DIY Stone Block Retaining Wall
A retaining wall is both a functional and an attractive hardscape feature for most any outdoor living space where an elevation change exists. Retaining walls can help assist with property drainage and, with a little design ingenuity, can also serve as a raised flower bed – you could even include built-in wall seating!
Building a retaining wall is an advanced DIY task – but Envision’s expert tips can help you get the job done right the first time!
It looks so easy when you see the display of stacked blocks at the big box home improvement retailer. And, truth be told, it’s not all that difficult to stack the wall blocks. The hard part is ensuring they’ll remain stacked in position for years to come. Retaining walls need to have a firm and level foundation (often packed gravel), solid backfill for stability, and some method to relieve pressure during heavy rainfall. Professionals estimate that 20% of the project is stacking the blocks, while the other 80% of your time will be spent preparing the foundation and managing the backfill soil and existing grade while building your architectural masterpiece!
Before starting work or even buying materials, remember to check in with your HOA and review local building codes. You may need a permit to install your retaining wall depending on the wall’s height and your home’s location.
Any good project begins, of course, with a plan. Consider your gutter downspouts and how changing a slope will affect your property once the wall is in place. Also, if you plan to build your retaining wall to include a raised garden along an exterior wall of your home, be sure to keep any elevated soil or mulch below your home’s siding to prevent wood rot.
Once you’ve determined the general location for your new retaining wall, it’s helpful to roughly mark the area to scale. A rope or a hose can be used to get a rough approximation of the size of the wall. To fine-tune your view of the final project – and to ensure straight lines, stakes and string are also helpful. Once the project boundaries are finalized, use a shovel to mark the outline.
Call Before You Dig
As noted before, it’s important to not jump too quickly into your project. Gas lines, water lines, sprinkler tubing or even lighting wires may be hidden below your yard’s surface. For Kansas and Missouri residents, just call 811 and the city will send out a team to surface-mark below the surface utility lines.
Remember to also check with the company that installed or services your irrigation system so you’ll know where the those lines are.
Selecting Stone for Your Wall and Materials Management
There are a wide variety of manufactured stone block products with a natural appearance available for the construction of your wall. It’s good to talk to a materials professional at your local home improvement store to estimate how much block will be needed for the size of wall you intend to build. Bring along height and width dimensions and an idea of the color of block you’d like. Note: many colors of block may be on back order as supply chains for the big box stores have slowed to a crawl – so you may need to go with your second choice in color. You’ll also want to purchase fine gravel for the foundation of your new wall.
All of these materials can be delivered – for a fee – to your property. Typically the drop area for materials is a driveway or front yard area. A wheelbarrow is a handy tool to have on hand when it comes time to move construction items from the drop area to your wall construction area.
Dig the Foundation Trench
Once you’ve received your building materials, marked the layout, and called about underground utilities, start by digging a trench along your marked lines. The first row (or “course”) of block should be buried about halfway so dig your trench about half the block height deep plus another two or three inches for gravel base, and a trench width twice the width of the block.
For example, if you have 6” tall blocks, dig three inches (for half the block height) plus three inches (for gravel base) for a total of a 6 inch deep trench. If the block is also 6” wide, the trench should be 12 inches wide. Note: If you are cutting into an existing grade the job becomes more complex as you’ll need to remove all of the soil in front of your planned retaining wall, level out the base, and also carve out an extra 6″ of soil behind the planned block installation.
Lay the Gravel Base
Once your your trench is dug, it’s time to lay the 2-3 inch layer of gravel. Use a wheelbarrow for transporting the gravel from your materials drop spot (often the driveway) to your new wall area. (Larger scale retaining walls may require a walk-behind front-loader or even a small tractor with a front-end loading capability to move the gravel.)
The gravel should spread evenly with a garden rake and then uniformly compacted and leveled (using a long carpenter’s level). For deeper trenches, compact every 2” depth of gravel before adding more gravel.
Install Water Drainage Pipe
Depending on the grade of your property, it’s possible that rainwater can wash out your retaining wall’s base material and weaken your wall. However, water damage more commonly originates behind the wall. Excess rainwater can build up behind your retaining wall and apply heavy pressure – which, over time, can cause your wall to bulge, lean, or even topple. For a long-lasting landscaping wall, you’ll want to install a flow route to relieve water buildup and damage.
It’s often easiest to install your water drainage system after you’ve completed the first row or two of your wall.
To allow satisfactory drainage, create a slight downward grade on the backside of your wall that will serve to move water to a lower area of your property – being careful not to direct water toward your home’s foundation. Then lay perforated corrugated piping on top of the downward grade allowing seeping water to enter the perforations in the pipe and drain away from the back of your new wall. The piping should extend along the entire length of the wall and end its course in an area where water can efficiently funnel off of your property. Cover the pipe with a drain sleeve to allow water entry but prevent soil and sediment clogs. Then add a layer of gravel backfill – completely covering the drain pipe – except for the exit end of course. Soil will be added on top of the gravel backfill in a later stage of the project as the wall is completed.
Build Your Wall
After you’ve laid the first course of block along your gravel-based trench, you’ll want to fill the hollows of the retaining wall blocks with more gravel for stability and durability. For strength, stability and visual appearance, blocks on every other row will be staggered so the end of the block on the second row is in the center of the block of the first row. To clarify, the first row you lay and the third row (and every odd-numbered row) will have full end blocks. The second and fourth row (and every even-numbered row) will have half blocks at their ends. To get this effect, you’ll need to cut your start and end blocks in half on every other row – using either a hammer and chisel or, for harder block, a masonry saw (which can usually be rented by the day from most home improvement stores). Make sure to wear eye and ear protection, and preferably a dust or respirator mask when cutting wall blocks.
As noted above, install the drainage pipe after laying the first two rows or, if not including back-drainage, add a 6” layer of gravel backfill behind your block rows. As with with the previous steps, you’ll need to evenly rake and compact the gravel well, preferably in 2” layers as you go.
Use Geogrid to Further Stabilize Your Wall
Geogrid is a reinforcing framework within the backfill to help your gravel and your retaining wall remain in place. Make sure the geogrid covers the entire wall length; overlap pieces if necessary to ensure full length. If this overlap is necessary, shovel a thin layer of gravel between the overlap and – you guessed it – compact well!
Continue Building Wall Rows
After building the first couple of rows you’ll get a feel for the rhythm. Just stack, compact and grid for each row. Always check for level and adjust your block rows accordingly as you go. It’s also a good idea to use an outside broom to brush excess gravel or soil from each row of blocks to remove any debris before laying the next level. This will keep the wall sturdy – and level.
Once you’ve laid all the rows of your retaining wall, it’s time to backfill! If you decide to use sand to help with the fill, you’ll want to add landscape fabric to prevent sand from seeping in between your wall blocks. With gravel as backfill, you’ll be able to backfill after every row you lay – which allows the gravel to uniformly settle. Again, compact the gravel in layers as you add backfill. The gravel backfill should be well tamped and filled all the way up until slightly below the height of your retaining wall.
The top layer of the cavity behind your new wall should be covered with soil, sod, or mulch to match the area behind the back of wall-build cavity.
Your wall is nearly complete, all that is needed is capstone! Clear any debris from your last layer of block, then place a layer of capstone block to enhance your wall’s attractiveness. If you like, you can use construction adhesive to firmly attach the capstones and add sturdiness (especially if the wall is also to be used for bench seating). This step often depends on how heavy your retaining wall blocks are (and if they have an overhang). Easily liftable stones the size of bricks should likely be glued down; heavy, larger capstones may not need adhesive.
Add sod to the area in front of your retaining wall, as well as behind the wall (as noted above). Alternatively, you may desire to add topsoil instead of sod if you plan to add planting or other landscaping behind the wall.
Need a Hand with Your Wall – Call Envision!
Both an aesthetic and functional addition, a new retaining wall can beautify your own great outdoors, help make the most of your outdoor space – and even alleviate drainage issues. If constructed properly with the correct materials, a DIY retaining wall can be a fun project – and a way to save a little money on labor.
However, without proper tools, appropriate materials, or the patience and strength required to tackle this project, it all may seem like a bit much. If that’s the case, don’t panic, you can still get that new wall built before winter sets in. Help is just a phone call away with your landscape friends from Envision. Drop us a line and we’ll be right out to discuss your project and provide a complete project estimate. Our experienced team of professional landscapers have the tools and the skills needed to build you a fabulous, functional retaining wall that will enhance your property for years to come!