Repair a Concrete Floor

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.

Steps

 * 1)  Determine the scope of the problem.  The illustrations in this article show a repair where a slab reinforcing bar was too near the surface, and the concrete cracked.  Other possible problems may include the following.
 * 2) *Ridges or humps left by the finishers.
 * 3) *Expansion or contraction cracks.
 * 4) *Debris like chunks of wood floating out of the concrete while it is still plastic (wet).
 * 5) *Damaged caused by heavy objects being dropped on the slab before it is cured.
 * 6)  Use a ruler to determine the length and width of the area to be repaired if the condition does not define itself.  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.
 * 7)  [[Image:Concrete_repair_15_307.jpg|thumb|Chipping with an electric chipping hammer]]Chip the surface of the concrete to remove any high material, and to create a rough surface for the repair cement mixture to bond to.  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 jack hammer.
 * 8)  [[Image:Concrete_repair_16_12.jpg|thumb|Sweeping the dust from the area to be repaired]]Clean the dust and debris from the area you have chipped.  This will allow the new material to have a solid surface to adhere to.
 * 9)  [[Image:Concrete_repair1_37.jpg|thumb|Mixing the dry materials]]Mix the cement/sand material you will use to fill in the area you have chipped out.  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.
 * 10)  [[Image:Concreterepair3_847.jpg|thumb|added bonding admixture]]Add a latex or polymerized liquid bonding agent to the dry sand/cement mixture, 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.
 * 11)  [[Image:Christmas_in_New_Orleans_07_109_120.jpg|thumb|wet the surface with a sisal brush]]Wet the area where the patch is to be applied with clean, fresh water.  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.
 * 12)  [[Image:Concrete_repair_6_244.jpg|thumb|placing the cement mixture into the repair]]Scoop some of your cement mixture out of your mixing container with a bull-nosed pointing trowel (or other suitable tool).  Place the mixture into, or on the patch location, and work it into the space forcefully with the trowel to force out any air bubbles.
 * 13)  [[Image:Concrete_repair_7_55.jpg|thumb|Smooth the cement mixture into the hole.]]Level the surface of the wet cement with the trowel, leaving it slightly higher than the adjacent edges, to allow for settling and shrinkage.  Allow it to dry and become stiff for an hour or so, depending on humidity and temperature.
 * 14)  [[Image:Concrete_repair_9_22.jpg|thumb|Trowelling the concrete with steel finishing trowel]]Trowel the area with a steel finishing trowel when the patch material has become stiff.  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.
 * 15)  [[Image:Concrete_repair_12_617.jpg|thumb|Bear down hard on the trowel when the concrete has set.]]Give the area another hour or two so that it sets up, or becomes hard, then finish trowelling it.  At this point, you may need to splash a little water on the surface to retard 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.
 * 16)  Clean your tools, and remove any excess material.

Tips

 * Mix enough cement and sand to finish the entire patch at one time.
 * For very small patches, you may purchase polymer fortified or premixed dry patching material.
 * For high spots in a concrete floor that will receive a floor covering, you may be able to remedy the problem using a grinder equipped with a masonry grinding wheel.
 * Once the repair is done, keep it wet for a few days if possible. Use lots of water.
 * Protect the repair from direct sunlight. A cardboard box will work.
 * Cement with high lime content is more flexible and may be more appropriate for the repair.

Warnings

 * Wear eye protection, a dust mask, and gloves when chipping, grinding, or placing concrete.

Things You'll Need

 * Portland cement
 * Clean masonry sand
 * Bonding agent
 * Clean water
 * Concrete tools

Related Tips and Steps

 * How to Build Forms for a Curving Concrete Sidewalk
 * How to Make Concrete
 * How to Finish Concrete