How to Thicken Up Acrylic Paint


How do you thicken acrylic paint? There are several ways. Some of them involve DIY mixtures and some are more art-material related. Many times, if you choose the right consistency you should not have a problem with your paint’s thickness…such as making a deliberate selection of “heavy body” which is thicker on average.

But sometimes it does happen, if you are trying to work on something in impasto, or just tackle a bottle that has become unusually thin, here are some solutions.

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how to thicken acrylic paint

What Causes Paint to Become Too Thin?

Many times, I’ve found – it’s the environment. If your storing practices are not optimal (such as keeping it tightly capped and in a location around 68 degrees) it can happen. Sometimes, it’s the age of the paints. If I’ve stored any of mine for too long (and I’ve especially noticed this in the craft paints under the Plaid label) the binder and pigment may separate. Sometimes a good shake is all it takes to get the mixture back to a normal consistency again.

Other times, it’s not so easy If the paint bubbles up too much, it’s not a good sign. That’s where an add-in, like the ones I am about to tell you about in this post, come in!

Proprietary Pastes

Modelling paste can be a good additive, they are sold alongside paint additives and mediums, and can work well.

how to thicken acrylic paint

Baking Soda

Baking soda is a wonderful household staple, used for deodorizing and freshening up some environments, but did you know it can definitely improve the thickness of your paint? It can also give it a matte look if you are wanting to paint in the antiqued-, rustic style. I tried it and it made the paint almost fluffy-like in texture, so you probably won’t need much. Start with a teaspoon per dispensed amount and combine, then do a test.

Thickening Paint with Cornstarch

Cornstarch is another well-known household staple –  cooks use it to thicken stews, soups gravy and puddings….so you can see it can do the same thing for paint, too. It has to be done a certain way, though, unlike the baking soda, you can’t toss in a teaspoon and stir it around.  To do this, you’d need to create a mixture from cornstarch (about 2 tablespoons) and a cup and a half of water.

Place into a saucepan on your stove, set it to medium heat and stir , it will slowly thicken. When you are satisfied with the consistency, if not maybe add a little bit more, then turn off the heat and let it cool. Now this mixture can be added to your paint, start with a little at a time to see how well it improves it.

A word of caution, however, as cornstarch is a food-based product, it’s not going to be archival quality. Be sure and seal the painting or sculpture appropriately with a good varnish to protect it against the potential of mildew, fungus, etc., developing.

Decoupage Glue and Plaster of Paris

Decoupage or PVA glue, has been known to bump up paint texture a notch. You can definitely try my approach here as I’ve heard of artists adding this as a quick fix. Plaster of Paris, which is used as a casting material used in molds, is a good additive.


Start with any of these suggestions, and don’t be afraid to experiment a little. Maybe do a test sample on paper to see how the results look? Then you can commit to one of them that works the best. Good luck 🙂


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