Trimming Concrete Patios: Can They Be Cut Back?

Concrete patios should not be in direct contact with the house siding. Concrete absorbs and holds water, which can cause the siding to crumble over time. To avoid this, a gap of at least 1-2 inches should be left between the concrete and the siding, and flashing should be installed to prevent water damage. If the concrete is already in contact with the siding, it may be necessary to trim the siding and install flashing to prevent further damage.

Trimming wood siding

Identify the Type of Siding:

Before starting any work, it is crucial to identify the type of siding on your house. In the provided image, it appears that the siding is HardiePlank, a type of fibre-cement siding. It is important to consult the manufacturer's guidelines for specific recommendations on clearance and installation requirements.

Clearance Requirements:

To prevent issues with the patio installation, it is necessary to ensure proper clearance between the siding and the concrete pad. A gap of at least 1 inch is generally recommended between the top of the concrete pad and the bottom of the siding. This gap allows for proper water drainage and helps prevent water damage to the siding and the structural components of your home.

Water Damage Prevention:

Water damage is a primary concern when trimming wood siding. To mitigate this risk, it is essential to prime and paint the cut edges of the siding to create a seal against water intrusion. Additionally, consider installing flashing, such as an L-shaped flashing, to direct water away from the siding and prevent water infiltration.

Cutting the Siding:

When cutting the wood siding, use the appropriate tools and techniques. A skill saw with the right blade is recommended. It is also advisable to set up a guide board to ensure straight and precise cuts. For inside corners, you may need a vibrating cutter with a carbide blade. After cutting, prime and paint the exposed edges to protect them from moisture.

Structural Considerations:

Be mindful of the structural components of your home when trimming the siding. The siding should hang down below the bottom plate or mudsill of your walls. The bottom edge of the siding should be at least 3/4 inch below the top of the slab or the underside of the door threshold, whichever is lower.

Alternative Approaches:

If trimming the siding is not feasible or creates an unacceptable risk of water damage, consider alternative approaches. You may need to lower the grade and dig out soil to create more space between the patio and the house. Alternatively, you could explore using thinner materials for the patio or consult with a siding company to discuss removing and reinstalling the siding with flashing.

Preventing water damage

Concrete patios can be trimmed away from siding, but it is important to be aware of the risks of water damage. Here are some ways to prevent water damage when dealing with concrete patios and siding:

• Maintain a Safe Distance: Ensure that there is a sufficient gap between the concrete patio and the siding. This gap should be at least one inch but ideally two inches or more. This distance helps prevent water from seeping up the siding and causing damage.
• Install Flashing: Install flashing, such as L-flashing, between the concrete patio and the siding. Flashing acts as a barrier and directs water away from the siding, reducing the risk of water infiltration.
• Seal the Siding: If you need to cut or trim the siding, be sure to prime and paint the cut edges to create a seal against water intrusion. This is especially important for wood siding to prevent water wicking and potential rot.
• Grade the Landscape: Consider the slope of your landscape and ensure that water drains away from the house. You may need to adjust the grade or create a drain field or French drain to direct water away from the concrete patio and siding.
• Inspect Regularly: Regularly inspect your home exterior, especially after rainfall or storms. Look for signs of water damage, such as peeling paint, rotting wood, mould growth, or changes in the position of siding nails. Catching water intrusion early can help prevent more extensive damage.
• Choose Water-Resistant Materials: When replacing or installing siding, choose materials that are water-resistant or waterproof. For example, fibre cement siding is known for its moisture resistance and can help prevent water damage.
• Maintain Caulking: Inspect the caulking around windows and doors twice a year and replace it if it is disintegrating or declining. This helps keep your home well-sealed and prevents water infiltration.

Using flashing

Flashing is a thin, continuous piece of material, usually metal, that is installed between the concrete and the siding to create a barrier against water intrusion. When installing flashing, it is essential to leave a gap between the siding and the flashing to allow for proper drainage and to prevent moisture from being trapped. This gap can be created by trimming the siding before installing the flashing.

One recommended method for installing flashing is to use a two-layer flashing system. The first layer is a self-adhering waterproof membrane applied over the wall sheathing. The second layer is a cover sheet of plastic (PVC) flashing. This method provides an effective barrier against water intrusion and protects the siding and wall structure from moisture damage.

It is also important to ensure that the concrete is sloped away from the house to facilitate proper drainage. Additionally, a bead of sealant can be applied to the concrete before setting the flashing to ensure a tight seal and further protect against water intrusion.

When installing flashing, it is crucial to follow the manufacturer's instructions and local building codes. In some cases, it may be necessary to consult a professional to ensure that the flashing is installed correctly and effectively.

By using flashing correctly and in combination with other water-management strategies, you can help prevent water damage and rot when concrete is poured against siding.

Choosing the right caulk

Concrete patios should not be in direct contact with siding or trim materials, including fiber cement, as concrete absorbs and holds water, and most siding and trim materials are not rated for contact with concrete. This can cause the trim and siding to crumble after a few years of freeze-thaw cycles, and wreak havoc on the wall sheathing, rim joist, and mudsill.

To prevent this, flashing should be installed between the concrete patio and the siding. A two-layer flashing system is recommended: first, a layer of self-adhering waterproof membrane is applied over the sheathing, then a cover sheet of plastic (PVC) flashing.

When choosing the right caulk for your project, there are several factors to consider, such as the surface you are caulking, the durability of the caulk, ease of use, curing time, and colour.

Kitchen and Bath Caulk

For kitchens and bathrooms, choose a caulk that is water-resistant to prevent mould and mildew buildup. Look for a siliconized acrylic or polymer caulk, often called kitchen and bath or tub and tile caulk.

Siding, Windows, and Door Caulk

For siding, windows, and doors, there are several caulk compounds that will create air and watertight seals, including polymer, silicone polymer, paintable silicone, and butyl rubber caulks.

Concrete Caulk

For concrete slabs, a polyurethane caulk works best, but silicone will also do.

Glass Caulk

For glass surfaces, silicone and siliconized acrylic work best. Be sure to read the label to ensure that the caulk adheres to glass surfaces.

Gutter Caulk

For gutters, look for a butyl rubber caulk, also known as gutter sealant. This caulk is ideal for below-grade applications and outdoor waterproofing.

Roofing Caulk

Roofing caulk is available in gun-grade or brush-grade and must adhere to metal, masonry, or asphalt roofing materials.

When choosing a caulk, consider the application. For exterior use, silicone or butyl rubber sealant is best, as it is more elastic and provides a better seal. For interior conditions, especially painted areas, acrylic or latex caulking works well.

Silicone or polyurethane is the most elastic, making it ideal for materials exposed to extreme temperature changes. Acrylic latex caulks are the easiest to apply and smooth out, and they are also the only sealants that clean up with water.

When it comes to curing time, silicone and acrylic caulks have similar drying and curing times (30 minutes to 2 hours for drying and 1-10 days for curing). Butyl rubber dries to the touch in one hour and cures in 24 hours.

Caulk and sealant come in different colours, so you can choose one that matches your surface. For example, Laticrete and Custom Building Products make silicone caulking in colours that match their tile grout.

In terms of adhesion, butyl rubber typically has better adhesion and holds up well under weather conditions.

Some common types of caulk include:

• Acrylic Latex: Easiest to apply and smooth out; clean up with water. Look for versions with added silicone for improved adhesion and flexibility.
• Silicone: Can be 100% silicone or a blend; more elastic than acrylic latex.
• Butyl Rubber Sealant: Oil-based and made from refinery cracking.
• Refractory Sealant: Designed for high temperatures, such as around brick; can be cement-based or silicone.
• Polyurethane: Tougher than other sealants, making it good for driveways and areas that take a beating; gooey consistency makes it hard to work with.
• Solvent-Based: Great for roofing as they don't degrade in direct sunlight and can be applied to wet surfaces; gooey and hard to apply neatly.
• Hybrid: Combines silicone and polyurethane for improved adhesion, flexibility, and longevity; easier to apply than polyurethane but not as easy as acrylic latex; usually the most expensive option.

When caulking, remember that a bead of caulk should be thin and consistent, and it's important to clean up any residue quickly before it dries.

Concrete and siding materials to avoid

Concrete patios can be built using mortared brick, mortared flagstone, tile, or a concrete pad. Concrete is also used as a solid base to prevent materials like brick from cracking due to temperature changes.

However, when building a concrete patio, it is important to avoid placing the concrete step in direct contact with the siding and trim materials. Concrete absorbs and holds water, and most siding and trim materials, including fiber cement, are not designed for contact with concrete. This can lead to water damage and crumbling over time.

For instance, fiber-cement trim can wick water and fail over a few years of freeze-thaw cycles. This can cause decayed trim and even rotten rim joists and mudsills.

Therefore, it is recommended to use flashing to separate the concrete patio from the siding. Flashing will prevent water from reaching the wall sheathing, rim joist, and mudsill. A two-layer flashing system can be used, consisting of a self-adhering waterproof membrane and a cover sheet of PVC flashing.

Additionally, when building a concrete patio, it is important to ensure proper drainage. The patio must slope away from the house to prevent water pooling.

In summary, when constructing a concrete patio, avoid direct contact with siding and trim materials by using flashing as a barrier and ensure proper drainage by sloping the patio away from the house.

Frequently asked questions