Why do thresholds rot and when is it time to repair them?
Car sills are one of the most vulnerable parts of the body. They are constantly exposed to moisture, salt, sand and mechanical damage. Even on new cars, after 3-5 years you can detect the first pockets of corrosion, and on cars older than 10 years through holes in the thresholds - not uncommon. Models with poor factory anti-corrosion treatment suffer especially: VAZ 2108-2115, Daewoo Nexia, Renault Logan first generation.
The main signs that the thresholds require repair:
- 🔍 Visible paint bubbles or swelling on the surface
- 💧 Traces of rust on the inside of the doors or under your feet
- 🔊 Characteristic creaking or knocking noise when opening doors
- 🕳️ Through holes (even small ones are a signal for urgent repairs)
Many car owners put off repairs, considering them too complicated. Actually You can replace or repair thresholds yourself with a minimum set of tools and patience. The main thing is not to let the problem progress to the point where the rust reaches the side members or body pillars.
Preparation for repair: tools and materials
Before starting work, prepare everything you need. Without the right tools, repairing thresholds will turn into agony. Here minimum setwhich you will need:
| Category | Required items | Notes |
|---|---|---|
| Tools | Grinder (115-125 mm), welding machine (semi-automatic), drill, set of screwdrivers, hammer, chisel, grinder | An inverter with a power of 160-200A is suitable for welding. |
| Consumables | Welding wire 0.8 mm, grinder wheels (cutting, grinding), sandpaper (P80-P1200), putty, primer, paint | Select paint according to the color code of your car |
| Spare parts | Repair threshold inserts or new thresholds (if completely replaced), anti-corrosion compounds | For VAZ and GAS easy to find ready-made repair kits |
| Protection | Respirator, glasses, gloves, overalls | Definitely! Sanding dust is toxic |
If you are planning partial renovation (sealing holes without completely replacing), you can do without welding - just fiberglass, epoxy putty and a good primer. But remember: such repairs will last 2-3 years, after which corrosion will return.
⚠️ Attention: Do not use mounting foam or ordinary putty without reinforcement to repair thresholds! These materials cannot withstand stress and crack quickly.
Diagnostics of the condition of thresholds: what can be saved and what can only be cut out
Before you take up the grinder, you need to assess the scale of the destruction. Take a flashlight, a mirror on a telescopic handle and carefully inspect the thresholds inside and out.
Critical zones, which are worth paying attention to:
- 🔹 Connection of the threshold with the spar (often rots first)
- 🔹 Threshold corners (moisture accumulates)
- 🔹 Places for attaching door seals
- 🔹 Internal cavity of the threshold (check through with a thin screwdriver)
Do a simple test: press the threshold with your foot. If the metal bends or a crunching sound is heard, this is a sign complete destruction of the internal structure. In this case, only a complete replacement. If the rust is superficial (up to 1-2 mm deep), you can get by with local repairs.
How to check the threshold for hidden corrosion?
Use an endoscope (or a smartphone with a flexible USB cable) to examine internal cavities. Pay special attention to the places where the threshold connects to the body - dirt often accumulates there, which cannot be removed without disassembling.
Step-by-step instructions: repairing a threshold without welding (for minor damage)
If corrosion has not had time to eat through the metal, you can do without radical methods. This method is suitable for spot rust spots up to 5-7 cm in size.
Algorithm of actions:
- Clean off the rust with a grinder with a flap wheel until bare metal.
- Treat the surface with a rust converter (for example, Tsinkar).
- Apply 2-3 coats of epoxy primer, letting dry between coats.
- Cut out a patch from fiberglass (with a margin of 2-3 cm at the edges).
- Glue the patch with epoxy resin, carefully sealing the edges.
- After drying, sand the surface and apply putty.
- Prime and paint in body color.
Remove all rust to bare metal|
Treat the surface with an anti-corrosion compound |
Use only epoxy putty and fiberglass|
Apply primer and paint in 2-3 layers and let dry |
Check for bubbles after painting -->
Such repairs will cost 3-5 times less than welding, but remember: this is a temporary solution. After 2-3 years the procedure will have to be repeated.
⚠️ Attention: Do not use regular fabric or cardboard for patches! They do not withstand vibrations and moisture. Fiberglass or carbon fiber only.
Complete replacement of the threshold: welding and anti-corrosion treatment
If rust has eaten up more than 30% of the threshold or through holes have appeared, the only reliable way is a complete replacement. To do this you will need a welding machine and skills to work with it.
Work order:
- Remove the doors, bumper and all interfering elements.
- Using a grinder, cut off the old threshold, retreating 1-2 cm from the weld line.
- Clean the joints to a shine, remove welding residues.
- Try on the new threshold (repair insert), adjust if necessary.
- Tack the part at 3-4 points, then weld it with a continuous seam.
- Clean the seams and apply an anti-corrosion compound to the internal cavities.
- Treat with putty, primer and paint.
For welding use wire 0.8 mm and carbon dioxide (if semi-automatic). Set the current within 80-120A depending on the thickness of the metal. Make the seams short (2-3 cm), allowing the metal to cool.
Before welding, apply copper non-stick spray to the joints - this will prevent burns through the thin metal and improve the quality of the weld.
After welding, be sure to treat the internal cavities anticorrosive (for example, ML oil or Dinitrol 4941). Use a flexible tube sprayer to reach all corners. Do not skimp on the composition - it is better to overdo it than to leave unprotected areas.
Anti-corrosion treatment: how to protect thresholds for a long time
Even after high-quality repairs, the thresholds will remain at risk. To extend their life, comprehensive anti-corrosion protection is needed. Here 3 levels of protectionthat are worth applying:
| Level | Materials | Validity period |
|---|---|---|
| Basic | Primer + paint | 1-2 years |
| Medium | Epoxy primer + bitumen-based mastic | 3-5 years |
| Maximum | Galvanized + ML-oil + liquid wheel arch liners | 7-10 years |
For maximum protection, use a combination of methods:
- 🔧 Treat internal cavities ML oil or wax
- 🎨Apply to external surface anti-gravel mastic (for example, Body 930)
- 🛡️ Install plastic or aluminum wheel arch liners for protection against sandblasting
- 🔄 Repeat treatment every 2-3 years (especially before winter)
⚠️ Attention: Do not use cheap waste-type oils for anticorrosion! They contain sulfur, which accelerates corrosion. Only specialized compounds.
Common mistakes when repairing thresholds
Even experienced craftsmen sometimes make mistakes that ruin all their efforts. Here TOP-5 missesthings to avoid:
- 🔥 Overheating of metal during welding — leads to deformation of the threshold and weakening of the seam. Solution: cook in short "stitches" intermittently.
- 🧹 Poor cleaning before painting - Remains of rust or grease will cause the paint to peel off. Solution: use a degreaser and anti-silicone.
- 💦 Ignoring internal cavities - if you do not treat the threshold from the inside, it will rot in 1-2 years. Solution: use a sprayer with a flexible nozzle.
- 🎨 Saving on primer — cheap primer does not protect against corrosion. Solution: use epoxy primer in 2 layers.
- ⚡ Painting without drying - Moisture under the paint will accelerate rusting. Solution: dry each layer for at least 20-30 minutes.
Another common mistake is incorrect choice of repair inserts. For example, for Toyota Corolla E12 Only original spare parts or high-quality analogues from Febi, and cheap Chinese inserts often have inaccurate geometry, which complicates welding.
High-quality repair of thresholds depends 80% on preparation: thorough cleaning, proper welding and competent anti-corrosion treatment. Take your time - it’s better to spend an extra day preparing than to redo the work a year later.
FAQ: Frequently asked questions about repairing thresholds
Is it possible to repair thresholds without welding if the holes are through?
Yes, but it will be a temporary solution. For through holes, you need to use fiberglass + epoxy resin in 3-4 layers with metal mesh reinforcement. Such repairs will last 1-2 years, after which a complete replacement will be required.
How much does it cost to repair thresholds at the service?
Prices greatly depend on the region and scale of work:
- Local repair (patch) - from 3,000 to 8,000 rubles. over the threshold
- Partial replacement (insert) - from 8,000 to 15,000 rubles.
- Complete replacement with painting - from 15,000 to 30,000 rubles.
Self-repair will cost 3-5 times less (the main costs are materials).
Which welding machine is best for repairing thresholds?
Optimal choice - semi-automatic (MIG/MAG) with the ability to work in a carbon dioxide environment. Good options for beginners:
- Resanta SAIPA-190 (budget, up to 5 mm metal)
- Svarog EASY MIG 200 (good price/quality ratio)
- Fubag IRMIG 200 (professional level)
The power must be at least 160A in order to confidently weld metal with a thickness of 0.8-1.5 mm.
How to treat the thresholds after repair to prevent them from rusting?
Recommended protection scheme:
- Internal cavities: ML oil or Noxudol 700 (apply by spray)
- External surface: epoxy primer + Body 930 (anti-gravel)
- Additionally: installation of plastic fender liners and regular washing in winter
The treatment of internal cavities must be repeated every 2 years.
Is it possible to drive with rusty sills?
Technically yes, but it's dangerous. Rusty thresholds lose up to 70% of their strength, which threatens:
- Body deformation in a minor accident
- By tearing off the threshold on bumps (if the rust gets to the welds)
- Problems with passing technical inspection
If the rust is superficial, you can postpone repairs for 1-2 seasons. If there are through holes, they need to be repaired urgently.