In spite of the concrete finisher’s best efforts, sometimes the finished product has significant imperfections. Even a carpet laid on a pad or vinyl flooring cannot be expected to cover up every flaw, so repairing a slab is the builder or homeowner’s best choice for correcting the problem. Before patching, make sure your concrete is structurally sound. Much like medicine, it is better to treat the cause than just address a symptom. Sometimes surface defects are a clue that there is a bigger problem at hand. Hav a professional assess whether patching is the right solution.
The illustrations in this article show a repair where a slab reinforcing bar as too near the surface, and the concrete cracked. Other possible problems may include the following.
This may include bumps, depressions, or ridges. Small areas of shallow surface irregularities may be concealed with a floor leveling compound, rather than chipping out and replacing the actual concrete.
For small jobs, a chipping hammer will be all you need, but larger repairs are much easier with an electric chipping hammer or even a jackhammer. Professionals also use grinding machines to prep the surface f
This will allow the new material to have a solid surface to adhere to. A wire brush is a good choice for this step. A stiff bristled broom or paintbrush will also work. Depending on the age and condition of the concrete chemical cleaning may be required, it is best to consult a pro.
Mix the dry ingredients first, using a proportion of 1 part Portland Cement (type I or II) to 2 1/2 parts clean masonry sand.
using enough to thoroughly wet the material and bring it to a stiff, plastic consistency. Note that some bonding agents are applied directly to the area to be patched, like glue, so follow the instructions on the manufacturer’s label.
Do not flood the area, but make sure all surfaces are dampened, to assist in adhering the new cement mixture, as well as keeping the mixture from drying too quickly. Dry surfaces simply draw the moisture from the cement mixture too quickly and will cause it to shrink, and ultimately, to crack.
Place the mixture into, or on the patch location, and work it into space forcefully with the trowel to force out any air bubbles.
Allow it to dry and become stiff for an hour or so, depending on humidity and temperature.
This will flatten and smooth the surface, and cause cement paste to rise to the surface. Very large, deep areas may be floated with a magnesium float to bring more cement paste-up. This paste is the material that forms the surface of the finished slab
At this point, you may need to splash a little water on the surface to slow the drying, as well as making the finishing process somewhat easier. Use the edge of your trowel to shave, or scrape off any of your cement mixture which has spread to the adjacent, finished surface. Another good choice for patching materials is hydraulic cement. They usually set up in less than 30 min.
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