How to Thicken Acrylic Paint? Easy Methods To Go For

If you want to know “how to thicken acrylic paint” then you are on the right page. Today, here we’ll help you to get the right techniques and ways to thicken acrylic paint.

But another question is why does acrylic paint need to be thickened? So, let me tell you that acrylic paint feels too thin and there are some situations where you need to go with thick paint but with the acrylic ones.

So, this is why it is important to thicken the acrylic paint and with the right guidance you can do it. When I first used it on my room walls, I realized the paint consistency was too light for the textured effect I wanted.

The paint slid down the wall in some spots.

I was trying to create a raised, dimensional look for an accent wall in my living room. But the acrylic paint I considered from the craft store was more like colored water than paint.

That’s when I started experimenting.

And some methods worked better than I expected, meanwhile others turned out so bad that I had to take it off and start again. But through all this, I figured out what works and what’s a waste of time and materials and most importantly how to thicken acrylic paint.

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Why is it Important to Thicken Acrylic Paint?

Not every project needs thick paint but when you DO need it, nothing else will work.

And remember, thin acrylic paint won’t hold texture.

I learned this when I was working on a client’s dining room and wanted to create an impasto technique effect around the ceiling border. The regular paint I used flattened out. All the beautiful brushstrokes were gone as the paint self-leveled.

Here’s what thick paint actually do:

It holds brushstrokes and palette knife marks so your technique shows. When you’re paying for custom decorative work, you want it to LOOK custom, because thin paint makes everything look flat and boring.

Heavy body acrylics or thickened paint gives you dimensional effects. Light hits it differently, shadows form in the texture. It’s the difference between a boring wall.

The other thing nobody talks about is coverage. Thick paint covers better in a few coats. And if you’ve ever tried to create textured abstract art or any decorative finish, you NEED it. The paint consistency determines whether your vision translates to the wall or canvas.

Also, when acrylic paint is around too long or gets stored improperly, the binder and pigment can separate. The paint becomes thin and watery and useless for anything except basecoating. 

How to Thicken Acrylic Paint? Best Ways to Consider

So there are methods and then there are the budget-friendly DIY methods. I’ve tried all of them. 

Let me walk you through what works and what’s just anything. Some of these methods worked really well while others are not in my recommendation. Each method changes the paint differently, texture, finish, drying time and color sometimes. So choosing the right one depends on what you’re trying to do.

Use Gel Medium

Gel mediums are the most professional way to thicken acrylic paint. They’re specifically made for this, which means they won’t mess up your paint’s chemistry or make it fall off the wall.

I keep a jar of heavy gel medium in my supplies and it’s saved me many times.

The thing about gel medium is that it maintains the archival quality of your paint. If you’re doing fine art or any kind of permanent installation, this matters. The gel is made with the same acrylic polymer base as the paint, so everything plays nice together.

You’ve got options too like matte gel if you don’t want shine, gloss gel if you do want shine. Extra heavy gel for thick applications.

When I did that textured feature wall in my own bedroom, I mixed about 40% extra heavy gel with my paint. The consistency became almost thick but it held every mark from my palette knife. 

One thing to know is that gel medium can make colors slightly transparent. It is not always a bad thing, but if you’re using it with light colors, you need an extra coat to get coverage. 

Add Modeling Paste

Modeling paste is like gel medium’s more aggressive version.

I first used modeling paste when a client wanted their home office to have the sculptural, almost three-dimensional quality to the painted designs. Regular paint, even with gel medium, wasn’t doing it. They wanted texture you could FEEL from across the room.

Modeling paste is white or off-white before you mix it, which is something you need to know. It WILL lighten your paint colors.

I made this mistake on a navy blue project when it was mixed in modeling paste without testing first, and my beautiful deep navy turned into a weird dusty blue-gray. I had to remix everything and add more pigment to compensate.

But for the thickening power, it is unmatched. You can create raised designs, fill in areas, build up texture that feels almost sculptural. I’ve used it with palette knives to create designs that stick out from the wall.

Winsor and Newton make a good one. Their Galeria line is affordable if you’re testing it out. The paste can be sanded after it dries too, which is very nice. You can SCULPT with this.

Mix Cornstarch

So cornstarch, this is where we get into the DIY category.

I’ve used this method three times. Once for testing, once because I had no other option, and once because a client’s budget was so tight that buying a professional medium is not considered.

Here’s how it works: you heat cornstarch and water until it thickens into this paste-like consistency, let it cool completely, then mix it into your paint.

It DOES thicken the paint effectively, but….

The archival quality is questionable. Cornstarch is organic matter and organic matter can grow mold, attract bugs and can break down with time. I used it on a temporary installation piece that was only meant to last three months, so that was fine.

The texture it creates is also kind of chalky. It is not the same smooth workability you get from professional acrylic mediums.

Add Flour

I tested this once out of curiosity after seeing it recommended in some online craft forums.

But I recommend you after using this that please don’t do this. 

I mean flour will thicken your acrylic paint. But it also makes it lumpy, weird, prone to cracking, and a science experiment later when things start growing in it.

The texture was gritty and unpleasant. It didn’t spread smoothly. The brushstrokes looked rough in a bad way, not in an artistic textured way. And the finish dried with an odd chalky-matte surface that managed to look dirty even though it was fresh paint.

With Baking Soda

Baking soda is kind of interesting….

It creates a gritty, almost sandy texture which sounds bad, but depending on what you’re going for, it can work.

I used it for a textured abstract art piece where I wanted a rough, stone-like appearance. I mixed like a tablespoon of baking soda into about half a cup of paint and the texture was IMMEDIATE.

It thickens the paint and gives it a matte, chalky finish. The grittiness is very visible and you’re not getting a smooth texture but it creates a rough, almost abrasive texture.

For decorative work where you want that rough aesthetic, iIt works. For anything where you need a smooth, workable, professional-looking texture, then don’t consider this.

Also similar to cornstarch and flour, the longevity is questionable. And it can sometimes react with some pigments and change colors slightly.

Different Techniques to Thicken Acrylic Paint

So now that you know WHAT to use for thickening, let’s talk about WHY you’d choose different techniques for different applications. Because the technique you’re using should determine which thickening method you pick. 

I learned this after using the wrong method for a specific technique and have to redo an entire section of wall art.

For Palette Knife

Palette knife work needs THICK paint. If your paint is sliding off the knife instead of holding its shape, it’s too thin.

When I’m doing palette knife applications, I always use either heavy gel medium or modeling paste mixed with my acrylic paint. The consistency needs to be like soft butter, thick enough to hold peaks and ridges but spreadable.

I did this accent wall where the design was palette knife work, it was thick, sculptural strokes in different directions to create a dynamic texture. I mixed about 50% extra heavy gel with my paint, and the consistency was PERFECT. The raised texture caught the light differently throughout the day and the clients loved it.

The key is that the paint needs to be stiff so that when you drag the knife through it, it holds that ridged pattern. 

For Impasto

Impasto technique is about visible brushstrokes. Thick, expressive, dimensional paint application where the texture IS the art.

This technique traditionally comes from oil painting, but you can do it with acrylics if you thicken them properly. And acrylics may be better because they dry fast.

For impasto, I use modeling paste or extra heavy gel medium and sometimes both mixed together if I want an extreme texture.

The paint should hold the shape of your brush bristles. When you lift the brush away, you should see defined ridges and peaks. 

I did an impasto piece above a fireplace mantel once, it was thick, expressive brushstrokes in warm colors that created an organic, flowing texture. I used about 60% modeling paste mixed with heavy body acrylic paint. The texture stuck out from the canvas by almost half an inch in some spots.

For Textured Abstract Art

Textured abstract work is where you can experiment with different thickening methods because there are no rules.

I’ve used everything from gel mediums to baking soda to sand mixed with paint for abstract textured pieces. It depends on the effect you want.

If you want smooth, glossy raised areas, then go with gloss gel medium. And if you want a rough, stone-like texture, then you go with baking soda or sand.

If you want a sculptural, dramatic dimension, go with modeling paste.

The best part about abstract textured art is that you can mix different methods in the same piece. 

I did this large canvas where some areas were smooth gel medium texture and other areas had a rough, gritty baking soda texture. The contrast between smooth and rough created an interesting visual and tactile experience.

For Pour Painting

Sometimes pour painting needs slightly thickened paint for some cells and effects. 

I don’t do much pour painting, but I’ve experimented with it and sometimes adding a tiny bit of gel medium to your pouring mixture can help with cell formation and paint movement.

The key word here is small, like around 10-15% gel medium max. You want the paint to flow but with a bit more body and control.

This is more advanced territory though. If you’re starting with thickening paint, skip this application until you’ve known the others well.

For Miniature and Model Paint

For miniatures and models, you want precision, not texture. So heavy thickening agents like modeling paste are overkill.

A small amount of gel medium can give you better control and coverage without making the paint so thick that it obscures fine details.

Or buy heavy body acrylic paint designed for detail work. 

The one time I helped a friend with a miniature project, we tried using regular craft paint and it was too thin for good coverage. Then I added a small amount of matte gel and the paint looked perfect with the good coverage and nice workability.

Step-by-Step Guide to Thicken Acrylic Paint

Alright, here’s how I do this when I’m on a project:

First – figure out what consistency you need. Are you doing delicate detail work or heavy textured applications because this determines your thickening method.

Second – start with small amounts. I ALWAYS test on a separate surface first. I learned this lesson when I ruined an entire batch of custom-mixed paint by adding too much modeling paste.

Third – mix thoroughly. You don’t want streaks of thick and thin running through your paint. I use a palette knife to mix, not a brush, because it blends more evenly.

Fourth – test the consistency. Put some on your brush or knife and see how it behaves.

Fifth – if you’re using gel medium or modeling paste, mix it in gradually. Add like 10-20% of your paint volume, mix completely, test, then add more if needed.

Sixth – if you’re going the DIY route with cornstarch, make your paste first, let it cool, then add it bit by bit to your paint.

Seventh – remember that paint gets slightly thicker as it sits. What feels perfect right after mixing may be thick 20 minutes later.

Eighth – work in small batches because thickened paint can dry out fast, so don’t mix more than you’ll use in your working session.

Ninth – seal your containers tightly. Acrylic paint dries fast through water evaporation, and thickened paint can develop a skin even faster.

The last one– if you’re using non-archival thickeners like cornstarch or flour, SEAL YOUR FINISHED WORK with varnish. 

Conclusion

So there you have it about how to thicken acrylic paint by years of trial, error, and having to redo sections because of the wrong method and technique.

The short version is to use gel medium or modeling paste for professional work. Use DIY methods only when budget or availability forces your hand, and understand the limitations.

Thickened paint opens up many possibilities for texture, dimension, and visual interest but only if you do it right.

My recommendation is to buy one jar of heavy gel medium and experiment. Try different ratios, see how it affects your brushstrokes and test it on different surfaces. You’ll learn more from hands-on experimentation than from reading from the guide.

And don’t be afraid to mess up. I’ve wasted a lot of paint figuring this out. But now I can walk onto any project and know what consistency I need and how to get there.

FAQs on How to Thicken Acrylic Paint