Corrosion, chips and microcracks on the car body are a headache for every owner. Even small defects in the paintwork over time turn into pockets of rust that destroy the metal from the inside. Pore-filling primer (or filler primer) becomes the first barrier to destruction: it not only levels the surface before painting, but also protects the metal from moisture and chemical reagents.

However, not all soils are equally effective. Some are designed for “deep” pores and scratches, others are designed to work with aluminum or plastic, and others contain anti-corrosion additives. In this article we will look at how to choose the right composition, avoid common mistakes during application and achieve a professional result even in a garage environment.

Is it worth overpaying for branded soils like Novol or Body, or can we get by with budget analogues? What tools will you need for the job, and why do some craftsmen insist on using epoxy primer before filler? The answers are below.

What is porosity-filling primer and why is it needed?

Pore-filling primer is a two-component composition (base + hardener), which is applied to the treated surface of the body before painting. His main tasks:

  • 🔹 Leveling out micro-irregularities - fills pores after sanding, sandblasting or corrosion scratches, creating a smooth base for paint.
  • 🔹 Corrosion protection - contains rust inhibitors (for example, zinc or phosphates), which block the oxidation of the metal.
  • 🔹 Improved adhesion — provides reliable adhesion of paint to the surface, preventing peeling.
  • 🔹 Reduced paint consumption — thanks to an even layer of primer, the paint coating applies more evenly.

Without a filler, even a perfectly polished surface will have microdefects, which will appear after painting in the form of “shagreen” or subsidence. This is especially critical for metallics and pearlescent paints, where any flaw becomes noticeable.

⚠️ Attention: Pore-filling primer does not replace putty! It is intended for micropores (up to 0.1 mm deep), and not for sealing through holes or deep dents. For such defects, putty is first used, and only then primer.

Types of void-filling primers: which one to choose for your car

All soils are divided into types according to composition and purpose. The choice depends on the body material, the degree of damage and operating conditions of the vehicle.

Soil type Features When to use Examples of brands
Acrylic Versatile, dries quickly, good adhesion. Does not contain isocyanates (less toxic). For most work on steel and aluminum bodies. Suitable for local repairs. Novol Protect 360, Body 960, Mobihel
Epoxy It has high chemical resistance and anti-corrosion properties. Demanding on surface preparation. For protection against salt and reagents (for example, on the underbody or sills). Often used as the first layer before acrylic primer. Reoflex Epoxy, PPG DP40
Polyurethane High elasticity and vibration resistance. It takes longer to dry, but gives a durable coating. For plastic parts (bumpers, spoilers) or areas with high loads (hood, trunk). Sikkens Autoclear, Spies Hecker Permahyd
With anti-corrosion additives Contains zinc, phosphates or other inhibitors. Often has a gray or yellow tint. For rusty areas or cars operating in aggressive conditions (coastal climate, winter reagents). Novol Protect 520, Body 980

Ideal for most garage work acrylic primer — it forgives small mistakes in preparation and is easy to polish. Epoxy primer is best left to professionals: if mixed incorrectly, it may leak or fail to harden.

📊 Which soil do you use more often?
Acrylic
Epoxy
Polyurethane
I don't know what it is
Other

Step-by-step instructions: how to apply pore-filling primer

The technology for applying primer requires care, but is not overly complicated. The main thing is to maintain consistency and not skip preparation steps.

1. Surface preparation

Before priming, the metal must be:

  • 🧹 Cleaned from rust - use a metal brush, sandblast or rust converter (for example, Tsinkar).
  • 🧼 Low fat - wipe the surface White spirit or a special degreaser (App Cleaner).
  • 📏 Polished - for bare metal use sandpaper P80–P120, for old paint - P180–P240.

⚠️ Attention: If traces of silicone or wax remain on the surface, the primer may swell or peel off. Check the cleanliness by running a clean cloth over the metal - there should be no greasy marks left on it.

2. Soil preparation

Porosity-filling primers are sold in the form of two components:

  • 🟦 Basics (a jar of thick liquid).
  • 🟪 Hardener (small bottle).

Mixing proportions are indicated on the packaging (usually 4:1 or 3:1). Use measuring containers - you can make a mistake “by eye” and the soil will not harden.

Maintain the proportions of base and hardener|Mix thoroughly with a mixer (2-3 minutes)|Filter through a 120-150 micron mesh|Apply within 30-40 minutes after mixing-->

The room temperature should be 18–25°C. At a lower temperature, the soil will take longer to dry; at a high temperature, it may bubble.

3. Application of primer

Use spray gun with nozzle 1.4–1.6 mm and pressure 2–2.5 atm. Application technique:

  1. Keep the gun at a distance 20–25 cm from the surface.
  2. Apply primer crosswise movements (first horizontally, then vertically).
  3. Each layer should be thin (“wet to wet”). The optimal number of layers is 2–3.
  4. Pause between layers 5–10 minutes (for acrylic primers).

Critical error: applying too thick a layer in one pass. This leads to “boiling” of the soil (the appearance of bubbles) and prolonged drying.

4. Drying and sanding

Drying time depends on the type of soil:

  • 🕒 Acrylic — 2–4 hours at 20°C (full curing - 12–24 hours).
  • 🕒 Epoxy — 8–12 hours (can be accelerated by IR drying).

After drying, the soil is sanded sandpaper P320–P400 (for the finishing layer - P500). Use manual grinding or an orbital machine with a soft sole.

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If the soil sags after sanding (pores are visible), apply another thin layer and repeat sanding. This is better than trying to fill the defects with putty.

Typical mistakes when working with void-filling primer

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

  • 🚫 Application on dirty or greasy surfaces → the soil peels off in “layers”.
  • 🚫 Ignoring mixing instructions → incorrect proportions lead to the soil not hardening or cracking.
  • 🚫 Operating in low temperature or high humidity conditions → a “matte” coating or condensation appears on the surface.
  • 🚫 Sanding with too coarse sandpaper → scratches the primer and the paint goes on unevenly.
  • 🚫 No interlayer drying → layers “set” unevenly, which leads to subsidence.

Another common problem is incompatibility of primer and paint. For example, if nitro paint is applied to epoxy primer, it may wrinkle. Always check material compatibility with the manufacturer!

What to do if the soil is leaking?

If smudges appear after application, do not try to sand them right away - wait until they dry completely (24 hours). Then carefully cut off the drip with a sharp knife or a sander with coarse sandpaper (P180), then apply a thin leveling layer of primer and sand again.

Comparison of popular brands: Novol, Body, Reoflex

The market is dominated by a few manufacturers whose soils have earned the trust of professionals. Let's look at their features:

Brand and model Type Pros Cons Price (per 1 l)
Novol Protect 360 Acrylic Good coverage, dries quickly, suitable for beginners. Average resistance to aggressive reagents. ~1 200 ₽
Body 960 Acrylic High adhesion, can be applied to old paint. Requires thorough mixing (otherwise lumps). ~1 100 ₽
Reoflex Epoxy Epoxy Excellent anti-corrosion protection, resistant to salt. Difficult to sand and takes a long time to dry. ~1 500 ₽
Mobihel Primer Polyurethane Elastic, does not crack on plastic. Expensive, requires professional equipment. ~1 800 ₽

Suitable for budget renovations Body 960, and for long-term protection (for example, thresholds) it is better to take Reoflex Epoxy. If you work with plastic, use only polyurethane primer!

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There is no point in saving on primer: cheap compounds often shrink after drying, which leads to the appearance of defects under the paint.

Primer for rust: how to stop corrosion

If there are already pockets of rust on the body, ordinary pore-filling primer will not cope. This requires specialized compounds with rust converters or zinc filler.

Algorithm for working with rusty areas:

  1. Remove loose rust with a brush or sander.
  2. Apply rust converter (for example, Tsinkar or Runway) and wait for the reaction (the appearance of a gray coating).
  3. Rinse the surface with water and dry.
  4. Apply primer with anti-corrosion additives (for example, Novol Protect 520 or Body 980).
  5. For maximum protection, add a layer epoxy primer before painting.

⚠️ Attention: If the rust is through (a hole in the metal), first seal the defect by welding or seal it with fiberglass with epoxy resin, and only then prime it.

Pro-tip: To treat the sills and bottom, use soil in aerosol cans (for example, Kudo or Hi-Gear). They are convenient for hard-to-reach places, but require 3-4 layers.

Frequently asked questions about void-filling soils

Can porosity-filling primer be applied to old paint?

Yes, but only if the old paint holds up well (does not peel off). Pre-matt the surface with sandpaper P240–P320 and degrease. If the paint is glossy or chipped, it is better to remove it completely.

How many layers of primer should be applied?

Optimally - 2–3 layers. The first layer should be thin (“dust”), the second and third should be denser. Avoid “wet” drips!

Is it possible to sand the soil after 24 hours?

It is possible, but it is better to adhere to the time specified by the manufacturer. For example, acrylic primers cure completely within 12–24 hours, and epoxy - up to 48 hours. Sanding under-dried soil leads to clogging of the sandpaper and an uneven surface.

What primer is best for aluminum?

For aluminum bodies (e.g. Audi or Jaguar) use special primers with high adhesion (for example, PPG DP40LF or Sikkens Autowave). Regular acrylic primer can peel off due to the oxide film on the aluminum. Pre-treat the metal acid soil (wash primer).

Is it possible to paint without primer if the surface is flat?

Technically possible, but highly not recommended. Without primer:

  • The paint will lie unevenly (micropores will appear).
  • Adhesion will be weak - over time, the paint will begin to peel off.
  • The metal will remain without protection from corrosion.

Exception - local chip repair (for example, using touch-up pencil), but here too it is better to first apply a thin layer of primer.