Imagine how disappointed or irritated you will feel when you have created artwork, only to see it has cracked the next day. So you might wonder why acrylic paint cracks?
Acrylic paint cracks when the top paint layer dries faster than the layers below causing uneven paint drying. It is influenced by thick paint layers, high airflow, cold temperatures, low-quality paint, and the movement of the painting and not preparing the painting surface.
Even the highest quality acrylic paint has some potential to crack if other factors are not controlled. Therefore understanding why acrylic paint cracks, and how to prevent and fix them is important.
What is acrylic paint cracking and crazing?
Crackings are breaks that run deep in the paint with sharp edges. Cracking can break paint into pieces and these pieces are called ‘platelets’. Although acrylic paint is very flexible and can withstand stretching than other paints it can be cracked at some point after handling so much stress.
The stress of paint film occurs when the paint dries at different rates. The top paint layer may dry faster than the below layers. The moving below layers may cause stress to the top layers, causing cracks. Cracking can occur by flexing the paint film at cold temperatures. Also when there are more solids in paint it tends to crack. Each of these factors and more will be discussed in this article.
Crazing is different than cracking. It is like a tear in the top paint layer but can run down deep into other paint layers as well. Craze happens when acrylic paint on top forms a skin while the paint underneath is still wet. Where the craze happens the water and other volatiles in the paint film are released.
“Crazing is usually caused by over-extending thicker acrylic products with water and then applying thickly or in puddles. It also happens due to uneven drying of the paint and creates crazes that look crack-like but are different,” said Scott Bennett from the technical support team of Golden Paints.
Adding water to acrylic paints and pouring tend to create crazes and surface defects. The surface paint layer can repair itself in case of crazing. But the scare of the original tear may be visible on the paint film. Crazing does not harm the long-term stability of the painting. Also, it does not disturb the film formation ability of paint.
Where do cracking and crazing occur?
Cracking and crazing occur in both acrylic brush paintings and pour paintings. They can occur in any acrylic paint film that might have an overload of solids, be over-thinned, or be force dried too quickly. Crazing is typically more common in liquid acrylic products or mixtures as opposed to thicker products.
I have written an article series about common acrylic paint questions and answers: part 1 and part 2. You can find answers to questions like this in the articles even before you face them.
Why acrylic paint cracks when drying?
Cracking and crazing occur as a result of reducing the stress of the paint film. This stress builds up during the drying process. There are several reasons why acrylic paint cracks. I have described each of them below in detail.
1. Stretching the paint film in cold climates
“One of the main reasons for acrylic paint cracking is sudden flexing when cold, as the acrylic gets harder and less flexible when cold”, said Scott Bennett from Golden Paints.
“Most acrylic paints crack when they are exposed to temperatures around 50 degrees Fahrenheit or lower as they dry,” said Patrick, a product specialist for Blick Art Materials. This is because the minimum film-forming temperature (MFFT) of acrylic paint or medium is around 50° F (10°C).
Also, acrylic paint is a thermoplastic material meaning it becomes plastic upon heating but becomes stiff or hardened upon cooling. Therefore cracks can happen when a painting is rolled in a cold environment or climate. Because the paint film cannot stand stretching in low temperatures. Therefore it breaks out of shear stress.
2. Cheap paints have more fillers and less flexibility
“Adding other materials not meant to be used with artist-grade acrylics or adding additional solids or powders can contribute to cracking as the paint dries,” said Scott Bennett from Golden Paints.
This is one of the major reasons why acrylic paint cracks in most cases. Many go for cheap paint choices when doing the acrylic painting or pouring without any guarantee of longevity. These paint films cannot hold much stress compared to good-quality paints.
Cheap or low-quality paint manufacturers like to extend their products by adding fillers. Fillers are materials like calcium carbonate or marble dust which can be stained with paint pigments. These solid fillers do not contribute to film formation. Thus low quality cheap paints are less flexible during stress.
Less flexibility of the paint film eventually contributes to cracking. The flexibility of acrylic paint is given by the acrylic polymer binder. It acts as the glue that holds everything together in a paint film.
How crackle pastes work
Crackle pastes have a less binding ability. Meaning it has less binder and more fillers or solids. Therefore it cracks when drying on the surface and produces a cracking pattern as intended by the artists. However, the binder to filler ratio needs to be maintained just enough to create the pattern but stable enough to use in a painting.
The patterns created by crackle paints need to be sealed after finishing. Also, they should be done on a well-prepared surface. These ensure the stability of the artwork. This is a scenario where cracking is turned into an advantage for the artist.
I have written a whole article about the 17 pros and cons of acrylic paint. You can find all the important aspects of acrylic paint there.
3. Applying acrylic medium or paint too thickly
The thick application of acrylic paint or medium that can move or flow causes cracks. Especially when using low-quality products on canvas thickly during acrylic pour art. When doing acrylic pour art it might be tempting to leave paint thickly on the canvas.
When the paint layer is thick it is easy for a paint film to dry unevenly. First, the top paint layer dries. Then the moist, moving bottom paint layer can cause stress to the top paint layer and crack the paint.
However, cracking or crazing does not happen with paint or mediums that do not have movement or flow when applied on the canvas. Some examples are heavy body acrylic, acrylic modeling pastes, and gels.
4. External factors that affect cracking
Changes in environmental factors can greatly affect acrylic paint film and thus cracking. If there is high humidity in the environment, the water might be pulled out from the paint quickly and dry the paint quickly making cracks.
Speedy drying is one of the main causes of cracking. Because it causes the top paint layers to dry before the bottom layers causing uneven drying and cracking. If you have a fan or AC pointing to the painting, the paint might dry faster causing cracks.
AC in the studio creates a cold environment and reduces humidity causing uneven paint film drying and reducing paint film flexibility.
5. Using house paints for acrylic pours
House paints are used by a lot of pour artists. Especially as a base coat in the color white. But it can be a hit or miss. Most complain about cracking their painting when using house paints.
If you are using house paints make sure to apply thinly and not thickly. Also, mix in a fluid medium such as Floetrol or acrylic pour medium with a little water to avoid cracking.
6. Changes in the painting surface
Sometimes acrylic paint cracks when the painting surface swells. Swelling can happen in the case of wood due to absorbing moisture. Therefore paint cracks when the wood swells. However acrylic paint is very flexible and can hold stress due to swelling of the painting surface.
But there can be a point where acrylic paint film cannot endure the stress anymore. It may result in cracking.
How do you keep acrylic paint from cracking?
Acrylic paints can be prevented from cracking by avoiding the above aspects. I have described how to keep acrylic paints from cracking in detail below.
1. Control temperature, airflow, and humidity
Paint at room temperature with less movement of air. It is best to maintain the temperature in the studio between 65-75° F (18-24°C) when painting and drying. Never paint or dry paint in temperatures below 50° F (10°C) because paint film flexibility loses in cold temperatures.
When it is cold never flex the painted surface. Because it can easily break the paint film and cause cracks.
Controlling the airflow at the studio is also important, especially when doing acrylic pour art. Turn off any fans and AC, and avoid central air ducts in the studio. Never use any heat guns, hair driers, or fans to speed up drying the acrylic pour art.
It ensures even drying throughout the paint film. You can also put a tent above the acrylic pour to minimize stresses caused by airflow. This creates a high humid environment above the acrylic pour art.
Tenting prevents crazing and other acrylic paint film defects while slowing the drying process. You can make a tent, 3 to 12 inches above the acrylic pour without touching the acrylic pour. Let it dry in the tent for 3 days.
The ideal relative humidity for painting and drying the painting is above 50%. If it is below that you can use a humidifier or diffuser for a few hours in the room before doing the acrylic pour.
When the humidity is high there is an elevated moisture level in the air. Therefore moisture will not be pulled out of the painting and speed up the drying process. It prevents cracking.
2. Avoid applying paint too thickly or thinly in puddles
Thick paints tend to crack as described before. Therefore go for the right thickness when doing acrylic pour art. When mixing pouring medium and paint, use the right proportions.
If using craft paints for the pours use a 1 :1 paint to medium ratio, if using student grade paints use a 1: 2 paint to medium ratio. If using artist-grade acrylics you can use a 1: 3-6 paint to medium ratio.
Artist-grade acrylic paint brands like Golden even use a 1:10 paint to medium ratio. It uses very little paint compared to the medium while still being opaque. When using craft paints, add only little to no water. With student grade and artist grade paints, you can add slightly more water.
Also, over-thinning thick acrylic products and then using them thickly in puddles cause crazing. Therefore over thinning is not a good idea. Follow the general mixing ratios above when doing an acrylic pour. You can also test the mixtures separately before doing the actual artwork.
3. Avoid cheap low quality acrylic paints
Low-quality paints have a tendency to crack. Especially when using low-quality white paints. There might be more solids in cheap white paints causing cracking. However, if you want artwork that lasts for long and does not crack use decent quality paint.
You can use Liquitex Basics for acrylic pours or brush painting. It is the best affordable acrylic paint. Another best brand is Amsterdam standard acrylic paints. They are also affordable. You can also use Artist’s Loft acrylic paint but not their white color. Some have experienced cracking with that paint.
Be cautious when using craft-quality paint like Apple Barrel, especially when using their white paints. Use Amsterdam standard and Liquitex Basics white paints to prevent cracking.
You can also use artists-grade acrylic paints for both brush painting and pouring. They maintain the integrity of the paints very well. You can use very little artist-grade acrylic paint and do the pour. It will save the bucks even though they are expensive.
4. Keep the painting undisturbed when drying
Acrylic pours arts need to be kept undisturbed as disturbing the paint film can cause stress and breakage. Therefore leave the pour art undisturbed at least for 3 days until it is fully cured. This time is totally worth it as it helps not to ruin the painting you have put all the effort and creativity into.
If you have done acrylic pour art, it takes several days to dry. You can even leave the painting for 1 to 3 weeks for it to fully cure without moving the paint during this time.
In this case, it is important to have several painting areas in the studio. So you can leave on painting to dry undisturbed and start working on another piece in a different area.
5. Allow drying in between paint layers
If you are applying paint in layers it is very important that you let each paint layer dry before moving to the next one. This is true in both brush painting and acrylic pour painting. Always apply paint after allowing the previous layers of paint to dry. Drying time can be a few hours or days depending on the paint thickness.
Drying in between layers helps each paint layer to dry evenly. This can minimize cracks.
6. Have a leveled painting surface or table
When doing acrylic pour art, the work table needs to be leveled. because off-level surfaces tend to move paints. It disturbs paint layers drying evenly. These will result in cracking, crazing and changing the initial pattern of acrylic pour art. It may also cause product loss from the surface.
7. Prepare the pouring or painting surface well
The surface you are doing the artwork on may change how the paint dries and may contribute to painting cracking.
Therefore if using a canvas, make sure it is primed with gesso. If not it results in uneven pours with cracks. Canvas can also sag towards the middle. Therefore use a backing board under the canvas. Otherwise, the thick puddle of paint in the middle of the canvas can crack.
If you are using a wood that is a moisture-absorbing surface make sure to prime it with gesso. Never paint directly on wood as it is most likely to cause cracking as the wood swell, warps, or bow.
You can also use acrylic mediums and paints to seal the painting surface instead of gesso. Acrylic gloss medium is one of the best choices if using mediums to seal and smooth the surface.
Allow the primer to dry well before applying acrylic paint. The smooth surface provided by primers will help paint glide over the surface easily in acrylic pours.
“One of the main reasons why acrylic paint can crack in an acrylic pour is indeed cheap quality paint. Another reason paints can crack is if the surface of the pour is not even, as well as all the additives that artists use in their mixtures, dry at different rates, causing crazes and cracks. The best advice is to use high-quality, compatible materials and take notes like scientists on the environment, application, mixtures, and surfaces.”Jennifer VonStein from Chroma Atelier
How to stop acrylic paint from cracking?
Acrylic paint cracking can be stopped by quickly identifying cracks. Then consider all the factors that contribute to cracking, and narrow it down to the factors that caused your painting to crack. Then control factors such as temperature, airflow, humidity, leveling of the surface, and tenting.
When you want to stop acrylic paint from cracking, the faster you act the better. You can refer to why acrylic paint cracks when drying section to identify all the factors contributing to cracking. Then you can control those identified factors and see if cracking stops.
If you are not able to identify what caused the cracking, you can contact your paint manufacturer. They will help you to identify what went wrong.
How to fix cracked acrylic painting?
Acrylic paint cracking can be fixed by filling the crack with a complementary color, metallic color, white or black color, and epoxy resins. After filling the cracks varnish the painting for longevity. This way cracks can be turned into a piece of artwork that adds dimension.
When filling the cracks use more paint or resin than you think will need. Because paint or resin can sink into the cracks. Mix the colors with a little water before filling the cracks.
Any artist can face the problem of cracking their painting at some point. It is frustrating to see the beautiful painting you have created is full of cracks after drying. However, you can turn the cracks on the painting as a part of the painting that adds different dimensions. It is also important that you recognize what caused cracking to control the factors or you can prevent cracking in future paintings as well.
Can you paint over cracked acrylic paint?
Painting over cracked acrylic paint does not hide or fill the cracks. Instead fill the cracks with a metallic color like gold or silver, complementary colors, or epoxy resin. This will hold the cracked paint parts together and add another dimension to the painting. Finally, seal the painting.