Repairing Wash Out: Concrete Patio Maintenance Guide

how to repair wash out under concrete patio

Erosion under concrete patios can lead to dangerous broken slabs. This can be caused by a variety of factors, including soil erosion, water penetration, and burst pipes. To repair washout, you can use the slab-jacking method, which involves injecting a stable grout mixture beneath the surface to fill voids and restore strength. Alternatively, you can use poly foam and CPVC pipes to fill the gaps.

Characteristics Values
Cause of void under concrete Soil erosion, water leak, settlement
Solution Polyurethane foam, slab-jacking
Tools CPVC pipe, 3/8 concrete drill bit, packing tape, protective clothing

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Identify the cause of the void under the concrete patio

Voids under concrete are empty spaces that can form when the soil beneath settles or erodes. There are several factors that can cause these voids, including soil erosion due to poor drainage, uncompacted substrate during initial construction, underground water leaks from pipes, natural soil settling over time, and poor soil composition or quality.

  • Cracks in the concrete surface
  • Sinking or uneven sections of the slab
  • A hollow sound when tapping on the concrete
  • Water pooling in certain areas after rain

If you suspect a void under your concrete patio, it is important to identify the cause to prevent further damage and determine the best repair method. Here are some common causes of voids under concrete patios:

  • Soil Erosion: This is one of the most common causes of voids under concrete. Over time, natural elements can degrade and cause the soil to settle, leading to erosion and the formation of voids. This can be exacerbated by improper drainage or a downspout that is not extended properly.
  • Uncompacted Substrate: If the soil beneath the concrete was not properly compacted during construction, it can settle over time, creating voids.
  • Underground Water Leaks: Leaking pipes can wash away the soil beneath the concrete, leading to void formation.
  • Natural Soil Settling: Soil will naturally settle over time, and if the concrete is not properly supported, it can create voids.
  • Poor Soil Composition: The quality of the soil beneath the concrete can also play a role in void formation. If the soil is not strong enough to bear the weight of the concrete, it can settle or erode, creating voids.

To confirm the presence of a void and determine its extent, you can use a tape measure to see how far the gap goes. You can also use a ground-penetrating radar system to detect gaps without having to physically look underneath the concrete. Once you have identified the void and determined its cause, you can choose the most appropriate repair method to fix the issue and prevent further damage to your concrete patio.

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Wear protective clothing when repairing the patio

When repairing a washout under a concrete patio, it is important to wear protective clothing to shield yourself from any hazardous materials and potential accidents. Here are some key considerations for protective clothing:

Respiratory Protection

It is crucial to wear a respirator to protect yourself from inhaling toxic fumes and dust. Concrete construction work often involves exposure to various chemicals and dust from concrete mixing, cutting, and grinding processes.

Eye Protection

Always wear safety goggles or eye protection to shield your eyes from dust, debris, and any chemicals used during the repair process. This is especially important when working with concrete, as concrete dust and chemicals can cause eye irritation and even permanent damage.

Skin Protection

Wear long-sleeved shirts and long pants made from durable and protective materials. This will help protect your skin from any splashes or spills of concrete, chemicals, or other hazardous materials. Concrete and certain chemicals can cause skin irritation or even chemical burns, so it's important to keep your skin covered.

Additionally, consider wearing gloves to protect your hands. Gloves made from durable materials, such as rubber or acid-resistant materials, can provide a good barrier against chemicals and other irritants.

Head Protection

It is essential to wear a safety hat or helmet when working on a concrete patio repair. This will protect your head from any falling objects or potential hazards. Look for a safety hat with a hard exterior surface and a flexible inner cradle for added comfort and protection.

Footwear

Sturdy footwear, such as work boots, is crucial for protecting your feet and providing stability on the job site. Choose footwear with slip-resistant soles to prevent slipping and good ankle support to reduce the risk of sprains or twists.

High-Visibility Clothing

If you're working near moving vehicles or in low-light conditions, consider wearing high-visibility clothing. This will help make you more visible to others and reduce the risk of accidents.

Weather Protection

Depending on the weather conditions, you may need additional protective clothing. For example, if it's cold, wear insulated jackets and trousers to trap body heat. Conversely, if it's hot, opt for lightweight, breathable clothing that allows for adequate ventilation.

Remember, when repairing a washout under a concrete patio, taking the time to don the appropriate protective clothing can help ensure your safety and well-being.

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Use poly foam to fill the void

If you're looking to repair wash out under a concrete patio, one option is to use poly foam to fill the void. This method is also known as polyjacking or polyurethane foam injection. Polyurethane foam is an expanding foam made from two chemicals that mix and react in the nozzle to create a foam that hardens within minutes.

To start, you'll need to observe where the void exists under your concrete slab. Use a tape measure to see how far the gap extends, then make some estimated calculations for the depth and length of the void to determine how much poly foam you need to buy. Use chalk to mark where the void is and how many CPVC pipes you will need and where to place them. You can purchase Secure Set poly foam from their website.

If you can access the void using a CPVC pipe, this is the easiest method. The Secure Set website has instructions on how to use Secure Set with CPVC pipe extensions. If you cannot access the void, you will need to drill holes in the concrete. Secure Set also has a tutorial video on this.

Before you start, do a couple of dry runs. Polyurethane foam hardens very quickly, so you won't have a lot of time to make mistakes once you get going. Start with one pipe and slowly pull the pipe back while squeezing the trigger. The foam will expand, so you need to move quickly. One method is to pull the pipe back about 1 foot every 7 seconds.

Once you see foam coming through, use caution. The pipe is under pressure, so do not just remove the nozzle from the CPVC pipe or you will get blasted with foam. It will also be very difficult to get the foam off your skin and clothing. Once you finish one pipe, wait at least 2 minutes before disconnecting the pipe. Place a big towel over the nozzle/CPVC pipe connection to prevent the pressure from causing the foam to spray. Then you can disconnect the pipe from the nozzle while the towel is over it, blocking and containing the spray.

Polyurethane foam injection is the preferred method for filling voids to lift and level an uneven concrete slab. It is a neater process than the alternative, mudjacking, as there is no mess since the foam stays under the slab and doesn't spill out. It is also a much more precise method of filling voids because the foam can be injected exactly where it is needed. Polyurethane foam is also a green solution as it doesn't leach into the soil, so it poses no environmental threat. Additionally, polyurethane foam injection takes less time to complete than mudjacking, with most jobs completed in just a few hours.

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Use CPVC pipes to access the void

If you can access the void using a CPVC pipe, this is the easiest route to go. Before you start, make sure to wear protective clothing, including a respirator, goggles, and long-sleeved shirts and pants.

First, observe where the void exists under your concrete patio. Use a tape measure to extend as far as possible, so you can easily see how far the gap goes. Make some estimated calculations for the depth and length of the void to determine how much poly foam you need to buy. Use chalk to measure/estimate where the void is and how many CPVC pipes you will need and where to place them.

Purchase Secure Set poly foam from their website. The Secure Set website has instructions on how to use Secure Set with CPVC pipe extensions. Get the foam kit set up and ready. Do a couple of dry runs. You will not have a lot of time to make mistakes once you get going as the foam hardens very, very fast.

Start with one pipe and slowly pull the pipe back while squeezing the trigger. The foam will expand, so you need to move quickly. The method we used was to pull the pipe back about 1 foot every 7 seconds. Once you see foam coming through, take caution. The pipe is under pressure, so do not just remove the nozzle from the CPVC pipe or you will get blasted with foam. And it will be very difficult to get the foam off your skin and clothing.

Once you finish one pipe, wait at least 2 minutes before disconnecting the pipe. This is very important! We highly recommend placing a big towel over the nozzle/CPVC pipe connection and put this on the grass. If you don’t do this, the pressure will cause the foam to spray, which did happen to us the first time. From there, you can disconnect the pipe from the nozzle while the towel is over it, blocking and spraying back.

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Drill holes in the concrete if the void is inaccessible

If the void under your concrete patio is inaccessible, you will need to drill holes in the concrete to fill the gap. This is a common method used to fill voids under concrete slabs and is often carried out by professionals.

First, you will need to determine the cause of the erosion. Take any necessary steps to correct the source of the issue. For example, if the erosion is caused by a leaking sprinkler, you will need to fix the sprinkler before filling the void.

Next, you will need to clean the area around the void thoroughly. Wear protective gear, including gloves, long sleeves, pants, and safety goggles. It is also important to ensure that children and pets are kept away from the work area.

Then, you can begin drilling small holes through the concrete slab to access the void. The number and size of the holes will depend on the extent of the void. Once the holes are drilled, you can mix a sand and cement slurry according to the package instructions, and pour or pump the mixture into the holes until the void is filled.

Finally, allow the mixture to cure completely before using the patio. This process may need to be repeated in the future if new voids form, so be sure to address any underlying issues to prevent further erosion.

Frequently asked questions

You may notice sloping or settling of the concrete or spots around it. You can also use a tape measure to extend as far as possible to see how far the gap goes. Another option is a ground-penetrating radar system, which can detect gaps without having to look underneath the concrete.

In most cases, it is caused by soil erosion. This could be due to a tree trunk or something large underneath the house when it was built. After 20 years or so, natural elements slowly degrade and land settles, causing erosion and, therefore, a gap.

You can use poly foam and CPVC pipes. First, observe where the void exists under your concrete slab and use a tape measure to estimate the depth and length of the void to determine how much poly foam you need. Then, drill holes in the concrete and get the foam kit set up. Slowly pull the pipe back while squeezing the trigger and move quickly as the foam will expand. Once you finish one pipe, wait at least 2 minutes before disconnecting. Continue with other pipe connections or areas to spray into the concrete.

Ensure that the soil is packed down properly before pouring concrete to release air pockets and provide a firm foundation. Direct water away from your concrete patio and ensure proper water drainage.

Written by
  • Lara Beck
  • Lara Beck
    Author Home Renovation Professional
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