Before you start welding thresholds, it is important to understand: this is not just a repair, but a restoration of the load-bearing part of the body. Thresholds are a key element of a car’s rigidity, and their poor repair can lead to deformation of the body in an accident or even refusal to pass a technical inspection. In this article we will analyze the entire process - from rust diagnosis to final anti-corrosion treatment - taking into account the nuances for different types of cars (from VAZ 2107 up to Toyota Camry).

Welding thresholds requires not only the ability to operate a welding machine, but also an understanding of the metal, the thickness of the body panels, as well as the features of anti-corrosion protection. Mistakes here are costly: overheating of the metal leads to its deformation, incorrect welding leads to rapid re-rusting, and failure to comply with safety regulations leads to burns and fires. If you have never held a semi-automatic machine in your hands, it is better to entrust the work to professionals. But if you decide to do it yourself, read on.

1. Diagnostics: when thresholds need to be welded, and when local repairs can be done

Not all rust on door sills requires complete replacement. Sometimes it is enough to cut out a small area or even get by with putty and anticorrosive. Here's how to determine the extent of damage:

  • 🔍 Surface corrosion (saffron caps, paint bubbles) - can be cleaned, treated with a rust converter and coated with anti-corrosive. No welding needed.
  • 🚗 Through holes with a diameter of up to 3–5 cm — cut out the damaged area, weld a patch of metal of the same thickness (usually 0.8–1.2 mm).
  • 💥 Global rot (the threshold crumbles when pressed, the internal cavity is visible) - a complete replacement of the section or the entire threshold is required.
  • 🔧 Deformation after an accident - even if the metal is intact, the threshold could bend. This requires straightening or replacement.

For an accurate diagnosis, use endoscope (flexible camera) or simply shine a flashlight through the threshold from the inside. If light passes through holes, things are bad. Also note welding points (they can be seen from below): if they are rusty or missing, the threshold has already rotted away from the body and is kept “on word of honor”.

⚠️ Attention: On vehicles with a galvanized body (for example, Volkswagen Passat B6, Skoda Octavia) rust is often hidden under a layer of zinc. Clean the area with sandpaper - if there is red metal under the zinc, get ready for welding.
Type of damage Recommended Repairs Cost (on your own) Cost (in service)
Local holes (up to 5 cm) Patch + welding 1 500–3 000 ₽ 5 000–10 000 ₽
Full length corrosion Replacing the threshold section 8 000–15 000 ₽ 20 000–40 000 ₽
Deformation after impact Straightening + welding 10 000–20 000 ₽ 25 000–50 000 ₽
Complete rot (missing weld points) Replacing the threshold assembly 15 000–30 000 ₽ 40 000–80 000 ₽
📊 What experience do you have in body repair?
Never cooked
Tried patches
I change the panels myself
Professional welder

2. Tools and materials: what you will need to weld thresholds

Without the right equipment, welding thresholds turns into torture. Here is the minimum set that you cannot do without:

  • 🔥 Welding machine - optimal semi-automatic (MIG/MAG) with the ability to work in a carbon dioxide environment. Suitable for beginners Resanta SAIPA-190 or Svarog EASY MIG 180. Power - at least 160 A.
  • ⚡ Carbon dioxide (CO₂) cylinder - to protect the seam from oxidation. An alternative is a mixture of argon and CO₂ (for stainless steel).
  • ✂️ Grinder (angle grinder) with cutting wheels for metal (thickness 1–1.2 mm). For cleaning - a petal disk.
  • 🛠️ Protective equipment: chameleon mask (for example, ESAB Sentinel A50), pigskin gloves, fire-resistant clothing.
  • 📏 Measuring tool: caliper, ruler, square. Thresholds must be symmetrical to the nearest millimeter!
  • 🔧 Clamps and Clamps - for fixing patches and new panels.
  • 🧴 Anti-corrosion materials: epoxy primer, mastic (for example, Dinitrol 4941), zinc spray.

For spot welding (if you are restoring factory seams) you will need spotter or an inverter with spot welding function. An alternative is drilling holes and riveting, but this is less reliable.

⚠️ Attention: Do not use a household welding transformer for thresholds! It produces a too rough seam, which will burn through metal 0.8–1 mm thick. A semi-automatic machine with 0.6–0.8 mm wire is the only right choice.

Remove plastic trims and door seals|

Disconnect the negative terminal of the battery|

Clean the metal to a bare shine (grinder + brush) |

Blow out the internal cavities of the threshold with compressed air|

Apply markings for cutting (marker + masking tape) -->

3. Preparing the car: how not to burn the wiring and not deform the body

Before welding, the car must be prepared so as not to damage the electronics or cause burns. Here's the step-by-step plan:

  1. Removing body kits. Remove plastic door sill trims, door seals, fender liners. On some machines (for example, Renault Logan) you will have to remove the front seat to get to the inside of the sill.
  2. Turning off electronics. Remove the negative terminal from the battery. If you weld near the control unit (ECU), it may burn out from a power surge. On foreign cars, the ECU is often hidden under the front panel - check the location in the manual.
  3. Protection of glass and interior. Cover the windows and seats with a fire-resistant blanket or damp cloth. Sparks from the grinder and welding fly 2-3 meters!
  4. Metal cleaning. Using a grinder with a petal disc, clean the threshold down to bare metal. Remove rust, old paint and mastic. If there are traces of welding, cut them flush.

Critical mistake: welding over rust or paint leads to the formation of pores in the seam, which will become sources of new corrosion within 6-12 months. If the metal is rusted through, cut it out with a margin of 1-2 cm to capture healthy areas.

For precise markings, use masking tape + marker. Draw the cutting lines so that the new piece of metal overlaps the old one by 15–20 mm - this is necessary for a strong seam. If you are replacing an entire section of the threshold, make a cardboard template in the shape of the old part.

💡

Before welding, apply to the edges of the cut. zinc spray - this will protect the metal from oxidation during operation and will simplify subsequent processing of the seam.

4. Welding technology: how to weld thresholds so that the metal does not leak

The main problem when welding thresholds is metal deformation due to overheating. Body panels are thin (0.8–1.2 mm), and if welded with a continuous seam, they will move in a wave. Professionals use spot welding or interrupted seam in increments of 2–3 cm. Here are step-by-step instructions:

  1. Potholder. Secure the patch or new section of the threshold with clamps. Make 3-4 tacks (short seams of 5-10 mm each) at different ends so that the part does not move out.
  2. Setting up the device. For semi-automatic:
    • Current: 80–120 A (depending on the thickness of the metal).
    • Wire feed speed: 4–6 m/min.
    • Gas: CO₂ (flow 8–12 l/min).
    • Wire: 0.6–0.8 mm (eg ESAB OK Autrod 12.51).
  • Welding. Guide the arc at an angle of 10–15° towards you. The length of the seam is no more than 2 cm, then pause for 5–10 seconds to cool. The total length of the seam should not exceed 30% of the length of the joint (the rest is tack welding).
  • Deformation control. After each seam, check the evenness of the metal with a ruler. If the threshold “goes like a wave,” cool it with a wet rag and tap it with a mallet.

    • For spot welding (if you are restoring factory seams) use a spotter or inverter with the “dot” function. The dot spacing is 2–3 cm. After welding, clean the seams with a grinder with a flap disk to remove slag.

    ⚠️ Attention: On vehicles with aluminum thresholds (for example, Jaguar XE, Audi A8) MIG/MAG welding is not suitable - you need a argon arc apparatus (TIG) and special wire (for example, AlMg5). It's better not to take it without experience!
    What to do if the metal still leads?

    If the threshold is deformed after welding, try:

    1. Heat the convexity with a gas burner (temperature ~200°C) and cool it with a wet cloth - the metal will “shrink”.

    2. Tap with a mallet through a wooden block (not on bare metal!).

    3. As a last resort, cut off the deformed area and re-cook it.

    If the wave is small (1–2 mm), it can be smoothed out with putty, but this is a temporary solution.

    5. Post-welding treatment: how to protect seams from rust

    A weld without protection will rust in 1–2 years. To prevent this from happening, you need multilayer anticorrosive:

    1. Cleaning up. Using a grinder with a flap disc, remove slag and scale. The seam should be smooth, without sharp edges.
    2. Degreasing. Wipe the seam with solvent (for example, White spirit or Antisilicone).
    3. Primer. Apply epoxy primer (for example, Reoflex 2K) in 2 layers. It protects the metal from moisture and serves as a base for paint.
    4. Mastic. For internal cavities use wax anticorrosive (for example, Tectyl ML), for external ones - bitumen mastic (for example, Dinitrol 4941). Apply by brush or spray.
    5. Galvanizing. Finish the seam zinc spray (for example, Zinc Rich Primer) - this imitates factory galvanization.
    6. Painting. After the primer has dried, apply paint in the body color (the color code is indicated in the vehicle title or on the plate under the hood).

      7. For hidden cavities (inside the threshold) use anticorrosive aerosol with a long tube. Blow out the cavity with compressed air, then fill in the anticorrosive agent so that it flows over all internal surfaces.

      Material Purpose Protection period Approximate price
      Epoxy primer Moisture protection, paint adhesion 5–7 years 500–1,000 ₽/l
      Wax anticorrosive (Tectyl) Protection of internal cavities 3–5 years 600–1,200 ₽/l
      Bitumen mastic (Dinitrol) Protection of external surfaces 4–6 years 400–800 ₽/kg
      Zinc spray Imitation of factory galvanization 7–10 years 300–600 ₽/cylinder
      💡

      Anti-corrosion treatment should be multilayer: primer + mastic + zinc. One layer (for example, just mastic) will not protect the seam for a long time.

      6. Common mistakes and how to avoid them

      Even experienced craftsmen sometimes make mistakes when welding thresholds. Here are the most common ones and how to prevent them:

      • 🔥 Metal overheating → leads to deformation. Solution: cook in short seams (2–3 cm) with pauses for cooling.
      • 💧 Welding on rust → the seam is porous and rusts quickly. Solution: clean the metal until it shines.
      • ⚡ Ignoring Grounding → risk of electric shock or damage to electronics. Solution: Attach the “mass” as close as possible to the welding site.
      • 📏 Uneven joints → the threshold looks crooked, gaps are possible. Solution: use templates and check symmetry with a ruler.
      • 🧲 Lack of anticorrosive → seams rust in 1–2 years. Solution: primer + mastic + zinc are required!
      • 🚗 Welding with closed doors → risk of damage to the wiring in the door hinges. Solution: the doors must be open and the wiring must be disconnected.

      Another common mistake is using wire that is too thick (1 mm or more). It will burn through the thin metal of the threshold, and you will have to weld patch upon patch. The optimal wire diameter is 0.6–0.8 mm.

      If you are welding thresholds on a car with electronic assistance systems (ESP, ABS), disconnect them first via the diagnostic connector (for example, OBD-II). Voltage surges during welding can throw off sensor settings.

      Each car has its own sill design features. Let's look at the nuances for the most common models:

      • 🚘 VAZ 2101–2107, 2110–2112:
        • The thresholds are load-bearing, welded to the side members. When replacing, you need to cut off the old welding points and weld new ones in increments of 3-4 cm.
        • There is a wiring harness running inside the threshold - do not damage it when cutting!
        • The optimal metal thickness for patches is 1 mm.
      • 🚗 Renault Logan, Sandero, Duster:
        • The sills are removable and are attached to the body by spot welding and bolts. Can be replaced entirely without cutting.
        • There are drainage holes inside the threshold - do not weld them shut!
        • When welding, turn off the airbag control unit (located under the front panel).
      • 🚙 Toyota Corolla, Camry:
        • Thresholds are often galvanized - strip down to bare metal before welding.
        • Use wire with a high silicon content (eg ESAB OK Autrod 12.51) for better fluidity.
        • After welding, be sure to restore the factory anti-gravel protection (for example, 3M Stone Guard).
      • 🚛 Nissan Qashqai, X-Trail:
        • Thresholds are part of the supporting frame. When replacing, check the body geometry on a stand.
        • Fuel lines run inside the threshold - be careful with sparks!
        • For anticorrosion use materials with high adhesion to galvanization (for example, Würth Underbody Protection).

      On German cars (Volkswagen, BMW, Mercedes) thresholds often have a complex shape with stiffening ribs. In this case, it is better not to weld patches, but to replace the entire section - otherwise the geometry of the body will be disrupted.

      💡

      On foreign cars with aluminum thresholds (for example, Audi A6, Jaguar XF) MIG/MAG welding is not suitable - you need argon (TIG) and special wire AlMg5. Without experience, it is better to contact the service.

      8. Alternatives to welding: when you can do without it

      Welding is not the only way to repair thresholds. In some cases, you can get by with simpler methods:

      • 🔧 Riveting. Suitable for thin metal (0.6–0.8 mm) if you do not have a welding machine. The downside is that it is less durable than welding.
      • 🧲 Cold welding (epoxy glue). Only for small holes (up to 2 cm). For example, ABRO Steel or Poxipol.
      • 🖌️ Fiberglass + putty. Temporary solution for cosmetic repairs. Does not withstand loads.
      • 🔩 Bolted connection. If the threshold is bolted (as on Renault Duster), you can replace it without welding.

      However, remember: any alternative to welding is a compromise. Riveting and cold welding do not restore the rigidity of the body, and the putty cracks over time. If the threshold is a load-bearing element (as in VAZ 2107 or Toyota Corolla), welding is required.

      ⚠️ Attention: On vehicles with subframe (for example, Volkswagen Golf, Ford Focus) the thresholds are connected to the suspension. Poor quality repairs can lead to changes in wheel alignment!

      FAQ: Frequently asked questions about welding thresholds

      Is it possible to weld thresholds with an inverter (manual arc welding)?

      Theoretically it is possible, but it is extremely difficult. The inverter produces a high temperature that will burn through the thin metal of the threshold (0.8–1.2 mm). To do this, you need electrodes with a diameter of 1.6–2 mm and experience working with thin sheet metal. It's better to use a semi-automatic.

      How much does it cost to digest the thresholds in the service?

      The cost depends on the amount of work:

      • Local patch - 3,000–8,000 RUR.
      • Replacement of a threshold section—RUB 15,000–30,000.
      • Complete replacement of both thresholds - 40,000–80,000 rubles.

      Prices are valid for 2026 (Moscow and regions). On foreign cars, work is 20–30% more expensive.

      Which gas is better to use for welding thresholds: CO₂ or argon?

      For steel thresholds (most cars) optimal CO₂ - it is cheaper and provides good penetration. Argon or its mixture with CO₂ (80/20) is needed for welding stainless steel or aluminum (for example, on Audi or Jaguar).

      What happens if you don’t cook the thresholds, but just putty them?

      Putty is cosmetic repairs, which does not restore the strength of the body. Consequences:

      • Rust will continue to spread under the putty.
      • The threshold will lose its rigidity, which is dangerous in case of an accident.
      • The next technical inspection may not allow it due to through corrosion.

      Putty can only be used as a temporary solution (1-2 years) or for minor scratches.

      Is it possible to cook thresholds outside in winter?

      It is possible, but with reservations:

      • The metal temperature should not be lower than +5°C (in frost the seam becomes brittle).
      • Use heater (for example, a gas torch) to heat the metal before welding.
      • Store the CO₂ cylinder in a warm room - the gas loses pressure in the cold.
      • Apply anti-corrosion materials (primer, mastic) in a heated garage - they do not polymerize in the cold.