Photo: Marian Fil (Shutterstock)
Concrete is amazing. All you have to do is look at ancient Roman ruins to realize how durable, flexible, and strong concrete can be as a building material. This can lead to the occasional moment of mental dissonance, however, when your outdoor steps are crumbling into dust while the 2,000-year-old Pantheon in Rome still looks pretty solid. And this gets worse when you gamely try to repair the cracking, crumbling concrete and it lasts a hot minute before falling apart.
If your experience repairing concrete around your home always ends with the repair basically breaking off, you’re almost certainly missing the one key ingredient that no one ever tells you about: cement paint.
Why your concrete repairs have been doomed to failure
Concrete is strong and durable, but it doesn’t stick well to things, and it definitely does not stick to itself. Your concrete repairs, whether you’re using a pre-mixed patching material or you’re mixing up your own Portland Cement blend, always fail because you’re just slapping concrete on top of concrete, which is just stacking pieces of concrete on top of each other. There’s no “grab” between the layers, so the repair will pop off pretty easily. It might last a little while depending on the conditions, but it is guaranteed to fail sooner rather than later.
What is cement paint?
In order to make your concrete repairs last, you need to provide some kind of bond between the two layers of concrete. There are a few different ways to accomplish this, but they all basically work the same: You “paint” a coating of bonding agent onto the portion of concrete in need of repair, then apply your fresh concrete to fill the cracks and voids. Creating a “cement paint” to act as a bonding agent between layers of concrete can be done in a few different ways:
A pre-mixed product. The easiest thing to do for most small repair jobs is to purchase a bonding adhesive from a store. This can be painted directly onto the repair with a brush or roller, and the concrete applied on top of it. You can also purchase acrylic concrete products that you combine with the mix directly, making it stiffer and giving it more adhesion. A concrete slurry. Concrete slurry is just a very thin, soupy mix of Portland cement (or the concrete mix you’re using for the repair) and water. You don’t have to be too careful with your measurements; you just want the mixture to have the consistency of thick soup. Dampen the broken area with a little water and paint your slurry onto the repair area, working it into all the crevices and cracks so it can grab onto your fresh concrete effectively. A combination. When mixing up a concrete slurry, you can substitute bonding adhesive for water. You still want the same soupy consistency, but adding the bonding adhesive can make the slurry extra grabby and really encourage a bond between the original concrete and the fresh repair material.One thing to keep in mind is that whenever you’re bonding concrete, you need to prepare the area properly first. This always involves cleaning the area so it’s free of debris and dirt, and if the area has soaked up oil or paint or another material that concrete will never bond to, you’ll need to physically chip away affected areas. If you’re using a pre-mixed bonding agent of some sort, read the instructions—you might have to roughen the surface or dampen it with water before applying it.
Unless you just really enjoy mixing up concrete and slapping it onto things, you want your repair work to last. If you take the time to prep the area and use a cement paint of some kind, fixing broken or crumbling concrete will be a lot more effective and long-lasting.
