When you’re trying to decide on paint for your project, the choices can be confusing. Beyond the color itself, there are decisions like whether to use single-stage or a base/clear system, for instance. And then there’s all the ratios – 4:1, 3:1, 2:1 – or none at all with ready-to-spray base coats.
For many novices, it’s this last factor, ratio of paint material to activator/catalyst/hardener, that can be the most perplexing. But it doesn’t have to be that difficult. Here’s a brief explanation of what you need to know when you see a mixing ratio on the paint label.
Why all the numbers?
Each paint type and system is developed with specific performance goals in mind. Some paints are formulated for cost or ease of application, while others may prioritize durability or gloss.
Varying the ratio between a paint material and its chemical additives allows for different results based on these priorities.
For instance, a 4:1 paint (4 parts paint, 1 part activator) offers better flow and leveling compared to a 2:1 paint. The composition tends to be thinner and helps produce a smooth finish with fewer runs when applied properly. This ratio is often seen on specialty finishes and clear coats, like Eastwood’s Premium Show Clear.
A 3:1 ratio allows for a little heavier application, providing a margin of safety for sanding. This is ideal for primers or other layers where a heavy build is preferred. Many single-stage paints will also use this ratio, which holds up well to cutting and buffing.
Paints and clear coats with a 2:1 ratio tend to work well for applying heavy layers without excessive dry times. These often result in smooth, high-gloss finishes that are also more durable and chip resistant. Eastwood’s European Urethane Clear produces a deep finish with fewer coats.
Heavier still are paints with a 1:1 ratio. These tend to be epoxy primers and other high-build finishes.
Some paint formulations forego a hardener or catalyst altogether. These air-drying or ready-to-spray paints tend to go down very thin and require multiple coats for durability. For automotive body paints, these are almost exclusively used for base coats such as Eastwood’s OEM Select colors that will eventually receive additional clear top coats.
Understanding the ratios
Usually with two-part paints, the first number in the ratio represents the paint component and the second represents the catalyst. You may also encounter multi-component ratios such as 4:1:1. The third number, in this case, typically represents a reducer (to modify the paint viscosity), but might could also represent other additives like a flex agent. Always make sure you read your product instructions thoroughly to understand what components are being added to the paint mixture.
Caution should also be used when modifying the ratio of individual components. For instance, adding some extra catalyst to speed up the drying process might seem smart but could prove disastrous. Instead, you should maintain the intended ratio but substitute a faster catalyst to get the desired results. To help maintain a proper balance of all components, use graduated paint mixing cups. These are pre-marked with a variety of common mixing ratios for convenient measurement.
Some paints, however, are sold in containers that conveniently leave space for the catalyst to be mixed inside it. For instance, a “1-gallon” can of Eastwood’s 3:1 single-stage paint only contains 3 quarts of paint. The unfilled space in the can is for 1 quart of catalyst, completing the 3:1 formula. That’s an important fact to know when planning your project and figuring out how much paint you’ll need. Always ask about paint coverage when fully mixed. This will probably be expressed as cubic inches per gallon and will vary by the paint types already discussed.
If you can get beyond the numbers and follow these guidelines, your project should turn out shiny and durable regardless of what you choose.