How to paint thresholds with your own hands: a complete guide

The appearance of blistering paint and red spots on the lower edges of the doors indicates that moisture has penetrated under the paintwork and started an irreversible process of metal corrosion. Ignoring these symptoms at an early stage leads to a through hole, the repair of which will no longer require cosmetic painting, but complex welding or replacement of the entire element. Self-restoration of thresholds allows you not only to save a significant amount on the services of specialized service stations, but also to guarantee the quality of the materials used, monitoring each stage of applying anti-corrosion protection.

Before starting work, it is necessary to carefully assess the extent of the damage, since the choice of restoration technology will depend on the depth of rust penetration. If the metal is still intact, it is enough to clean the surface to the base, degrease and apply primer, but if there are through holes, you will need to install repair inserts or use epoxy compounds with fiberglass. High-quality surface preparation accounts for up to 80% of the success of the entire operation, determining the adhesion of materials and the service life of the new coating.

To complete the task, you will need a set of tools, including a sander or drill with attachments, sandpaper of various grits, degreaser, putty, primer and finishing enamel. It is also important to take care of personal protective equipment, since working with chemicals and abrasive dust requires a respirator, safety glasses and gloves. A properly organized work process in a well-ventilated area or outdoors will be the key to a safe and effective result.

Selection of materials and tools for restoration

The success of the event directly depends on the correct selection of chemicals and consumables, which must correspond to the operating conditions of the vehicle. The main enemy of thresholds is moisture, salt and mechanical damage from stones flying from under the wheels, so ordinary nitro enamel will not work here. It is necessary to use specialized epoxy primers, which create an impenetrable barrier to oxygen and water, stopping the development of corrosion even in microcracks.

For the finishing coating, acrylic two-component enamels or special high-strength compositions are most often used, such as anti-gravel. The latter option is especially relevant for the lower part of the body, as it contains crumb rubber that absorbs impacts from small stones. If an exact match to the body color is required, then a paint code is selected and tinted enamel is used, followed by the application of varnish for a glossy shine.

The list of necessary tools and materials includes:

• 🛠️ Sanding machine with wheels of different grain sizes (P80, P180, P320, P600).
• 🧪 Degreaser (anti-silicone) and lint-free wipes.
• 🎨 Spray gun or aerosol cans with primer, paint and varnish.
• 🧤 Painting tape, covering film and personal protective equipment.

Surface preparation and corrosion removal

The first and most labor-intensive step is to completely clean the damaged areas to bare metal. The use of rust converters often gives only a temporary effect, since they do not remove the volume of oxides, so mechanical removal of corrosion is mandatory. It is necessary to clean not only visible pockets of rust, but also the area around them with a margin of 3-5 centimeters to ensure that there are no hidden defects.

During the grinding process, it is important to maintain a gradation of abrasives, starting with coarse grains to remove the main layer of rust and old paint, and gradually moving to fine grains to create scratches under the ground. Gross risks from sandpaper P80 it is necessary to grind with a finer abrasive P180 or P240 so that they do not appear through the finishing coat after painting. The surface should become matte and rough, which will provide maximum adhesion area for the primer layer.

⚠️ Attention: When working with a grinder, do not allow the metal to overheat, as this can lead to its deformation (“leash”) and paint peeling off in the future. Move the tool evenly, without staying in one place for too long.

After mechanical cleaning, the final degreasing of the surface is carried out. This step is critical as any traces of oil, silicone or dust left on the metal will cause craters and paint peeling. You need to wipe the surface with a generously moistened cloth, changing it as it becomes dirty, and allow the solvent to completely evaporate before applying the primer.

Puttying and alignment of geometry

If after removing the corrosion, dents or irregularities are found, they must be removed using automotive putty. For thresholds subject to vibration loads, reinforced compounds with aluminum powder or fiberglass, which have high strength and elasticity, are best suited. The putty should be applied in thin layers, carefully smoothing with a spatula and trying to minimize the number of air bubbles.

The polymerization time of the putty depends on the ambient temperature and the amount of added hardener, but there is no need to rush with grinding. Insufficiently dried material will clog the abrasive and stretch, forming unevenness, and an excess of hardener can lead to brittleness of the layer. After drying, the surface is sanded first with coarse grains to form a contour, and then with fine grains to obtain ideal smoothness.

It is convenient to check the quality of alignment by touch or using developing powder, which is applied before grinding and shows the high and low points of the relief. Perfectly flat surface without drops and steps - this is the foundation for high-quality painting, since the paint only emphasizes the existing relief and does not hide it.

Metal priming and insulation

A primary primer, which can be acidic (phosphate) or epoxy, is applied to the prepared and degreased metal. Acid primers work great on bare metal, creating a chemical bond, but require a mandatory coating with a secondary acrylic primer. Epoxy primer is a more versatile and reliable option, creating a durable hydrophobic film that completely isolates the metal from the external environment.

Priming is carried out in 2-3 thin layers with interlayer drying specified by the material manufacturer. The material must be applied in perpendicular movements, overlapping the previous pass by 50% to avoid streaks and unpainted areas. It is important not to overfill the primer, as this can lead to its slipping and prolonged drying, which complicates further sanding.

After the primer has dried, the surface often requires light sanding (P400-P600) to remove shagreen and dust particles that have fallen during the work. If materials from the same manufacturer are used, sometimes it is not necessary to sand the epoxy primer if no more than a certain time has passed since its application (usually up to 24-48 hours), but the exact data should be looked at in the technical data sheet of the product.

Epoxy primer application technology

Epoxy primer is applied in 2 wet layers. The first layer is a thin, binding (foggy) layer, the second is a full wet layer. Drying at 20°C takes about 30-60 minutes between coats and several hours until completely dry for painting. You only need to sand the epoxy if it is too dry, otherwise it will ruin its adhesive properties.

Technology of painting and applying anti-gravel

The final painting is carried out after thoroughly degreasing the primed surface. The paint is applied in 2-3 layers, maintaining interlayer drying to evaporate the solvent. The first layer is made thin to avoid drips, and subsequent layers are made more saturated to cover the primer and obtain a uniform color. When working with metallics or pearls, a layer of clear varnish is required to protect the pigment and add depth.

For the lower part of the thresholds, which is not visible during normal inspection, they are often used anti-gravel coating. It is applied with a special gun or from a can with an adjustable spray pattern. Anti-gravel creates a rough but durable texture that effectively absorbs stone impacts and prevents the spread of corrosion. It should be applied in 2-3 layers, allowing each layer to dry.

The table below shows approximate parameters for drying various materials at a temperature of +20°C:

Material	Drying time between coats	Time before polishing/use	Temperature
Epoxy primer	30-60 min	12-24 hours	+20°C
Acrylic putty	20-40 min	1-2 hours	+20°C
Base enamel	10-15 min	30-60 min (under varnish)	+20°C
Anti-gravel	15-30 min	24 hours	+20°C

Assembly, polishing and coating protection

After the varnish or anti-gravel has completely dried, you can begin to dismantle the covering materials and masking tape. You need to remove the tape carefully, at an angle of 45 degrees, so as not to damage the fresh edge of the paint. If the visible part of the threshold was painted with varnish, shagreen may appear or dust may enter, which requires subsequent polishing with abrasive pastes.

Polishing is carried out by machine using wheels of different hardness and polishes with abrasiveness from P1500 to P3000 and finishing. This process returns the coating to a mirror-like shine and eliminates minor defects that occurred during the drying process. It is important not to overdo it and not to rub the varnish down to the paint, especially on the edges and corners of the thresholds, where the layer of material is always thinner.

For additional protection and extending the service life of the new coating, it is recommended to apply wax preservative or ceramic composition. Particular attention should be paid to the internal cavity of the thresholds, if access is technically possible. Treatment of hidden cavities with anti-corrosive agent through technological holes will prevent rotting of the metal from the inside, which is a common problem in modern cars.

⚠️ Attention: Complete polymerization of paints and varnishes takes from 7 to 14 days. During this period, it is not recommended to wash the car using active chemicals or abrasive sponges.

Frequently asked questions (FAQ)

Is it possible to paint the sills without removing them from the car?

Yes, this is possible, but it requires careful preparation and high-quality pasting of adjacent elements (doors, arches, floors). Removing the thresholds allows them to be processed from all sides, including the ends and the inside, which significantly improves the quality of anti-corrosion protection.

Is it necessary to use primer for zinc?

Zinc-containing primers have excellent anti-corrosion properties, but they require specific application conditions and are often incompatible with some types of topcoats. For DIY repairs, it is more often and safer to use epoxy or acid primers intended for body repairs.

How long does anti-gravel dry?

The surface drying time of anti-gravel is 15-30 minutes, but complete drying and strength gain take from 12 to 24 hours at a temperature of +20°C. During cold seasons or high humidity, drying time may increase significantly.

What is the best way to paint over chips on thresholds?

For spot repairs of chips, it is best to use a restoration pencil or brush with enamel matched in color. The chip must first be cleaned, degreased and primed to stop corrosion, and then paint must be applied in several thin layers.