Thresholds on a car: how to make them yourself - from selection to installation

Thresholds are one of the most vulnerable parts of a car body. They are constantly exposed to mechanical damage (from stones, curbs, dirt), corrosion and wear. Over time, the metal rusts, holes appear, and the appearance of the car deteriorates. Restoring or replacing thresholds is a task that you can handle on your own if you know the technology and have a minimum set of tools.

In this article we will look at all stages of work: from diagnosing the condition of the thresholds to finishing. You will learn what materials to choose (original, analog or homemade), how to weld and putty correctly, and how to protect the metal from future corrosion. We will pay special attention typical beginner mistakes, which lead to rapid re-rusting or unsightly seams.

The material will be useful both to owners of used cars with rotten sills, and to those who want to strengthen the standard elements for tuning or off-road use. All recommendations are based on the experience of bodybuilders and tested in practice.

1. Diagnostics of thresholds: when replacement is needed, and when repair is enough

Before you take up a welding machine or grinder, you need to objectively assess the condition of the thresholds. The amount of work and the choice of materials depends on this. Here are the key signs to look out for:

• 🔍 Surface rust - red spots on the paintwork that do not eat through the metal. In this case, stripping, priming and painting is enough.
• ⚠️ Through holes - visible openings through which the road or the interior of the body can be seen. It is necessary to cut out the damaged area and weld a patch.
• 🚗 Deformation after an accident — dents, bends or displacement of the threshold relative to the body. This requires straightening or complete replacement of the element.
• 🔧 Rotting from within — if, when tapped, the metal makes a dull sound or crumbles, the threshold is completely rotten and must be replaced.

A simple test: press on the threshold with your foot from the side of the door. If the metal bends like foil or a crunching sound is heard, this is critical wear and tear, and half measures cannot be done. Also check the condition threshold amplifiers (internal metal plates). Their corrosion often goes unnoticed, but they are the ones who maintain the rigidity of the body.

If the damage is local (up to 30% of the threshold area), you can get by repair inserts. In case of extensive corrosion or after a serious impact, it is more rational to install a new threshold entirely. For old cars (for example, VAZ 2107 or Mitsubishi Lancer 9) it is often cheaper to make a threshold yourself from sheet metal than to buy an original.

⚠️ Attention! If the thresholds are rotten on both sides, it is better to replace them sequentially: first one, then the other. Removing both elements at the same time may disrupt the body geometry, especially on vehicles without a space frame (e.g. Daewoo Nexia or Renault Logan).

2. Choice of materials: original, analogue or homemade thresholds?

Not only the appearance, but also the durability of the repair depends on the quality of the material. Let's consider all the options:

Threshold type	Pros	Cons	Cost (example)
Original (OEM)	Perfect fit, factory quality metal, full compatibility	Expensive, long wait (made to order), not always in stock	from 8,000 ₽ per piece
Analogs (aftermarket)	Cheaper than the original, wide range, often with anti-corrosion treatment	May not match in shape, thin metal, risk of defects	from 2,500 to 6,000 ₽
Homemade (from a sheet)	Minimum price, the ability to strengthen the structure, adjustable to any size	Requires metalworking skills, risk of corrosion if welding is poor	from 1,000 ₽ (material + consumables)

For most budget cars (Lada Granta, Chevrolet Aveo, Kia Rio) optimal choice - high-quality analogues from trusted brands (for example, Febi, Meyle or SASIC). They are 30–50% cheaper than the original, but at the same time have acceptable metal quality (thickness 0.8–1.2 mm).

If you decide to make thresholds yourself, use sheet metal 1–1.5 mm thick (for example, St3 or 08kp). For reinforcement, you can add internal stiffeners from strips 2–3 mm thick. Do not use galvanized steel for welding - it emits toxic fumes! It is better to process the finished threshold zinc spray or primer with zinc after installation.

3. Tools and equipment: what you need for work

Minimum set of tools for replacing thresholds:

• 🔧 Bulgarian (125 mm) with cutting and cleaning discs (thickness 1.0–1.6 mm).
• 🔥 Welding machine (semi-automatic MIG/MAG or inverter for MMA). For beginners, a semi-automatic machine with wire is better 0.8 mm.
• 🛠️ Set of straightening tools: hammers, supports, spoons, smoothers.
• 🧲 Magnetic square (90°) for geometry control.
• 🧴 Consumables for anticorrosion: rust converter (Tsinkar), epoxy primer, mastic (Body 930, Dinitrol).
• 🎨 Painting materials: putty, primer, paint (selection according to car color code).

To accurately adjust the threshold you will need jack or lift, and also clamps for fixing parts before welding. If you work on the ground, use goats or wooden blocksso that the car is level.

Be sure to prepare protective equipment: Auto-dimming welding helmet, canvas gloves, respirator (when sanding and painting). Do not ignore safety precautions - corneal burns or zinc vapor poisoning take a long time to heal!

⚠️ Attention! When working with an angle grinder, use a disc only for metal (labeling A or INOX). Rock or universal discs can fly apart at high speeds! Also check the integrity of the disk before installation - cracks or chips are unacceptable.

4. Preparing the car: removing body kits and protecting against damage

Before starting work, it is necessary to dismantle all elements that interfere with access to the thresholds:

1. Remove doors (or at least disconnect the stops and seals).
2. Remove plastic linings thresholds (they are attached with clips or screws).
3. Disable wiring (if harnesses pass through the threshold, for example, on Toyota Corolla E12).
4. Tape it up glass and body masking tape and film to protect against sparks.

Pay special attention drainage holes in the rapids. They often become clogged with dirt, which accelerates corrosion. Before welding, clean them with wire and blow with compressed air.

If the threshold is welded to spar or A-pillar, you will need to carefully mark the cutting line. Use metal marker and rulerto cut exactly along the factory seam. Leave an allowance of 5–10 mm to adjust the new threshold.

Doors or seals removed|

Disconnected wiring (if available)|

Glass and paintwork protected |

Drain holes cleaned|

Marking the cutting line with a marker -->

5. Threshold replacement technology: step-by-step instructions

Let's consider the process using the example of a complete replacement of the threshold. If you only need partial welding of the patch, skip the steps to dismantle the old element.

Step 1: Cutting out the old threshold

Start with drilling welding points (if the threshold was secured by spot welding). Use a drill Ø6–8 mm. Then use a grinder to cut the threshold along the markings, leaving 1–2 mm metal for subsequent adjustment. Be careful - people may pass under the threshold fuel or brake pipes!

Step 2: Preparing a new threshold

Try the new threshold on the installation site. If necessary, adjust it with a grinder or metal scissors. Check clearances:

• Between the threshold and the door - 3–5 mm.
• Between the threshold and the wing - 2–4 mm.

If the gaps do not match, bend the metal with a hammer or use straightening levers.

Step 3: Tack welding

Secure the threshold with clamps, then make potholders (short seams 1–2 cm long) every 10–15 cm. After checking the geometry with a square, weld the seams continuous seam with a distance of 1–2 mm from the edge (so as not to burn the metal). For a semi-automatic machine, use wire ER70S-6 and gas Ar/CO₂ (80/20).

After welding, clean the seams petal circle on a grinder, then process them rust converter (even if there is no rust, this is prevention).

Step 4: Anti-corrosion treatment

Apply to the inner surface of the threshold:

1. Layer epoxy primer (for example, Reoflex).
2. Layer mastics on a bitumen or rubber basis (Dinitrol 479, Body 930).
3. For additional protection - wax composition (Tectyl or Waxoyl).

The outside threshold is covered acrylic primer and paint in body color.

6. Repair of thresholds without replacement: patches and partial restoration

If the threshold is rotten locally (for example, only at the bottom or on the side), you can get by welding the patch. The technology is similar to a complete replacement, but there are nuances:

• 🔩 Cutting out the damaged area: Use a grinder to cut out rusty metal with a margin of 10–15 mm to capture the “live” area.
• 📏 Making a patch: Use metal of the same thickness. The edges of the patch should overlap cut out area of 10–15 mm.
• 🔥 Overlap welding: weld the patch from the inside threshold so that the seam is less noticeable from the outside.
• 🛠️ Putty and painting: after welding, fill up the uneven areas and paint the threshold completely (so that transitions are not visible).

For small holes (up to 2–3 cm) you can use welding without a fee - just weld the hole and then sand it. But this method is only suitable for thick metal (from 1.2 mm). On thin rapids (Hyundai Solaris, Skoda Octavia) such repairs will lead to warping.

Alternative way - overhead thresholds (for example, from 3M or Heyner). They are attached with double-sided tape or rivets and hide the rust, but do not eliminate it. This is a temporary solution that will last 1-2 seasons.

What to do if the threshold is rotten under the jack mount?

In this case, you need to cut out a section of the threshold along with the jack and weld a new plate 3–4 mm thick. The jack mounting must withstand a load of up to 1.5 tons (for passenger cars), so use high-quality electrodes (for example, LB-52U) and weld the seam on both sides.

7. Common mistakes and how to avoid them

Even experienced craftsmen sometimes make mistakes that ruin all the work. Here are the most common:

Error	Consequences	How to avoid
Welding without stripping metal	Poor fusion, corrosion under the seam	Clean metal until it shines petal circle or a brush.
Using thin wire (0.6 mm)	Burns, weak seam	For thresholds, take wire 0.8–1.0 mm.
No anticorrosive inside the threshold	Rust from the inside after 1–2 years	Treat the inner surface mastic or wax.
Painting without primer	Peeling paint, bubbles	Apply epoxy primer before painting.

Another common problem is geometry mismatch after replacing the threshold. This happens if:

- Didn’t check the gaps between the threshold and the door before welding.

- Not used clamps for fixation.

- Welded the threshold in in a tense state (for example, when the body is distorted on a jack).

To avoid distortions, after tacking, remove the threshold and check how the door closes. If there is friction or the gap is too large, adjust the metal until final welding.

8. Caring for thresholds after repair: how to extend their service life

Even after high-quality repairs, thresholds need regular maintenance. Here's what to do:

• 🚿 Washing in winter: remove salt and reagents from thresholds every 2 weeks (use Karcher or hand washing with a brush).
• 🛡️ Anti-gravel protection: paste transparent film (for example, 3M Scotchgard) to the lower part of the threshold.
• 🔧 Checking drains: Clean the drainage holes with wire every six months.
• 🎨 Touch up of chips: If scratches appear, apply immediately anticorrosive pencil (for example, Permatex).

For additional protection, you can install plastic linings (for example, from Hella or OSRAM). They are attached to self-tapping screws and cover the lower part of the threshold from stones. However, please note that moisture may accumulate under the pads - so treat the metal before installation wax composition.

If you drive off-road or in heavy snow conditions, consider enhanced thresholds made of stainless steel (thickness 2 mm). They are more expensive than usual, but will last 2-3 times longer.

FAQ: Frequently asked questions about repairing thresholds

Is it possible to weld thresholds using electrode welding (MMA), or is a semi-automatic machine required?

It's possible, but it's more difficult. Electrode welding produces a rougher seam that is more difficult to clean. For MMA use electrodes Ø2–2.5 mm (for example, ANO-21 or LB-52U) and weld with short seams so as not to overheat the metal. Semi-automatic is preferable for thin thresholds (up to 1 mm thick).

How much does it cost to replace thresholds at the service?

The cost depends on the car model and the amount of work:

• Partial repair (patch) - from 3,000 to 8,000 ₽ per side.
• Complete replacement of one threshold - from 10,000 to 25,000 ₽ (with painting).
• Reinforced thresholds (for example, for SUVs) - from 15 000 ₽.

The price usually includes anti-corrosion treatment, but check this in advance.

Which metal is better for homemade thresholds: galvanized or black?

For welding galvanizing cannot be used — when heated, zinc evaporates, forming toxic fumes (“zinc fever”). Take it black metal thickness 1–1.5 mm (grades St3, 08kp). After installation, treat the threshold zinc spray (for example, Zinc Rich Primer) or primer with zinc.

What should I do if, after replacing the threshold, the door does not close well?

This means the threshold has been set not in geometry. Solutions:

1. Check the gaps between the door and the threshold - they should be 3–5 mm.
2. If the gap is too large, bend the threshold inside straightening hammer.
3. If the door rubs against the threshold, bend it back outward or sharpen it with a file.
4. As a last resort, cut off the tack welds and reinstall the threshold.

Do not try to “grind” the door - this will damage the seal.

Is it possible to restore thresholds without welding?

Yes, but these are temporary measures:

• Fiberglass + epoxy resin — suitable for small holes (up to 5 cm). After hardening, it is sanded and painted.
• Overhead thresholds - hide rust, but do not eliminate it. Attached with rivets or tape.
• Cold welding (for example, Poxipol) - only for microcracks, does not withstand loads.

All these methods will last maximum 1–2 years, then the rust will return.