Why would you ever want to bother painting a mural with concrete, you ask? Why not just use normal paint? Well, there are several benefits to using concrete as paint instead of, ya know, the boring kind.
First, it is a lot cheaper to use concrete than acrylic paint by volume. Second, you can make your desired color and shade very easily by mixing the pigments yourself. Third, it has a very interesting texture that no normal paint can achieve. And last but not least, it's coooool!
My team and I were asked to paint a mural in our concrete research lab, and so it was only fitting that we should make it out of concrete. So, this instructable will teach you how to paint with concrete.
Before I jump into the tutorial, I want to note that the actual technical term for your "paint" may be either concrete or mortar, depending on whether or not you add aggregate into your mix. But for simplicity's sake, I'm just going to call it concrete throughout this instructable.
Anyway, let's get started!
Step 1: Materials and Tools
Here's a list of all the things you will need. Make sure you read through this whole instructable before you jump into gathering all of your materials, because there are several different ways to do certain steps. So, not all of these materials might be necessary depending on which methods you choose.
Concrete Materials (I've included links for buying the materials)
Newspaper/any large scrap sheets of paper/plastic (this will be used to protect the wall from dripping concrete)
Sandpaper (I used 60 and 120 grit sandpaper)
Transfer tape for vinyl
X-acto knife (or box cutter, etc... any small maneuverable blade will do)
Spatula or spoon for mixing the concrete
Containers for holding your concrete (one for each color)
Step 2: Plan Your Design
Sketch your idea by hand on paper or with a graphics editor such as Adobe Illustrator or Photoshop. We will use this to make a stencil for applying the concrete.
We will paint our design onto our wall using a stencil. There are two ways to make your stencil: by cutting it out yourself with masking tape and an X-acto knife, or by cutting it out of vinyl with a vinyl cutter. I'll discuss this process in further detail in Step 4.
I made two murals, using both the masking tape method and the vinyl cutting method. One mural is an illustration of four bears holding a canoe, and the other mural depicts a row of three bears surrounded by the word "concrete" in multiple languages.
If you're going to cut out your stencil by hand, then using software is just optional. But if you're going to cut your design out of vinyl using a vinyl cutter like I did, you're definitely going to need a vector graphics editing program. I used Adobe Illustrator to plan my design. Make sure to set up the digital vector file correctly according to your vinyl cutter's instructions.
My mural was way too large to cut out the whole design in one go on the laser cutter. So, since my vinyl cutter cuts a maximum width of 22 inches, and my mural design spans 4 ft x 9 ft, I had to divide my design into slices and cut each slice individually. In Adobe Illustrator, I did that by drawing lines over my design and using Pathfinder's divide function to split it into slices. Then I copied and pasted each slice into a new Illustrator file. I won't go into detail since this is a concrete tutorial, not an Illustrator tutorial, but here's a link if you wanna learn more.
Step 3: Sand the Wall
The wall, or your chosen surface, needs to be rough in order for the concrete to stick properly. If it's completely smooth, it'll just slide off and give you a lot of trouble when you're applying it. So, we'll have to sand it.
Sand the wall using the 60 grit sandpaper until the wall feels textured and a little bit rough. The time it will take to sand a given area depends on how hard or soft your surface is. Mine was a painted white wall, so it took about 4 minutes per square foot to sand to an adequate texture, but use your best judgment. The more textured the wall is, the easier it will be to apply the concrete.
If the surface is painted, you might have to be a bit more careful with sanding so that you don't end up with ugly, blotchy spots of exposed wall in the areas that won't be painted with concrete. In my case, the surface was white drywall painted with white, so it didn't matter if I sanded too much.
Step 4: Make and Apply the Design
There are two ways you can make your concrete stencil. Both have their advantages and disadvantages.
The first way is to use masking tape or another adhesive material to cut your stencil by hand. If you're just making geometric shapes and lines, like the three bears in my design, masking tape is an easy option. Simply apply the tape to the surface, and then use the X-acto knife (or other blade of your choice) to make extra cuts if you'd like. Depending on the size of the design and the level of detail you want to achieve, using the X-acto knife to manually cut your design can require a lot of time and dexterity.
As you can see on in Photo 1, I used an X-acto knife to round the corners of the geometric triangles made out of masking tape. If you have access to a projector, you can also project your design on the wall as a guide when applying the stencil.
The second way is to use a vinyl cutter and let it do the cutting work for you. If you have access to a vinyl cutter, this is option is a lot less tedious and time-consuming than the masking tape method if you want a lot of detail in your design (especially when it comes to lettering!). I used a Roland CAMM-1 GX-24 vinyl cutter to cut out the vector file I designed in Adobe Illustrator. As I mentioned previously, I had to divide my design into smaller slices in order to be able to cut out the whole thing on the vinyl cutter.
Once you've cut the vinyl, use tweezers or your fingernails to "weed" or remove the pieces of vinyl where you plan to apply concrete. Then carefully cover the cut vinyl with transfer tape, making sure to remove air bubbles for a smooth finish. Finally, you're ready to apply your stencil onto the wall! Flip your design over and slowly remove the backing paper from the vinyl design, revealing the sticky side of the vinyl. I recommend starting from the corner and pulling it off diagonally, until the only thing holding the vinyl design is the transfer tape. Sometimes pieces of the vinyl might want to stick to the backing paper instead of the transfer tape, so peel the backing paper off slowly and carefully so that you can reposition the vinyl if needed. This will inevitably happen if you have a lot of detail and tiny cut-outs in your design, so have patience! Once you're done, you can stick the vinyl to the wall, the peel off the transfer tape in the same way you peeled off the vinyl backing paper.
**** Remember that we are making a stencil, so we want to cut out only the inversion of the final design! Only cut out the areas where you plan to apply concrete, and leave vinyl/masking tape where you want the wall to be exposed. ****
Once you're done applying the stencil, just to play it safe, I recommend placing additional pieces of masking tape around the borders of your design and spots of exposed wall where you don't want any concrete. Applying concrete paint can get messy and sometimes you might accidentally smear or drip concrete where you don't want it to go. This makes the clean up a lot easier! I also recommend taping large sheets of newspaper, plastic, or anything you have on hand directly underneath your mural design to protectively cover the wall from drippings.
Step 5: Mix the Concrete
Here is the rough recipe for concrete paint:
White cement ~ 500 g // 1lb
Liquid latex ~ 250 g // 0.5 lb
Water ~ 250 g // 0.5 lb
Concrete pigment ~ 30 g // 0.06 lb or more (unless you're using blue pigment... in my experience, blue is always *super* vibrant and so you probably only need a few pinches)
Sand or fine aggregate (optional)
Mix the white cement, latex, and water together first, and then add the color pigment last. When you're adding the pigment, start small and keep mixing and gradually adding more pigment powder until you get your desired color. You can't really go back if you've added too much pigment, unless you make more concrete paste, so better safe than sorry. Add more concrete pigment (or even black pigment) if you want a darker or a more vibrant color. After you reach the desired color you want, if you think it is too thin, add some more cement; if it is too thick, add some more water. Just eyeball it and follow your maker instinct. Basically you want a paste with a milkshake-like consistency that's thin enough to easily paint on the surface of your wall. If you've mixed your concrete and you're still unsure about the texture/consistency, you'll be able to tell easily once you try to put it on the wall later. As long as the concrete sticks on to the wall and dries well, and the color looks fine, you're good to go.
There are two things you should keep in mind when mixing color pigment into the mix:
First, the color of the concrete in your bowl will look different from the color of the concrete when it's painted on the wall. Be sure to test it on a scrap surface to check before you start painting.
Second, the concrete, water, and latex mixture might look a little bit blue-ish before you even mix the color pigment in. That is because of the color of the latex, which sometimes has a subtle purple-blue tint depending on the brand of latex you use. The tint will go away once the mortar is applied to the wall and dried, so don't worry.
You can also add some sand or fine aggregate into the mix to lower the cost even further. But the mortar paint is already cheap enough. In the picture, we used waste unknown cementitious material that was left in our lab as an ingredient in our concrete paint. You can see tiny black dots in our mix: that is the waste sand.
In our concrete lab, we have a mixer for mixing concrete and we use a stainless steel bowl to mix our paint. To be honest, it is really tedious to clean all of our concrete-covered bowls, spatulas and tools every time we mix concrete. We washed everything in a huge barrel and then neutralized the concrete-water inside of the barrel once it was full and dumped it. If you aren't mixing concrete that often, then it's a lot easier to just use a disposable container to mix your paint.
Caution: DO NOT DUMP YOUR MORTAR INTO THE SINK
Do not dump your concrete into the sink because cement paste has a high pH. So, it is harmful to the environment and also your sink will CLOG!
Step 6: Apply the Concrete to the Stencil
Put on your disposable gloves and wear clothes you don't mind getting dirty. You'll need several pairs of gloves on hand if you plan on using multiple colors of concrete.
To apply the paint, dip two or three fingers into your bowl of concrete paint and smear the glob onto the wall, carefully staying within the boundaries of your stencil. Then use your fingers to drag and spread the paint around the stenciled area until it's evenly covered in a thin layer of concrete. You want to make the layer of concrete thick enough so that the color is opaque and the wall underneath does not show through, but you want it to be thin enough so that the stencil can still be peeled off easily. If the concrete is too thick, it will be difficult to peel the stencil off once the concrete has dried.
To get a nicely opaque layer of concrete, you might have to apply more than one layer. One or two layers is ideal, and any more than that might be too thick.
Finding the right technique that works for you will take a bit of practice. What works best for me is to apply a layer of concrete that is a little bit too thick, and then let it sit for a little bit. I wait until the concrete has dried so that it no longer has a fluid consistency and doesn't easily wipe off if I rub it. Then, I use two fingers and rub it gently until I'm satisfied with the thickness. Doing this will also make the concrete a bit smoother, since I am also rubbing away some of the aggregate. If the concrete is dry enough and the wall is sanded enough, then outermost film of concrete should easily rub away, revealing a thin film of concrete closest to the wall surface.
If the wall wasn't sanded enough, it will be slippery and difficult to apply an even, opaque layer of concrete onto the wall. Ideally, the concrete paint needs a rough surface to adhere nicely. If you find yourself having a lot of trouble getting the concrete to stick to the wall, just sand the surface until it's rough enough.
Step 7: Sand the Concrete
Once the concrete is completely dry, you can sand the concrete for a smoother finish. I chose to sand the concrete before peeling the stencil off, so that I don't dirty the surrounding wall with colored concrete dust.
Keep in mind that sanding will dull the color of the concrete a little bit. Applying sealer will make the colors pop vibrantly again, which I will discuss in more detail later in this instructable.
I didn't mind a slightly rough finish for my concrete, so I didn't spend very much time sanding. I started with 60 grit to roughly remove the large chunks sticking out of the thin layer of concrete, and then stepped up to 120 grit to even it out a bit more.
Be careful when sanding the areas where the concrete is chunky, so that you don't accidentally break off a whole piece of concrete and expose the wall underneath.
Step 8: Remove the Stencil
Now for the fun part: removing the stencil! There's something oddly satisfying about peeling off the messy, concrete-caked tape/vinyl, revealing the crisp and clean lines of your artwork. If the concrete is too thick, the stencil might be hard to pull off smoothly, so you might have to pick and jab at it with your fingers or a tool and remove it in smaller pieces. A thick layer of concrete might also hide the boundaries of your stencil altogether, making it difficult to see where you're supposed to peel the stencil off. To work around this, you can refer back to your hand-drawn sketch or digital design file to see where you're supposed to peel.
Step 9: Apply Sealer
If your concrete is dusty, brush it off and make sure it's clean before you apply sealer. Then, you can paint one coat of sealer on top of your layer of concrete. I used a thin paintbrush for navigating narrow areas of concrete and a large foam brush to efficiently cover larger surface areas.
The color of the pigment will bleed a little bit when you apply sealer, so you should wash your paintbrush when switching between different colors. If you make a mistake and accidentally paint sealer outside the boundaries of your concrete, wipe it off with a damp paper towel. It cleans off easily when it's still wet, but it's difficult to remove once the sealer dries, so act quickly.
Huzzah! You're done!