Why does Caulk Crack when Painted?

It can be frustrating when you’ve just spent a lot of time caulking a bathtub, floor tiles, moldings, and more just to have it crack. After all that work you are left with the option of having to remove it again and reapply or live with having unsightly cracks in the caulking.

So why does caulk crack when painted? The answer is not anything singular. There are multiple causes, such as caulk that are not meant to be painted in the first place, the temperature is too cold, you’re applying it wrong, and a few more.

The answer sounds like it’s complicated and may even make you think that you should hire a contractor. But in reality, it’s just a few simple tips and tricks to go over before you start a project. Even though we may not think of temperature as an issue, it makes a lot of sense when we think about the basic concept of contracting and expanding with cold and hot environments. So let’s get into it and figure out when exactly it starts to go wrong.

The Caulk

Assuming all caulks are the same would be a mistake. The first thing you want to distinguish is if the caulk is paintable or non-paintable. The label will always say whether you can or can not, in fact, paint the caulking. Typically, most companies make either latex or a silicone caulk or sometimes a combination of both.  

Latex

This type of caulk can be painted. The “painters caulk” is another nickname for acrylic latex caulk because it’s typically the go-to for the paint job. Inexpensive and fast-drying, which makes it easy to paint quickly after. We will get into why this is also an important feature in preventing the caulk from cracking when painted.

Pure Silicone

Silicone is one of the more expensive caulks, but it is worth the money if you’re looking for long-lasting results. It’s flexible and meant for jobs that are outdoors because of its mildew-resistant qualities. This is the ideal silicone to use outdoors. If you buy a silicone caulk that does say it can be painted, then it is definitely not 100 percent silicone, or the manufacturer is being misleading.

Specialty

There are other caulking types that are considered to be a specialty. Refer to the label and check out the materials used to see if it’s paintable or not. Usually, they are made out of a combination of silicone and latex with a few other things in them to suit the project’s needs.

The Paint

Even though you may have a paintable caulk, that doesn’t mean it’s not going to crack still. Paints nowadays don’t have the same chemical makeup, and one of the things they have lost over time is the ease of shrinking and expanding. The paint in a dry finish is a lot stiffer and cracks and breakdown due to the surface underneath expanding and shrinking due to temperature.

Acrylic paint, in general, is a good direction to go because, just like the acrylic latex caulk, this paint has more flexibility and is a versatile medium. Perfect for outdoor projects because it is typically water-resistant.

Temperature

One of the biggest culprits of why your paint (or even caulk) will crack is because of your environment. Avoiding extremes on either end makes a big difference, but it may not be something we think about when starting a project. Anything below 40 degrees won’t work because as soon as it gets hot, the expansion threshold for your caulk or paint simply won’t hold.

The same goes for the opposite. If you’re caulking in the summer on a 90-degree day, then chances are it’s going to shrink an extreme amount, and you’ll end up having to do the project again because it just simply won’t work.

Mild temperatures are good for doing these sorts of projects. Some people recommend between 40 and 80 degrees, but even then, that is a large range. The closer to the middle number, you can get the better.

How you Paint

How you do the project also has a big impact on whether your paint is going to crack or not after all is said and done. If you paint the caulk well before it’s fully dried, then you’re going to run into the same shrinking issue that you would with temperature problems. The paint is likely to dry well before the caulk, so rushing to paint the caulk when it hasn’t completely set isn’t a good idea. The labels on the product will tell you how long roughly it will take to dry.

Also, the smoothness in which you set the caulk makes it easier to paint the caulk itself. It might go without saying, but a bumpy caulk job will make painting much more difficult and lead to cracks in the creases or edges that weren’t smoothed out.

This can be solved by forgoing the tube caulk form and opting for the cartridge. A caulking gun will help you do the job in a continuous smooth fashion, whereas a tube is more difficult to squeeze out on your own at a steady pace.

What if you have the Pure Silicone?

If you have pure silicone, that’s OK, a lot of people like the product. The good thing about this is that nowadays caulk comes in a wide variety of colors, so there is a good chance that the color you are trying to match also comes in a caulking color.

Most of the time, caulking projects are natural colors, especially with outdoor ones. But if for some reason you find yourself not being able to match the exact color, that might be OK. Often times, grout and caulk may be a slightly different color to enhance the eye appeal to the project. If you’re caulking a window on the outside of your house and the color is a slight white-beige, but your windows are a fraction lighter, it’s unlikely anyone will notice this from a few feet away.

Does Cost Play a Role?

A general rule of thumb is to always buy the brands that get the best reviews and are widely used by contractors, painters, etc. Places like Lowe’s, Home Depot, or other home improvement stores will usually sell an array of quality products. However, that doesn’t mean that every caulk is right for your project. Research is always a good idea.

When it comes to pricing, some are more expensive than others. As with any good product, the cheapest ones are sometimes not the best quality, and it’s worth spending the extra penny or two to get more bang out of your buck. This goes for the paint you select as well.

Also, be sure to read the fine print. If you are buying a pure silicone product and the label says it can be painted, check to see if it is mixed with something else. If it’s not, chances are it cannot be painted, at least not without cracking at some point in the future. In that case, you’ll be better off buying a colored caulk that matches the paint color you intend to use.