Proper wall construction is extremely important since it will delay wall failure for as long as possible. I'm sure we've all seen bowed walls or walls leaning outward in the wrong direction, looking as if they are ready to fall.
Even though most walls will need to be rebuilt at some point in their lifetime (due to natural forces such as the freeze-thaw cycle and soil settling) proper wall construction techniques will greatly prolong the life of a retaining wall.
Extremely high walls require special engineering to ensure their strength and safety. Walls over 4-feet tall may require a building permit from your local municipality.
Constructing walls from odd-sized natural stone is an art, especially when each stone needs to be cut to a specific shape and size or the wall needs “cobbled” together by fitting in natural shapes.
Fortunately for the do-it-yourself crowd, there are several products available today using standard sized wall stones to help ease construction. That being said, most medium to large wall stones are heavy, and require a heavy duty truck for delivery and a strong back for construction.
Some suppliers will deliver wall construction products on pallets to your home using small forklifts, but they will need proper access for placing those pallets. Fences, narrow gates and steep slopes can all create problems for deliveries so plan ahead. Ideally, you will find an area to stockpile stones close to your construction site, but not in the way.
The wall stones shown in the photos below weigh 59 pounds each, with a full shipping pallet of 48 stones weighing close to 1-1/2 tons (3,000 lbs.)
Determine the dimensions of the finished wall. Lawn areas can be marked with marking paint in a spray can or by using a string line.
Dig the wall footer to the manufacturer's specified depth and width, according to your site and local conditions. This wall project required enough depth for 6-inches of compacted fill and one base course of wall stone (6" base + 6" base course = 12" depth below the soil surface)
To create 6-inches of well compacted fill for the base leveling pad, this project used 'rock dust' (fine limestone) which is easy to work with due to its small particle size.
Most recommendations call for using an 'angular' gravel as opposed to rounded gravel, since angular stone 'locks' together. Ask your wall stone supplier for specific local recommendations.
The most important step in wall construction is installing the base course properly. Take your time!
A stretched mason's line can be used to ensure the blocks are in a straight line. Use a level to make sure each wall stone is level side-to-side and front-to-back (unless adding “batter”).
Any mistakes on the base course will compound themselves as additional courses are added.
This is also the stage of wall construction to add a perforated drain pipe along the lower back edge of the wall base for taller retaining walls. It's important to have good drainage behind a wall to reduce damage from the freeze-thaw cycle in colder climates. Plan ahead where water from that drain pipe will go.
Once the base course has been leveled, more granular fill can be added around the base course of the wall stones.
Now you can start adding the additional courses of wall stone to your base course. Clean off gravel and burrs from precast products to ensure each stone sits solid and doesn't wobble.
For maximum wall strength use a 'running bond' alignment (like seen with a brick wall on a house). In other words, cover joints between stones by placing wall stones above them so they straddle the joint below. This construction arrangement helps 'lock' the wall together. Avoid lining up joints with one joint above another!
Cutting wall stones
Use a brick hammer or hammer and stone chisel to cut wall stones. Most precast products are pre-notched to aid basic cuts. More complicated cuts can be made by scoring a stone completely along the intended cut. Wear good quality safety goggles to protect your eyes and alert bystanders to flying fragments. Rent a block splitter or diamond-edged cutoff saw for more precise cuts and larger scale projects.
Many wall products have a built-in 'step back' in their design. The pictured stones have a 2-inch lip on the lower back edge to create the proper step back.
With other wall stone you may need to create step back, or what is known as 'batter,' with the rule of thumb being a one-foot step back for every four-feet of wall height. This 'leans' the wall into the slope making it stronger.
Finishing the planter
Ensure there is good drainage behind your wall by adding more granular fill along the back of the wall stones and in the joints, prior to adding your topsoil mix. 2b limestone usually works best for drainage situations in our area, check your local supply yard for product availability and their recommendations.
Raised beds, like the one seen here, provide the perfect opportunity to create a good soil mix for excellent growing conditions. In this case, shredded topsoil was mixed with mushroom manure and 10-10-10 fertilizer. Other soil amendments might include compost, sharp sand or peat moss. If your soil mix needs lime to raise the pH into the proper range, this is the best time to mix in the lime. Reseed damaged lawn areas around the new wall as needed.