How to Use Cornstarch to Thicken Acrylic Paint


Trying to work with runny, watery acrylic paint can leave you frustrated and annoyed. Before you throw out that seemingly useless paint, however, try to thickened it up with some cornstarch. Cornstarch acts as a thickening agent commonly used in soups, stews and gravies. It can also successfully change the texture and consistency of acrylic paint.

Store your homemade cornstarch paint thickener in an airtight jar.
Store your homemade cornstarch paint thickener in an airtight jar. (Image: AwakenedEye/iStock/Getty Images)

Why is Acrylic Paint Runny?

The water-based nature of acrylic paints means it can sometimes have a runny or watery consistency, which leads to the desire to thicken it up. But that isn’t the only cause of runny paint. In fact, there are a few reasons as to why your acrylic paint is runnier than normal, and they are:

  • Environmental causes
  • Poor paint quality
  • Age of the paint

You may also want to thicken acrylic paint to give texture to your painting. This is not an uncommon occurrence in the art world. Artists will often add a thickener to acrylic paint to help create a unique and dramatic surface to their artwork.

No matter what the cause, cornstarch can thicken that runny acrylic paint.

Thicken Paint with Cornstarch

Before you add the cornstarch to the acrylic paint, you must first mix it with water. Use a ratio of 1 ½ cups of cold water to 2 tablespoons of cornstarch. Once it is well-mixed, place it on the stove over low heat. Heat the mixture while stirring continuously until it has a consistency similar to paste. Let the mixture cool to room temperature before adding it to the paint. You want to add a little of the cornstarch and water mixture to the paint at a time, making sure to stir the paint thoroughly with a paint stick after each addition. Continue adding the cornstarch and water mixture until you achieve the desired thickness.


While cornstarch will thicken acrylic paint, it can also affect the longevity of the paint. If you are concerned about shortening the life of the paint, consider purchasing commercial paint thickener, which is available at department stores and home improvement centers.

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