Concrete Patio Installation: Voiding Your Foundation Warranty?

Pouring a concrete patio can transform your backyard, but it's a big job that requires careful preparation. One of the most important considerations is whether it will void your foundation warranty. While there is no definitive answer to this question, there are a few things to keep in mind. Firstly, it's crucial to ensure proper drainage by sloping the concrete away from the house. This will prevent water from seeping into the foundation and causing potential damage. Secondly, the concrete patio should not be attached to the foundation. It should be left independent to allow for movement and prevent cracks. Finally, it's essential to use quality materials and proper construction techniques to avoid future issues. Voids under concrete slabs can lead to serious structural problems, so it's always best to consult a professional for guidance.

Voids under concrete slabs

• Structural Integrity: Voids can compromise the structural integrity of the concrete slab, leading to uneven settling or cracking. This can result in an uneven surface, trip hazards, or even the complete failure of the slab.
• Soil Erosion: Voids allow water to penetrate and erode the soil beneath the slab, creating larger voids and further weakening the support for the slab.
• Moisture Issues: Voids can create pathways for moisture to enter the slab, leading to issues such as mould growth, deterioration of the concrete, or damage to structures built on top of the slab.

There are several methods to detect and fill voids under concrete slabs. Here are some common approaches:

• Ground Penetrating Radar (GPR): GPR is a cost-effective and rapid method to screen large concrete slabs for potential voids. It requires minimal preparation and can provide valuable insights on the location of voids.
• Impulse-Response Method: This non-destructive method offers a rapid and cost-effective way to assess the condition of concrete structures. It uses stress waves to evaluate the likelihood of damage and helps in the quality assurance of concrete repair.
• Ultrasonic Pulse Echo Tomography (UPE): UPE is a non-destructive testing method that uses acoustic stress waves to study the properties of sub-surface layers and locate defects. It is valuable for assessing the condition of concrete slabs, particularly for detecting voids or deterioration beneath the surface.
• Polyurethane Foam Injection: This method involves drilling small holes into the slab and injecting void-filling foam, which spreads out and rapidly expands to fill all voids. It also consolidates the soil, rock, and any organic material under the slab, providing support, lift, and levelling.
• Mudjacking: Mudjacking is an older method that uses a cement slurry injected through holes in the slab to fill voids. It is less expensive than polyurethane foam injection but may not fill all voids, and the concrete slurry needs time to cure before the slab can be used again.
• Replacing Part of the Slab: This involves tearing up sections of the slab to access the voids, filling them with a mix of sand and concrete, and then pouring new sections of the slab.
• Replacing the Entire Slab: If there is extensive damage, it may be necessary to dig up and replace the entire slab. This is one of the most costly and time-consuming repair options.

Expansion gaps

The gap should be cleaned out to a depth of about 3 inches, and then filled with a hybrid urethane sealant that incorporates silane and end-capped polymer technology. This type of sealant will produce a strong bond with the concrete slabs while allowing for expansion and contraction.

It is important to follow the manufacturer's directions when working with these sealants and to use the recommended backer rod to ensure the repair is long-lasting. The colour of the sealant can also be matched to the concrete, and sand can be patted onto the wet sealant to improve the appearance of the gap.

Some people suggest using a self-levelling sealant, but it is important to ensure that this is flexible to prevent cracking. Others recommend filling the gap with sand or topsoil before sealing, to provide a more flexible base. Pea gravel is also suggested as a filler that will allow for shifting and provide drainage.

In summary, when pouring a concrete patio against a foundation, it is important to leave an expansion gap and to fill this gap with a flexible material such as sealant, sand, or pea gravel, to allow for the natural expansion and contraction of the concrete.

Concrete patio thickness

The thickness of a concrete patio depends on the type of structure it will support. While four inches is the minimum thickness for a concrete patio, it is recommended to make it six to eight inches thick if the patio will support a structure such as a gazebo or hot tub.

The thickness of the concrete patio also depends on the foundation. A gravel base is the most common and practical support. While you could use a 1:1 ratio for the slab and gravel, it is advisable to stick to 4-6 inches of gravel as the foundation. If you opt for the minimum of 4 inches, you will need to work with an 8-inch pit minimum.

The quality of the concrete mix is also important. A high-quality mix with fibre mesh is recommended, as well as the use of steel reinforcement or concrete reinforcing fibres to increase durability and crack resistance.

Concrete patio reinforcement

Pouring a concrete patio likely won't void your foundation warranty, but it's important to check with your builder or warranty provider to be sure. Here are some tips for reinforcing your concrete patio:

Use Rebar or Wire Mesh

Reinforcing your concrete patio with rebar or wire mesh will help to strengthen the slab and control cracking. Rebar is a steel bar composed of steel wires that aid concrete under tension. It is placed within the concrete to provide structural strength and help hold cracks together, keeping the slab level. Wire mesh can also be used as a reinforcement option and is placed in the middle of the slab's thickness.

Create an Isolation Joint

When pouring concrete next to an existing structure, such as your home's foundation, it is important to create an isolation joint. This can be done by gluing a 1/2"-thick piece of asphalt-impregnated fiberboard to the structure. This will prevent the new concrete from bonding with the foundation, allowing them to move independently and minimising the risk of damage.

Ensure Proper Drainage

Proper drainage is crucial to prevent water from pooling and causing issues with your concrete patio and foundation. When pouring concrete against an existing structure, create a slight slope away from the structure to direct water runoff. Additionally, adding a compactible gravel subbase improves drainage and provides a level foundation for the concrete.

Follow Local Regulations and Guidelines

Before beginning your project, be sure to research and adhere to all local regulations and guidelines for building a concrete patio. This includes obtaining any necessary permits and following safety protocols.

Prepare the Site and Excavate

Before pouring concrete, it is important to properly prepare the site and excavate to the planned depth. Remove any sod or existing structures and evaluate the soil conditions. Dig a test hole to get a better idea of the excavation process and consult a landscape engineer if you have sandy or loose soil.

Use a Form to Contain the Concrete

A form is a frame, typically made from 2 x 4 lumber, that is used to contain the poured concrete and establish its thickness. Cut and position the form boards according to the size of your project, staking them in place to support any joints. Coat the insides of the forms with vegetable oil or a commercial release agent to prevent the concrete from bonding to them.

Pour and Finish the Concrete

After mixing your concrete, pour it into the forms and use a 2 x 4 in a sawing motion to level and remove excess. Float the concrete surface to create a smooth and skid-resistant finish. You can also create a broomed finish or a smooth steel-trowel finish. For larger patios, cut control joints to help control cracking if the ground shifts. Finally, treat the concrete with an acrylic cure and seal.

Concrete patio excavation

Excavating for a concrete patio is a big job that requires determination and arm strength. Here is a step-by-step guide on how to excavate for a concrete patio:

Step 1: Lay Out the Shape

Use batter boards and mason's line to outline the patio or walkway. Use powdered chalk to mark the outline.

Step 2: Cut the Sod

Use a garden edger to cut straight through the sod. Work your way along the layout lines, cutting 1-foot strips with the edger. A sod lifter will save you from having to bend over too much.

Step 3: Dig a Trench

Tie mason's lines between the stakes to represent the height of the finished surface. The lines will be level with the patio line on the house. Excavate a 1-foot-wide trench outside the lines to the required depth. If the patio will be against the house, snap a chalk line under the door, about 1-3 inches below the threshold. This marks the finished surface of the patio and sets the excavation depth.

Step 4: Measure the Trench

Use a tape measure to periodically check the depth of the trench to ensure consistency.

Step 5: Excavate Interior

Remove the lines but keep the stakes. Excavate the interior, removing soil to the depth of the perimeter trench. Check the depth periodically with a level or slope gauge. If you remove too much soil, fill the dips with sand or gravel, not loose soil. Use a flat spade or square shovel to dig the final inch of soil.

Step 6: Prepare the Subbase

Dig a test hole to evaluate soil conditions and determine how easy the excavation will be. Sandy or loose soil may need amending; consult a landscape engineer. Add a compactable gravel subbase to provide a level foundation and improve drainage. Pour a 5-inch layer of gravel and tamp it down to a depth of 4 inches.

Step 7: Create an Isolation Joint

When pouring concrete next to structures, glue a 1/2-inch piece of asphalt-impregnated fiberboard to the adjoining structure. This creates an isolation joint, allowing the concrete and structure to move independently and minimising damage risk.

Step 8: Lay Out & Excavate the Site

Lay out a rough project outline with a rope or hose. Use a carpenter's square to set perpendicular lines. Drive wood stakes near each corner of the rough layout, positioning them outside the actual project area but aligned with the borders. Connect the stakes with mason's strings, following the project outlines. Use the 3-4-5 triangle method to ensure the strings are square. Adjust the strings until the entire project area is exactly square.

Step 9: Level the Strings

Attach a line level to one of the mason's strings as a reference. Adjust the string up or down until it is level. Adjust the other strings accordingly, ensuring intersecting strings contact one another.

Step 10: Create a Slope

To direct water runoff, most concrete surfaces should have a slight slope, especially if they are near your house. Create a standard slope of 1/8" per foot by multiplying the distance between the stakes by 1/8 and moving the strings down accordingly.

Step 11: Excavate the Site

Start by removing the sod with a sod cutter or square-end spade. Strip off the sod at least 6 inches beyond the mason's strings. The subbase should extend at least 6 inches beyond the project area. Use a story pole as a guide for excavating the site, ensuring the bottom of the site is consistent.

Step 12: Lay the Subbase

Lay a subbase for the project (unless a frost footing is required). Pour a 5-inch layer of gravel and tamp it down until it is even and compressed to a depth of 4 inches.

Frequently asked questions