Corrosion is a silent but merciless killer of any metal product, and cars are no exception. Owners often notice with horror that car thresholds They begin to rust first, turning into a sieve long before the body loses its strength in other places. This is not just a cosmetic defect, but a serious safety hazard, since these elements carry a huge load.
In this article, we will analyze in detail the anatomy of corrosion, explain why modern technologies cannot completely defeat rust, and offer real ways to combat it. You will learn where to look for hidden areas of destruction and why simple exterior painting is often useless without a comprehensive approach.
Ignoring the first signs of rot can result in the cost of restoration exceeding the market price of the car. Let's figure out how to prevent this and keep the body intact for as long as possible.
Design features and risk areas
The sills are complex strength elements that connect the front and rear parts of the body, and also provide torsional rigidity. In modern cars they are often performed according to three-layer scheme: External decorative panel, internal reinforcement and connecting shelf. It is in the space between these layers that most often it arises. hidden corrosion.
The design is such that water and dirt, getting inside through drainage holes or microcracks, stay there for a long time. The lack of normal ventilation inside a closed profile creates ideal conditions for a chemical reaction of metal oxidation. Externally, the part may look intact, but inside a cavity has already formed, filled with rusty dust.
Welding and joint areas are particularly at risk. Spot welding, used in factories, creates heat-affected zones where the metal changes its structure and becomes more susceptible to an aggressive environment. If the factory zinc layer was damaged during assembly or damaged during operation, the rotting process begins rapidly.
⚠️ Attention: Do not judge the condition of the thresholds only by appearance. Tap them with your knuckle - a dull sound may indicate the metal is peeling off from the inside.
Risk areas are distributed unevenly. The lower edge of the threshold suffers the most, where sand and stones fly from the road. The jack's attachment points are also vulnerable, since mechanical stress often tears off the protective layer of anti-corrosion.
Why are the thresholds the first to rot?
The answer lies in the combination of several factors that create a "perfect storm" for the metal. Firstly, this is a constant mechanical impact. Sand, small stones and salt flying from under the wheels act as an abrasive, gradually erasing the paintwork and anti-corrosion protection. This process is called abrasive wear.
Secondly, the chemical composition of the reagents that are used to sprinkle roads in winter. Chlorides and other salts are powerful corrosion catalysts. Getting into microcracks in the paint, they accelerate oxidation hundreds of times, especially under conditions of temperature changes when water either freezes, expands, or melts.
The third factor is the design features of the drainage. If the drain holes in the thresholds become clogged with dirt or leaves, water remains inside the profile. Moisture stagnation combined with a lack of air access, this is a sure way to rapid destruction of the metal from the inside out.
- 🚧 Constant bombardment of sand and gravel from the road surface.
- 🧪 Aggressive effects of road reagents and salts.
- 💧 Design features that promote moisture stagnation inside the profile.
- 🔨 Mechanical damage when using a jack or careless parking.
It's also worth noting that some car models have a more severe problem due to thin metal or poorly designed drainage systems. Owners of such cars need to pay special attention to body protection.
Use plastic door sill covers - they take the brunt of the impact from stones and dirt, keeping the paintwork intact.
Types of corrosion and their diagnosis
Understanding the type of corrosion helps you choose the right treatment strategy. The most common is surface corrosion, which begins with small “saffron caps”. If measures are not taken at this stage, it becomes deep, penetrating the metal right through.
Of particular danger is under-film corrosion. It develops under a layer of paint that is not yet damaged. Visually, you can only see a slight swelling of the varnish, but underneath the metal has already turned to dust. It is difficult to diagnose this condition without special devices, but it is possible by the characteristic change in the color of the paintwork.
For accurate diagnosis, professionals use a thickness gauge. This device allows you to measure the thickness of the paint coating and identify places where it was carried out. body repair or where the paint layer has become critically thin.
| Type of corrosion | Visual cues | Danger level | Treatment method |
|---|---|---|---|
| Superficial | Small red dots, scratches | Low | Polishing, local touch-up |
| Underfilm | Blistering of paint, change in shade | High | Removing paintwork, cleaning, primer |
| Through | Holes, holes, crumbling metal | Critical | Cutting out rotten metal, welding patches |
| Slotted | At joints and welds | Average | Disassembly, cleaning, anticorrosive |
It is important to regularly inspect the arches and mudguard attachment points. This is where dirt most often accumulates, which holds moisture near the metal.
Methods of struggle and recovery
If the process has already started, simple washing and polishing will not help. Radical measures are needed. The first step is always mechanical cleaning of the damaged area. Sandblasting or brushing to bare metal is used.
After cleaning, the surface must be treated with a rust converter. This chemical converts iron oxides into stable compounds that can be primed. However, if the metal has already lost its load-bearing capacity, it will have to be cut out and replaced with a new one.
To restore the integrity of thresholds, two main methods are used: welding repair inserts or using fiberglass and putty (less reliable). Welding work require high qualifications, since thin metal is easy to burn through.
☑️ Threshold restoration plan
⚠️ Attention: Never paint over rust without first cleaning and priming. This will only preserve moisture under the paint and accelerate destruction.
After welding, the seams must be carefully insulated from moisture. For this purpose, special sealants and mastics are used. The final stage is painting in body color or applying a protective decorative coating.
The secret to long lasting welds
Use zinc-containing primers before painting welds. Zinc works as a protective protection; even if the paint layer is damaged, the metal will not rust as long as there is zinc nearby.
Prevention: how to extend the life of the body
The best treatment is prevention. Regular car washing, especially in winter, helps wash away aggressive reagents. Particular attention should be paid to the wheel arches and underbody, where the most dirt accumulates.
High quality anti-corrosion treatment - this is not a marketing ploy, but a necessity for our conditions. Modern materials, such as paraffin-containing compounds or cannon fat, are able to penetrate microcracks and displace moisture, creating an elastic protective film.
It is important to monitor the condition of the drainage holes. Their periodic cleaning ensures that water does not stagnate inside the thresholds. You should also avoid parking in the grass or near snowdrifts, where the body is constantly in contact with a damp environment.
- 🚿 Regular body washing using active foam to remove salt.
- 🛡️ Renewal of anti-corrosion coating once every 2-3 years.
- 🔍 Visual inspection of thresholds and arches after the winter season.
- 🌬️ Cleaning drainage channels in thresholds and doors.
Don't skimp on protective materials. Cheap bitumen mastics crack over time, and corrosion underneath them develops even faster, remaining unnoticed.
Regular washing of the bottom in winter and timely renewal of anticorrosive coating can extend the life of thresholds by 2-3 times.
Legal aspects and security
Severe corrosion of thresholds is not only an aesthetic problem, but also a safety issue. In the event of a side impact, the rotten threshold will not be able to absorb the impact energy, which can lead to deformation of the passenger compartment and injuries to passengers. Therefore, the technical condition of the body directly affects safety.
When selling a car, the presence of through corrosion may be a reason to reduce the price or refuse to purchase. In addition, when passing a technical inspection in some countries and regions, the presence of through holes in the power elements of the body is grounds for refusal to issue a diagnostic card.
Owners should remember that restoring heavily rotted thresholds is a complex and expensive process that requires professional equipment. Cheap repairs often lead to the problem returning in an even larger form after a year or two.
Is it possible to completely stop corrosion if it has already started?
It is impossible to completely stop a process that has already begun "chemically", you can only slow it down. The only way is to mechanically remove all pockets of rust to bare metal and subsequent high-quality insulation from oxygen and moisture.
How often should anti-corrosion treatment be done on a new car?
Factory treatment usually lasts 2-3 years. In conditions of aggressive use (urban reagents, primers), the first preventive treatment is recommended to be carried out 1-2 years after purchase, and then repeated every 2 years.
Is it true that a galvanized body does not rust?
Galvanizing significantly slows down corrosion, but does not make the metal immortal. If the zinc layer is damaged (stones, scratches) and lack of care, rust will appear, although later than on ordinary steel.
Should I weld the holes or change the entire thresholds?
If the affected area exceeds 30-40%, it is better to replace the entire threshold with a repair insert. Welding many small holes (“patchwork”) reduces the rigidity of the structure and the quality of anti-corrosion protection.