Corrosion of metal elements of the body is not just an aesthetic problem, but a real threat to the safety and durability of the car. Most often, rust attacks the lower parts of doors and threshold zones, where moisture, dirt and reagents from winter roads constantly accumulate. If you notice through holes or swollen paint in this area, you can not hesitate: the process of metal destruction is rapid and can spread to the power elements of the structure in just one season.
The question of how to fix the holes in the sills is a question that many used car owners face, and the decision depends on the degree of damage and your technical skills. There are several proven methods of recovery: from simple preservation with epoxy compounds to full-fledged welding and replacement of metal sections. Choosing the right approach will not only return the car to its presentation, but also prevent further rotting, keeping the body intact for many years.
In this article, we will analyze in detail all the stages of preparatory work, consider the necessary tools and analyze the pros and cons of various repair technologies. You will learn why simply installing plastic linings does not save you from rust, but only masks the problem, and what materials really work in an aggressive environment.
Threshold diagnostics and disaster assessment
Before grabbing a Bulgarian or welding machine, it is necessary to soberly assess the front of work. The appearance is often deceptive: a small hole on the surface can hide a vast cavity under it, where the metal has already turned into debris. A thorough diagnosis will help you to understand whether you should try. restore the existing element or it is easier to cut it completely and boil a new one.
Start with a visual inspection and gently tapping. Use a hammer handle or a special scraper to tap the entire length of the threshold. A deaf, rattling sound or the feeling that the metal is being smacked under a light press indicates strong corrosion from the inside. If the sound is ringing, but you can see the bloating of paint, then the process has just begun, and you can do with gentle methods.
⚠️ Attention: When diagnosing, never rely on the appearance of the paint alone. Rust often develops under the LCP layer, creating a “fungus” that bursts at the slightest mechanical impact.
For precise determination of the boundaries of damage, it is recommended to use a magnet wrapped in a thin fabric. Where the magnet stops holding or is held weakly, the metal is no longer there or it has become too thin. It is also worth looking inside the threshold zone through the technological holes in the bottom, highlighting with a flashlight - this will allow you to see the real picture from the inside.
Required tools and materials for quality repair
The quality of the repair depends on what you use. You can not close the holes in the rapids "on the knee", using random rags and ordinary plasticine. For a long-lasting result, a specific set of materials will be required to provide strength and anticorrosion protection.
If you are planning welding, you will need a semi-automatic welding (MIG/MAG) with gas or a manual arc welding inverter, although the latter requires higher qualifications to avoid burning through the thin metal of the body. For cutting metal is indispensable Bulgarian (USM) with a set of metal cutting discs with a thickness of 1 mm. Also prepare a drill with a crib or sandblaster to clean the surfaces.
- 🛡️ epoxy A mandatory base coating that creates a barrier between the metal and moisture, preventing the reappearance of rust.
- 🧱 Repair inserts Prefabricated profiled pieces of metal that perfectly replicate the geometry of the thresholds of popular car models.
- 🧪 Anti-corrosion formulations (e.g., Movieville or analogues with zinc) for treatment of hidden cavities after completion of work.
Do not forget about personal protective equipment. Working with metal, especially when welding and grinding, generates many small particles and sparks. Glasses, tight gloves and a respirator are not just a recommendation, but a necessity for maintaining health.
Use the copper plate as a substrate when welding a fine metal. It removes excess heat and allows you to make a high-quality seam, without burning through the metal.
Preparatory stage: cleaning and removal of corrosion
The most important step, which depends on 90% of success, is surface preparation. Any residue of rust, paint or dirt will negate all efforts. The metal should be cleaned to a characteristic shine. If you skip this step, corrosion will continue to develop under a new layer of material, and after a few months the repair will have to be done again.
First, remove all attachments: moldings, plastic linings, splashers. Then mechanically (metal brush, petal circle Bulgarian or sandblast) remove all loose layers of oxides. The edges of the hole should be cleaned to a "living" metal with a margin of 2-3 centimeters. This is necessary to ensure good adhesion of repair materials or a quality weld.
After mechanical cleaning, be sure to degrease the surface. Use it. White Spirit Or a special degreaser. Do not wipe the surface with gasoline or solvents that may leave a greasy film. The cleanliness of the surface is the guarantee that soil He will lie flat and hold on tight.
☑️ Preparation for the repair of thresholds
Method 1: Welding and insertion of repair inserts
This is the most reliable and professional way, which allows you to fully restore the geometry and strength of the body. The essence of the method is to cut out the rotten area and weld a new metal insert into its place. Such repairs return the car factory characteristics of strength.
The process begins with the careful cutting of the damaged area by the Bulgarian. Try to make the cuts even to simplify the docking of a new part. If the whole threshold rots, it is cut off on the racks. A new insert (remon element) is tried on, adjusted in size and fixed with rods or screws before welding.
Welding should be performed with short seams (by 2-3 cm) in a staggered order, allowing the metal to cool. This prevents overheating and deformation (wiring) of the body panels. After cooling, the seams are cleaned with a petal circle in level with the main metal, which makes the joint almost invisible after painting.
| Parameter | Insertion of metal (Welding) | Epoxy resin | Plastic linings |
|---|---|---|---|
| Durability | High (10+ years) | Medium (3-5 years) | Low (hiding the problem) |
| Difficulty of work | High (skill required) | Low/Mediocre | Low. |
| Impact on bodywork | Restoration of strength | Hermetization | Acceleration of rotting under the lining |
| Cost | Tall. | Low. | Medium |
Method 2: Repair with epoxy resin and fiberglass
If the holes are small and there is no welding machine or welding skills are not enough, a chemical method can be used. It is suitable for areas that do not carry a high power load, and allows you to effectively preserve damage, stopping the access of oxygen and moisture to the metal.
For this method, a two-component epoxy resin and a reinforcing material - fiberglass or fiberglass are used. The technology is like creating a multi-layered pie. A layer of resin is applied to the pre-prepared and fat-free surface (from the outside and inside, if there is access), then a glass fabric is applied, which is again impregnated with resin. The layers must be 3-4 to ensure sufficient strength.
The main advantage of this method is the absence of thermal effects on the body, which eliminates the risk of deformation. In addition, epoxy compositions have excellent adhesion and chemical resistance. However, such repairs do not restore the initial stiffness of the threshold, but only create a strong patch.
⚠️ Attention: Epoxy resin will not stay on rust or fat. Quality cleaning to shiny metal is critical, otherwise the patch will fall off along with pieces of oxides in a month.
After polymerization (usually 24 hours at room temperature), the surface is grinded, ground and painted over. To enhance the effect, you can add aluminum powder to the resin, which will increase the heat resistance and strength of the composition.
The secret to a durable epoxy patch
Use a fine mesh glass mesh (as for plastering facades) as the first layer. It penetrates better into irregularities and creates an excellent basic layer of clutch, on top of which the main fiberglass is already placed.
Anti-corrosion treatment and finishing painting
Once the hole is sealed, whether by welding or epoxy, the protection stage comes. Metal, even new, without protection will rust very quickly. The first layer is always applied epoxy. It is not hygroscopic and completely isolates the metal from the environment.
After drying the soil, the surface is put down (if you need to level the plane), then acrylic soil-filler is applied, which is sanded for painting. The finishing layer of paint is selected by the code of the car. But the work doesn’t end there – it is critical to treat the inner cavities of the threshold.
For hidden cavities, special anticorrosive compounds (anticores) with long spray nozzles are used. They penetrate into all the crevices, displace the remains of moisture and create a wax or oily film on the walls. Processing must be carried out through the technological holes, as well as from the bottom of the car.
- 🔫 Use an anticorical gun with a long tube and spray nozzle at the end.
- 💧 Carry out the treatment in several stages: primary washing of the cavity, drying, applying the main layer.
- 👀 Control the output of the composition from opposite holes to make sure that the volume is fully filled.
High-quality painting and anticor is a guarantee that your repair will not go to waste in a year. Do not skimp on materials for finishing.
Without high-quality treatment of internal cavities anticory any repair of the thresholds loses meaning, as rotting will continue from the inside.
Frequent errors in repairing threshold areas
Many motorists, trying to save or speed up the process, make critical mistakes. One of the most common is the installation of decorative plastic linings on top of a rotten threshold. This creates a “greenhouse effect”: moisture accumulates under the plastic, air access is limited, and the metal rots many times faster, turning into unnoticed rubbish.
Another mistake is the use of conventional construction mounting foam or bitumen mastics to seal through holes. The foam is hygroscopic (absorbs moisture like a sponge) and, when in contact with metal, accelerates corrosion. Bitumen mastics without preliminary primer and drying also seal moisture inside, preserving the process of destruction.
Ignoring the internal treatment is the way to re-repair. Even if you put the perfect patch on the outside, but forgot to spill the anticort inside, the threshold will rot from the inside in 2-3 winters. The repairs should be comprehensive.
Can a hole in the door be sealed with cold welding?
Cold welding (two-component plasticine) is only suitable for temporary sealing of very small holes or cracks in places not subject to vibration. For rapids that experience constant loads and vibrations, this is a bad option. The material can crack and fall off. It is better to use epoxide with glass or metal.
Do I need to remove the old threshold completely or can I boil a part?
If the threshold has rotted by more than 50% or has multiple through corrosion foci along the entire length, it is advisable to replace it entirely. The boiling of individual lats ("patch sewing") often leads to the fact that after a year the rust gets out between the seams. A complete replacement will guarantee the best result.
How to protect the welds from rust?
The weld is the heat zone where the metal is most vulnerable. After cleaning the seam, it must be covered with epoxy soil. Conventional acid soil can oxidize over time, so epoxy is preferable here. You can apply anti-gravel for mechanical protection.
How much does epoxy dry before painting?
The time of complete polymerization depends on the air temperature and the type of hardener. At +20°C, it usually takes 24 hours. However, many compositions can be grinded after 40-60 minutes. Before painting, make sure the material is completely hardened, otherwise the paint solvent can cause bubbling.
Will galvanizing the powders before installation help?
Yes, if you use repair inserts made of ordinary (black) steel, it is advisable to treat them with zinc-containing soil or to conduct cold galvanizing before cooking. This will create an additional barrier of protection. However, finished repair elements often already have a factory zinc coating, which is checked by a magnet or visually (grey matte color).