How to repair a hole in a car threshold: 5 proven methods with photos and prices

Through corrosion on the sills is one of the most common problems with cars older than 5 years, especially if the car was operated in regions with aggressive winter chemicals or high humidity. Even a small hole with a diameter of 1-2 cm can turn into a rusty sieve within a year if it is not fixed in time. At the same time, many car owners put off repairs, fearing high prices in body shops (from 8,000 to 25,000 rubles per threshold) or not believing in their abilities.

In practice fix a hole in the threshold with your own hands it is possible even without welding experience - the main thing is to choose the right method depending on the size of the damage, body material and budget. In this article we will analyze 5 ways to repair (from temporary to capital), compare their pros/cons, give step-by-step instructions with photos and videos, and also reveal the secret to preventing re-rotting after renovation (90% of car owners skip this step!). The material is relevant for cars produced from 2000–2026, including popular models VAZ, Renault, KIA/Hyundai, Volkswagen and Toyota.

1. Diagnosis of damage: when you can do without welding

Before choosing a repair method, you need to evaluate degree of corrosion and the condition of the metal around the hole. Take a flashlight, a mirror on a telescopic handle (or a smartphone with a front-facing camera) and inspect the threshold from the inside - this will help you understand how deep the rust has spread.

Key features that determine the repair method:

• 🔍 Hole diameter up to 3 cm — you can do without welding (putty + fiberglass or epoxy resin are suitable).
• 🔧 3–10 cm hole with rust around the edges — you will need a patch made of metal or fiberglass + epoxy.
• 🚗 Through corrosion of more than 10 cm or rotting of threshold amplifiers - only welding or replacing the threshold section.
• ⚠️ Rust inside the threshold cavity (determined by a crunch when pressed) - requires complete disassembly and processing ML oil or Dinitrol 4941.

⚠️ Attention: If the threshold is rusted through and through at the place where the jack is attached or next to the side member, DIY repairs are dangerous! In this case, even after filling the hole body rigidity will be compromised, which can lead to deformations in an accident. Contact a body shop to install reinforcement strips.

2. Method 1: Epoxy resin + fiberglass (for holes up to 5 cm)

This is the most accessible and fastest method for small through holes, requiring no welding or special tools. Suitable for temporary repairs (1-2 years) or if you plan to sell the car soon. Materials will cost 300–800 rubles.

What you will need:

• 🛠️ Epoxy resin (eg. EPON 828 or PEP-2) — 200–400 rub.
• 🧵 Fiberglass (density 200–300 g/m²) — 100–150 rub. per meter
• 🧴 Degreaser (Antisilicone or acetone).
• 🔨 Sandpaper P80 and P240.
• 🎨 Resin brush (preferably disposable).

Step by step instructions:

1. Sand the rust around the hole down to bare metal (use a drill with a brush attachment or sandpaper).
2. Degrease the surface with acetone.
3. Apply the first coat of epoxy to the edges of the hole (it should flow in).
4. Cut out a patch of fiberglass with a margin of 2-3 cm and glue it to the resin.
5. Cover the patch with 2-3 more layers of resin, saturating the fabric. Each layer should dry for 15–20 minutes.
6. After complete drying (24 hours), putty the surface and paint.

⚠️ Attention: Epoxy cannot withstand strong mechanical loads! Do not use this method if the hole is in an area where the threshold is subject to impacts (for example, when parking at a curb). Also, epoxy resin turns yellow over time - if you plan to paint the threshold, use a primer with UV protection.

What is the difference between epoxy and polyester resin?

Polyester resin is cheaper (150–250 rubles), but less durable and shrinks when dried. Epoxy is more expensive, but does not crack over time and holds its shape better. Epoxy is preferable for thresholds, as it is more elastic and does not burst during vibrations.

3. Method 2: Metal patch + cold welding (for holes 3–10 cm)

If the hole is large, but the metal around it is still strong, the best option is metal patch, glued with cold welding or epoxy. This method is cheaper than argon welding (the cost of materials is 500–1,500 rubles) and more reliable than pure putty.

Advantages of the method:

• 🔧 Strength is close to welding (withstands loads when jacking up).
• 🛠️ Does not require a welding machine.
• 🎨 Can be painted immediately after drying (after 1-2 hours).

Disadvantages:

• ❌ Not suitable for heavily rusted thresholds (the patch will fall off if the metal continues to rot).
• ❌ The joints are visible if you don’t know how to putty.

Step by step instructions:

1. Cut a patch from sheet metal 0.8–1 mm thick (you can use a tin can or a piece from an old threshold). The patch should cover the hole by 1.5–2 cm on all sides.
2. Sand the threshold and patch until shiny with sandpaper P80.
3. Apply cold welding to the edges of the hole (e.g. ABRO Steel or Poxipol) layer 2–3 mm.
4. Press the patch and secure with clamps or a heavy object for 30–60 minutes.
5. After drying (1-2 hours), putty the joints and paint.

Material	Brand/Model	Price (RUB)	Drying time
Cold welding	ABRO Steel	250–350	1 hour
Epoxy glue	Poxipol	400–600	24 hours
Fiberglass	Density 300 g/m²	100–150	—
Putty	Novol Plus 770	300–500	30–60 min

💡 Helpful tip: If the patch is glued to the bend of the threshold, make cuts on it along the fold line - this will prevent peeling due to vibrations. You can also use rivets for additional fixation (if the patch is thicker than 1 mm).

4. Method 3: Welding a patch (overhaul)

For holes of size more than 10 cm or if the threshold is rotten through in several places, the only reliable way is welding. At a car service center, they ask for this work from 8,000 rubles, but if you have an inverter welding machine (from 5,000 rubles) and minimal skills, you can do it yourself.

What you will need:

• 🔥 Welding machine (preferably an inverter with a current of 60–100 A).
• 🛠️ Metal patch 0.8–1.2 mm thick (can be cut from an old threshold or purchased from Bosal).
• 🧲 Magnetic corners for fixing the patch.
• 🔨 Grinder with cutting wheel.
• ⚡ Anti-corrosion primer (Reoflex or Body 992).

Step by step instructions:

1. Using a grinder, cut out the rusty metal, capturing 1–2 cm of the healthy surface. Clean the edges of the cut until shiny.
2. Adjust the patch to fit the cutout. It should extend 5–10 mm under the threshold for strong welding.
3. Tack the patch at 3-4 points by welding, then weld the seam in a continuous layer.
4. Clean the seam with a grinder and process anticorrosive and putty.

⚠️ Attention: When welding thresholds Toyota, Honda and Mazda (especially models after 2010) use argon welding - these cars have galvanized sills, and ordinary welding can damage the protective layer. Also, don’t cook the thresholds Volvo and Mercedes without preliminary sandblasting - their metal contains alloying additives that are difficult to weld.

5. Method 4: Ready-made repair pads (for popular models)

For many mass-produced cars (VAZ 2108–2115, Renault Logan/Sandero, KIA Rio, Hyundai Solaris) are issued ready-made repair sill plates. They are made of galvanized steel and follow the shape of the original threshold. Cost - 1,500–4,000 rubles for a couple.

Benefits:

• 🔧 Exact fit - no need to cut out patches yourself.
• 🛡️ Galvanization protects against re-corrosion.
• 🚗 The factory threshold geometry is preserved.

How to install:

1. Cut off the rusty section of the threshold with a grinder.
2. Try on the overlay and adjust it to fit (trim the edges if necessary).
3. Weld the overlay with an interrupted seam or glue it to epoxy (if there is no welding).
4. Finish the seams ML oil and paint it.

💡 Where to buy: The pads are sold in parts stores (for example, Exist.ru, Autodoc) or on Avito. For foreign cars, search by VIN code or body model. For example, for Renault Duster 2015–2020 an overlay will do Febi 36636.

6. Method 5: Complete replacement of the threshold (extreme case)

If the threshold has rotted by more than 50% or rust has started amplifiers and spars, the only way out is complete replacement of the threshold section. This is a difficult job that is best left to professionals, but if you have a garage and tools, you can do it yourself.

Cost of spare parts:

• 🚗 Threshold for VAZ 2110 — 2,500–4,000 rub.
• 🚗 Threshold for Toyota Corolla E150 — 8,000–12,000 rub.
• 🚗 Threshold for Volkswagen Polo Sedan — 6,000–9,000 rub.

💡 Important: When replacing a threshold, be sure to:

1. Check the geometry of the body on the slipway (even a slight displacement of the spar will lead to problems with the doors).
2. Treat all cavities ML oil or Dinitrol 4941.
3. Use spot welding — it heats the metal less and does not drive the body.

⚠️ Attention: On vehicles with air suspension (for example, Mercedes S-Class, Audi A8) or adaptive shock absorbers (BMW 5 Series) replacing the threshold may change the suspension settings. After repair you will need calibration on dealer equipment (cost - from 5,000 rubles).

7. Anti-corrosion treatment after repair: why 90% of car owners do it wrong

The main mistake when repairing thresholds is ignoring the internal cavity. Even if you have perfectly repaired the hole on the outside, the rust will continue to spread inside, and the repair will have to be repeated after a year.

How to properly treat a threshold from the inside:

1. Remove the plastic threshold trim (it is attached with clips or screws).
2. Process the cavity through technological holes (or drill new ones with a diameter of 8–10 mm) ML oil or Dinitrol 4941.
3. Use flexible nozzle for uniform spraying.
4. Seal the holes with rubber plugs (e.g. 3M).

💡 Advice: For better protection, add to ML oil 10% Movilya - this will increase viscosity and improve adhesion. You can also use paraffin inhibitors (for example, Tectyl 506), which do not drain and form a protective film.

Comparison of anticorrosives for thresholds:

Composition	Brand	Price (RUB/l)	Protection period	Features
ML oil	Noxudol 700	800–1 200	3–5 years	Penetrates rust and displaces water
Wax anticorrosive	Tectyl 506	1 500–2 000	5–7 years	Does not flow, forms an elastic film
Bitumen mastic	Body 930	300–500	1–2 years	Cheap, but cracks in the cold
Paraffin inhibitor	Dinitrol 4941	1 800–2 500	7–10 years	Best for hidden cavities

8. Common mistakes and how to avoid them

Even experienced car owners make mistakes when repairing thresholds, which lead to repeated corrosion or deterioration of appearance. Here are the most common:

• ❌ Using auto putty without reinforcement. Putty without fiberglass or metal mesh will crack after 3–6 months. Always use reinforcing layer!
• ❌ Painting without primer. Paint applied directly to metal or putty will peel off. Be sure to use epoxy primer (for example, Reoflex).
• ❌ Ignoring drainage holes. If you clog the technological holes in the threshold with putty, water will begin to accumulate inside. Clean them with wire before repairing.
• ❌ Welding without protecting adjacent parts. When welding the threshold, you can burn the wiring or damage the paintwork of the door. Close adjacent elements asbestos sheet.

💡 Useful lifehack: If, after repair, the threshold begins to “bounce” when tapped, it means that the putty or resin is peeling off. To fix this, drill a small hole in the problem area and inject epoxy resin syringe and close the hole.

FAQ: Answers to frequently asked questions

Is it possible to repair a hole in the threshold without welding for a long time?

Yes, but only if the hole is no more than 5 cm and the metal around it is strong. The best option is epoxy resin + fiberglass + metal patch (for example, from a beer can). With proper anticorrosive treatment, such repairs last 3–5 years. For holes larger than 5 cm, welding is indispensable.

Why is rust in thresholds dangerous?

Thresholds are body strength element, which is involved in the distribution of loads during an accident. If they rot, then:

• The rigidity of the body will decrease (the car will “play” on bumps).
• Doors may warp and close poorly.
• Upon impact, the body will fold unpredictably, which is dangerous for passengers.

The critical case is when the rust reaches spars (carrying beams of the body). In this case, the car is recognized unusable and must be recycled.

How much does it cost to repair a threshold at a service center?

Prices depend on method and region:

• Putty + painting (hole up to 3 cm) - 3,000–6,000 rubles.
• Cold welding patch — 5,000–10,000 rub.
• Argon welding — 8,000–15,000 rub.
• Replacing the threshold section — 15,000–30,000 rub.

In Moscow and St. Petersburg, prices are 20–30% higher than in the regions. Also, many services charge an additional fee for anti-corrosion treatment (RUB 1,000–3,000).

Which anticorrosive agent is better for thresholds: ML oil or Dinitrol?

The choice depends on the budget and operating conditions:

• ML oil (Noxudol 700, Tectyl ML) - cheaper (800–1,200 rub./l), penetrates rust well, but requires re-treatment every 2–3 years.
• Dinitrol 4941 - more expensive (RUB 1,800–2,500/l), but lasts 7–10 years and does not drain from vertical surfaces. Optimal for cars that drive off-road or in regions with salty winters.

For internal cavities of the threshold it is better Dinitrol, for external processing - ML oil + Movil.

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

Technically yes, but it is dangerous and fraught with problems:

• 🚗 Legally - if the hole does not interfere with driving, the traffic police inspector does not have the right to fine (Article 12.5 of the Code of Administrative Offenses does not provide for punishment for corrosion). However, questions may arise during the inspection.
• 💰 Financially - a car with rotten sills loses up to 30% of its value upon sale.
• ⚠️ Safe — in the event of an accident, a deformed threshold will not be able to properly distribute the load, which increases the risk of injury.

If the hole is small (up to 2 cm), you can temporarily seal it epoxy or cold welding, but there’s no point in delaying repairs.