Repairing Your Concrete Patio: A Step-By-Step Guide

Repairing a concrete patio slab can be a challenging task, but with the right tools and knowledge, it is possible. The first step is to identify the cause of the damage, which could be due to natural occurrences such as freeze-thaw cycles, ground movement, or improper pouring conditions. Once the cause is identified, repairs can be made. For example, if the patio slab is uneven or sunken, it can be levelled using professional concrete levelling services or by injecting polyurethane foam to raise the slab. Small cracks can be repaired with a caulk-based product, while larger cracks may require a concrete resurfacer to create a smooth, uniform surface. If the corners of the slab are crumbling, they can be repaired with a concrete cleaner and patching compound. To prevent further damage and enhance the appearance of the patio, it is recommended to seal the concrete with a penetrating sealer. In some cases, it may be necessary to remove tree roots that are lifting the patio or to repair expansion joints to prevent water damage. While repairing a concrete patio slab can be a DIY project, hiring professionals may be the best option to ensure proper and long-lasting results.

Level uneven slabs

There are several ways to level uneven concrete slabs, depending on the severity of the issue and the time and money you want to spend on the project. Here are some methods to consider:

Concrete Leveling

Concrete leveling is a process where small, strategically placed holes are drilled into the uneven slabs, and a compound or expanding polyurethane foam is pumped beneath the surface. This method is also known as polyjacking and is considered a fast, non-toxic, and cost-effective solution that can be done indoors and outdoors. The compound or foam fills any voids under the slab, lifting it back into place, hardening, and creating a durable new base. This method can save up to 70% of the cost of replacement and usually takes less than a day to complete. It is also long-lasting, as polyurethane foam will last indefinitely if the property is sloped away from the slab to prevent water washout.

Grinding Down

Grinding down the uneven areas of the concrete slab is another option, which can be one of the cheapest and fastest ways to eliminate trip hazards, especially if the affected area is small. However, grinding can leave the surface looking splotchy and discoloured, and it opens up the pores of the concrete, making it more susceptible to damage during freeze-thaw cycles. It also makes the slab's structure thinner and weaker. Therefore, grinding is usually considered a temporary fix until a more permanent solution can be implemented.

Adding New Concrete or Patch Compounds

You can also try to level uneven slabs by adding additional concrete or patching compounds onto the uneven surfaces to even out the difference. Concrete patch kits are available at hardware stores, or you can mix and apply your own concrete to create a grade between the high and low points of the slabs. However, this method usually does not last long, as the new concrete or compound can chip or crack off as the existing concrete expands and contracts during freeze-thaw cycles.

Self-Levelling Concrete

Self-levelling concrete compound is typically used on interior concrete floors to remove texture or dips. While it can be an effective way to create an even surface, it is not recommended for exterior slabs or slabs that have sunk more than an inch. Self-levelling concrete is also a temporary solution, as it can break down over time, especially if applied too thickly, and it is susceptible to crumbling and cracking off due to expansion and contraction of the existing concrete.

Replacing the Slab

If none of the above methods are suitable or effective for your situation, you may need to consider replacing the affected slabs entirely. This option can be costly and time-consuming, and it is challenging to match the colour and texture of the existing concrete. Additionally, pouring new concrete carries risks such as potential resettling and property damage due to heavy equipment. Therefore, replacement is usually considered a last resort.

Before deciding on a method, it is essential to identify the cause of the unevenness, such as poor drainage, tree roots, expansive soil, or improper compaction. This will help determine the best course of action and prevent future issues.

Fill and seal cracks with caulk

Filling and sealing cracks in a concrete patio with caulk is a straightforward process that can be done in a few simple steps. Firstly, ensure that the crack is cleaned of any dirt, debris, or weeds. If the crack is hairline, use a chisel to widen it slightly so that the caulk can adhere properly. It is also important to wear safety glasses during this process to protect your eyes.

Once the crack is prepared, you can move on to choosing the right caulk. A flexible, caulk-based product is best for sealing concrete cracks. Look for a product that is specifically designed for concrete repair, such as Quikrete Concrete Repair, a matte grey, acrylic-based caulk that blends in with the surrounding concrete. Alternatively, you could use a durable urethane caulk or polyurethane caulk, which will keep water out and protect your patio from further cracking and erosion.

When you are ready to apply the caulk, cut the tip of the tube with a utility knife and load it into a caulk gun. Fill the crack with the caulk, using a smooth and even motion, and bevel the caulk if it is against the house. For wide joints, use the back of an old spoon to smooth the caulk, wiping the spoon with a rag and mineral spirits as needed. If the crack is narrow, you can simply draw the caulk gun down the crack, smoothing the caulk with the tip as you go.

By filling and sealing cracks in your concrete patio with caulk, you can not only improve the appearance of your patio but also protect it from further damage.

Remove tree roots

Removing tree roots from under a concrete patio slab can be a challenging task, but it is possible to do so by following these steps:

Assess the Situation:

Before starting the removal process, it is important to understand the extent of the problem. Inspect the patio slab to identify the areas where the tree roots are causing damage or lifting the concrete. Take note of the size and location of the affected areas, as this will help determine the best course of action.

Gather the Necessary Tools and Equipment:

Ensure you have the right tools for the job. For smaller roots, a shovel, a pickaxe, a spade, and a chainsaw or reciprocating saw should suffice. If you're dealing with larger roots, you may need a jackhammer or a root saw to cut through the concrete and roots effectively. Don't forget to wear protective gear, including safety goggles, gloves, and other necessary safety equipment, when using these tools.

Dig Out the Roots:

Carefully dig around the affected areas to expose and lift out as much of the root structure as possible. Try to minimise damage to the concrete slab and the surrounding landscape during this process. If there are large roots that cannot be easily removed, use a chainsaw to cut them into sections for easier removal.

Apply Herbicides:

Consider using herbicides to kill the tree and prevent regrowth. Herbicides containing glyphosate or triclopyr are effective at targeting the tree without harming nearby vegetation. Be sure to follow the application instructions carefully to avoid any unwanted damage.

Prune Small Rootlets:

If the tree is still alive, pruning can be an effective way to remove smaller roots and reduce regrowth. Cut away any small rootlets that are growing through or near the concrete slab.

Cut a Channel in the Concrete:

For stubborn roots that cannot be removed easily, you may need to cut a channel into the concrete using a masonry saw. This will allow you to access and remove the root system more effectively. Once the roots are removed, fill in the void with fresh concrete to restore the slab.

Smother Roots with Plastic Sheeting:

If mechanical or chemical methods are not successful, you can try smothering the roots by covering them with plastic sheeting or tarps during the hot summer months. This method takes advantage of the roots' vulnerability to heat. Secure the sheeting with soil or rocks to prevent it from blowing away.

Hire a Professional:

If the tree roots are particularly stubborn or extensive, consider hiring a professional tree service for assistance. They have the necessary tools and expertise to safely and effectively remove large roots without causing damage to the surrounding area.

Expose Roots with Hydro-jetting:

Hydro-jetting is a technique that uses high-pressure water jets to cut through and expose tree roots for removal. This method can be very effective in stubborn cases without requiring the use of power tools or extensive digging.

Break Up the Concrete:

In some cases, you may need to break up the concrete to fully access and remove the root system. Use a grinder, jackhammer, or similar tools to break up the concrete carefully. Once the roots are removed, fill in any gaps or cracks with fresh cement or sealant to restore the patio slab.

Remember, safety should always be a top priority when undertaking such projects. Be sure to wear protective clothing, have a first-aid kit nearby, and stay clear of any electrical or gas lines during the removal process.

Clean and seal the surface

To clean and seal a concrete patio slab, you'll need to first clean the surface and then apply a sealer.

Cleaning the Surface

Concrete patios can be cleaned using a pressure washer. Before cleaning, remove any stains on the surface, such as oil, grease, paint, or rust and dirt stains. Use a degreaser for deep stains and scrub with a brush. For paint stains, apply a paint stripper or solvent and scrub with a brush or rag. For rust and dirt stains, apply a rust or concrete cleaner.

Once the stains have been removed, use a pressure washer to clean the concrete. First, wet the concrete surface with a garden hose. Then, add a concrete cleaner to the pressure washer and thoroughly spray the concrete. Let the cleaner soak for a few minutes, and then rinse the concrete with a low- or medium-pressure spray tip. Keep the tip about 8 to 24 inches away from the surface and use overlapping strokes. You may need to go over some areas twice to ensure the cleaner is removed. Allow the concrete to dry for at least 24 hours.

Sealing the Surface

Before applying a sealer, check if your concrete has been previously sealed. To do this, pour a cup of water onto the concrete. If the water beads up and stays on the surface, it has been sealed. If the concrete absorbs the water, it hasn't been sealed.

If the concrete has been previously sealed, you will need to remove the old sealer. This can be done using a chemical stripper or a less toxic, environmentally friendly product made from soy or citrus. Apply the stripper to the concrete and let it sit for the recommended time. Then, use a long-handled scraper to remove the sludge and discard it properly. Finally, scrub the floor with trisodium phosphate (TSP) and water, and let it dry for at least 24 hours.

To apply the new sealer, use a roller or a garden sprayer. Apply the sealer in overlapping strokes, being careful not to let it build up. If you are using a roller, apply the sealer in the same way you would paint a wall, using a large paintbrush for the edges and seams. Allow the first coat to dry for at least two hours, and then apply the second coat at right angles to the first. Make sure to follow the manufacturer's instructions for drying times, as it can take up to three days for the sealer to fully cure.

Seal expansion joints

Sealing the expansion joints in a concrete patio slab is important to prevent plants, bugs, water, and other undesirable objects from taking residence in the cracks and causing damage. The process is relatively straightforward but requires some specific tools and materials. Here is a step-by-step guide to sealing expansion joints:

• Clean the expansion joints: Use a brush to remove any dirt, dust, pebbles, or other debris from the joints. If there is any oil or grease present, use a scrub brush and a concrete cleaner to remove it. Ensure that the surface is completely clean, dry, and free of any chipped or poorly bonded components.
• Insert a backer rod: If the expansion joints are deeper than 1/4 inch, it is recommended to use a backer rod. Choose a backer rod with a diameter slightly larger than the width of the joint. Press the backer rod into the joint, leaving a sealant depth of between 1/8 inch and 1/2 inch.
• Apply a suitable sealant: Choose a flexible sealant designed for expansion joints, such as a polyurethane-based or acrylic-based product. Cut the tip of the sealant cartridge and insert it into a caulking gun. For horizontal joints, use a self-levelling sealant and move the nozzle slowly along the joint, allowing the sealant to settle. For vertical joints, use a non-sag polyurethane sealant and press it into the joint.
• Smooth and clean up: If needed, use a trowel or the tip of the nozzle to smooth the sealant. Immediately remove any excess sealant with a commercial solvent or a citrus-based cleaner.

By following these steps, you can effectively seal the expansion joints in your concrete patio slab, helping to protect it from water damage and other issues caused by plants and insects.

Frequently asked questions