Rust showing through the paint at the bottom of a door frame often indicates that the original anti-corrosion coating was damaged during the first pressure wash or was poorly applied at the factory. It is at this moment that the owner wonders, the best way to treat car sillsto stop metal oxidation and prevent through holes after a couple of years. The effectiveness of protection directly depends on the chosen composition, since there is no universal remedy that works equally well in all conditions.
The choice of a specific material is dictated not only by the budget, but also by the current state of the metal, as well as the availability of the possibility of full surface preparation. An erroneous choice, for example, applying wax to already rusty and uncleaned metal, will only preserve moisture and accelerate destruction from the inside. Therefore, before purchasing a can or bucket of mastic, you must clearly understand the difference between penetrating oils, hardening mastics and modern polymer films.
Factors for choosing an anti-corrosion composition
When determining the optimal product, it is important to consider the design of the hidden cavities of your car. The thresholds of modern cars are complex labyrinths of thin metal, where moisture stagnates in the lower pockets. If the composition turns out to be too thick, it simply will not flow into the upper parts of the hidden cavity, leaving the metal there without protection. On the other hand, excessively thin oils may leak through the drain holes or damage the rubber seals.
Climatic operating conditions play a decisive role. For regions with a mild climate and rare use of reagents on roads, lighter formulations are suitable. In severe winter conditions, when roads are generously sprinkled with salt, it is required corrosion inhibitors with long service life and high adhesion. Ignoring this factor will lead to the need to repeat the procedure in six months.
It is also worth considering whether additional sound insulation or filming of the threshold is planned. Some materials, such as asphalt mastics, can dissolve the adhesive underneath the film or create a sticky surface that collects dirt. Critical choose a composition that, after drying (if provided), forms an elastic but not sticky surface.
- 🚗 Operation type: city traffic, highway or off-road.
- 🌡️ Climate: humidity, temperature changes and the amount of reagents.
- 🛠️ Metal condition: the presence of pockets of corrosion or clean metal.
- 🔧 Training options: the presence of sandblasting, a compressor or just a brush.
⚠️ Attention: Never apply new anticorrosives over old, flaking rust without mechanical cleaning. This will create a “compress” effect, accelerating the decay of the metal under the layer of protection.
Review of popular types of anticorrosion agents
The market offers a wide range of solutions, each of which has its own physical properties. Traditional asphalt mastics create a thick, hardening layer that provides excellent protection against gravel impacts, but can crack over time. Oil formulations such as classic Movil, remain in a liquid state, constantly penetrating into microcracks, but require regular updating.
Modern wax and paraffin compositions occupy an intermediate niche. They are elastic, do not crack in the cold and have excellent moisture-displacing ability. However, their mechanical strength is lower than that of bitumen analogues. Polymer spray coatings, often referred to as “liquid plastic,” create a durable, rubber-like film that is resistant to abrasion.
Comparison of the chemical basis of the compositions
Bitumen mastics are based on petroleum products and crumb rubber, which makes them heavy and prone to dripping when heated. Oil-based anticorrosives contain solvents that evaporate, leaving a protective film. Wax compositions are based on synthetic or natural waxes with the addition of rust inhibitors. Polymer coatings are complex compositions based on polyurethane or rubber that require careful surface preparation for adhesion.
Choosing how to treat thresholds, many drivers combine materials. For example, flowing oil is poured into hidden cavities, and the outer part is covered with a hardening compound. This double protection allows you to combine the benefits of different chemical formulas.
- 🛢️ Oil: high penetrating power, but short service life.
- 🪨 Bituminous: excellent sound insulation and protection against stones, risk of cracking.
- 🕯️ Wax: elasticity and durability, average mechanical strength.
- 🧪 Polymer: maximum wear resistance, difficulty of application and removal.
Surface preparation: a critical step
The quality of anti-corrosion treatment depends 80% on surface preparation. Even the most expensive and high-quality composition will not adhere to a greasy, wet or loosely rusted surface. The first step should always be a thorough wash of the underbody and threshold areas using active shampoos to remove tar stains and road reagents.
After washing and drying, all areas of corrosion must be mechanically removed. For this purpose, metal brushes, drill attachments or, ideally, sandblasting are used. If the rust is not removed to bare metal, the oxidation process will continue under the anticorrosive layer. Degreasing is the final and mandatory step before applying any protective coating.
☑️ Threshold preparation checklist
Particular attention should be paid to hidden cavities. To clean them, special spray nozzles are often used that supply a stream of air or a cleaning solution under pressure. This allows you to knock dirt out of hard-to-reach corners where it usually accumulates for years.
Technology for applying protective compounds
The application process depends on the selected material. It is convenient to apply liquid oil compositions and “Movil” using long spray tubes, inserting them into the technological holes. It is important to ensure complete filling of the cavity by controlling the release of material from the drainage holes. Excess should be removed promptly to avoid staining the body.
Thick mastics and bituminous compounds are applied with a brush, spatula or thick gun. When working with a brush, it is important to rub the material into the surface, ensuring penetration into the pores of the metal. When using the gun, be sure to monitor the pressure to avoid creating excessive mist and to ensure an even layer thickness.
For the outer parts of thresholds that are susceptible to stone impacts, an anti-gravel gun is often used. This allows you to create a textured layer of a certain thickness that dampens vibrations and protects the paintwork. Application must be carried out at an ambient temperature of at least +10°C for proper polymerization.
| Type of composition | Application tool | Drying time | Difficulty |
|---|---|---|---|
| Maslyany (Movil) | Spray tube | 2-4 hours (superficial) | Low |
| Bitumen mastic | Brush, spatula | 24-48 hours | Average |
| Wax spray | Aerosol with a tube | 1-2 hours | Low |
| Liquid plastic | Gun, brush | 12-24 hours | High |
Treatment of hidden cavities and arches
Hidden threshold cavities are a high-risk area, since it is impossible to visually control the condition of the metal there. To process them, you need to remove the decorative plastic covers and find the technological holes. If there are not enough holes, they sometimes have to be drilled, guided by technical data sheets for a specific model car.
The ideal solution for hidden cavities are compounds with high penetrating ability and thixotropy (the ability to liquefy when shaken and thicken when rested). They must fill the entire volume, displace moisture and create a protective layer on the ceiling of the cavity, where condensation most often begins to drip.
⚠️ Attention: When processing arches and hidden cavities, be sure to seal the brake mechanisms and exhaust system elements with masking tape. If anticorrosive gets on the brake discs, it can lead to loss of braking efficiency.
After treatment, it is important to ensure that the drainage holes are not clogged with excess material. Water must flow freely from the thresholds, otherwise the effect will be the opposite: the water will remain inside and quickly destroy the metal.
Errors in self-protection of thresholds
One of the most common mistakes is applying anticorrosive paint over paint without checking its condition. If there is already a “thread” of rust under the paintwork, no anticorrosive agent will save you - the metal will rot under the layer of protection. In such cases, stripping down to metal, priming and only then anticorrosive is required.
Another mistake is using inappropriate solvents to dilute thick formulations. This can disrupt the chemical formula of the product, depriving it of its anti-corrosion properties or making it aggressive towards rubber parts. Always use original thinners or follow the manufacturer's instructions.
Main conclusion: The durability of the protection does not depend on the price of the can, but on the thoroughness of cleaning and degreasing the surface before application.
Regular inspections are often forgotten. Anticorrosive is a consumable material that over time loses its properties, is washed off or damaged. Regular inspection (every 1-2 years) allows you to identify damage in time and carry out local repairs without resorting to complete rework.
- ❌ Application to a dirty or damp surface.
- ❌ Ignoring cleaning of existing corrosion.
- ❌ Clogging drainage holes with excess material.
- ❌ Use of aggressive solvents that destroy rubber.
FAQ: Frequently asked questions
How often does the anti-corrosion coating of thresholds need to be renewed?
Oil formulations require updating every 1-2 years, as they are gradually washed out. Bitumen and polymer coatings last longer - from 3 to 5 years, but require annual visual inspection for chips and cracks.
Is it possible to apply anti-corrosion over existing rust?
Strongly not recommended. Anticorrosive does not stop corrosion, but only slows down the access of oxygen. If loose rust is not removed mechanically, the rotting process will continue under the protective layer at the same or greater speed.
Is anticorrosive material harmful to rubber seals?
Some aggressive solvents in cheap anticorrosive compounds can cause rubber to swell or crack. For modern cars with many rubber elements, it is better to choose compounds with neutral chemicals or those specially marked as “Safe for rubber”.
Do I need to remove the thresholds for high-quality processing?
Removing the outer plastic covers is mandatory. Whether to remove the metal threshold itself (which requires welding) depends on the degree of corrosion. For prevention, treatment through technological holes with the plastic removed is sufficient.