Although concrete is more eye appealing then other paving surfaces, it does require repair. Concrete is constantly absorbing water and does break down over time or due to other problems such as drainage. The following will help you in your efforts to repair a concrete sidewalk.
Clean the crack or hole in the cement sidewalk. Use a hose to thoroughly spray in the hole to remove dirt, pebbles, chunks of broken cement and such. Scrub the crack or hole with a stiff brush.
Enlarge the hole into a V shape by chiseling it with a cold chisel and hammer.
Clean again making sure all debris is removed from the hole.
Fill the bottom of the hole with sand if the hole is deeper than half an inch.
Mix cement and water into a thick paste.
Dampen the crack, the hole (even if it has sand in the bottom) and the surrounding cement area with a hose.
Fill the area with the cement mixture. Use a caulking gun for cracks and a putty knife to get the cement into the holes.
Fill it above the surface so it can settle. Lightly tap the top surface.
Scrape away the excess cement mixture with the putty knife so it is level with its surroundings.
Leave it alone for 2 hours.
Spray the area and its surroundings again.
Cover with plastic for 3 days. Spray it each day until the cover is removed.
Repeat the cement filler if the new cement settles below the surface.
Put on a pair of rubber gloves to prevent skin irritation from the chemicals. Fill a 5-gallon bucket with 2 cups of warm water. Add 1 cup of trisodium phosphate (TSP) to the water and mix thoroughly. Alternatively, substitute 1 cup of bleach for 1 cup of TSP.
Saturate a stiff-bristled brush in the mixture.
Begin scrubbing the sidewalk in a vigorous back-and-forth motion until all the mold is removed.
Allow the mixture to sit on the sidewalk for 15 minutes. After the allotted time has passed, rinse the sidewalk clean with a water hose.
Allow the sidewalk to air dry.
Sweep the sidewalk clean with a broom regularly. This will remove decaying vegetation that can cause mold to grow on your sidewalk.
Widen the bottom of the gap with a chisel and hammer. Place the tip of the chisel at an angle against the inner wall of the gap and hit the flat end with a hammer. Chip down the length of the gap.
Scoop chunks and debris from inside of the gap with a wire brush.
Measure the surface width and depth of the gap with a measuring stick. If it is deeper than 1/2 inch, fill the bottom until it is 1/2 inch from the sidewalk surface.
Add a light coat of bonding adhesive inside and around the surface of the gap with a paint brush. The adhesive helps strengthen the bond between the fill and the sidewalk.
Stir a container of vinyl-reinforced concrete patching compound with a wooden stirrer. If the surface of the gap is less than 1/2 inch wide, use a putty knife to fill the remaining 1/2 inch expanse of the gap.
Smooth the compound around the surface of the gap with a trowel to make the filled gap even with the sidewalk.
Stir pre-made sand mix concrete with concrete fortifier if the surface of the gap is wider than 1/2 inch. Fill the remaining 1/2-inch gap with the fortified sand concrete instead of the vinyl patching compound. Smooth the concrete over the sidewalk so the surface is even.
Cover the patched gap with moist burlap to dry it slowly. The added moisture prevents the fill from absorbing moisture from the old concrete.
Measure the length and width of the area where you will pour the sidewalk in inches. Multiply these two numbers together, then multiply the resulting number by 4, as 4 inches is the standard minimum thickness for a sidewalk. Divide the final number by 12 to find the cubic feet of concrete you will need.
Visit a hardware or home improvement store and read the packaging of the available ready-mix concrete. Locate concrete labeled 4,000 psi and examine the label, since it will tell you how many cubic feet one bag will fill. Purchase enough bags of the same brand of concrete to fill your sidewalk, rounding up if necessary.
Rent a concrete mixer large enough to hold the amount of concrete you need. Transfer the dry concrete mix to the barrel of the mixer. Add the amount of water directed by your brand of concrete, since this will vary.
Turn on the concrete mixer and allow the barrel to rotate at least 70 times. This not only mixes the concrete but also traps necessary air in the mixture. The concrete is now ready for pouring.
Determine the amount of concrete needed based on the cubic yardage of the sidewalk form. To determine cubic yardage, multiply the length, width and depth of the form. Divide that number by 27. You will need approximately six to seven 94 lb. bags of cement, 1/2 cubic yard of sand and 3/4 cubic yard of gravel for each cubic yard of sidewalk you need to pour.
Add the dry ingredients into the mixer drum.
Start the mixer and gradually add water until a thick, soupy mixture forms. Add water bit by bit, so as not to use too much. Too much water will weaken the concrete. Too little water, on the other hand, will make the concrete stiff and difficult to work with. Use approximately 27 to 35 gallons of water per cubic yard.
Cutting a Concrete Sidewalk
Purchase a diamond concrete cutting blade from your local hardware store. Rent or purchase a cutoff saw and screw the diamond blade into the cutoff saw blade mount.
Mark a straight line across the section of sidewalk you will be cutting with a square.
Read the cutoff saw operator's manual and safety precautions. Put on your protective eyewear, mask and gloves.
Align the blade with the line you will cut. Pull the cutoff saw trigger to turn the saw on and push the saw through the concrete sidewalk slowly and steadily. If the saw is running for close to a minute, pull the blade out and release the trigger to let the saw cool down for several minutes and then continue cutting.
Chip and pry with the large iron pry bar to remove the piece of concrete you just cut free. You may also want to rent a jackhammer from your local hardware store and break the section of concrete into smaller pieces for easy removal.
Sweep away loose dirt and debris from the sidewalk.
Fill the garden sprayer with a concrete de-greaser and spray it over the sidewalk. Wait 15 minutes for the de-greaser to break up any oily residue on the concrete, then brush down the sidewalk with a nylon-bristled brush.
Rinse off the concrete de-greaser with a garden hose.
Allow for the sidewalk to dry for 24 hours before continuing.
Pour self-leveling compound into the unlevel spots on the sidewalk. As soon as the compound is poured, smooth it down with a trowel. The trowel is useful for spreading the compound as well. The compound will automatically level itself so that the surface of the sidewalk is even. Refrain from using the sidewalk until it has cured for 48 hours.
Use landscape paint to outline the area where you plan to lay the sidewalk. With a flat shovel, remove grass and debris from the outlined area, and continue digging down to 6 inches below the surface.
Rake the surface of the ground until it is level. Use a compactor machine or tamper tool to compress the surface. Compressing the surface prevents the ground from settling over time, which can cause a sidewalk to crack or sit uneven.
Pour 4 inches of gravel over the compacted surface, and rake the gravel to spread it evenly. Tamp the surface of the gravel until it is even. Place a carpenter's level on the base to make sure it is completely level.
Roll landscaping fabric over the surface to improve the site's drainage and prevent weeds from growing below the base.
Spread a 1-inch layer of gravel over the landscaping fabric, tucking the edges of the fabric beneath the gravel so it won't show through on the sides of the walkway.
Pour a 1-inch layer of sand over the gravel to shore up the surface. Dampen the sand and allow it to dry before laying your sidewalk. As the sand dries, it will cling to the gravel like concrete powder, increasing support to the base.
Use a water hose to rinse the sidewalk clear of the moss. The pressure from the hose will push most of the moss off the sidewalk. Remove any remaining moss with a brush broom.
Wear a pair of rubber gloves to prevent skin irritation caused by cleaning chemicals.
Fill a bucket with 1 gallon of water. Add 1/2 cup of bleach. Alternatively, substitute the bleach with trisodium phosphate (TSP).
Scrub the sidewalk with a scrub brush saturated in the mixture. Or you can use a brush broom saturated in the mixture, so you do not have to bend down while scrubbing.
Continue scrubbing the sidewalk in a vigorous motion and saturating the brush until you have removed all traces of the moss and thoroughly cleaned the sidewalk.
Rinse the sidewalk clean with the water hose. Begin at one end of the sidewalk and move the water hose in a steady back-and-forth motion that slowly moves upward.
Allow the sidewalk to air dry. Sweep your sidewalk regularly with a broom to keep it clean and clear of debris.