Repairing a car threshold: how to repair a rust hole yourself

Why do thresholds rot and when should they be boiled?

Car sills are one of the most vulnerable parts of the body. They are constantly exposed to moisture, reagents and mechanical damage. Through corrosion on the thresholds not only spoils the appearance, but also threatens safety: Rust weakens the structure, which can lead to body deformation in an accident.

The first signs of a problem are swelling of the paint, red spots or crunch when you press the threshold. If a hole has already formed, you cannot delay repairs: the metal will continue to deteriorate, increasing the area of ​​damage. You can brew the threshold yourself, but this will require welding machine, skills in working with metal and adherence to technology.

In this article we will analyze the entire process: from diagnosis to final painting. You will find out which electrode choose for welding, how to properly cut out the rust and how to treat the seams so that corrosion does not return.

Tools and materials: what you need for work

Before you begin the repair, prepare everything you need. Without the right tool, it will not be possible to weld the threshold efficiently. Here minimum set:

• 🔧 Welding machine (semi-automatic or inverter with MIG/MAG function for thin metal)
• 🔨 Bulgarian with cutting and grinding wheel (diameter 115–125 mm)
• 🧲 Magnetic holder for fixing patches
• 🧴 Anti-corrosion primer (for example, Body 960 or ML)
• 🎨 Auto enamel in body color (paint code can be found on the plate under the hood)
• 🛠️ Metal patches (thickness 0.8–1 mm, preferably galvanized)
• 🧤 Protective equipment: welder mask, gloves, respirator

If you are a beginner, it is better to choose semi-automatic welding (MIG/MAG) - it is easier to learn than a manual arc. For thin metal thresholds, a wire with a diameter of 0.6–0.8 mm and gas Ar/CO₂ (80/20). Experienced craftsmen can use spot welding, but it requires special equipment.

⚠️ Attention: Do not use ordinary steel for patches without anti-corrosion treatment! Galvanized metal or stainless steel will extend the service life of the repair by 2–3 times.

Preparing the threshold: removing rust and marking

The quality of repair depends 70% on preparation. If you leave even a small area of rust, corrosion will quickly return. Start with complete cleaning damaged area:

1. Remove the trim threshold (if there is one) and unscrew all fasteners.
2. Clear surface Bulgarian with grinding wheel or drill with a brush. Remove paint, primer and rust until bare metal.
3. Assess the extent of damage. If the hole is more than 5 cm in diameter, you will need tenderloin damaged area and welding of a new part.
4. Apply the markings marker, stepping back from the edge of the rust 1–1.5 cm - this is a guarantee that you will remove all affected areas.

For precise markings, use ruler or template. If the threshold has a complex shape, do cardboard mockup patches and transfer it to the metal. This will help avoid mistakes when cutting.

Critical: Prepare the edges of the cutout before welding. anti-corrosion composition (for example, Tsinkor-Auto). This will prevent the metal from oxidizing during operation.

Tool	Purpose	Alternative
Bulgarian	Rust cutting, metal stripping	Metal scissors (for small areas)
Welding machine	Connecting the patch to the body	Cold welding (temporary solution)
Grinder	Alignment of seams after welding	Sandpaper (80–120 grit)
Primer	Protecting metal from corrosion	Zinc spray (less durable)

Welding technology: step-by-step instructions for beginners

If you've never welded metal, practice on scrap parts. Welding a threshold requires care: too strong a current will burn through the metal, a weak current will not provide a strong connection. Optimal settings for semi-automatic:

• 🔌 Current: 60–80 A (depending on metal thickness)
• 🌀 Wire feed speed: 4–6 m/min
• 💨 Gas consumption: 8–10 l/min
• ⚡ Polarity: reverse (minus details)

Procedure:

1. Grab the patch at 3-4 points so that it does not move during welding.
2. Lead the seam short joints (by 2–3 cm), allowing the metal to cool. Start from the edges and work towards the center.
3. Control failure: the seam should be convex, but no more 1–1.5 mm. If the metal burns, reduce the current.
4. Clean the seams Bulgarian or sander, removing scale and sagging.

For difficult areas (such as threshold bends), use spot welding in increments 1–1.5 cm. This will reduce the risk of metal deformation from overheating.

⚠️ Attention: Do not cook the threshold at temperatures below +5°C! Humid air and cold metal result in porous seams that quickly rust.

Post-weld treatment: primer and paint

Welding seams are the most vulnerable place for corrosion. Without proper treatment, rust will return within a few months. Protection algorithm:

1. Degrease the surface acetone or white spirit.
2. Apply acid primer (for example, Reoflex) for passivation of metal. It converts rust residues into an inert compound.
3. Cover with acrylic primer (2–3 layers) to level the surface.
4. Apply anti-gravel (for example, Body 950) to the lower part of the threshold - this will protect against chips.
5. Paint threshold in body color using spray gun or a spray can.

For durability, use multi-layer protection:

1. 1st layer: epoxy primer (metal insulation)
2. 2nd layer: acrylic primer (alignment)
3. 3rd layer: base enamel (color)
4. 4th layer: varnish (protection and shine)

After painting, let the parts dry 24–48 hours before installing the cladding. Avoid washing your car during the first 24 hours!

What happens if you don't prime the seams?

Without a primer, the metal will begin to oxidize within 1–2 weeks. Moisture and salt will penetrate through microcracks in the paint, causing under-film corrosion. After 3-6 months, the seams will swell and the paint will peel off.

Common mistakes and how to avoid them

Even experienced craftsmen sometimes make mistakes when repairing thresholds. Here the most common:

• 🔥 Metal overheating → leads to deformation of the threshold. Solution: cook in short seams intermittently.
• 🧲 Use of non-galvanized patches → rust returns within 6–12 months. Solution: take metal with zinc coating.
• 🎨 Painting without primer → the paint peels off after 2–3 months. Solution: Apply 2-3 layers of primer.
• ⚡ Welding on dirty metal → the seams are porous. Solution: Clean the surface until it shines.
• 🚗 Ignoring anti-gravity → chips from stones expose the metal. Solution: Apply a protective layer to the bottom edge.

Another common problem is color mismatch after painting. To avoid this, use computer paint selection by VIN code or original sample. If you paint with a spray can, buy aerosol with the same code, as on the plate under the hood.

⚠️ Attention: If after welding the threshold “leads” (deforms), do not try to straighten it with a hammer! Use straightening tool or vacuum suction cupso as not to stretch the metal.

Cost of repairs: comparison of independent and professional approaches

The cost of threshold repair depends on the extent of the damage, the make of the car and the region. The table below shows approximate prices:

Type of repair	On your own (RUB)	In service (RUB)	Notes
Local welding (hole up to 5 cm)	1 500–3 000	5 000–10 000	Cost of patch and consumables
Replacement of the threshold section (up to 30 cm)	3 000–6 000	12 000–20 000	Includes cutting, welding, painting
Complete threshold replacement	8 000–15 000	25 000–40 000	Requires welding equipment and skills
Anti-corrosion treatment	1 000–2 000	3 000–6 000	Primer + bottom protection

Do-it-yourself repairs cost 3–5 times cheaper, but it takes time and skill. If you have never held in your hands welding machine, it is better to entrust the work to professionals - mistakes during welding can result in additional expenses for rework.

You can save on materials: buy primer and paint at car analysis or online stores (for example, Exist.ru, Emmegi). Please note threshold repair kits - they include patches, primer and instructions.

FAQ: Frequently asked questions about repairing thresholds

Is it possible to weld a threshold without welding?

Yes, but this is a temporary solution. Alternatives:

• 🧰 Cold welding (for example, Poxipol) - lasts 1–2 years, but does not withstand loads.
• 🧵 Fiberglass + epoxy — suitable for small holes (up to 3 cm).
• 🔧 Rivet patches - less reliable than welding, but better than nothing.

For long-term repairs, welding is required.

What gas should I use for welding thresholds?

Optimal mixture - Ar/CO₂ (80/20). It provides:

• ✅ Stable arc
• ✅ Minimal splashing
• ✅ Good penetration of thin metal

For semi-automatic also suitable clean CO₂, but it produces more spatter and requires a more highly qualified welder.

How long does it take to repair a threshold?

Approximate dates:

• 🕒 Local welding: 4–6 hours (with painting).
• 🕒 Replacement area: 8–12 hours (extends over 2 days due to drying of the soil).
• 🕒 Complete threshold replacement: 1–2 days (requires disassembly of the interior).

Please note that primer and paint dry 24 hours until complete polymerization.

What to do if after welding the threshold rusts again?

Causes and solutions:

• 🔍 Bad stripping: rust remains under the patch → you need to cut out the area and digest it.
• 💦 No primer: metal comes into contact with moisture → apply acid soil and paint.
• 🧲 Non-galvanized patch: ordinary steel rusts faster → replace with galvanized steel.
• 🚗 Damage to anti-gravel: chips from stones → restore the protective layer.

Is it possible to drive with a hole in the sill?

Technically yes, but this dangerous:

• 🚨 Body rigidity decreases → in case of an accident, the threshold will not withstand the load.
• 💨 Ingress of water and dirt → accelerates corrosion of other elements.
• 📜 Problems with passing maintenance - a hole in the threshold can cause failure.

If repairs are delayed, close the hole temporary patch made of fiberglass or sealant.