Repairing A Sunken Concrete Patio: Quick And Easy Solutions

A sinking concrete patio can be a real eyesore, and it's more than that – it's a safety hazard and a source of trouble. So, what can be done to fix it? There are several methods to repair a sinking concrete patio, including jackhammering and replacing the entire patio, a method called mudjacking, and polyurethane concrete raising.

Mudjacking is a cost-effective and efficient way to raise sunken concrete slabs. This process involves pumping a grout or concrete mixture beneath the slab to lift it back to its original position. It can often be completed in a single day and costs around $3 to $6 per square foot. However, it may not be suitable for severely damaged slabs or slabs that have sunk more than eight inches.

Polyurethane concrete raising is a newer method that uses the same concept as mudjacking but with some added benefits. It is extremely lightweight, durable, and stable, and the injection holes are much smaller. It is also less expensive than replacing the concrete and has a shorter curing time.

For smaller slabs, it may be possible to lift the slab and fill the space underneath with rocks or sand. This method requires some heavy lifting and manoeuvring but can be done without the need for specialized equipment.

Before deciding on a repair method, it is important to identify the cause of the sinking. Has the soil below the concrete shifted or eroded? Are there drainage issues that need to be addressed? By fixing the underlying problem, you can help ensure that the repair will last.

Identify the cause of the sinking

Before attempting to raise a sinking concrete patio, it is important to identify the cause of the sinking. This will help determine the best course of action to take and prevent further issues. Here are some possible reasons for a concrete patio to sink:

Soil Shifting or Settling: One of the most common reasons for concrete to become uneven is that the soil beneath it has sunk or shifted. When the soil below the concrete shifts, it often leaves behind empty spaces. As the concrete relies on the soil for support, it will eventually sink into these empty spaces. This can cause the concrete to become uneven and may even lead to cracking. Not only does this make the patio difficult to use, but it also creates a trip hazard.

Poor Drainage: Excessive water can be a significant contributor to concrete sinking. If your patio is pitched towards your house, rainwater can pool underneath, causing the soil to become softer and the patio to sink deeper. Proper drainage is essential to prevent this issue.

Ground Pressure: The weight of the concrete itself, along with any loads placed on it, can exert pressure on the soil below. Over time, this can cause the soil to compact and settle, leading to the concrete sinking.

Movement and Settling: Soil is not completely static; it can shift and move over time. This movement can cause the soil beneath the concrete to become unstable and no longer able to support the weight above, resulting in sinking.

Tree Roots: Large trees or shrubs with extensive root systems can exert pressure on the soil and affect the stability of the ground beneath the concrete. As the roots grow and expand, they can push against the soil, causing the concrete to lift or sink.

Poor Installation: If the concrete was not properly installed or the soil was not adequately compacted before pouring, it can settle unevenly and cause the concrete to sink in certain areas.

To determine the cause of your sinking concrete patio, start by examining the area for any visible signs, such as cracks, uneven surfaces, or nearby trees or shrubs. Consider the age of the concrete and any changes in the surrounding landscape. If you notice water pooling on or around the patio, poor drainage may be a contributing factor. Understanding the underlying cause will help guide your decision-making process when choosing a repair method and ensure that the issue does not persist or worsen over time.

Evaluate the unevenness of the concrete patio

Evaluating the unevenness of your concrete patio is a crucial first step in deciding how to proceed with repairs. Here are some detailed steps to help you assess the condition of your patio:

Step 1: Determine the Extent of Unevenness

Begin by measuring the difference in height between the highest and lowest points on your concrete patio. If the variation exceeds the manageable limit for a repair, which is typically around 1/4 inch to 1/2 inch, it may be more appropriate to consider removal and re-pouring of the concrete.

Step 2: Inspect for Cracks and Damage

Thoroughly examine your concrete patio for any cracks, chips, or other types of damage. Look for signs of shrinkage or rapid drying, which are common causes of cracking in concrete. Small cracks can be marked with scotch tape to make them more noticeable during the repair process.

Step 3: Assess the Surrounding Area

Take into account the surrounding area of your concrete patio. Are there any nearby structures, such as stairs, that the patio is attached to? Is the patio adjacent to any landscaping or other features that could be affected by repair work? Identifying these factors will help you determine the best approach for repairing the unevenness.

Step 4: Evaluate the Cause of the Issue

Try to identify the root cause of the unevenness. This could be due to a variety of factors such as soil settling, erosion, improper installation, tree roots, excess weight, ground movement, or extreme weather conditions. Understanding the cause will help you choose the most effective repair method and prevent the issue from reoccurring.

Step 5: Decide on a Course of Action

Based on your evaluation, decide on the best course of action to address the unevenness. Common repair methods include concrete leveling (mudjacking or slab jacking), grinding down the uneven areas, adding new concrete or patching compounds, or complete replacement of the affected slabs. Each method has its advantages and disadvantages, so consider factors such as cost, durability, and the level of disruption to your property when making your decision.

Drill holes through the concrete slab

Drilling holes through a concrete slab is a complex process that requires the right tools and safety precautions. Here is a step-by-step guide to help you drill holes effectively and safely:

Choose the Right Tool and Bit

Select a suitable tool for drilling, such as a rotary hammer or a hammer drill. Rotary hammers are ideal for creating larger holes, while hammer drills are typically used for smaller holes. Ensure you have the appropriate tungsten carbide masonry drill bit for your desired hole size and chosen tool.

Prepare the Work Area

Clear the work area by removing any furniture or artwork near the desired hole location. Place a drop cloth below to catch any falling debris. Ensure you have ample space to work and a stable surface to stand on. Put on safety gear, including gloves, eye protection, ear protection, and heavy pants. Concrete drilling can generate a lot of dust and noise, so it's crucial to take the necessary precautions.

Mark the Hole Location and Depth

Use a pencil to mark the desired position of the holes on the concrete surface. Double-check the locations before proceeding. If your drill has a stop bar feature, set it to the exact depth you want by following the manufacturer's instructions. If your drill lacks a stop bar, wrap tape around the drill bit to indicate the desired depth.

Drill a Guide Hole

Hold the drill with both hands, one gripping it like a gun and the other bracing the back of the tool. Start drilling at a slow speed or in short bursts to create a shallow guide hole. This initial hole will help guide your drill for the actual hole.

Continue Drilling with More Power

Turn on the hammer function of your drill if it has one. Apply firm but controlled pressure to push the drill forward. Gradually increase the speed and force as needed, maintaining stability and control at all times. Concrete can be unpredictable due to air pockets and pebbles, so be prepared for some recoil and kick from the drill.

Clear Obstructions and Cool the Drill

Periodically pull the drill out to clear any blockages with a masonry nail. Concrete drilling can generate a lot of heat, so it's important to let the drill cool down briefly from time to time.

Blow Out the Dust and Clean the Area

Once you've reached the desired depth, use compressed air to blow out the concrete dust from the hole. Then, vacuum the area to remove any remaining debris. Keep your goggles on during this process to protect your eyes from dust and debris.

Drilling through concrete is a challenging task that requires the right tools and safety measures. By following these steps, you can effectively drill holes through your concrete patio slab to prepare it for lifting or other repairs.

Inject a levelling material

Injecting a levelling material, such as a slurry or polyurethane foam, under a concrete patio is a cost-effective and efficient way to raise and level a sunken patio without having to replace it entirely. This method is known as mudjacking or polyjacking, and it can be done by drilling small holes in the slab and injecting the material through them.

Mudjacking

Mudjacking is a process that involves injecting a slurry, or cement mixture, under a concrete slab to lift it back to its original position. The slurry is typically made with a combination of water and sand, clay, topsoil, or limestone dust, along with Portland cement. This mixture can be ordered from a concrete supplier or mixed on-site if you have the correct materials. The consistency of the slurry should be thick like pancake batter but still pourable, providing support without clogging the pump.

To perform mudjacking, you will need to:

• Plan the desired height of the concrete slab and mark it on your home's foundation.
• Cut the concrete slab, if necessary, to 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 and through the slab.
• Mix or order the cement slurry.
• Pump the slurry into the injection holes using a hydraulic slurry pump until the slab reaches the desired height.
• Check the slab's height and adjust as needed by filling in more slurry.
• Fill in the injection holes and any cracks with a concrete patching compound or repair caulk.
• Allow the slurry to dry for 24 to 72 hours before placing heavy loads on the slab.

Polyjacking

Polyjacking, or polyurethane foam injection, is another method for raising and levelling a concrete patio. This process involves injecting a polyurethane foam under the slab through small, dime-sized holes. The foam expands to fill any voids beneath the slab, raising and levelling it. Polyjacking is typically done by professionals as it requires training and special equipment.

The steps for polyjacking are as follows:

• Drill small, dime-sized holes into the affected area of the concrete patio.
• Pump the polyurethane foam under the patio through the small holes.
• As the foam expands, it fills the voids and raises the slab.
• Patch the holes with a compound that matches the colour of the concrete.
• The slab is typically ready for use again within 15 minutes after the repair.

Both mudjacking and polyjacking are effective methods for raising and levelling a sunken concrete patio. Mudjacking is a DIY-friendly technique, while polyjacking should be performed by professionals. Consider the advantages and disadvantages of each method before deciding which one is best suited for your needs.

Allow the material to dry

Once you have injected the concrete-raising mixture, the next step is to let the material dry and harden. The curing time will depend on the material used. For instance, polyjacking cures in just a few minutes, while concrete can take a few days.

During the curing process, it is typically okay to walk on the slab right after the material has been installed, but it is best to avoid placing heavy loads on the slab for 24 to 72 hours. If you have used concrete, you will need to keep off the patio for a few days while you wait for it to cure properly. If hot weather is in the forecast while it's curing, you may need to water the new concrete to keep it from curing too quickly.

If you have used polyurethane concrete raising, the curing time is substantially less than concrete, so the patio can be used within a few hours of completing the work.

It is important to note that the curing process is crucial for the stability and longevity of your concrete patio. Allowing the material to dry completely will ensure that the slab is strong and durable.

Additionally, it is worth mentioning that the drying time may vary depending on environmental factors such as temperature and humidity. In some cases, you may need to take additional measures, such as watering the concrete or providing shade, to ensure optimal curing conditions.

Frequently asked questions