Building A Concrete Patio Wall: A Step-By-Step Guide

Building a concrete patio wall is a challenging task that requires careful planning and execution. It involves several steps, from site preparation to pouring concrete and finishing. Before starting, it is essential to check local building codes and obtain any necessary permits. The process begins by excavating the area and establishing a solid, level base. This is crucial for the stability of the wall. After compacting the base material, a layer of sand is added and levelled. Then, the concrete blocks are installed, with proper alignment and reinforcement. The blocks are secured using pins or other methods, depending on the chosen system. Backfilling with gravel or crushed rock provides stability and drainage. Finally, the wall is capped with concrete or stone, ensuring a smooth finish. Constructing a concrete patio wall can be a rewarding DIY project, but it requires attention to detail and may be better suited for those with some prior concrete experience.

Excavate and level the area

To build a concrete patio wall, you'll need to begin by excavating and levelling the area. This is an important step to ensure the patio wall is stable and secure. Here's a detailed guide on how to do it:

Firstly, remove any existing sod or grass from the area where your concrete patio wall will be built. Give yourself a little extra room around the edges to make it easier to place the form and screed the concrete later on. Next, use a shovel, rake or spade to scrape, rake and shovel the patio area to make it as level as possible. Depending on the grade and the finished height of your patio, you may need to add or remove some soil to level it out.

Now, you need to establish a common stake height to mark the top of your sand levelling bed. Drive stakes into the ground at the corners of the patio and every 2 feet in between. These stakes will be a reference point for the height and level of your patio wall. Use a transit level or a 4-foot level taped to a straight 2x4 to ensure the stakes are level. Make sure the patio slopes away from any nearby buildings at a rate of 1/8 to 1/4 inch per foot—check your local building code for the correct slope rate.

Once the stakes are in place, you can start to excavate the area. For a standard concrete patio, dig out a space 8 inches deep. This accounts for 4 inches of gravel base, 4 inches of concrete and 2 inches to allow for mortar and brick. If you're building a retaining wall, the depth of your excavation will depend on the height of the wall. For example, for a 4-foot-tall retaining wall, you'll need to excavate a trench deep enough to accommodate 4 to 6 inches of compacted base, 1 inch of levelling sand and half the height of the first course of blocks.

After excavating, it's important to compact the exposed surface. Spread gravel in 2-inch layers, compacting each layer with a hand tamper or a gas-powered tamper, depending on the size of your project. For small projects, a hand tamper will suffice, but for walls longer than 30 feet, you'll need a gas-powered tamper. Keep adding and compacting gravel until you have a bed about 4 inches deep.

Finally, add a layer of sand on top of the gravel base. Use a long, straight screed board to level the sand, creating a flat-as-a-pancake sand base for installing the first course of blocks. With the tops of the stakes as guides, screed the sand until it is level with the stake height. A hand trowel is useful for fine-tuning small dips and bumps in the sand.

Prepare the base

Preparing the base for your concrete patio wall is a crucial step that will ensure the stability and longevity of your structure. Here is a detailed guide to help you through the process:

Clear the Area

Remove any existing sod or vegetation from the area where you plan to build your concrete patio wall. Give yourself a little extra room around the edges to make it easier to place the form and screed the concrete. This step will create a clean slate for you to work on and ensure that your base is level and sturdy.

Excavate and Level the Base

Use a transit or a 4-foot level taped to a straight 2x4 to establish a common stake height. This will indicate the top of your sand levelling bed. Excavate and level the area, creating a flat area at least 4 to 6 inches deep and 24 to 28 inches wide for installing the compactable base material. Provide a clear area of at least 12 inches behind the wall for installing the crushed rock backfill.

Install the Base Material

Install 4 to 6 inches of compactable base material, levelling it to the tops of the stakes. Compact the base material until it is about 1 inch below the tops of the stakes. For small projects, you can rent a hand tamper, or for longer walls, consider renting a gas-powered tamper. This step is crucial, as it provides a solid foundation for your concrete patio wall.

Add Sand and Screed

Provide a flat and level sand base for installing the first course of blocks. Using the tops of the stakes as guides, use a long, straight screed board to level the sand. A hand trowel is useful for fine-tuning small dips and bumps in the sand. This step ensures that your first course of blocks will be level, which is essential for the stability of your wall.

Install the First Course of Blocks

With your level sand base ready, it's time to lay the first course of blocks. Use a taut string line to establish a straight row and a 4-foot level to level the blocks lengthwise and a torpedo level to level them front to back. Once the first row is installed, pack native soil to grade level on both sides of this course to anchor the wall firmly in place.

Now that you have a solid base, you can continue building your concrete patio wall by following the subsequent steps of your chosen guide. Remember to always refer to local building codes and regulations to ensure your project complies with safety standards.

Install blocks and backfill

Now that the base is level, you can start installing the blocks. For a 4-foot-tall wall, you'll need to excavate a trench deep enough to accommodate 4 to 6 inches of compacted base, 1 inch of levelling sand, and half the height of the first course of blocks.

Start by laying the first course of blocks, using a taut string line to ensure a straight row. Use a 4-foot level to level the blocks lengthwise and a torpedo level to level them front to back. Once the first row is down, pack native soil to grade level on both sides of this course to anchor the wall in place.

Drive in the pins to lock each course to one another and to help establish a 3/4-inch backset for each row. Use an extra pin to set the installed pins below the surface of the blocks so they don't interfere with the next row. Remember to offset the vertical joints of each row by at least 4 inches from the row below to maintain wall strength.

Continue installing the blocks, course by course, until you reach the desired height. If you need to cut blocks to size, first score the top and bottom with a block chisel, then turn the block on its side and finish the cut with a series of solid blows.

Once you've reached the desired height, backfill the wall with crushed gravel. Crushed gravel locks together better than smooth gravel and helps direct backfill pressure downward rather than outward. The backfill also provides a fast path for water drainage and acts as a tree root barrier.

Finally, install a "cap" of native soil, about 6 inches deep, on top of the backfill to help keep surface water out of the trench. Use concrete adhesive to secure the cap blocks in place.

Pour concrete

Pour the concrete

Mix enough concrete to complete the wall in one go. If you can't do the whole wall in one go, divide it into smaller sections.

Pour the concrete directly into the wood form using a chute or hose attached to the mixer. To achieve a strong wall, keep the layers of concrete 20 inches thick or less. Work from one end of the wall to the other, moving back and forth until the concrete is as high as you want the wall to be.

If you have to wait to pour additional layers, pour a store-bought concrete bonding adhesive onto the settled concrete so the next layer bonds to it.

As the forms fill, watch the concrete levels. When the concrete reaches the wood spreaders, pull the spacers out. Have a ladder ready so you can reach the top of the forms. Tug the wire up to keep the spreaders out of the concrete. Gradually raise the spreaders as you fill the space between the forms.

Take the spacers out as you work to prevent the concrete from curing around them. Leaving them in will leave gaps in the layers, weakening the wall.

Smooth out the concrete with a screed or another tool. Climb up a ladder and level out the concrete with the top of the form you built. If you can’t get a screed up there, try using a float or a trowel. Screeds and floats are better for covering large areas in a short amount of time. Drag the tool along the concrete to remove the excess.

Pack down as much concrete as you can before scraping off the excess. Any air bubbles or empty space left behind reduces the integrity of your wall. To help pack and level the concrete properly, tap the forms with a hammer or mallet.

Finishing touches

Cover and cure the concrete for up to four days. Cover the concrete with something that holds water. Burlap and straw are two options, but you can also buy polyethylene sheeting or concrete curing blankets. Dampen the covering with water and moisten it every day until the concrete hardens.

Some concrete mixes take 28 days to solidify, but you will need to remove the forms before then to finish the installation.

Remove the forms and the wires attached to the concrete. Cut the wires to pull them out of the concrete. Since the concrete hasn’t solidified yet, you won’t have trouble removing the ties. Then, pull the forms away from the concrete to remove them. Remove nails as needed to deconstruct the forms.

Cover the wall and let it finish curing for up to 24 more days. Look for any holes in the wall before you continue. Normally, you won’t need to do any additional work. Put the cover back in place, wet it again, and wait. After the concrete hardens, remove the cover to admire your work.

Cure the concrete

Curing concrete is an essential step that should not be skipped when building a concrete patio wall. The curing process ensures the concrete gains strength, prevents shrinkage cracks, and improves the durability of the slab. Here are the steps and methods to cure concrete effectively:

Maintaining Slab Moisture

One of the key objectives of curing concrete is to retain moisture in the slab. This is achieved by preventing the concrete from drying out too quickly. The traditional "wet-curing" method involves covering the slab with special curing blankets and continuously wetting the surface for 28 days. While effective, this technique is time-consuming and expensive.

Using Curing Compounds

A more modern and popular approach is to use curing compounds, which are liquid chemical formulations sprayed onto the concrete surface. These compounds form a film that slows down the dehydration process, allowing the concrete to hydrate properly. These compounds can be left to dissipate on their own or removed after 28 days using a cure and seal remover.

Applying Densifiers

Some curing products also act as densifiers, which increase the hardness, durability, and stain and water repellency of the concrete. An example of such a product is PROSOCO's DensiKure, which is designed for indoor, smooth, steel-trowel-finished concrete. A single application with a pump-up sprayer is sufficient.

Covering and Insulating

If you are pouring concrete during cold weather, it is crucial to prevent the water in the concrete from freezing for at least a week to ensure proper curing. Cover the slab with plastic and spread a layer of straw, approximately 4 to 6 inches thick, to retain heat and protect against freeze damage.

Timing and Protection

Regardless of the curing method chosen, it is important to allow the concrete to cure undisturbed for at least 48 hours. During this period, prevent anyone or anything from walking on the surface. After curing, the concrete will be ready for use, but it will continue to gain strength over time.

Frequently asked questions