Fixing Sunken Concrete Patio: Raising And Repairing Solutions

Sunken concrete patios are a common problem for homeowners, and there are several ways to address the issue. One popular method is mud jacking, which involves injecting a slurry mixture or polyurethane foam beneath the slab to lift it back to its original position. This process is cost-effective and efficient, but it requires specialized equipment and expertise. Another option is to remove and replace the sunken concrete entirely, which can be costly and time-consuming. For smaller slabs, DIY methods such as layering new concrete on top or using a concrete grinder to level the surface may be feasible. Ultimately, the best approach will depend on the specific circumstances of the project, including the severity of the sinking, the condition of the slab, and the homeowner's budget and time constraints.

Mudjacking

Plan the Concrete Slab's Height

First, determine the desired height for your concrete slab. If you are raising a section of a sidewalk or driveway, you will want the sunken concrete to be level with the other sections. If you are raising an entire concrete patio slab or a set of stairs, mark the desired height on your home's foundation with marking tape to ensure you don't raise the concrete too high or not enough.

Cut the Concrete Slab, if Necessary

If you only need to raise a section of a concrete sidewalk or driveway, use a circular saw with a diamond blade to cut the concrete at an existing joint and fully cut through so that the slab you will be raising is separated.

Drill Injection Holes

Drill several 1- to 2-inch-diameter holes into the concrete slab for injecting the slurry mixture. Drill one or two holes in a particular corner if you just need to raise that corner. Drill a hole in each corner and a few others across the slab if you need to raise the entire slab, ensuring the holes go all the way through the slab and into the dirt or stone below.

Mix the Cement Slurry

The slurry is typically made with a combination of water and sand, clay, or topsoil, and limestone dust, or Portland cement. You can order this mixture from a concrete supplier or mix it yourself if you have the correct materials available. Ensure the slurry is thick like pancake batter but still pourable, thick enough to provide support but not so thick that it clogs the pump.

Pump Slurry Into the Injection Holes

Using a hydraulic slurry pump, pump the slurry mixture into each injection hole, starting at one side of the concrete slab and slowly moving to the other side. Fill each hole until the concrete slab begins to lift to the desired height, checking the level of the slab frequently to ensure it's rising evenly. Be careful not to overfill any of the voids, which can cause the concrete to lift past the desired height.

Check the Concrete's Height and Adjust as Needed

Once every injection hole has been filled, evaluate the slab to see if it has reached the desired height. If the slab is still too low or if certain areas need to be raised further, continue pumping the mixture into those specific injection holes, filling slowly and coming back to an injection hole later if needed.

Fill Cracks and Injection Holes

Once your concrete slab reaches the desired height, stop pumping in the slurry and gently rinse down the entire surface with a hose. Patch the injection holes and any concrete cracks with a concrete patching compound or repair caulk. You may also want to use a trowel to smooth the surface for a seamless finish.

Wait for the Slurry to Dry

After the mudjacking process is finished, it is typically okay to walk on the slab right away, but avoid placing heavy loads on the slab for 24 to 72 hours.

Polyurethane foam injection

The process is similar to mudjacking, but polyjacking may be easier because the polyurethane foam is easier to inject below the slab, requiring less disruption to the area. It is also faster, cleaner, cheaper, and longer-lasting than mudjacking.

• Plan: Determine the desired height for your concrete patio slab. If you are raising an entire patio, mark the desired height on your home's foundation with marking tape to ensure you don't raise the slab too high or too little.
• Prepare: If you only need to raise a section of the patio, use a circular saw with a diamond blade to cut the concrete at an existing joint and separate it from nearby sections.
• Drill: Using a hammer drill and a diamond drill bit, drill holes into the concrete slab for injecting the polyurethane foam. Drill several 1- to 2-inch-diameter holes across the surface and through the slab. If you are raising a corner, drill one or two holes. For an entire slab, drill a hole in each corner and a few others across the slab, usually every 3 feet or so.
• Inject: Attach a polyurethane injection gun securely to the ports. Perform controlled injections, resulting in a two-part polymer flowing through the space between the slab and its sub-base. The polymer will expand and form a structural foam that fills voids while raising and levelling the patio.
• Cure: Once the concrete has been raised, allow the polyurethane foam to cure. This typically takes about 15 minutes, after which you can use the patio without any restrictions.
• Patch: Remove the injection ports and fill the holes with a high-quality grout, making them virtually unnoticeable.

Concrete replacement

If your concrete patio has sunk, the oldest and most expensive method to repair it is to replace it entirely. This involves breaking up the existing concrete with a jackhammer, levelling the ground, installing forms, and pouring a new patio. This method is disruptive to your landscaping and may require further repairs to your garden. It is also costly and time-consuming, as you will be unable to use your patio for several days while the new concrete cures.

However, concrete replacement may be the best option if your patio has suffered severe damage or cracking. While other methods can repair minor sinking, they may not be suitable for more extensive damage.

Jacking

• Plan the desired height of the concrete slab: Before starting, it is important to know the desired height for the concrete slab. This will ensure that the slab is raised evenly and to the correct level.
• Cut the concrete slab, if necessary: If only a section of the slab needs to be raised, use a circular saw with a diamond blade to cut through the concrete and separate it from nearby sections.
• Drill injection holes: Using a hammer drill and a diamond drill bit, drill several 1- to 2-inch-diameter holes across the surface of the slab. Drill holes in each corner and a few others across the slab to ensure the slurry mixture can fill in everywhere beneath the concrete.
• Mix the cement slurry: The slurry is typically made with a combination of water, sand, clay, topsoil, or Portland cement. It should have a thick consistency like pancake batter but still be pourable.
• Pump the slurry into the injection holes: Using a hydraulic slurry pump, inject the slurry mixture into each of the injection holes. Start at one side of the slab and slowly move to the other side, filling each hole until the concrete begins to lift to the desired height.
• Check the slab's height and adjust as needed: Once all the holes have been filled, evaluate the slab's height and level. Continue pumping the mixture into specific injection holes if the slab is still too low or if certain areas need to be raised further.
• Fill cracks and injection holes: After reaching the desired height, stop pumping the slurry and gently rinse down the surface. Patch the injection holes and any concrete cracks with a concrete patching compound or repair caulk.
• Allow the slurry to dry: While it is typically okay to walk on the slab right after the process, avoid placing heavy loads on the slab for 24 to 72 hours to allow the material to dry completely.

Mudjacking is a complex and challenging DIY project that requires specialized equipment and skills. The cost of DIY mudjacking is around $1 to $5 per square foot, but this does not include the cost of renting equipment and purchasing supplies, which can range from $100 to $500. There is also a risk of property damage, so it is recommended to leave this task to professionals who can ensure the concrete slab is raised correctly, completely levelled, and does not crack during the process.

Grinding down high spots

To grind down a high spot, you can use a handheld angle grinder with a diamond cup wheel or a walk-behind grinding unit for larger areas. This process will create a lot of dust, so it is recommended to attach a vacuum to the grinder to minimise the mess.

When grinding, it is important to not remove more than two inches of concrete to avoid thinning and weakening the slab. This may cause the concrete to break or crumble over time. Additionally, grinding exposes more pores in the concrete, making it more susceptible to damage from freeze-thaw cycles.

• Prepare the area by setting up a reference or guide to ensure a level grinding process. You can use a 4' level and mark a 2" path to follow as you grind.
• Put on the appropriate safety gear, including a respirator, eye protection, and a dust mask. The concrete dust produced during grinding can be harmful if inhaled.
• Start grinding the high spot by moving the grinder from the centre of the spot outwards in a feathering motion. This will help create a smooth and even surface.
• Check your progress regularly with a level to ensure you are grinding down the area evenly.
• Once you have reached the desired level, clean the area thoroughly to remove any remaining dust or debris.
• If necessary, you can apply a concrete patching compound or repair caulk to fill in any cracks or holes left by the grinding process.
• Allow the area to dry and cure completely before using the patio.

Remember that grinding down high spots on a concrete patio is a quick fix, but it may not be a long-term solution. It is important to address the underlying cause of the unevenness to prevent future issues.

Frequently asked questions