Many of us already own a patio. We may be happy with it just the way it is. Time will take its toll on our patios. A concrete patio may develop cracks. I am going to explain to you how to fix a crack in concrete.
The crack
There are many reasons why concrete cracks. An improper installation will increase the chance of cracks developing. Many cracks are started as soon as the concrete starts to dry. These are called shrinkage cracks. They form as the large volume of water,
used in mixing the concrete, begins to evaporate and seep out. They are almost certain to appear at 90 degree, inside corners, protruding into the concrete if action such as placement of a control joint was not taken in construction.
Another type of crack is from settlement. During construction, the earth was most likely excavated below your concrete to make way for the concrete and its needed pitch. When this area is not properly compacted it will eventually settle, leaving a gap between the bottom of the concrete and the base below. The concrete, left unsupported, may settle into this void and crack.
One more type of crack appears from freeze-thaw cycles in cold climates. The earth or base below the concrete expands and pushes up against the concrete when it freezes in the Winter. When temperatures rise in the Spring and the earth begins to thaw it recedes away from the concrete. This up and down motion over time can cause the concrete to crack.
So, these are a few of the reasons that concrete cracks. Because our concrete is constantly being acted upon by outside forces, these cracks may be in need of being repaired repeatedly over time. Therefore, it is to your benefit to be able to make these repairs yourself.
Preparation
Preparation is the key in how to fix a crack in concrete. The first thing you must do is to clean out any debris, such as leaves, dirt, etc. This can be accomplished with a broom, brush, leaf blower etc. After this use a good quality wire brush to clean a few inches away from 
each side of the crack. Also, make sure to clean down into the crack along each vertical face, if possible, with a wire brush.
Wash the whole area well with a stiff bristled brush and clean water then rinse. Allow the area to dry some before proceeding with the repair.
The repair
There are many concrete crack repair materials you can purchase from local hardware and big box stores. I like to use my own mix as it allows me the option of using different sand / cement ratios for different needs.
Concrete is made with portland cement, so this is my main repair ingredient. The basic mix consists of :
- 1 part Portland Cement
- 2 part Mason Sand
- Acrylic Admix
Mix the dry ingredients together well first then, add water and some acrylic admix slowly until you have a mix that is not to runny, about like peanut butter. The amount of admix you use is usually determined by how much water you use and may be found on the container’s side panel. If you are mixing about a 5 Gallon bucket of material, which is a lot for most crack repairs, you would probably need about 8 fl. oz. of admix.
Before you start placing your material into the crack, pour some acrylic admix into a cup, and using a paint brush, brush it on to the sides of the inside vertical faces of the crack. Allow this application to dry a little, you do not want any puddling of the admix. Now press your repair mix into the crack using pointer and margin trowels or jointer trowels for small cracks.
Smooth the repair material even with the top of the concrete surface. Allow this to dry slightly. While it still is plastic, you should be able to make a slight impression with your thumb, take a masons brush or a rubber float and texture the surface to blend it with the surrounding surface.
What to expect
Generally repairs like this will be quite lighter than the surrounding area once fully cured. If you would like to darken your repair mix, a dry cement coloring can be added to the dry ingredients before adding water. Mix well and use sparingly. One tablespoon of a black color will darken a 5 gallon pail mix substantially.
The concrete you have repaired has already had some kind of stress force applied to form this crack. This force is possibly still going to cause further movement. The repair will not hold the concrete together, it just fills the gap to prevent more rapid deterioration of the concrete surface. In time, you may need to make further repairs.
If you have mastered this technique you will be equipped to handle any future repairs that must be made and add many useful years to your concrete.
Use your new found knowledge
Even if you do not wish to tackle these repairs yourself, you can use this knowledge to aid in determining what type of repairs your concrete needs. If there is a crack coming off a protruding inside corner, you may need to have a control joint cut, in addition to the repair.
Ask your contractor what is his or hers process in repairing a crack. Compare their method to my process and decide for yourself if their repair process is the way to go.
It is not a difficult job and you are probably not going to make anything worse by attempting to make the repair by yourself. Go ahead and give it a try. You may be pleasantly surprised.
