How to use acid soil on your car before painting: a step-by-step guide

If after grinding bare metal on the car body you notice that the surface is quickly covered with rusty coating or the paint peels off after a few months - the problem is incorrect processing with acid soil. This material is known as phosphate or wash primerIt creates an anticorrosive layer, but only if the technology is observed: from metal preparation to drying time before applying acrylic soil. Errors at this stage lead to swelling of the LCP, paint drawdown and through corrosion in a year.

Acid soil (e.g., Reoflex Wash Primer or Novol Protect 340) works by chemical reaction with metal, forming a protective film with a thickness of 8-12 μm. However, it cannot be applied to old paint, putty or aluminum without pre-treatment. This article provides a proven application scheme, including the selection of materials, tools and quality control at each stage.

What is an acid soil and why it is needed

Acid (reactive) soil is a two-component composition based on phosphoric acid, which reacts with the metal, forming an insoluble protective film. Its key functions are:

• 🛡️ Anti-corrosion protection - blocks the oxidation of bare metal, even in microcracks.
• 🔗 adhesion - improves the adhesion of subsequent layers (acrylic soil, paint) with the surface.
• 🧪 Neutralization of salt residues Removes invisible contaminants after grinding.

Unlike acrylic soils, acidic soil does not fill irregularities, but penetrates into the structure of the metal. It is used by:

• 🚗 On new body parts (wings, rapids, hood).
• 🔧 After welding or removing rust.
• ⚡ In areas with zinc coating (e.g., Volkswagen, Audi with a galvanized body.

⚠️ Attention: Acid soil cannot be applied to aluminum, magnesium or stainless steel without a special converter. For these metals, use epoxy soil (for example, PPG DP40/DP402).

Preparation of the surface before applying acid soil

The quality of protection is 70% dependent on the preparation of metal. Even microscopic particles of rust or fat will reduce the effectiveness of the soil to zero. The preparation algorithm:

1. Removal of old coating. With a grinder (e.g., with a grinder). Makita 9227C) or sandblaster (Karcher HD 5/15 C) remove the paint, rust and putty to pure metal. For hard-to-reach places, use squirt on the drill.
2. Degreasing. Wipe the surface. antisilicone (e.g., Body 700) and a napkin without pile. Repeat until the napkin is clean.
3. Grinding. Treat the metal with abrasive P80–P120 It's a micro-rough. For galvanized parts, use P180–P220.
4. Cleanliness control. Blow the surface with compressed air (pressure 4-6 bar) and wipe with a sticky napkin. Tack Cloth. If there are particles left, repeat grinding.

To check the quality of preparation, apply a drop of distilled water to the metal: if it is not going into a ball, but spreads out, the surface is not fat-free enough.

1. All old paint and rust removed

2. The surface is polished with an abrasive P80–P120

3. Degreasing was done twice

4. No traces of moisture or dust (checked with a sticky napkin)

5. Metal and air temperature within +15 ... +30 °C

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Choosing acid soil: what brands are suitable for cars

Not all acid soils are equally effective. For body repairs, only professional compositions with a high content of phosphoric acid (at least 30%) are suitable. Popular brands and their features:

Marka.	Type	Time to dry	Features	Price for 1 L, RUB
Reoflex Wash Primer	Two-pronged	10-15 minutes	Universal, suitable for galvanizing	1 200–1 500
Novol Protect 340	single-component	5-10 minutes	Fast-drying, for local repairs	900–1 100
PPG DP40/DP402	Two-pronged	20-30 minutes	For aluminum and magnesium (with converter)	1 800–2 200
Body 960	single-component	15-20 minutes	Economical, for small areas	700–900

For home repairs is optimal Novol Protect 340 It does not require mixing with a hardener and dries quickly. For professional jobs, better Reoflex or PPG (especially for premium cars).

⚠️ Attention: Do not use cheap acid soils of unknown brands (for example, "autochemistry" from Chinese online stores). They often contain less than 10% phosphoric acid and offer no protection.

Reoflex Wash Primer|Novol Protect 340|PPG DP40|Body 960|Other (write in the comments)->

Step-by-step instructions for applying acid soil

The technology of applying acid soil is different from working with acrylic materials. Here it is critical to observe the exposure time and thickness of the layer. Algorithm of action:

1. Preparation of the lineup.
   • For two-component soils (Reoflex, PPG) mix the base with the hardener in the proportion shown on the jar (usually 4:1). Use it. measuring-glass and scale for accuracy.
   • Stir the mixer at low revs (300-400 rpm) for 2-3 minutes to avoid bubbles.
2. First layer application.
   • Use it. sprayer (e.g., SATAjet RP or DeVilbiss FLG-5).
   • Keep the gun at a distance of 20-25 cm from the surface at an angle of 90 °.
   • Apply "wet over wet" without interruptions, blocking each passage by 50%.
3. Thickness control.
   • The optimal thickness of the layer is 8-12 microns. Use it. thicknesser (e.g., Elcometer 456).
   • If the soil drains, reduce the air pressure to 2.0-2.5 bar.
4. Drying.
   • At +20°C, drying time is 10-15 minutes (for single components) or 20-30 minutes (for two components).
   • Do not dry with a hair dryer - it disrupts the chemical reaction.

After drying, the soil should have a matte shade without shine. If the surface is sticky, then the mixing proportion or humidity in the room above 70% is not observed.

Typical mistakes when working with acid soil

Even experienced painters make mistakes that negate the protective properties of the soil. Here are the most common:

• 🔥 Applying to rust or old paint. Acid soil reacts only with pure metal. If you apply it to corrosion centers, the reaction will go with oxides, not with a base - the protection will be point.
• ⏳ Drying time disruption. If you apply acrylic soil earlier than after 15-20 minutes, acidic will not have time to react with the metal. If after 24 hours, the adhesion will worsen.
• 🌡️ Working at low temperature. At +10°C and below, the reaction slows down 2-3 times, and the soil may not harden.
• 💦 Use of ordinary water for washing. Tap water contains salts that neutralize the acidic composition. Use the tools to wash the tools distilled.

Another critical mistake is the application of acid soil on the putty. It erodes the polyester resins that make up the putty, which leads to swelling and detachment of the layers. In this case, first applied epoxy soil, and then acidic on bare metal.

What to do if the acid soil is applied incorrectly?

If the soil is left sticky or cloudy after drying

1. Remove it. purifier (e.g., Body 710).

2. Re-strain the metal with abrasive P120.

3. Re-sink the soil by following the technology.

If the soil is already covered with an acrylic layer and bubbles appear:

1. Cut the swollen areas to metal.

2. Process. rust converter (e.g., Permatex Rust Treatment).

3. Repeat the priming from scratch.

Compatibility of acid soil with other materials

Acid soil cannot be applied over other coatings, but it can be combined with them in the correct sequence. Compatibility scheme:

Materials	Can be applied on acidic	You can apply acid soil. top-up
Naked metal	✅ Yeah (acrylic soil, paint)	✅ Yes.
epoxy	✅ Yes.	❌ No (metal only)
Acrylic soil	✅ Yes.	❌ No.
Shpatlyovka	✅ Yeah (after drying completely)	❌ No (eating)
Old LCP	❌ No (only after removal)	❌ No.

The optimal scheme for body repair:

1. Bare metal → acid soil → drying 15-20 minutes → acrylic soil.
2. For galvanizing: bare metal → acid soil for zinc (for example, PPG DP402) → drying → acrylic soil.
3. For aluminum: bare metal → converter (e.g., Bondo Aluminum Prep) → epoxy soil → acrylic soil.

How to check the quality of acid soil application

Before applying acrylic soil or paint, be sure to check the quality of the acid layer. Use these methods:

• 🔍 Visual examination. The soil should be uniformly matte, without glossy areas (they talk about incomplete polymerization) and streams.
• 🧴 Adhesion test. Stick to the surface scotch 3M 233+ And rip it off. If there are soil particles on the sticky side, the clutch is weak.
• 📏 Thickness measurement. Use it. thicknesser - the value should be within 8-12 μm. Less is insufficient protection, more is the risk of cracking.
• 💧 Reaction test. Apply a drop of water: if it is not absorbed and spreads, the soil is polymerized correctly.

If defects are found, remove the soil. abrasive P220–P320 or purifier and repeat the procedure. Do not ignore the check – this is a guarantee that the paint will not peel off after six months.

FAQ: Frequent questions about acid soil

Can I apply acid soil to aluminum?

No, standard acid soil corrodes aluminum. Use specialised formulations for this metal (e.g. PPG DP402) or pre-treat the surface aluminum converter (e.g., Bondo Aluminum Prep).

How long should the acid soil dry before applying acrylic?

The minimum drying time at +20°C is 15 minutes for single-component soils and 20-30 minutes for two-component soils. The maximum interval is 24 hours. If you exceed this time, before applying acrylic soil, the surface must be matted. scotch-bright (gray or red).

Can I paint directly on acid soil without acrylic?

Technically possible, but not recommended. Acid soil does not fill micro-uncertainties, and the paint will lie unevenly. In addition, without an acrylic layer, the adhesion and impact resistance of the LCP decreases. The exception is local repair of small areas (up to 10 cm2).

How to remove acid soil if it is applied incorrectly?

Fresh (non-polymerized) soil can be washed away solvent 646 or acetone. The dried layer is removed by grinding (P120–P180or purifier (e.g., Body 710). For galvanized parts, use flushing (e.g., Permatex Gasket Remover) so as not to damage the zinc coating.

What is the difference between acid soil and epoxy?

Acid soil provides chemical-protection from corrosion, penetrating into the structure of the metal, but has no filling properties. Epoxy soil creates mechanical barrierIt fills the pores and protects against moisture, but does not react with metal. For maximum protection, they are combined: first acidic (on bare metal), then epoxy (on top).