How to Thin or Dilute Acrylics That Are Too Hard

Paint palette with six paint colors and red background.

Sometimes with acrylic paints, you can find yourself in a position where you walk away from the easel for just a few minutes only to come back to find your paint half-dried on the palette.

While the quick drying time of acrylic paint is one of its biggest advantages for making art, it is also one of its biggest disadvantages too. 

How do you thin or dilute acrylics that are too hard? As long as they aren’t completely dried, acrylic paints can be diluted with either water or a gel medium. Paint thinner should not be used to thin acrylic paints because it dissolves the bonds in the plastic. Acrylic paint can be thinned to stretch paint that has hardened or to create an acrylic wash. 

Before throwing out acrylic paint that’s gotten too hard, there are a couple of things to try that could salvage it. Read on to find out more about thinning out acrylic paints that have hardened from age or exposure.

Reviving Hardened Acrylic Paint

Some paints may harden past the point of no return, but that is not always the case. Before looking at how to bring paints back to life, let’s learn how to determine if they can be saved or not.

Identify Whether the Paint Can Be Thinned or Not

The first thing you need to do when assessing whether you can salvage hardened acrylic paint or not is to check and see how dry it is. Here are a few rules of thumb for assessing hardened acrylic: 

  • The thinner a spot of acrylic paint is, the more quickly it will dry. If acrylic has dried to a thin film on the palette and can be scraped up with a fingernail or a palette knife, it will likely be too dry to use again.
  • In a blob of acrylic paint on a palette, the outside will become a hard shell first, protecting the soft, wet paint on the interior. These blobs can be broken open with a finger or a palette knife to expose the wet paint underneath.
  • A blob of acrylic paint can be tested to see if it’s salvageable with a finger test. When you touch the acrylic paint on the palette, if it still has some give or feels squishy, the paint has only partially dried and can be revived using a thinner.
  • If a blob of acrylic is dry enough to peel off of a plastic or metal palette, it is likely too dry to use, though there may still be a wet layer of paint in the very middle of the blob that can be salvaged.

Once you’ve determined whether your hardened acrylic paint is still soft enough to use, you can choose a thinner to revive it.

Can You Thin Out Acrylic Paint With Water?

The answer is yes, acrylic can be thinned out with water and this method is arguably one of the best ways to thin hardened acrylic paint.

One advantage of water is the fact that you, as an acrylic painter, likely have some right by the workstation already to wash brushes. 

If up to 30% or less of water is added to hardened acrylic paint, it will simply thin the acrylic paint out and give it back its original elasticity.

However, if water is added to acrylic paint at a rate of 60% or more, the resulting mixture is called a wash

This light mixture of paint can either be used to build up layers in a painting or can be used to do underpainting (a base layer) to be covered over by thicker acrylic or other mediums later.

Thinned acrylic can be used as a substitute for gesso when preparing a canvas. Acrylic can even be thinned to the point it can be worked in a similar manner to gouache or watercolor paints.

Can You Thin Out Acrylic Paint With Paint Thinner? 

Acrylic paints should not be thinned out with paint thinners (such as turpentine) that are traditionally used on oil paints. This is because acrylic is plastic based, and the chemicals in paint thinner break these plastics down and cause them to separate. 

However, since acrylic’s popularity has blossomed, manufacturers of acrylic paints have developed their own paint thinners called flow aids.

Not only can a flow aid be used to thin out a hardening acrylic paint, but it can also be used to help keep paint that is on a palette or canvas wet for a longer time period to delay drying. 

Liquitex Professional works great for me.

Liquitex Professional Effects Medium, 118ml...

A major benefit of using acrylic paint is that it doesn’t require the kinds of poisonous paint thinners that force oil painters to work in well ventilated studios.

Even though acrylic paint has a bad reputation for drying prematurely, acrylic paint thinners have leveled the playing field and have given acrylic paints some of the properties of oil without the associated drawbacks. 

Can You Thin Out Acrylic Paint with Gel Medium? 

Hardened acrylic paint can be thinned out by gel medium as well as water or acrylic paint thinners. Gel medium is essentially the same chemical composition of acrylic paint, but without the added pigments.

The main use of a gel medium is to add body and adhesive properties to the acrylic paint. 

While gel medium can be used to revive hardened acrylic paint, it should be noted that gel medium will have other effects on the acrylic too, since it is designed for use with impasto techniques (applying thick, undiluted paint to a canvas for texture).

Paint that is cut with gel medium will tend to show brushstrokes more readily than paint that isn’t. This may or may not be desirable depending on the painting techniques you’re using.

How Do You Keep Acrylic from Drying Too Fast?

Along with ways to thin or dilute acrylic paint after it has slightly hardened, there are also ways to prevent acrylics from drying too quickly while you’re working in the studio.

Here are a few tips to help prevent you from having to revive your acrylics with thinner:

  • Mist your paints. Instead of having to add water to hardened acrylic and having to worry about the proportions of water to paint, you can use a water bottle to spray your palette occasionally to keep your acrylic paints from drying.
  • Cover your paints with plastic wrap. Acrylic paint dries with exposure to the air, so to keep your palette fresh and wet longer, lay a piece of plastic wrap over the top of your paints to prevent drying if you have to walk away from your canvas. 
  • Use a retarder. A retarder is a chemical that is used to keep acrylic paints from drying quickly and gives them some of the versatility of oils.

I recommend Liquitex Retarder.

Liquitex Professional Effects Medium, 118ml...

Acrylics can be diluted once they’ve begun to dry, but often it’s easier to prevent them from drying up in the first place.

Using the above methods, you can keep your acrylic paint fresh without being forced to thin or dilute it with additional chemicals.  

Acrylics Dry Fast

Learning how to effectively thin and dilute hardening acrylic paints is one of the most important skills you can learn as an acrylic painter.

Back when acrylics first hit the artistic scene they were more difficult to work with, but now with the introduction of thinning mediums specifically designed for acrylics, these paints are just as versatile as any other medium. 

For more great tips and information on paint thinning techniques, head on over to my in-depth article on paint thinning.

Last update on 2024-05-26 at 15:38 / Affiliate links / Images from Amazon Product Advertising API

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I'm a hobby enthusiast with a real love for painting miniatures. I also happen to run this site and write the majority of its content!