Single stage paints have been around for decades and are still commonly used today for their simplicity and cost-effectiveness. Unlike basecoat-clearcoat systems, single stage paints combine color, gloss, and protection all in one product, eliminating the need for a separate clear topcoat. However, some may wonder if applying a clear coat over single stage paint is possible or beneficial. This article will examine the ins and outs of clear coating over single stage paint.
What is Single Stage Paint?
Single stage paint, also called one-stage paint or 1K paint, refers to a coating that provides color and gloss in one layer. The name comes from the fact that only one painting stage is required instead of a basecoat-clearcoat system which requires two stages.
Single stage paints have been used for decades on all types of surfaces including automotive, marine, industrial, and architectural applications. They are a popular choice today thanks to their straightforward application and lower cost compared to basecoat-clearcoat systems.
Composition of Single Stage Paint
Single stage paints contain four main components:
- Pigments – Provide color and hide. Common pigments include titanium dioxide for white/light colors and carbon black for black. Organic pigments are used for bright colors.
- Binder resins – Form the protective paint film after curing. Common resins include acrylic, acrylic melamine, alkyd melamine, and urethane.
- Solvents/thinners – Allow adjustment of viscosity/thickness for spray application. They evaporate as the paint dries.
- Additives – Enhance paint properties. Examples are UV absorbers for sun protection and flattening agents to reduce gloss.
The resin is the largest percentage of the paint formula at 30-60%. It is dissolved in the solvent and surrounds the pigment particles once dried.
Gloss and Protection Properties
The type of resin used in single stage paint gives it an inherent glossy finish right out of the can without a clear topcoat. Acrylic, urethane, and alkyd melamine resins provide a high gloss level. The resins also impart protection against UV rays, oxidation, and chemical/environmental damage.
However, the protection afforded by single stage paints is not as durable or extensive as a dedicated clear coat. They lack the toughness and thickness of a separate protective clear layer.
The Role of Clear Coat
Applying a clear topcoat over properly prepped single stage paint can provide benefits by boosting gloss and adding a thicker protective coating.
Enhancing Gloss
The main job of a clear coat paint is to provide maximum light reflection for an ultra-glossy finish. Because clear coats are designed specifically for high gloss, applying one over single stage paint can enhance the existing gloss to a much deeper, glass-like wet look.
This extra layer of clear coat also provides additional protection against oxidation, UV damage, and weathering to help the single stage paint better retain its original gloss over time.
Adding Protection
Clear coat paints are formulated with tough, durable resins that form a hard protective film, including acrylics, polyurethanes, and epoxy. This added sacrificial top layer provides complete protection against scratches, UV rays, corrosion, and chemical damage compared to single stage paint alone.
An Optional Extra Step
It’s important to note that adding a clear coat over properly cured original single stage paint is an optional extra step – unlike a basecoat, single stage does not require a clear coat since it already contains gloss and protection properties.
But the extra gloss boost and thicker protective film offered by clear coat can provide great benefits by enhancing and extending the durability of single stage paint in many situations.
Preparing Single Stage Paint for Clear Coat
To achieve successful clear coat application over single stage paint, proper preparation of the existing paint surface is imperative.
Ensure Proper Curing
The single stage paint must be allowed to fully cure following the manufacturer’s recommended cure times before applying clear coat. Insufficient cure can lead to loss of gloss, solvent pop, wrinkling, or delamination when clear coat is applied on top.
Most single stage paints cure in 2-7 days at 70°F before being ready for clear coat. Cure times are extended at cooler temperatures. Always verify full cure by testing hardness and solvent resistance.
Sanding
After curing, the single stage paint needs to be sanded to remove any surface imperfections present and to create a mechanical profile for the clear coat to bond to.
Start by dry sanding with 600-800 grit sandpaper to remove dust nibs, contaminants, and other flaws. Then wet sand up to 1000-1500 grit for an ultra-smooth surface profile optimal for clear coat adhesion.
Special Handling of Metallic Paints
When sanding metallic, pearl, or flake single stage paints, take extra care not to sand through or damage the metallic particles which will affect appearance. Use light pressure and avoid over-sanding.
Clear Coating Techniques over Single Stage Paint
Here are some application techniques that can help ensure proper clear coat bonding and appearance over single stage paint:
- On fully cured single stage paint, sanding is not always required for clear coat application. The clear may bond sufficiently without sanding depending on the paint type. Always test first on a small section of paint to verify compatibility.
- Today’s clear coats rely on both a mechanical bond by penetrating the paint surface’s pores and a chemical crosslinking bond. Make sure to use a clear coat designed to bond with the existing paint chemistry.
- When spraying clear coat over single stage paint, apply two to three thin even coats allowing proper flash time between coats to prevent runs or drips. The multiple thin coats help build up the clear thickness gradually.
Clear Coating Specific Paint Types
Certain single stage paint types have specific considerations when clear coating to ensure optimal results:
Acrylic Enamel Paint
- Acrylic enamel is a widely used single stage paint known for its color and gloss qualities. Most acrylic-based clear coats are compatible and will bond successfully over cured acrylic enamel paint. Urethane clear can also be used.
- Avoid fast-dry clear coatings which can wrinkle or lift uncured layers of acrylic enamel rather than forming a proper bond.
- Due to the curing process of acrylic enamel, apply mist coats first to slowly build up the clear coat thickness without disturbing the paint film.
Lacquer Paint
- Lacquer paint dries by solvent evaporation vs. chemical cure making compatibility with clear coat more difficult. Test a small area first and allow extra cure time.
- Acrylic clear coat is usually not recommended over lacquer as it can cause lifting or cracking due to the difference in flexibility. A compatible lacquer clear is a better option.
- Spray light mist coats of clear and allow extra time between coats for proper solvent evaporation when applying over lacquer paint.
Alkyd Enamel Paint
- Alkyd enamel paints cure by oxidation so they need to harden before clear coating fully. Allow 1-2 weeks minimum dry time.
- Surface preparation is critical. Sand thoroughly to ensure the clear coat can bond directly to the paint rather than oils on the surface.
- Urethane, acrylic urethane, and epoxy clear coats are good options for enhanced UV resistance over alkyd paint.
Restoration and Enhancement Using Clear Coat
Applying a clear coat over aged, oxidized single stage paint can dramatically improve its appearance and provide long-lasting protection.
Restoring Faded Paint
On older vehicles or signs with faded, chalky single stage paint, a high-quality clear coat effectively seals, restores gloss and color richness, and protects from further fading and corrosion. It adds back depth and vibrancy to the paint.
Renewing UV Protection
Over time, the UV inhibitors in single stage paint deplete leading to oxidation damage. A fresh clear coat over the paint surface provides a renewed barrier against sun damage and environmental wear extending the life of the existing finish.
Achieving Desired Finishes
When clear coating over single stage paint, adjust the clear coat formula to achieve different aesthetic looks:
- Add flattening agent to produce a matte/low-gloss finish for a vintage patina effect.
- Use a higher-gloss clear coat and add reducer to create an ultra-glossy wet-look finish.
Conclusion
Clear coating over properly prepped single stage paint can provide great benefits by boosting the paint’s gloss levels and longevity, especially on restoration projects. While not an absolute necessity, the additional clear coat protection can dramatically enhance the appearance and durability of single stage paint in many cases when applied following the proper procedures for preparation and application. With appropriate products and techniques, clear coat can supplement and extend the life of existing cured single stage paint finishes.
