Concrete structures tend to form cracks over time, but the important thing is that these cracks are not visible or affect the overall performance of the structure. To repair a thin crack in concrete yourself, you will need a concrete crack filler. Unfortunately, this problem cannot be solved with more concrete. Concrete crack fillers are known as masonry crack fillers and come in a wide variety of options. You have to cut a fine crack if you really want to repair it.
Crack injection requires pumps, ports, slow epoxy and a lot of time. You can try to repair cracks below the waterline with epoxy, but remember that it often doesn't work. In that case, substitution is the only option. Crack repair materials for concrete are usually polymer-modified cement grouts, silicone or latex caulking or epoxies. Polymer-modified cement grout is the typical material used to fill pits and voids in concrete during manufacturing.
If cracks occur before the concrete is sealed, this is usually the material used to repair them. Repairing a fine crack in a concrete structure involves filling the gap with a material that adheres well to the concrete, restores its original appearance, and prevents liquids from penetrating inside the structure and staining the concrete. The main cause behind the generation of fine cracks in concrete is plastic shrinkage, which is the rapid depletion of moisture from fresh concrete into its plastic state. To repair fine cracks in concrete with a grout made of Portland cement and water, add enough water to the cement to form a thick paste. Moisten the old concrete along the fine crack with water for several hours before adding the grout. Fine cracks in concrete can be difficult to repair.