Acrylic Paint Extender: What Is It and How to Use It

I started this blog to help educate newbies about miniature dollhouse building (you’d think I’d have made more progress by now!). I had a lot of trouble finding information, so a blog was born.

A reader asked me to fill in a gap: how to use acrylic paint extender. Frankly, I had to ask what is acrylic paint extender, because I had never heard of it. But, as always, with a little bit of research and a willingness to experiment, I learned that acrylic paint extender is pretty darn useful, and now I highly recommend it.

What Is Acrylic Paint Extender (or Retarder)

Acrylic paint extender and acrylic paint retarder are the same things, just with different names. I won’t get into the reasoning behind “same product different name,” but there you go. I’m going with acrylic paint extender.

Most store-bought solutions are made with propylene glycol, which is water-soluble and pretty much harmless. 

Propylene glycol is often used as a food additive because it’s good at retaining moisture. It’s also why it makes a great acrylic paint extender. What’s interesting about propylene glycol is that it’s also found in some injectable medications as well as topical creams and used in things like paint and antifreeze.

It is surprisingly versatile.

Are There Homemade Alternatives for Acrylic Paint Extender?

Sure, but for us newbies, I don’t recommend it. You have to get the ratios just right. If that’s your thing, go for it, but it’s not mine (see: making my own polymer clay tiles).

That said, if you’re interested, here are some of the things you could use for a homemade acrylic paint extender:

• Glycerin
• Lactic Acid
• Glycolic Acid
• Hydrolyzed proteins
• Citric Acid

To make homemade acrylic paint extender, water your chosen extender down and mix with paint. 

Yeah, that’s it. Like I said, you have to get the ratios just right, and that requires a lot of experimenting. Perhaps not the best thing for us newbies, all though, as you’ll see, using store-bought extenders involves a lot of guesswork, too!

Why Use Acrylic Paint Extender

Acrylic paints usually take between 10 and 20 minutes to dry. Dry time will, of course, vary by circumstances. Are you painting on wood or canvas? Is the wood primed (it should be!)? What brand of acrylic paint are you using? How thick is the paint (thick ones take longer to dry)?

Acrylic paint dries through evaporation. As the water evaporates, what’s left behind (the pigment), dries and attaches to whatever you’re painting. Acrylic paint contains very little water, so it dries quickly. Adding extender means adding moisture, which increases the evaporation time, which means longer dry times.

Extending the dry time of acrylic paint has several advantages. First, you can keep a lot of paint on your palette (mine is a Mickey Mouse plate). If you’re doing a lot of one color (say, the exterior of a dollhouse), you might want to keep a lot of paint handy. That could mean putting a bunch on your palette or simply keeping the tube open (or not tightly closed) for fast and easy access. The faster the paint dries, the less paint you can keep out. Adding extender eliminates that worry.

Second, if you’re working with several different colors, you don’t have to worry about your blues drying out while you’re painting with reds and vice versa. You can have multiple colors out and are able to switch back and forth as you see fit without worrying about your paints drying out. That said, I wouldn’t put the whole rainbow out at once. Acrylic paint extenders can only do so much.

Lastly, when you’re not worried about fast dry time, you can slow down and take your time painting. This means you’re less prone to make mistakes (cough, me, cough) and aren’t rushing your paint job.

Keep in mind, though, that dry doesn’t mean “dry.” Acrylic paint has to cure completely, like glue, so just because the paint is dry to the touch doesn’t mean it’s fully dry. You could still damage your project if you do something else to it too soon. Give your project a solid 24 hours to dry and cure.

How to Use Acrylic Paint Extender

As it turns out, there are a ton of ways to use acrylic paint extender. It really just depends on what you’re doing and what method you’re most comfortable with.

You can:

• Add the extender directly to the paint (as long as you’re careful and don’t add too much)
• Dip your brush in the extender, then into the paint
• Put the extender right on whatever you’re painting, then paint (I wouldn’t recommend this for wood)
• Use the extender as a brush cleaner

There are other methods, but you get the idea.

For dollhouse painters, I recommend the add extender directly to the paint method. Personally, I got the best results with that, but the dip your brush method works, too.

So, here’s how to use acrylic paint extender!

1. Measure it out

Here’s the extender and paint:

You’ll see two notices on the instructions. First, it says for thick applications, don’t use more than one part extender to eight parts paint. Second, it says for thin applications, don’t use more than one part extender to one part paint.

Cool. I like a good recipe and clear instructions, but, uh… how the heck do you measure paint?

In theory, you could use a measuring spoon (or cup if you have a big project) and measure your paint and extender out perfectly. But that strikes me as a bit impractical.

I measured my ratios using the “eyeball” method, and the reality is, that’s probably how you’ll measure your ratios out, too. And it’s exactly why using extender is kind of, well, difficult.

Here are the supplies I was working with.

Let me explain. I grabbed the two foam brushes because they were handy and easier to clean. Since this is just a demo, I didn’t want to kill myself getting bristles clean. I also didn’t want to mix brushes, meaning I wanted one brush strictly for plain acrylic, the other for paint plus extender.

At the top is a wood scrap, and yes, it’s painted but unfinished on the side. It’s all I had handy but ended up being a good thing to practice on because the painted part acts like a primed surface.

Finally, I picked the Mickey plate on purpose, so you could see the paint and the extender clearly. On a white plate, I don’t think you would see anything. 

Here’s my test blob of paint. It’s cerulean blue and acrylic.

It’s very thick, though, I will say, not hard to work with.

Here’s a drop (give or take) of extender.

Even on Mickey, it’s hard to see, so I circled it. The point is it’s clear, so it won’t mess up your paint job. It’s also thicker than I imagined. Kind of like lotion.

2. Mix the Extender and Paint

To see how acrylic paint extender changes things, the first thing I did was paint the wood with plain old acrylic paint. I painted on both the finished side and unfinished side of the wood.

As you can see, the unfinished side sucked up the paint and has a much different finish than the paint on the “primed” side.

Always prime your wood, I say!

Then, I mixed the small amount of extender into the leftover blob of paint. I did this because, in my estimation, the amounts were about one-to-one.

Next, I dipped the foam brush into the acrylic paint extender, then mixed that into the paint.

I ended up with next to nothing in terms of usable paint. So, using method two (add extender directly to paint), I made a bigger blob of paint, then poured some extender on it.

As you can see, it’s not a one-to-one ratio, but I figured that was fine.

Then I mixed it with the brush and got this:

It’s thinner and shinier than the plain acrylic paint. Here’s a side by side

Actually, in that picture, they have the same level of shine, but I think that’s bad lighting. The acrylic paint plus extender really is shinier.

3. Paint Your Project

Then it was a simple matter of painting the wood

and letting it dry.

But, because I’m curious, I decided to do one more experiment

That’s a lot less extender to a lot more paint. I wanted to see how it might affect finish and dry times.

Here’s what it looks like mixed up.

What struck me about this is that I could make the paint stand up in peaks, like whipped-up egg whites. That’s a cool feature of acrylics, but the more extender I added, the less I could do this. So, if you’re trying to do a textured thing with acrylics, I wouldn’t add too much extender.

I added that paint sample to the test wood.

4. Dry Time

What’s interesting about the above photo is that the edges of the plain acrylic were already dry to the touch by the time I finished with the other two paint experiments.

Here’s a close-up

It’s shiny in the middle, but not on the ends, and trust me when I say, it’s dry there. Not cured, but dry. Unfortunately, I wasn’t timing this, but it couldn’t have been more than 10 or so minutes.

I did, fortunately, time the rest of this project out.

At about seven minutes, 30 seconds, the plain acrylic was dry to the touch, as in, all the way through.

The middle strip took a bit longer, about 20 minutes, and the end one, about 30 minutes. There’s one spot on the edge of the sample with the most extender. That took even longer, but, as you can see, that’s a very thick coat of paint. Of course, it will take longer to dry.

Here’s what it looks like on the unfinished edge.

Dry times were about the same, but as you can see, the ultimate finish is very, well, unfinished. 

The End Result

Here’s what everything looked like the next day.

Honestly, they all look about the same to me.

So, it would seem that using extender doesn’t affect the final product, just how you get there!

And that’s how to use acrylic paint extender!

I’d argue it’s like baking a family recipe. It isn’t written down anywhere. You just follow these vague directions and mix it up until it’s right.

My advice to you is mix it up until you get the desired result. Start small and work your way up! And I also suggest using method two — paint and extender plopped together — as your mixing method. I found the brush-into-extender-then-into-paint-method a little ineffective and inefficient. Your results may vary.

Like I said at the top, my goal with this blog was to help fill in knowledge gaps. So, if you want to see something, let me know! I’m happy to research, experiment, learn, and report back!

Any thoughts on using acrylic paint extender? Any advice for newbies? Let me know in the comments!

Image Credit: Canva