The paint covering a car body consists of two or three layers: the first is a base coat or primer (for plastic parts), the second is the color, and the third is the clear coat.
All three of these products can be single-component or two-component.
In almost all cases, the base coat and clear coat are two-component for various reasons, including their hardness and consequent resistance.
The color, however, can be two-component or single-component depending on the specific situation.
If a two-component color is chosen, there is no need to apply a clear coat as this formulation is already sufficiently protective. However, these products offer more limited effects for the car body: there are no metallic or pearlescent two-component paints for cars and motorcycles available on the market.
Consequently, if a color with these types of effects is desired, it must be single-component, followed by the application of a two-component clear coat for protection.
But why are these products called two-component?
The role of hardeners in painting
Two-component paint can only be successfully applied if it is mixed with a second component, the hardener.
The hardener is a paint product that cannot be used on its own, its precise purpose being to react with the base to harden it.
Additionally, the hardener can apply specific effects to the paint surface to achieve the desired result, such as gloss or matte.
For car body painting with a two-component product, it is therefore necessary to have both the base and the corresponding hardener.
How are base and hardener combined?
On a two-component product, a percentage value for base B in relation to base A is indicated: by convention, base A is the two-component base, while base B is the hardener.
This means that once the quantity of two-component base to be used has been chosen, the indicated percentage of hardener must be added.
For example, if 20% of base B by weight is indicated and 100 grams of base are prepared, 20 grams of hardener will need to be added.
Attention must be paid to the instructions because the ratio between the two products can be by weight or by volume, depending on the manufacturer.
Indeed, depending on the substances used in the formulation, the density can vary significantly, and thus the ratio can change considerably, with the risk of adding too much or too little hardener, making the two-component paint thus prepared useless.
Typically, manufacturers recommend combining a base and a hardener from their own product line, thus ensuring compatibility between the two without causing too many problems for those approaching two-component products.
The different types of hardeners
There are many types of hardeners to choose from.
The main two aspects to consider when choosing a hardener are:
- Compatibility with the base color;
- The speed at which the hardener dries and solidifies.
While the reasons behind the first factor are easily understood, it is useful to elaborate on drying speed.
Generally, a paint hardener can be slow or fast drying:
- Slow drying is recommended during the hot season to counteract the effect of heat, which would otherwise lead to premature evaporation of the liquid part, and for work on large surfaces, so that it does not begin to solidify before the work is finished for a uniform result;
- Fast drying is recommended during the cold season to counteract the effect of cold, which would otherwise solidify the paint liquid without allowing the hardener time to act, and for detailed work, so that the effect of the intervention can be evaluated quickly.
The use of hardeners by experts
Based on one's familiarity with the use of two-component paint, the dosages can be adjusted.
For example, the greater the presence of hardener, the greater the resulting opacity, and conversely, less will be used for a glossy effect.
The quantity of hardener used also varies based on temperature conditions: instead of procuring products with different drying speeds, one can adjust the hardener concentration to make the process faster or slower and adapt to environmental conditions and the type of work.
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