DIY bumper crack repair

In detail: DIY bumper repair of cracks from a real master for the site my.housecope.com.

Often in the traffic flow you can find a car with a cracked or deformed buffer. What can you do, no one is safe from unsuccessful parking or a minor accident. Nevertheless, this is not a reason to continue driving a car that has lost its "shiny" appearance - there is a practical experience of restoring the original state of this element.

The external plastic components are mainly made of thermoplastic plastics. The technology for restoring such products is based on welding, it is this technology that allows you to get rid of through cracks and even recreate broken fasteners. Actually, the procedure is not much more complicated than preparing and spray paint damaged area of the car body.

Some car enthusiasts assure us that we repair the bumper with our own hands using metal brackets. But the experienced car owner knows that like is treated like this, that is, repair plastic rods are used for soldering. Their composition, color and profile are different; the required core is selected according to the marking on the buffer.

Making the right choice means guaranteeing a high-quality repair, because the mismatch of materials will significantly reduce the life of the automotive element. To find out what the cracked bumper is made of, it is enough to carefully examine the inside of the part. Depending on the marking, appropriate conclusions are drawn:

PP - polypropylene base.
ABS (GF, PAG 6) are hard plastics.
PUR - polyurethane.

Plastic welding requires high temperatures, for example, 400-450 ° C is suitable for propylene, and 500 ° C is necessary to restore an ABS structure. Many car owners will learn how to repair a bumper with their own hands in a video where craftsmen use an ordinary 100 W soldering iron.

Video (click to play).

You can also restore a damaged part using pieces from a bumper with a similar marking. They are cut into strips 8 mm wide for PUR, and 4-5 mm for polypropylene.

Almost any breakdowns are treated by welding, even broken parts are reanimated. However, no one canceled the economic feasibility of such work, because the restoration of numerous defects can hardly be called justified. The cost of a complete restoration and staining will be more expensive than a new buffer.

Certain tools are required to complete the repair. These can be both ordinary household appliances and professional tools. The ideal kit includes the following items:

Orbital sander or sanding block.
Grinding wheels of various grain sizes.
Mini drill like Dremel or drill.
Clamps and rubber spatula.
Soldering iron and hair dryer.
Metallic tape.

Of the materials for restoring a cracked buffer, you may need:

Putty and primer.
Brass mesh for crack reinforcement.
A can of paint or a can of paint.
Plastic repair rods of the required configuration and composition.

The damaged part must be dismantled in order to eliminate, firstly, excessive stress in the crack area. Those who have already done such work will say that now we clean the bumper and only then repair it with our own hands.

The cracked parts fit together. For reliability, they are fixed with metal tape from the outside of the part. If the breaks are quite significant, then clamps will be needed to clamp the edges of the cracks. Their number depends on the complexity of the repair.

When restoring PP-based parts, the reinforcing mesh is not used. The process begins with the fact that a nozzle with a nozzle with a diameter of 5-7 mm is installed on the hair dryer. In the future, work is carried out according to the following points:

On the inside of the buffer along the crack joint, use a Dremel mini-drill to make a groove for the plastic rod.
Using a hair dryer, melt and place the repair rod into the prepared groove.
Clean the front part of the bumper with an orbital sander with P240 attachment and repeat the welding procedure similarly to the operation on the inside.
Grind the cooled seam from the outside with a nozzle with the same grit P240, then remove dust from the surface.

Even out irregularities with a special putty for plastic, try to keep the layer as small as possible.
Dilute the primer with solvent 3: 1 and apply two coats to the degreased surface. Drying time for the first layer is 15 minutes.
Apply a developing layer in a contrasting color, followed by sanding with a disc or sandpaper with grit P800 and P1000.
Eliminate the detected defects with a nitro putty followed by sanding with P1000 sandpaper.
Remove dust with a damp cloth and degrease the part, then paint plastic decorative paint with overlapping borders 50-100 mm. Apply the paint in 3-4 coats with intermediate drying cycles.

Anyone who is interested in how to properly repair a bumper in a video with their own hands should take into account an important detail. 30-40 minutes after applying the last layer of paint, the part should be varnished. Thus, we get a flawless appearance of the repaired part. Do not forget to follow a few simple rules:

You should try to apply a minimum layer of putty.
Take a temporary pause for complete hardening of the putty layer.
To process the putty area with a grinding wheel or sandpaper with grit P800, and then - P1000.
It is desirable to apply a developing layer of primer.

In the case of a polyurethane buffer, the preparatory stage in the form of grooving work is excluded. A brass reinforcing mesh is applied to the crack; steel is not recommended for use, because it is prone to corrosion. Alternatively, stapling staples can be used every 10-20 mm. They are recessed into the body of the part across the seam, it is imperative to make sure that the bracket does not go through the part.

Further, the repair technology does not differ from the restoration of a polypropylene part. Wire mesh or staplers should be sunk into the plastic. Only after that, the seam is filled with repair plastic and soldered from the opposite side. Some important points of technology should be taken into account:

It is necessary to solder the mesh or staples carefully so as not to overheat the plastic, otherwise it may deform from the opposite side.
For a complete DIY repair of a polyurethane bumper, the width of the reinforcing mesh should be 15-20 mm.
It is better to press in the mesh or staples with a flat object.
If the legs of the staples pierce the plastic through and through, then they should be shortened using side cutters.
For the convenience of working with metal elements, you can use tweezers.
To prevent the new enamel from peeling off, it is necessary to grind the paint over the entire plane of the part.

Puttying and painting are performed in the same way as described above - according to the traditional scheme. Repair work on the restoration of the buffer can be combined with painting the car , so the consumption of materials will be more rational. It is important to determine in advance the feasibility of carrying out restoration work. If there are significant costs in the future, then it is better to buy a new part.

If your bumper is cracked on your car, there is no money to buy a new one, and the appearance of the repaired plastic part may differ from the new one by the presence of visible traces of repair, then the following life hack will definitely come in handy.

This repair option really does not differ in accuracy in the understanding of most car owners, but at the same time, it has its own special charm and appeal for young people, especially for those who adhere to the automotive sports subculture: drifting and motorsport in general. It is unlikely for whom it will be a discovery that car racing is often a tough contact sport, dents and cracks in the bumpers are common here, therefore, in professional racing circles, young athletes prefer to cope with breakdowns on their own.

Of course, there are some of the more popular ways to connect multiple pieces of a broken bumper (with resin, with an epoxy mesh, and even with a soldering iron), but we'll look at mechanical fastening with plastic clips. To make the process look clearer, first watch the video in English (you can turn on subtitles and translation):

Have you looked? Is the structure of the work clear? Then, you can start laying out the most important stages of work on the shelves.

To carry out repairs you will need:

The repair does not really take much time and does not require any special preparation. As they say: "There would be straight arms".

I. First, join the two pieces of the bumper crack together. The gap should be minimal, all parts and sides of the bumper should lie in a single plane. Then you will need to glue these parts with tape so that you can proceed to the next stage of the repair. At 2.50 minutes, the video shows how to pull together a cracked bumper.

As you can see, it is better to repair together. A helper can help you out when you run out of hands.

II. Now is the time to drill. But before that, another life hack is to apply duct tape along the crack. This will prevent the paint from cracking at the ends when pre-drilling. 4.20 minute video. You need to drill at a distance as thick as a finger. Thus, you will not damage the bumper even more if the drill jumps off to the side, as well as the plastic tie over time will not wipe the too narrow wall and the structure will not fall apart.

The pitch between the holes is as thick as a finger. A crack line is visible under the tape. Follow her line. The more accurately you can drill the holes, the stronger the structure will be.

III. 6.00 minute of video. Quilted bumper. There are two contraction patterns: parallel and criss-cross. The first one is easier to do, the second option holds the bumper pieces together better.

First stitch type: Parallel

In order to get to the inner side of the bumper, "crazy hands" remove the wheel arch liner. The workflow is shown in the 6.55 minute educational video. A couple of minutes and the bumper is ready!

Attention! The flat surface of the plastic fastener should be on top.

It is necessary to tighten the ties strongly until the characteristic clicks stop

Ready! It looks stylish, and most importantly it is a really working version. The bumper regained its rigidity and lost functionality.

None of the motorists is safe from the fact that his bumper will last all the time without damage. Therefore, when chips and scratches appear on it, many think that nothing can be done, and begin to look at something new. But there is a way out, since you can make repairs yourself. How to repair a bumper crack will be discussed below.

How to repair a cracked plastic bumper - in our new article

Before you talk about how to remove a crack on the bumper, you need to figure out what materials these structures are made of. Immediately it is necessary to make a reservation that if the part is metal, then its repair will have to be done in a specialized workshop, if the car enthusiast does not have the skills of a professional welder.

But on modern cars, these parts are made from two types of plastic:

a thermoactive material, its cracks are glued using a hair dryer or a soldering iron, as well as the formation of a special metal frame, its characteristic feature is that it melts under the influence of a certain temperature;
thermosetting material, to close cracks on it, it is better to use special fiberglass or reinforcing plastic mesh, which should be impregnated with epoxy resin, since when exposed to high temperatures on this plastic, it will not melt.

Thermoactive plastic is usually labeled as follows: PP, PPTV and other analogues. Typically, these markings are placed on the inside of the bumper.

The marking will tell you what material the part is made of.

The marking of thermosetting plastic is PUR, which classifies it as a polyurethane material, as well as PAG 6, GF, ABS - which classifies it as a hard plastic mass.

Based on these parameters, it will be necessary to select materials for repair.

It is important to understand that if there is no reliable information about the material from which the bumper is made, it is better to know it, since repairs can turn into buying a new one. This can be done at the service station or refer to the technical documentation for the car.

Before repairing a crack in a bumper made of thermosetting materials, you need to prepare the necessary tools.

a powerful soldering iron or a special machine hair dryer, which will be needed to soften and solder plastic;
primer, which is needed for processing welded surfaces;
paint in a special can for painting a repaired place or the entire bumper;
putty;
small diameter drill for drilling holes along the edges of the crack;
gasoline for degreasing treated surfaces;
metal fine mesh or furniture staples;
sandpaper, preferably zero, as well as one and two, for thorough grinding and sanding surfaces.

With everything you need close at hand, you can repair cracks yourself

This list of tools will be needed in order for the repaired bumper to be as good as new.

Before glueing the crack on the bumper, which is made of thermosetting material, you also need to prepare the necessary materials and tools:

a small diameter drill so that you can drill holes along the edges of the crack;
glue necessary for gluing the joints, or plain tape;
epoxy resin;
sandpaper zero, one and two;
putty.

This list of materials and tools will help you repair a cracked thermoset bumper.

How to repair a crack on a bumper made of such material will be described below, since you first need to find out the preparatory work. They will consist of the following steps.

This part must be removed, as it will work better and efficiently with it when it is located separately from the car. To do this, you need to unscrew it and put it on a separate stand or other elevated surface.
The next step is to clean the bumper from dirt and other deposits. First, it must be rinsed with water, and stubborn dirt and other layers must be removed with a spatula or coarse sandpaper. You need to clean everything carefully.
Next, you should carefully examine the crack. This is an important step, since the edges must be marked before filling the crack.
After all this, it is better to re-examine the product carefully for the presence of imperceptible cracks, chips and dents in order to carry out a complete and high-quality repair in one go. If nothing else is found, you can proceed with the repair.

Immediately it is necessary to make a reservation that the restoration of the bumper from a thermosetting material will occur without heating the surfaces. How to seal the crack will be described in the following algorithm:

first you need to clean the crack surfaces well with sandpaper until the paint and varnish surface is removed, and degrease everything with a rag soaked in gasoline;
then the edges of the crack need to be connected with glue or tightly tightened with tape, it is better to give preference to the first option, and for this you need to choose a special glue that acts instantly, the adhesive is applied evenly with a brush;
on the inner side of the bumper at the place of damage, stick fiberglass or its substitute;

Stick the fiberglass on the inside of the damaged part

then the fiberglass is impregnated with epoxy resin, and glued to the outer surface of the bumper at the place of damage, after such actions, the surface in the damaged place should be leveled;

then you need to wait about an hour for the surface to dry well, and start cleaning it, for this you need sandpaper, this happens with strong pressure and circular movements;

then the putty is prepared, as written in the instructions, and applied with a spatula to the damaged surface, after which it is smoothed;

after the putty has dried, a primer is taken and applied to the crack in vertical stripes, in two or three layers;

then the primer is rubbed with sandpaper, all this is wiped off with a rag soaked in water, and after everything is dry, a paint-and-lacquer coating is applied to the surface from a can.

The repair has been completed and the sealed bumper can be replaced.

If a bumper made of such plastic is cracked, then its repair will be carried out according to the following algorithm, while the preparatory work will be the same as for thermosetting plastic.

Use a special hair dryer to seal the edges of the damage

The algorithm is as follows.

Here's how to remove damage on a bumper like this.When the bumper is cracked, how to repair is of interest to many drivers. The repair process is not very difficult, and you can do it at home, while following the instructions above.It is quite difficult to imagine a vehicle that does not have such a necessary element as a bumper. The main purpose of the part is to protect the body from damage and deformation. When a difficult situation arises, he takes on all the shock and damaging factors. It is for this reason that the question of how to repair a plastic bumper with your own hands is one of the most relevant.It is easy to guess that the bumper with a high degree of probability can be damaged if the car is used quite intensively and even with very careful operation. The bumper can be damaged not only due to lack of driving experience, but for reasons such as:

actions of other sloppy and inexperienced drivers;

departure of small stones from the movement of other vehicles.

Regardless of the cause and nature of the damage, the appearance of the vehicle after a bumper breakage deteriorates significantly. The car owner automatically wants to solve a similar problem by doing a bumper repair with his own hands.Ways to eliminate the problem and mechanical damage directly depend on what kind of plan the defect was applied to the car part. Among the most basic types of damage are:

Scratches, which can be superficial and deep, that is, reaching the ground or to the base layer of the part. This damage must be repaired immediately, as later cracks may appear at the scratch site.

Cracks - this is a more serious damage to a car part, which belongs to the category of dangerous. Without removing it, it is not recommended to operate the machine.

Dents - are formed by a strong mechanical effect on the bumper. These injuries are very often accompanied by other adverse manifestations.Scratches and cracks almost always appear next to dents.

Chips and breakouts... This is a special through damage that has a fairly large area. They appear most often at the edges of the bumper after a collision of the car with a certain obstacle.

Of course, you can contact any service center, but in this case, the cost of restoring the bumper, even with minor damage, becomes much higher than the cost. Of all the options listed above, it is self-repair that will become the optimal and affordable method for restoring the bumper.Directly depending on the degree of damage, repair work aimed at restoring the bumper can be divided into local and complex ones. Scratches and small chips of various types on the surface of the paintwork can be eliminated without preliminary dismantling of the part.It is necessary to work with this element so that access to the outer and inner surfaces of the element is provided. The installation of the part in its original place is carried out after the implementation of the required repair and restoration work.When carrying out a process such as self-repairing a plastic bumper, you will need to prepare special tools and materials. Among the most important of them are:Competently thought-out protection will comprehensively protect the respiratory organs, eyes and hands from the effects. This is an automatic guarantee that the body will not be harmed by the spraying of harmful substances in the air and by high temperatures.Along with the acquisition of the necessary materials and tools, in the preparation process, you need to carry out certain work with the bumper itself. Among the most important points are:

Removing the bumper from the car body.

Thorough cleaning of the part from dirt and dust. The surface must be dry and clean.

Determination of the material from which the bumper is made.

In areas where restoration work will be carried out on the bumper, it is imperative to remove the applied paint. It is necessary to thoroughly clean and degrease not only the damaged area itself, but also the adjacent space.

The crack must be drilled with small through holes at the ends before repairing. This will avoid the subsequent spread of damage, its increase in size.

Any crack has special joint edges. Therefore, before repairing the crack, it will need to be filled at the joints with a special composite.

After completing all the above processes and manipulations, you can start repairing the bumper with your own hands.The scheme according to which the repair of plastic bumpers will be carried out depends directly on the degree and level of damage. The following recovery techniques may be applicable:

Gluing - it is used for parts produced by the cold forming method. A special polyurethane-based adhesive is used here.

Heat sealing - Suitable for bumpers that have been hot formed. The bumper fragments are connected using special welding equipment.

Lamination - the method is suitable for restoring lost fragments similar. It uses a special reinforcing mesh and putty.

Using flat electrodes... The technique is based on the use of a special construction hair dryer, which melts the electrodes and effectively repairs cracks.

Soldering - the best option for repairing a bumper in normal home conditions. You will need to use a soldering iron, sandpaper and paint.

Brazing with reinforcement - suitable for the elimination of large cracks. The process is based on the use of double-sided soldering and simultaneous reinforcement with special staples or metal mesh.

Pasting - crack elimination is carried out with fiberglass and epoxy glue. The restoration material is applied to the glue and strictly on both sides of the bumper.

Below is a description of the most common and labor-intensive methods of restoring a car bumper, depending on the damage caused.The previously prepared putty must be prepared according to all the rules of the instructions, add a special hardener there. After that, the resulting mass is applied to the area of the bumper where the damage is located. You need to wait about 10 minutes, take sandpaper No. 80 and grout the composition with special circular movements. The result becomes visible after several manipulations.Priming work is carried out just as easily. It is required to take a prepared rag and rinse the bumper very well. Once the surface is dry, the entire bumper should be inspected for correct shapes. If there are no dents, you can start priming. This process is carried out according to the following rules:

Apply the primer in a circular motion towards the left or right side of the element.

The composition must be allowed to dry completely.

After that, sandpaper No. 800 is taken and everything is thoroughly overwritten.

Using a regular water bottle, you need to wash the bumper. In this case, it does not matter where the crack or other damage has formed, the bumper must be washed out completely. As soon as one layer is completely dry, the plastic automatically takes on a matte shade. The top soil is then completely washed off.

Only then can the second layer of the primer be applied.

Once all the applied layers are dry, a thorough inspection of the part will need to be performed using a lamp. The layers should be perfectly even and make up one piece together.If, after examining the part, it becomes clear that all coatings are applied as efficiently and evenly as possible, you can proceed to such a process as painting. The room must be prepared, all surfaces that need to be protected from the paint used are closed. The pigment is applied strictly in two or three layers. Drying should take 5 to 10 minutes between each layer.After applying the required paint coating, the bumper is coated with two layers of varnish. Intermediate drying is also important here. At the end of the painting work, you need to check the quality of the applied compounds again; if smudges are found, light sanding and thoroughly polishing the surface are required.

In the process of restoring the integrity and appearance of the bumper, the upcoming work will depend on the type of damage found. This is an important point, since one option is used for scratches and chips, a completely different method is required to remove a dent.

If you need to carry out repairs with your own hands, or the insurance does not work, or there is no money and desire to contact the service center, you will need to carefully study the nature of the damage. If the driver realizes that the bumper is very badly damaged, you should not try to restore the part on your own, but it is better to purchase a new one. If relatively small chips or dents are found, the problem can be completely eliminated on your own, knowing how to act in this or that case. So, how can scratches, dents and cracks be repaired quickly and effectively?

Elimination of this problem can be carried out by using sandpaper. Material No. 50 is taken and grouting is carried out. In this case, it is necessary to carefully eliminate all irregularities, acting until the surface becomes completely correct in shape. In the course of this process, the damage may become slightly larger in size, but their depth will become much smaller. Do not be afraid of this, after thorough cleaning all the irregularities will be filled with putty.

If there is a desire and certain skills, then instead of putty, you can use a special liquid plastic, which fully corresponds to the type of material from which the plastic is made. After applying this composition, after it has completely dried, it will also be necessary to clean the surface and carefully sand it, sanding it to the most even surface.

To repair a minor dent that did not damage the paintwork, you just need to heat the deformed part of the bumper. The concave part of the plastic must be heated with a previously prepared heat or technical hair dryer until the material becomes soft enough. After that, the dent is manually straightened, at the same time giving the damaged section of the bumper the correct geometric shape.

If cracks appear on the surface of the bumper, it will be necessary to use a pre-prepared metal mesh and a soldering iron. The sequence of actions in this case will be as follows:

The edges of the damage must be brought together and soldered to one side of the mesh. It is advisable to drown it as deeply as possible in the plastic, but you cannot overdo it, as a hole may form.
The end of the mesh is covered with melted plastic.
Similarly, you need to walk along the entire crack.

If the damage to the bumper is minor, special construction brackets can be used instead of the mesh. In the process of soldering them, it is recommended to use tweezers, which will prevent burns of the brushes. Bonding actions should be spaced 2 cm apart and along the entire length of the crack.

To prevent the mesh and metal staples from rusting after a while, the items must be covered with special liquid plastic. At the end of all the work that is carried out on the inner surface of the bumper, its front side immediately takes on its original appearance.

The question of how to restore and repair a car bumper with your own hands is relevant for all modern motorists without exception. If you follow the instructions and tips provided in the article, you can repair damage to the bumper with minimal money and time.

The bumper of a car usually suffers from curbs when parking, stones on the road. And no one is insured against troubles on the roads in the form of a small accident. In car services, they ask for a lot of money for the restoration of this part. The ideal way out of this situation would be to repair a plastic bumper with your own hands. We will tell you how to repair a bumper with your own hands without huge material and time costs.

Plastic bumpers on modern cars are made from two main types of plastic - thermosetting and thermosetting. It is necessary to know the differences in these types of materials in order to select the correct auto bumper repair method. To find out what plastic the bumper is made of, you need to look at its back side.

Thermoactive plastics can be recycled, as they soften and become plastic when exposed to high temperatures. Easy to weld. These include:

various polyethylene (PET, PET, LDPE, HDPE) - used in the production of pipes, machine tanks, bottles, children's toys, food containers and packaging, bags, rugs;
polystyrene (PS) used in the manufacture of containers for dairy products, audio and video cassettes, various dishes;
polyvinyl chloride (PVC, PVC) It is used in the production of windows, flooring, bottles, film for packaging, cable insulation, credit cards and medical products;
polypropylene (PP, PP) used in the production of food containers, batteries, bottle crates, car parts.

This type of plastics is used in production much less often, because they are not recyclable.

When exposed to high temperatures thermosetting plastics do not melt and collapse. Very difficult to weld. But they are very durable and resistant to damage.

These are the following types of plastics:

polyurethane (PU, PU) used in coverings, trimmings, gears, membranes, pillows, mattresses, and car seats;
epoxy resin used in adhesives, sports equipment, electrical equipment, automotive equipment;
phenolic resins used in ovens, cutlery handles, automotive parts, printed circuit boards;
fiberglass (ABS / MAT) - used in automotive bumpers and other reinforced parts.

The bodies of modern sports cars are made of precisely such plastics - fiberglass and carbon fiber .

Both the front bumper and the rear are subject to various damages. Depending on the degree of damage, one should choose one or another method of restoring an automobile bumper. Damage are of the following types:

We repair the bumper with our own hands - remove scratches from the case. To remove scratches on the bumper, do the resurfacing... Take sandpaper and thoroughly smooth out all the irregularities to an even, smooth surface. Then apply a putty to the surface and, after drying, a primer. Now you can start painting.

You can also get by with a special liquid polymer, according to the composition corresponding to the marking on the bumper. Apply a layer of resin according to package directions, then sandpaper to a perfectly smooth surface.

To rid the bumper of the car from dents, use a hair dryer or a gas burner. Heat the deformed area, soften it, and give the correct geometric shape. This method is suitable for thermosetting plastics - polyvinyl chloride or polypropylene.

In case of significant geometry deformations, it is not recommended to straighten the bumper yourself - it is better to contact a car service specialist.

Carefully: do not overheat the treated area, this may cause even greater deformation.

Bumper repair with your own hands is impossible without knowledge of crack repair. Autobumper cracks can be eliminated in many ways. Be sure to look at the markings on the back of your part to select the one that suits you. Depending on the type of material, do-it-yourself plastic bumper repairs can be done:

welding with a hot air gun or electrodes;
with fiberglass and liquid polymer.

For various methods of repairing plastic bumpers may come in handy the following materials:

A soldering iron or a hair dryer, or a soldering station with a hairdryer, you can use a gas torch.
Soldering iron, industrial or household.
Solder for plastic (like bumper plastic).
Fiberglass fabric.
Metal mesh.
A set of liquid polymers.
Epoxy or polymer two-component adhesive.
Sandpaper of various grain sizes.
Primer.
Putty.
A rag or rag.
Roller for painting works.
Glue brush.

Using various techniques at home, you can restore an autobumper from various types of plastic. Consider the most common methods on how to repair a bumper with your own hands.

The best way for repairing bumpers made of fiberglass or polyurethane - restoration with a glass cloth patch. You will need a piece of fiberglass cloth, liquid resin, or epoxy (two-part). Procedure is like this:

Preparatory work: remove paint and carefully sand and degrease the surface.
After stripping, cut a piece of fiberglass to fit the damaged area.
Mix the two components of the glue and stir.
Apply glue to the surface and stick the fiberglass.
Apply several layers of glue using dabbing strokes until the glass fabric is whitened.
Roll over the resulting layer of fiberglass, moving in different directions. This is necessary to compact the layer.
After drying, carefully sand the surface with sandpaper, moving in a circle.
Then apply an even layer of putty to level the bumper.
When everything is dry, apply 2-3 coats of primer and dry. Sand with sandpaper.
Now you can start painting.

Only thermosetting types of plastics can be welded, and if your part turns out to be made of thermosetting plastic, choose a different repair method.

Before repairing the bumper with your own hands by welding or soldering, clean it thoroughly and dry well. Now you need to match the plastic solder to your car's bumper material. On the back there is a marking for the type of plastic - choose plastic rods with the same markings.

Work order would be like this:

Clear the place damage with sandpaper or sander.
Powerful soldering iron (from 100 watts) solder a uniform groove along the entire length of the crack. This should be done very evenly, try not to overheat the plastic so as not to smudge or damage it.
Take a welding rod made of plastic and attach to the resulting recess on the front side of the part. Warming up with a high temperature hair dryer for a better connection. It is recommended to heat both the solder and the groove at the same time throughout the crack. You should get a reliable, strong seam.
When the outer seam has hardened do the same with the inner side of the bumper.
To make the weld seam stronger, make over it several transverse "bridges"... To do this, weld alternately small pieces of solder 3-4 centimeters across the seam. Do not forget to put such bridges at the ends of the crack so that it does not spread further.
The resulting seam sandpaper or sandpaper to level the surface.
Now the autobumper can be putty, primed and started to restore the paintwork.