If you have a sloping area of your yard, the best way to avoid drainage problems or hard to mow elevated areas is to consider building a retaining wall on a slope.
There are two types of retaining walls: dry stack retaining wall and wet, meaning mortar is used. The dry wall is the easiest to build because you can construct it without mortar between the bricks. However, dry walls cannot be higher than 3 feet, sometime less depending on local codes, so that should be taken into consideration if the area you need to terrace is higher than that limit.
Wet cinder block retaining walls require mixing mortar to go between the brick or stones and is much more time consuming. However, these types of retaining walls can be built much higher than three feet.
The best type of material for the DIY’er to use for building walls are the landscape blocks made of precast concrete. The front side of the blocks look very similar to real stone. There are lipped and pinned versions.
For this article, I will describe the basic process of how to build a small retaining wall using a lipped landscaping block.
Making Preparations Before You Dig
When drawing up the plans for your masonry wall, you have to decide how thick it will be. As a general rule, the base of a wall should be half the overall height of the wall. So if you are building a wall 3 feet high, then the base should be 1.5 feet thick.
Finally, you need to call 811 to have someone come out and mark all of the buried utilities with spray paint so you do not run into those.
Once you have your plans drawn out, it’s time to head to the home improvement store to purchase the materials you need for your project.
Tools and Materials
The design plans you created in the previous step should help you estimate the amount of base material (typically sand and crushed gravel) and concrete or stone blocks. If the wall is going to require a significant amount of materials, it is best to have the store deliver the materials to you, usually the next day. That will save you from having to load the blocks and materials by yourself, but also unload them from your truck at home. Most stores will offer delivery for around $100 and deliver everything wrapped in plastic on a pallet. I have employed this method several times and it is well worth the extra delivery money.
Additionally, you will need:
- 2x4, 8 ft long
- 4-ft level
- Stakes, twine and batter boards
- Trenching spade and Round-point shovel
- Rebar and torpedo level
- Construction adhesive
- Perforated drainpipe
- Hand tamper and rubber mallet
How to Install a Retaining Wall
Excavate a Trench for the Foundation Wall
String twine out to indicate the layout of the wall, then follow with batter boards to outline the general shape of the wall.
Next, dig a trench as wide and deep as the manufacturer recommends. Dry retaining walls do not have to go down in the ground below the frost line. Depending on the type of soil you have, a 6 inch trench should be adequate and filled with an inch or two of sand, depending on what the manufacturer of the landscape blocks recommends.
Pour an inch or two of sand inside the trench and tamp down with a flat tool. Place some of the soil you remove on the downhill side of the trench to level the slope. Make sure the trench dirt is perfectly level.
Next, lay out landscape fabric along the back and bottom of the trench to prevent weeds and help with drainage. Unroll enough fabric so that you can cross back over the trench, then add an additional foot to the length. Cover the fabric with gravel and tamp it down.
Setting the Bottom Row of the Wall
There are a couple of different methods used to start the first row. Depending on the type of block, you may be required to set start the first block lip up or lip down.
Either way, set the first block in the sand base and wiggle it a bit then check for level from both side to side and back to front. It needs to be perfectly level so if necessary add sand underneath or tamp down with a rubber mallet until level.
Continue the first row using the same procedure. With each additional block, lay the level across the new block and the nearest blocks and make sure the tops of level with each other.
When you get to the end of the trench you excavated for the retaining wall, you will either have room for a whole block, or you will need to trim one to fit. Whenever this happens with me, I simply extend the wall a bit so that a whole block will fit.
Before you proceed with the second course, make sure that you place a level over the entire first row at different places to make sure it is perfectly level. If not, this will affect the balance and structure of the wall.
Now that you are starting a new row, it is important to stagger the block joints to provide structural stability to the wall as well as creating a more appealing look. You do not want all of the vertical joints to line up.
Therefore, if you ended the first row with a half block, you will need to start the second row with a full block so the joints do not line up.
Lay the second course with the lips of the blocks pointing down hanging slightly over the edge of the first row of blocks. Make sure the second row blocks do not line up with the vertical seams of the first row. As you lay each block, check for level. If you find that a three or four of the block do not line up level, you may need to shim on or more of the blocks with some folded up landscape fabric or part of an asphalt shingle.
At the end of the row, trim a block to fit in the remaining opening.
When you begin building the rest of the wall, alternate so one row begins with a full block and the next with a half block.
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Now that you are on your third row, you know the drill. Lay the landscape blocks in the same way as the first two rows making sure you stagger the seams.
The only difference in this row is that we are going to leave a small opening for a drain pipe at the end of the third row.
Next, go behind the wall and add gravel to that area making sure to tamp it down. Lay a perforated drain pipe lengthwise behind the wall. Make sure you put the white fabric sock over the pipe to keep dirt from entering the pipe.
Now pour gravel over the pipe and tamp it down. Since the fourth row will be your last, fold the landscape fabric over the gravel and trim off any excess.
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Your fourth row should get you to a 3 foot high retaining wall. However, if you purchased larger sized block, you may only need 3 rows.
Continue building the wall as you did for the previous three rows. As you complete the fourth row, add more gravel behind the wall and tamp it down.
Add the Finishing Capstone
When placed side by side, these types of landscape blocks leave a small gap between the each blocks so a capstone is required to create a finished look. These are held in place with some exterior grade adhesive like Liquid Nails.
Simple apply a bead of the adhesive along the top of the wall in a zig zag pattern and set each capstone in place.
Use the soil that you excavated earlier to back fill behind the retaining wall and whatever gaps are left in the trench you dug earlier for the wall. Tamp everything down and rake as desired.
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