Oil-based Enamel Paint Hardener – How to Use Correctly

Oil-based enamel paints are easy to work with and provide impressive resistance against wear and tear. However, there is no denying the fact that they dry too slowly and take even longer to fully cure. Enamel paint hardeners exist for this reason.

If you have ever considered the possibility of speeding up drying time so you can apply other coats or abrade the surface, paint hardeners provide this solution. When you need to complete a project during cold weather conditions, you will find enamel hardeners useful to tackle the slow drying rate. There are other benefits to using hardeners including their ability to improve durability and glossiness.

The best way to enjoy these benefits is by ensuring you are using the hardener correctly. This can be tough since most people make the mistake of using paint hardeners in the wrong ratio. Another common issue is using the substance without care for the reactive chemicals that it contains.

You will get a better understanding of oil-based enamel hardeners, know if you should be using them for your project, and the right way to use these paint accelerators.

How Do Oil-based Enamel Paint Hardeners Work?

Paint hardeners contain additives and solvents that combine to improve paint properties. Their primary aim is to accelerate the chemical reaction that makes curing possible and increases the paint’s strength. The degree, type of polyisocyanates, and other blends differ from product to product. This is why hardeners cure and deliver glossiness at different levels. It is also important to be certain the hardener you are getting is indeed suitable for oil-based enamel paints.

What is the Best Method for Applying Oil-based Enamel Paint Hardeners?

You can apply paint hardener using a roller, spray gun, or brush. Painting directly from a spray can is often convenient if you are working on a small surface. When painting larger surfaces like a car exterior, get a spray gun for more efficiency.

Spraying gets the job done faster, although you will have to thin the paint to increase workability. Here are some reasons to thin the paint before loading it into the spray gun:

  • The paint flow becomes better and you can spray faster.
  • Dry-time reduces since thinner coats evaporate quickly.
  • You can achieve an even sheen by spraying consistently
  • There is hardly the issue of jamming when you thin the paint before loading it.

What is the Right Mixing Ratio for Oil-based Enamel Paint Hardeners?

It is important to follow the correct mixing ratio when working with oil paints, reducers, and hardeners because this factor affects results. Most products come with directions to show the correct mixing ratio and this is what you should follow. Using incorrect quantities can ruin the paint’s surface during the curing phase.

Generally, four parts of paint to one part of hardener should be sufficient. If you are using a thinner, also add one part. Depending on the manufacturer, you might need to add each product at a particular time so always refer to the directions.

Aside from getting the mixing ratio right, stir the components properly and allow the mixture to sit for about half an hour to activate the hardener. Using measuring cups helps you work with the exact amount of product. A viscometer is also useful for gauging how well the paint is responding to the reducer.

Steps to Follow When Applying Mixed Enamel Paint with a Spray Gun

Using a spray gun to apply the paint mixture is considered the best method when working on large surfaces. Take the following steps for best results:

  1. Leave the mixed paint to settle for about 10-30 minutes depending on the hardener’s instructions.
  2. Use a funnel when loading the paint to prevent spills around your work area. This can also help you gauge the paint’s thickness.
  3. To be sure the paint is ready for spraying, test it on a hidden area of the surface to see if it flows out smoothly.
  4. Check and adhere to the recommended spraying technique provided by the manufacturer.
  5. Spray the paint on the surface and make sure it fully dries before going over with the next coat.

How Long Does It Take Oil-based Enamel Paint Mixture to Dry?

Enamel paint usually requires multiple coats for a perfect finish and you have to allow the previous coat dry before recoating. The drying process ordinarily takes up to 24 hours but the added hardener in your paint mix speeds up the time. This means the surface will be ready for sanding just a few hours after painting.

There are other methods to try out if you need to further speed up the paint drying time.

  • Use a Dehumidifier

Cool air and humidity are two factors that increase the drying time of oil-based enamel paint. You can use a dehumidifier to make the surface dry faster. Turn it on to produce dry air that absorbs moisture from the atmosphere.

  • Get a Heater

A heater or hairdryer will be more efficient if you need to focus on only a particular area. Give some inches between the surface and the dryer and ensure the heat from the device is not excessive. You want to avoid blistering and chipping. Alternatively, increase the radiator’s heat to speed up moisture loss.

  • Japan Drier Method

Japan driers contain naphtha and metallic salt that promote oxidation in oil-based enamel. Apply the drier to the painted surface with a paintbrush and leave it to dry.

Should You Use a Hardener in Oil-based Enamel Paint?

Paint hardeners are not mandatory for enamel paints but it is probably a good idea to use them, especially for automotive purposes. They are great for rust-inhibition and protecting surfaces from harsh outdoor weather,

Here are some advantages you get from adding a paint hardener to an enamel topcoat:

1) Speeds Up Drying Time

Oil-based enamel paint dries slowly, providing extra time for you to work with the topcoat and get smoother results. But sometimes, you just want to finish up the task and carry on with other projects. Enamel hardeners help you achieve this by speeding drying time. The surface becomes ready after a few days, compared to the many weeks you have otherwise had to wait without the hardener.

You can then go ahead to sand the surface or apply another coat of paint. In other words, paint hardeners make your job easier by speeding up drying time.

2) Better Appearance

Painting over a coat that hasn’t fully dried can cause the surface to wrinkle. Improper curing of thick paint layers also causes this. You can prevent these situations by adding paint hardener to your oil mix. The catalyst also helps boost shine, whether you are using it on metal, concrete, or wooden surfaces.

If you want that glossy appearance that attracts attention and increases the surface’s functionality, paint hardeners are worth it. Your project enjoys improved aesthetics and lasts longer.

3) Enhances Resistance

Another good reason to use a hardener with oil-based enamel is the level of resistance the addition provides. The surface has a better chance against scratches, abrasions, and chemicals.

External surfaces need paint hardeners to better withstand the extreme conditions outdoors. A single coat can increase the paint’s hardness and provide some level of UV resistance. The result is that your product becomes more durable

Asides from the benefits mentioned above, paint hardeners provide a wet edge that makes your job of blending coats easier. They are also useful in waste management for solidifying leftover paint before disposal.

Other Ways To Fix Cracking and Wrinkling in Oil-Based Enamel Paint

Part of the advantage of adding hardener to enamel paints is that the surface becomes less likely to develop wrinkles. A web of wrinkles usually forms when you apply another coat over a painted surface that hasn’t fully dried. The top layer becomes dry while the layer underneath stays wet. Here is a way to fix this without hardeners:

  • Scrape the wrinkled layer off with a trowel
  • Sand the scraped surface to get rid of paint remnants
  • Make it smoother with fine-grit sandpaper and clean the dust
  • Apply a thin layer of stain-blocking primer
  • Reapply the oil-based enamel paint

Cracking, on the other hand, occurs when the enamel paint dries too quickly. This results in poor bonding, leaving the paint weak, and eventually, it begins to fall off. The steps to fix cracking in enamel paint are similar to those you follow for correcting wrinkling. Although you may need to apply more than one coat of enamel paint after using the stain-blocking primer.


Adding a paint hardener to your oil-based enamel paint is a trusted way to boost the paint’s properties and drying time. Ensure you stick to proper application procedures as provided by the manufacturer and that the choice hardener is a good match for the paint. Also, hardeners contain toxic fumes so protect yourself by gearing up properly.