How to choose hardener for car paint, primer and clear coat

Choosing the right paint hardener can have a big impact on how your finish and durability end up being.

There are several different types of hardeners and there are certain factors that you should be aware of when buying your car paint. The wrong hardener choice can be the reason why your paint does not turn out as desired.

In this guide, I describe some of the essential factors and recommendations that you should consider when choosing a hardener for car paint, especially filler, primer and clear coat.

UNDERSTANDING HARDES AND ITS PURPOSE

A hardener, also called a reactor, activator, is a chemical additive that is mixed with paint (2-component product) to trigger a chemical reaction that leads to hardening (polymerization). This reaction is indispensable for the drying, hardening and film formation of the paint, which is especially important in products such as primer paint or clear coat. 2K paint, or 2-component paint, requires a hardener in order for the surface to achieve the correct durability, finish and functionality.

Component A is the paint, such as primer or clear coat, while component B is the hardener. Thinners are component C and are not always necessary.

 

IMPORTANCE OF PAINT HARDENERS IN THE REPAIR PROCESS

The importance of choosing and using hardeners correctly in automotive painting cannot be overstated. Incorrect choice of hardener or incorrect mixing can result in various paint defects. Using the right hardener can also contribute to significantly improving the productivity of the auto body shop.

Primarily, a hardener accelerates the chemical reaction, which speeds up the drying and curing of the paint and maintains its integrity after the reaction is complete.

If you have a workshop or work in different conditions, it is crucial to have access to a varied selection of premium hardeners that offer versatility through compatibility with different products such as primers or clearcoats.

That is precisely why we offer an incredibly comprehensive selection of different hardeners from different automotive paint brands, precisely for use in different situations. If you know which paint you need, you can also look at the technical data sheet and find out which hardener is right for you, otherwise you are welcome to contact us.

TYPES OF HARDENERS

Hardeners are divided into four groups based on their drying speeds:

Slow hardeners: These hardeners are suitable for high temperatures. They allow more time to work with the paint, which is useful in hot environments or for larger repairs where a slower drying time is desired.

Medium or standard hardeners: These hardeners have a moderate drying speed and are often the choice for most common repairs.

Fast hardeners: These hardeners speed up the drying process and are ideal for situations where faster work processes are required.

Ultra-fast hardeners: These hardeners are designed for low temperatures and allow for faster drying in cooler conditions. They are especially useful in cool climates or for repairs that require faster completion times.

FACTORS TO CONSIDER WHEN CHOOSING HARDES

Temperature: Temperature is the most important factor when choosing a hardener. For temperatures between 20ºC and 25ºC, standard or medium hardeners are appropriate, with adjustments based on specific application contexts.

Low temperatures and high humidity = fast or ultra-fast hardeners.

Conversely, high temperatures and low humidity require slow hardeners to maintain an open paint film. Consider both product and substrate temperatures for optimal results.

High temperatures and low humidity = slow hardeners.

Humidity: Relative humidity should ideally be between 55% and 65% for application. High humidity requires the use of slow hardeners to prevent finish defects and loss of gloss.

Size of repair: The choice of hardener depends on the size of the repair and whether it is partial or for the entire vehicle. Smaller repairs benefit from fast or extra-fast hardeners, which reduce drying and processing times. Larger repairs, such as complete vehicle renovations, require medium or slow hardeners for sufficient coverage time without compromising drying quality.

Mixing ratio: Adhering to the correct mixing ratio between hardener and product is essential to achieve a flawless finish. The ratios vary depending on the product and hardener type, which can be found in the "Mixing ratio" section of the technical data sheet of the main product such as clearcoat, filler or primer. For correct mixing ratio, you can use a mixing cup with a printed scale, and remember to stir the product thoroughly after mixing.

Pot-life: Consider the pot-life of the product, which varies with the type of hardener used. Faster hardeners allow less time from mixing the mixture (component a+b) to application completion. .

Productivity: Improving productivity is a key goal in bodyshop operations. The right choice of hardener, together with appropriate conditions, significantly affects productivity. Utilize fast or ultra-fast hardeners for repairs where conditions permit, which accelerates the drying of the paint film and increases the throughput of repairs in the booth.

SUMMARY

Does it matter which hardener I choose? The short answer is yes.

The choice of hardener can/does have a big impact on how your final finish will be.

Therefore, be aware of what type of paint you have, what the mixing ratio is, what environment you are painting in, and how you are applying it. Do you have any questions or need help choosing products? Contact us.

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