Rustoleum Enamel Hardener – How to Use and Why Is it Good?

Rustoleum and other oil-based enamels are very slow when it comes to drying and curing. But what if the drying process could be accelerated for you to apply other coats over it or even sand and buff the painted surface? That’s where a hardener comes in. It can be especially useful during cold weather where the drying rate is lower. This article will cover Rustoleum enamel hardener, how to use it, and why it is good.

What is a Rustoleum Enamel Hardener?

Enamel hardener is an additive to oil-based enamel paints such as Rustoleum, enhancing its dry paint properties. It can also be referred to as an enamel catalyst or accelerator. This is because its primary purpose is to speed up chemical reactions involved in curing and creating resilience of the paint mixture. Hardeners are designed to work with most single-stage synthetic and acrylic enamel topcoats.

Why is using a Hardener in Rustoleum Good?

The oil-based Rustoleum enamel dries slowly since the heavy solvent present in the paint has to migrate through for the paint to form a hard surface. Rustoleum hardeners improve curing and drying time to about 48 hours. This would otherwise take a week to a month before the paint fully cures if the hardener was not present or the weather was cold.

After completely drying, the surface can then be sanded and buffed or even another coat of enamel applied over it. The catalyst also prevents a wrinkle finish. That is when a web of wrinkles forms on the dry layer of paint. This happens when you apply a new coat of paint over a coat that has not fully dried. It also occurs when a thick layer of paint is not cured underneath the outer skin. This mainly occurs with oil-based paints.

What’s more, you can use paint accelerators in waste management to solidify leftover paint for curbside disposal. Other types of hardeners, called concrete hardeners, are used to simplify and speed up the mechanical sanding and polishing of concrete floors.

Apart from speeding up drying and curing, here are other reasons why you should use a hardener on Rustoleum enamel:

Pros of Hardener:

  • It increases the hardness of paint.
  • It enhances resistance to scratches and abrasions.
  • It improves the gloss of the paint.
  • It provides resistance to chemicals.
  • It improves durability.
  • It provides UV resistance.
  • It provides a wet edge to blend well on previous coats.

Cons of Hardener:

  • The chemicals present in the hardeners are toxic and reactive.
  • If the correct ratio of the hardener to paint is not followed, defects may appear on the dried film of the paint.

How Do Rustoleum Hardeners Work?

Common catalysts contain a mixture of polyisocyanates, additives, and solvents. Different catalysts have various types and levels of polyisocyanates and solvent blends. This determines their rate of cure, gloss level, and other properties. The solvent blend controls the flow out and dry times. A hardener can serve either as a reactant or a catalyst in chemical reactions during the mixing process.

The main ingredient of the paint hardener is sodium polyacrylate–a crystallized salt. The crystallized product can absorb moisture and rapidly convert the paint into a solid rubbery substance. Different manufacturers create hardeners for particular types of resins and their functional groups. That’s why it’s crucial to find out if the hardener you want to purchase is compatible with your choice of paint.

Can You Add Hardener to Enamel Paint?

Hardeners are not entirely necessary for enamel paints except for automotive ones. With Rustoleum being an oil-based enamel, it’s compatible with hardeners designed for enamel paints.

Why Use Rustoleum Enamel Paint?

Rustoleum enamel paint is famous for its rust-preventing feature. It’s also resistant to harsh weather conditions and corrosion. You can apply it on external and internal surfaces and materials made of metal, concrete, and wood. Apply it with a roller, brush, or spray gun. A spray gun is the fastest method of application. To apply through spraying, you have first to thin the paint.

How to Add Hardener and Reducer into Rustoleum Paint to Create a Mixture

Ready-to-use spray cans are convenient to use on small and medium-sized surfaces. But painting on large surfaces like that of tractors or cars is a different ball of wax. You need to use a spray gun on large surfaces. The Rustoleum enamel paint needs adjusting before you can load it onto the spray gun. You adjust it by thinning the enamel paint with a reducer which can be: acetone, mineral spirit, or xylene.

Reasons for thinning the paint before loading it into a spray gun:

  • It reduces the viscosity of the paint and allows it to flow easily and spray quickly.
  • It enables you to consistently spray thin coats on the surface and create an even sheen.
  • It lessens the drying time of the paint since it allows quick evaporation.
  • It prevents the paint from jamming the spray paint mechanism.

The mixing ratio of the paint to reducer to hardener is a significant factor in how a paint job will turn out. You can access the correct mixing ratio on the technical statistic sheet of the manufacturer or recommended thinning guidelines of the Rustoleum product you are using. An incorrect mixing ratio can lead to imperfections on the paint’s surface during the painting and curing process.

A typical ratio used on enamel paints is 4 parts paint to 1 part hardener to 1 part reducer(4:1:1). Some manufacturers recommend adding the hardener at a specific time during the mixing process. That’s why it’s always advisable to refer to the instructions before you start mixing for a successful paint job.

You can use a disposable moving stick for mixing the components. Proper stirring also ensures that the colorants redistribute evenly across the product. Use measuring cups to measure the correct amounts of the reducer and hardener before adding them to the paint. Another instrument to use is a viscometer to measure the viscosity of the paint after adding the reducer. It does this by checking the internal resistance to the flow of the paint.

How to Apply the Mixed Rustoleum Paint Using a Spray Gun

  1. After mixing the paint with thinner and hardener allow it to settle for about 10 minutes.
  2. Load the spray gun with the thinned paint mixed with hardener using a funnel. A funnel prevents spills of the paint onto the surrounding environment. You can also use it to determine the thickness of the paint.
  3. Test the paint on a scrap of metal, wood, or wall to check its consistency. If the paint flows out smoothly, it’s ready for spraying.
  4. Refer to the equipment manufacturer’s instructions on how to spray since different sprayers have different spraying techniques.
  5. Note down the correct ratio (paint: thinner: hardener) for future reference.
  6. Proceed with spraying on the surface and ensure the paint completely dries before you apply another coat.

Tips to Consider When Using Thinned Rustoleum with Hardener

  • Try to estimate the amount of paint you need before adding a hardener. Most hardeners have a pot life of about 8 hours. Therefore you won’t be able to use the paint after a day since it will harden. With that in mind, don’t store unused catalyzed paint.
  • During testing on scrap metal, if the paint flows out in splotches or has an uneven coverage, it means you need to add more reducer.
  • If the paint runs on the surface, it’s excessively dilute and needs adjusting by adding more paint to thicken its consistency.
  • You can use power-driven agitators to mix large quantities of Rustoleum paint.
  • Using incompatible thinners with Rustoleum may cause fading, wrinkling, blistering, gelling or solvent entrapment.
  • Hardeners are toxic, flammable, and have adverse environmental effects; hence you should wear a respirator and gloves and not expose the hardened paint to flames.

Other Ways to Speed up the Drying Process of Paint

  • Use a furnace 

High temperatures speed up the drying time. If the paint is left to dry in an environment that is too cold, it may crack. Turning up the furnace makes the air warm and dry quickening the drying time.

  • Using a hairdryer and heater

If a section you’ve painted is drying slowly, you can focus a hair dryer on it, ensuring it’s two inches away from the painted surface to avoid blistering. However, too much heating of the paint opens a can of worms by causing bubbles and chipping. Heating the painted surface to 150 degrees Fahrenheit (66 degrees Celsius) accelerates the drying time.

  • Use a dehumidifier

Paint dries slowly in a humid environment. Turn on the dehumidifier to absorb moisture from the air, leaving cool, dry air in the room conducive to drying.

  • Use a clay-based cat litter

Using cat litter is an easier way to dry out paint for disposal. Mix the litter with paint and leave it to dry. The cat litter helps the paint to dry by absorbing moisture.


There you go. How to use Rustoleum enamel hardener and why it’s good. Using a hardener is as reliable as it gets when it comes to improving the drying time and curing of your Rustoleum paint. Wear the right PPE to protect yourself from toxic fumes while applying the paint with a hardener. The hardener you use should also be compatible with Rustoleum enamel paint.