface.

But the fact is that initially, after casting, the properties of the plastic surface do not at all contribute to strong adhesion to the future paintwork, but quite the opposite.

The greatest difficulties when painting are created by the surfaces of non-polar plastics. They have a chemically inert, non-porous surface with low surface tension - and the lower the surface energy of the plastic, the worse its “adhesion” to the applied paints and varnishes.

Among all plastics, polypropylene and polyethylene have the lowest surface energy - these plastics and their modifications are considered the most difficult to paint.

When painting other types of plastics, problems associated with adhesion are not so pronounced, but this does not make it any easier for car repair workers, since polypropylene, as is known, is the most popular type of plastic used in the automotive industry. Almost all bumpers (and these are the main paintable plastic body parts) are made from various modifications of polypropylene - usually a dark gray material that can be soldered and is inert to solvents.

Try to take a polypropylene bumper and immediately apply paint on it - what will happen? A knowledgeable person will answer right away: nothing good... And indeed, the adhesive properties of the coating will be very weak. What should I do?

In the automotive industry, three main methods are most often used for the preliminary preparation of plastic before applying paintwork: corona discharge treatment, low-temperature plasma or gas flame treatment.

These operations are strikingly different from traditionally accepted surface preparation methods. For example, corona discharge treatment is the effect of an electric discharge on the surface being treated, generating “jet” of plasma. Plasma processing is carried out by exposing the plastic to a plasma flow generated by a plasma torch, and flame processing is carried out by the flame of gas burners.

The purpose of this treatment is to increase the wettability of the plastic surface, thereby improving its ability to form bonds with paints. In order for the surface to be well wetted by a liquid, the surface energy of the plastic must be higher than the surface tension of this liquid. If the surface tension of the liquid (paint) is greater, it will bead up instead of uniformly wetting the surface. Therefore, all processing methods are aimed primarily at increasing the surface energy of the polymer.

Wettability. On the left is the treated surface, on the right is the untreated surface.

As a result of this treatment, changes occur in the surface layer of the plastic: polar molecules are formed in the previously non-polar polymer, increasing the surface energy of the material. The surface at the micro level becomes rough, and its effective adhesion area to the paint increases.

There is no need to explain how complex and expensive the equipment is used for these processing methods. Its operation is justified only in large factories, in mass production, but for car service conditions all this is too expensive and complicated. For this reason, polypropylene has long been considered unpaintable.

Having put their brains to work, chemists have developed alternative, simpler methods for preparing polymer surfaces—the so-called “wet” chemical methods. The most convenient and used of them is priming the surface of the plastic. A special adhesive primer applied to the surface of the plastic serves as an effective intermediary between the polymer and subsequent coatings, and in some cases adhesion can even exceed the factory level!

Now let’s leave aside the complex chemical formulations and get down to business.

Why is a regular primer not suitable for plastic?

Plastic surfaces require priming more than others.
Plastic has features that distinguish it from other materials. The material is not perfect. In some parameters, plastic is superior to other materials, in others it is inferior to them. The high density of plastic elements made their adhesive properties worse. This affected the adhesion of paints and varnishes to the surface.

Painting on an unprimed surface will cause the paint to roll off and cause smudges. It is necessary to prime the plastic, otherwise painting will become impossible. The primer also allows you to repair minor inaccuracies or damage, which simplifies repair work.

Preparing plastic parts for painting

When starting to repair a plastic part, the first step is to determine what part we had to deal with. It could be:

• new part;
• old defective coating.

New plastic elements, in turn, can be supplied with factory primer already applied or in a “pure” form.

If you can't tell whether a part is primed or not, rub a small area of ​​the part with some rough sandpaper such as P500. If there is sanding dust, then the part is primed.

There are minimal problems with primed parts, but we'll talk about that later. Now we are interested in the procedure for working with “clean”, unprimed plastic elements.

New unprimed part

Plastic parts are made by injection molding, and special lubricants are used during the production process to ensure that the part can be correctly separated from the mold after casting. Naturally, remaining on the surface of the plastic, they do not contribute to the adhesion of the paintwork.

There are two types of such lubricants:

• external,
• internal.

External lubricants are used in diluted form and sprayed into the mold before each new production cycle. They are not always applied, but every 3-4 times, so some parts have more lubricant, others have less. All these greases can be removed in a workshop environment with a suitable degreaser.

Internal lubricants are introduced into the composition of the plastic itself, so there is no need for separate spraying into the mold. Such plastics are more difficult to paint, since they themselves are “greasy”. The same polypropylene belongs to representatives of fatty plastics. Internal lubricants do not dissolve and are not removed by water, and they can be completely removed from plastic only by heating.

But one way or another, the first step to remove dirt from the surface of the plastic should be washing.

Washing

The ideal option in this case would be a high-pressure washer, but if it is not available, you can get by with a bucket of hot water with any active detergent (liquid soap, car shampoo) and some kind of brush or hard paint brush.

The part must be washed both outside and inside, and then rinsed with plenty of clean, warm water.

Evaporation

To be sure that no lubricants or dirt will interfere with the creation of strong adhesion with the future paintwork, according to the technology, the unprimed part must be heated in a chamber at a temperature of +60°C for 30-40 minutes. During this time, the lubricants located in the pores of the plastic will rise to the surface, where we will remove them with a cloth moistened with a degreaser. This should be done quickly, while the part has not yet cooled down.

If the part has a rough textured surface or is heavily soiled (for example, an old bumper), then it is advisable to repeat the evaporation process, and then repeat the procedure with a cloth and degreaser. To better clean such parts when degreasing, you can use Scotch Brite (gray).

In addition to removing lubricants, heating helps reduce internal stress in the plastic, which in the future can lead to unexpected cracking of the paintwork. Evaporation also helps to identify shrinkage cavities (air inclusions) and then remove them by puttying.

To save time and energy resources of the camera, you can load several plastic parts and warm them up at the same time.

In garages, doing the warming up trick can be quite problematic, so in such cases it is best to work with already primed parts.

Degreasing

Before the first grinding operation on plastic parts, whether preparing for priming or puttying, the surface of the part must be degreased.

In addition to cleaning the surface, this procedure also removes static charge from the part. This is important because when applying the primer, the dust, which usually flies off the surface, will quickly stick to the “charged” plastic, as a result of which the primer will not be placed on a dry, cleaned substrate, but on an already dusty one.

For degreasing, it is advisable to use only branded degreasers, preferably special antistatic degreasers for plastic. They are not aggressive towards plastic and are excellent at removing static charges.

It is recommended to degrease a new plastic element both from the outside and from the inside.

Matting

To prepare a new, undamaged plastic element for priming, it is enough to matte it with Scotch Brite or a similar material. For hard types of plastic, red (Veryfine) Scotch-Brite is recommended, and for soft/elastic types, gray (Ultrafine) is recommended.

Matting can be done both dry and with water. If a matting paste is used, after it you need to thoroughly rinse the part with plenty of warm water - the remaining paste can interfere with normal adhesion to the paintwork material (and this is exactly what we have been struggling with so far).

If the surface has minor damage received during transportation (for example, shallow scratches), then they are sanded using a grinder and abrasive wheels P320-P400-P500, after which the rest of the surface is treated with Scotch Brite.

After grinding, the part is degreased again.

Padding

A simple rule will help us solve the problem of paint adhesion on plastic surfaces once and for all. As a primary primer, a special adhesive primer for plastic (also known as a primer, adhesion activator) must be applied to clean (unprimed) plastic.

This primer is most often a very liquid transparent material with small metallic additives (to control application). It is usually made on the basis of polyolefin resins. The thickness of the layer of such soil is minimal - only a few microns. Most of these primers are single-component, although there are also 2K primers.

Such primers have been developed primarily for use on plastics of the polypropylene group (PP/EPDM, PPC, PPE, PPO, etc.), but most of them can also be used on many other types of plastics: ABS, PA, PC, PVC, PRO , PUR, fiberglass (GFK, BMC, SMC), etc. Modern primers have virtually no restrictions on types of plastic, with the possible exception of pure polyethylene (PE).

To improve properties and guarantee paintability, plastic body parts (fenders, hoods, bumpers, etc.) are produced in a modified form, which means they can be painted, despite the fact that they are sometimes labeled as PP and PE. In fact, unmodified polyethylenes (PE) and polypropylenes (PP) can only be dyed after activation by a gas flame or corona discharge. Otherwise, adhesion will be very weak! Various tanks and other expansion containers, disposable tableware, etc. are made from “pure” PP or PE.

Primers are available in both cans and aerosol cans. Aerosol primer is very convenient for minor repairs, for example, when, when sanding a bumper, small areas were sanded down to plastic. The release form in a can allows you to avoid wasting time on preparing the soil for spraying from a spray gun and on its subsequent washing. Just remember to shake the can vigorously before use.

The primer is applied in one or two thin, even layers with a wide spray over the entire surface of the part. Be careful when applying! Since the soil is very liquid, beware of the possible excess of the application thickness and runoff of the soil (this is most likely at the ends and stiffeners, along the perimeter of the part). A significant excess of the layer thickness can impair the adhesion of the entire coating and lead to “compression” of subsequent layers of paintwork.

Also keep in mind that after application, the primer changes the chemical state of the substrate only for a certain time, during which time you need to apply the next material. Therefore, to achieve the best adhesion, subsequent layers of the system should be applied after 15-20 minutes.

Most primers can be immediately covered with topcoat, but to increase resistance to chipping, it is recommended to additionally apply a layer of acrylic leveling primer to the surface, after adding the required amount of plasticizer to it, depending on the hardness of the plastic.

Just remember that it is not advisable to apply such thick layers of filler primer, as when repairing metal surfaces. Plastic is an elastic material, so a layer that is too thick may not withstand the effects of deformation and mechanical stress during operation.

After applying the filler - painting. Either “wet on wet”, if the soil allows it, or with intermediate grinding of the soil.

By the way, in addition to classic primers, many lines also contain universal primers for plastics, combining the properties of both a primer and a filler with a plasticizer. They have good adhesion to plastic and at the same time allow you to level out minor irregularities (for example, small marks from abrasive grinding). Such primers do not require the preliminary use of an adhesion activator, and thus allow, in some cases, to save an entire layer and operation.

About epoxy primer

By analogy with the repair of metal parts, where anti-corrosion primers act as an adhesive intermediary between the surface and subsequent layers of coating, an appropriate adhesive primer is applied to plastic for the same purpose.

In this regard, I would like to say a few words about epoxy primer.

Although epoxy primer is intended primarily for application to metal, its high adhesive properties make it possible to use this material as a primary material on some types of plastics. But only on some, since this soil does not have sufficient elasticity, and a plasticizer is not used with it.

But if you are repairing hard plastics, such as fiberglass or Carbon fiber, applying epoxy as the first layer of the system on these plastics is not only acceptable, but even recommended. Its adhesion to the surface will be excellent!

New primed part

Practice shows that the quality of factory primer applied to plastic parts can vary greatly from case to case. There are usually no problems with original parts, but the primer on parts of dubious origin can easily have poor adhesion or increased sensitivity to solvents. It’s easy to check: take a napkin or rag soaked in solvent and apply it to the part for a minute or two.

If the coating has softened, it must either be completely removed mechanically (P150-P240-P320), or a layer of insulating primer must be applied, having previously treated the part with gray Scotch-Brite, and then painted.

If a satisfactory test result is obtained, conventional technology is used. The part is degreased, matted, degreased again and painted. For matting you can use:

• gray scotch-brite (ultrafine);
• abrasive material gradation P400-P500 (when working with a dry grinder);
• material grade P800-P1000 (when working manually “wet”);

Before starting any work, the part must be thoroughly washed and dried, and before the matting operation, as well as after it, it must be degreased.

Damaged plastic element

By repairing a damaged plastic part we mean repairing various scratches, dents, chips and similar minor damage to paintwork. We will talk about more complex cases of restoring plastic parts, such as cracks or significant deformations, in a separate article.

Before starting work, a standard set of procedures is performed: the part is washed, dried and degreased. The next step is to prepare the damaged areas for puttying.

Grinding

Before you start filling damage on a plastic part, the paintwork from the surface of the defective areas should be removed - this will avoid defects such as peeling and sagging of the putty.

An eccentric sander and a P180 abrasive wheel are suitable for sanding damaged areas.

When sanding, try to avoid excessive pressure and high speed. Remember that thermoplastics begin to melt when heated.

Puttying

Filling damage on plastic surfaces is necessary with special plastic putties that have high elasticity and adhesion to plastic surfaces.

These putties are fine-grained, dry quickly and are easy to sand. Due to the fact that the putty itself already contains plastic, the two materials (the substrate and the putty) have similar properties, and react equally to sanding and wear out equally. Therefore, the boundaries between them are perfectly zeroed and are not outlined after priming.

The putty is usually applied directly to the sanded surface of the plastic, without requiring the prior use of any primers.

Try to keep the volume of putty to a minimum. Chips, scratches, places of soldering, gluing, small dents are welcome, but completely filling up planes on a plastic part is quite a risky task.

As for large deformations, on most plastics they can be restored quite easily by heating with a heat gun or IR drying and squeezing out. But this is if the part did not crack during deformation. Reinforced fiberglass plastics break in almost all cases.

And one last thing. The use of liquid putty when repairing plastic parts is excluded, no matter how difficult the repair may be.

Sanding putty

Plastic is many times softer material compared to metal. If you process metal and plastic with an abrasive material of the same gradation, say P100, then the roughness parameter on these two surfaces will be significantly different: grinding marks on soft plastic will be more pronounced and deeper, with a larger number of burrs. Therefore, it is obvious that when working with plastic parts it is necessary to use abrasive materials of finer gradations.

For processing putty, suitable gradation wheels are P150 (or P180 for soft plastics) and P240, used sequentially. After the putty is completely leveled, the boundaries of the repair area are treated with P240-P320 materials.

When processing plastic elements, whether removing paintwork or sanding putty, it is not recommended to use an abrasive coarser than P150-P180. If the plastic begins to fray during the sanding process, this indicates that the gradation used is too coarse.

Let me remind you once again that you cannot work on plastic parts at high speeds and with strong pressure when using a grinder - this entails overheating and subsequent deformation of the plastic.

Padding

It all depends on the materials used. There are two options: either we apply an adhesion activator, and then a 2K primer-filler with the addition of a plasticizer, or immediately a special universal primer for plastic (1-2 layers).

Before priming, do not forget to remove dust and degrease the surface.

Soil grinding

When processing the primer, standard technology is used: first, the primed area is leveled by hand with a sander and an abrasive strip, for example P320, after which final processing is carried out using a grinder and P400-P500 wheels. When working in wet conditions, materials graded P600-P800-P1000 are used respectively.

In the case of partial painting, the area around the repair area (or the entire remaining element in the case of complete revarnishing) is treated with gray Scotch Brite using matting paste or P800-P1000 material using a dry sander. Read more about this here.

Hard-to-reach areas are treated with an abrasive sponge (P600-P800) and/or gray scotch-brite (Ultrafine).

How to properly prime a plastic surface

The air temperature in the box for painting cars (in the garage) should be +5-+25 ° C, humidity - no more than 80%.

How to properly prime a plastic surface

Priming is preceded by preparatory work:

1. Surface cleaning.
2. Sanding.
3. Degreasing.
4. Antistatic treatment.

After this, you need to prime the plastic before painting the car in several steps:

1. Apply the first topcoat using a soft natural fiber brush or sprayer.
2. The drying time for the film is indicated by the manufacturer, but it is wiser to wait 1 hour.
3. After this time, apply a second coat of primer.
4. Level the dried surface and matte it.
5. Finally dry the material and wipe with a non-fibre cloth soaked in solvent.

Now start painting.

What primer to prime a plastic bumper on a car

Bumpers on a car are the first to take impacts during collisions and suffer from stones and gravel from the road. In addition, protective parts are constantly deformed during vehicle operation. Therefore, in addition to the ability to adhere the paint to the base, the compositions must have elasticity: withstand the twisting and bending of bumpers.

When choosing what primer to prime a plastic bumper on a car, study reviews from real users. Look for trusted manufacturers. Make sure that the chemical base of the primer (polyacrylates or alkyd resins) matches the composition of the auto enamel.

Painting plastic parts

There is no point in going into detail at this stage, since painting a primed plastic surface is no different from painting a similar metal surface. Just don’t forget about adding the required amount of plasticizer to 2K paint or clear varnish.

But it’s worth taking a closer look at plasticizers and some other additives.

Plasticizers

It is necessary to add a plasticizer to standard 2K acrylic primers, enamels and varnishes for two reasons. Firstly, the additive gives the material elasticity, which means the paintwork will not crack when the plastic is deformed.

Secondly, when the temperature of the plastic surface changes, the paintwork will expand and contract at the same rate as it.

You can often notice microcracks on bumpers located in places that seem completely unaffected by deformation. The appearance of these cracks is due precisely to the thermal expansion of the plastic and the lack of plasticizer in the repair materials.

The coefficient of thermal expansion of plastic is much higher than that of metal. Therefore, paints and especially primers, which have a very low coefficient of expansion, simply cannot withstand temperature changes without a plasticizer and crack.

The amount of plasticizer added is important, which is always indicated in the technical documentation for the product. This amount depends on the hardness of the plastic - the harder the plastic, the less plasticizer needs to be added. Conversely, the softer/flexible the plastic, the more.

For example, for painting an elastic bumper this amount can be 30%, for a soft polyurethane lining - 50%. When painting fiberglass, adding a plasticizer is usually not required.

No plasticizer is added to base enamels!

Mixing sequence

When adding a plasticizer, it is recommended to prepare the material in a certain sequence: first, a plasticizer is added to the base material, be it primer, enamel or varnish, and then a standard amount of hardener and, if necessary, a thinner are added to the total volume of the resulting mixture.

This sequence is due to the fact that the plasticizer also contains a binder that requires polymerization. And if a hardener is first added to the material, and then a plasticizer, this can negatively affect the drying, strength and performance characteristics of the coating.

Matting and structure additives

A well-polished varnish or top enamel has a smooth surface and excellent gloss. This is very good, but these qualities are not always needed.

For example, on some cars, the plastic parts may not be as shiny as the rest of the body. They may also have some texture. Plastic bumpers of SUVs are often painted this way; on many Mercedes, plastic linings have such a “rough”, grainy surface.

Such a surface can be imitated by special structural additives to 2K top coat enamels and clear varnishes. They are usually produced in two types: coarse (grob) and thin (fein). As a result of using a structural additive, the paintwork becomes matte and acquires the desired degree of roughness.

When adding structural additives, additional plasticizer addition is usually not required.

There are also additives that do not change the surface texture, but are intended solely to reduce the gloss level of the coating. Depending on the amount of additive introduced, the gloss level can be changed within a very wide range, achieving a different matte effect - from silky to completely matte.

How to clean primer from plastic

When priming, sometimes it becomes necessary to wash off the remaining primer composition from the plastic. This must be done quickly and correctly, since if done incorrectly there is a risk of damaging the surface or leaving stains from the primer. The most accessible method of cleaning soil from plastic is vinegar essence. Since it has specific properties and odor, precautions should be taken: wear special protective clothing and ensure the room is ventilated.

Important! When cleaning plastic countertops and window sills, do not use acids, as the primer will melt and leave stains.

Also used to remove primer from a plastic surface:

• cleaner for polyurethane foam;
• window cleaner "Mr. Muscle";
• baking soda;
• fine-grained sandpaper.

You can also cover the contaminated area with a wet cloth. The soil will swell and can be washed away.

Priming in the case of plastic surfaces is a mandatory step. Without applying a primer, the paint coating will not adhere to the surface. Using the right primer will help create additional protection for plastic elements and ensure high-quality adhesion of the paint to the surface.

Drying

To dry painted plastic, it is often recommended to be on the safe side using natural drying or a temperature not higher than 40-45°C. It is worth noting that such a recommendation is not without meaning. It is better to dry plastic longer than metal, but at a lower temperature. It should also be taken into account that the introduced plasticizers and other additives increase the drying time.

But still, with the right approach to repair, which we discussed today, there is no need to be afraid of more intense heating at 60°C. This will not cause any problems, and the quality of the coating will only improve.

Be careful with IR drying as you will not be able to control the surface temperature of plastic parts.

About foam processing

The use of a primer is mandatory when external work is carried out on the facade. But the material itself is not applied directly to the foam, but to the surface that will be finished with insulation.

Deep penetration acrylic primer is used for walls that will be finished with foam plastic in the future. Thanks to this, the structure has an increased shelf life and receives additional protection from destruction ahead of time. 1 layer is enough if brick is primed under the foam. If the surface is porous, then at least double processing will be required.

Primer is required for any foam products located outside or inside the house. The main thing is to apply the composition directly to the plaster. The putty should be applied to the base in a very thin layer. After this, you need to wait until the decorative element is completely dry.

How to properly prime plastic (2 videos)

Types of primer for plastic (18 photos)

About adhesion after painting

Another interesting feature of plastic is that the adhesion on it does not become quite strong immediately, but after some time. So don’t be surprised if an accidental scratch on a repaired bumper leads to further peeling of the coating. A few days will pass and adhesion will reach its normal parameters.

For the same reasons, try not to high-pressure wash a freshly painted plastic part for 3-4 weeks after repair.

How to apply primer

The technology for applying the priming composition is important, since the final result depends on compliance with the priming rules. To ensure that the primer lays down perfectly and ensures maximum adhesion, work is carried out in the following sequence:

1. Washing and cleaning the plastic surface from dirt and dust.
2. Clean the plastic with sandpaper.
3. Degrease the base.
4. Use an antistatic agent to prevent dust from sticking.
5. Cover the surface with the first layer of primer. Spray with aerosol or apply primer with a brush.
6. Wait for the first layer to dry (10-15 minutes). Apply another 2-3 layers of coating.

Since the primer for plastic dries, the part is ready for painting within 15 minutes after coating with the last layer.

It is also better to apply the paint composition in several layers so that it is uniform and homogeneous.

Utilities

Procedure for repairing plastic parts

Designations of the most common plastics

Classification of plastics depending on hardness

Application of primer-enamel

Before applying primers in plastic cans, it is necessary to thoroughly clean the base from old paints, grease stains and various contaminants. If a glossy base is to be processed, it must be thoroughly sanded. When the cleaned base is dry, it needs to be degreased.

When aerosol spraying, the composition may fall on other nearby surfaces and products that need to be protected with cellophane film or paper. It is best to apply the primer to plastic at a temperature of 15 to 35 degrees, in which case the primer layer will stick to the surface as efficiently as possible. The application process includes the following steps:

• the can of primer is shaken several times so that the settled particles of the mixture are evenly distributed throughout the entire volume of the soil;
• The primer is applied to the plastic from a distance of approximately 30 centimeters from the base. If necessary, products can be coated with two or three layers of primer to give them maximum protection. Before applying each subsequent layer, the previous coating must be completely dry. Before applying each layer, the can must be shaken;
• During the application process, the can of aerosol primer must be positioned upside down. But if instead of liquid gas begins to come out of it, then the canister turns upside down.

Important! It is necessary to apply primer using personal protective equipment such as gloves, goggles and a respirator. If the primer gets on your skin or eyes, it is important to rinse them with running water as soon as possible.

Technology for repairing plastic bumpers with your own hands in a garage

Diagnosis:

Chips of paint and varnish coating, primer, minor stretching of plastic on the body of the car bumper

Stage 1: Removing the bumper and preparing for repair:

To carry out repairs, the bumper must be removed from the car; this will allow you to easily position the bumper in a position convenient for repair - soldering and painting.

The bumper must be washed and free of dirt. To solder the plastic of the bumper, an electric soldering iron or heated with a blowtorch can be used. Using burners will require more skill and skill, since plastic can “lead” under the influence of temperatures; if you do not have experience in this matter, then your option is still a soldering iron

Stage 2: Soldering the bumper:

– To prevent further extension of cracks, it is necessary to drill a hole at the end of the crack.

– It would be convenient to first secure the bumper with a clamp before soldering.

– We begin to solder the bumper parts from the inside, this will allow us to understand what properties the material has without significant damage to the appearance.

– Perform soldering in 2 stages.

First, grab the edges of the damaged area to fix the relative position of the fragments and correct minor deformation; this is where it is convenient to use clamps. Soldering tack is carried out approximately after 10-15 cm.

Only after tacking can you begin full soldering of the bumper along the entire length of the seam.

After soldering, the bumper looks something like this from the inside.

To do this, we reinforce the bumper by fastening the seam with staples from a stapler, every 2 cm along the entire length of the crack. It is advisable to shorten the legs of the staples first so that they do not pierce the bumper and do not extend to the front side; it is also convenient to use tweezers when soldering staples.

We fuse the brackets with a soldering iron and spread the seam more evenly.

The outside of the bumper has regained its shape.

To remove paint, primer and level the surface of the bumper, treat it with a wheel No. 240 using a grinding machine or a special attachment on a drill.

We seal the bumper from the outside.

We sew the sealed seam with the same circle No. 240

The appearance of the bumper after sanding.

Remove dust from the bumper. It is necessary to blow with compressed air using a compressor.

Using a hair dryer, we burn and fuse plastic hairs onto the surface of the bumper.

But do not overdo it so as not to overheat the plastic.

Stage 3: Bumper putty:

To finish leveling the bumper, we use a special putty for plastic.

Apply a thin layer of putty with a rubber spatula. The putty layer should be minimal.

In hard-to-reach places, use your finger as a spatula.

Bumper after putty. Minor differences in putty are acceptable. We wait for the putty to dry and proceed to the next stage.

Stage 4: Grinding the bumper:

After the putty has hardened and dried, we sand the bumper using abrasive no. 240

In hard-to-reach places we use sandpaper.

The appearance of the bumper after puttying and sanding.

Stage 4: Bumper primer:

We blow off the dust formed after grinding with compressed air.

We dilute the primer according to the manufacturer's recommendations, as described in detail on the primer can.

Using a spray gun and a compressor, apply the primer in 2 layers. Waiting time between application of primer is 15 minutes.

Apply developing paint. (Development paint is specialized aerosols or special powders)

Developer paint should only be applied to the primed part of the bumper.

Dry for 30 minutes using infrared drying.

We sand the bumper using 800 or 1000 sandpaper to develop a layer of primer.

It is necessary to sand over the entire surface of the primed bumper.

After grinding, in places where red spots remain, they indicate problematic areas and the need for improvement. These may be pits or scratches.

To eliminate minor flaws in the ground, we use nitro putty.

Degrease the surface and apply a thin layer of putty, wait until it dries

We perform wet sanding with sandpaper No. 1000

Degrease and wipe the bumper from dust with a napkin.

Primer for plastic that increases adhesion

There is a brutal way to increase the adhesion of plastic to paint by treating the surface with a flame from a torch. This is done very quickly. This causes an oxidative chemical reaction and the paint will adhere better. But since this method is not suitable for everyone, the surface of the plastic is etched with a chemical to create micro-irregularities and “open the pores” of the plastic, to which the paint will stick. These primers should only be applied to bare plastic.