Retaining-walls are built to hold back dirt on sloped property. A retaining wall can be built out of different types of block such as cinder block, interlocking blocks, natural stone and wood. There are even blocks specifically made to build a retaining-wall. While you don't need a specific type of concrete-block, these blocks look nice, work well and are easy to install. If you choose to, you can make your own concrete-block, but they are not as sturdy as manufactured block because commercially manufactured blocks are put under a lot of pressure while they are trying in order to make them stronger. Self poured blocks do not last nearly as long and will result in a wasted effort. There are many colors, sizes and shapes to choose from when picking concrete-block. Use your imagination and your sense of style to make the retaining wall a nice part of your yard rather than a wall that is purely functional and an eyesore.
Dig a trench 8 approximately 10 inches deep or so and about 10 inches wider than the than the concrete-blocks. The trench will be as long as you want the retaining wall to be.
Level the bottom of the trench so there are indentations, lumps bumps or holes.
Tamp the dirt down tightly at the bottom of the trench. Use a hand held tamper or a power tamper. Power tampers can be rented at tool rental centers, home improvement stores and some hardware stores.
Pour in approximately 5 to 6 inches of crushed stone into the trench.
Level the crushed stone with a straight flat board. Sweep the board over the top so it knocks down any hill and fill in valleys by hand.
Pour approximately 2 inches of masonry sand over the crushed stone.
Lightly compact the masonry sand and use a trowel or a straight, flat board to even out the masonry sand.
Put the first row of concrete-blocks on top of the masonry sand and butt it up to the dirt in front of it. The first row of concrete-blocks will be approximately 3 to 4 inches into the ground.
Mix mortar in a trough or wheelbarrow.
Apply 1 to 1/2 inches of mortar to the top of the concrete-block being used for the first course. Only add mortar to 3 to 4 blocks at a time, work in smaller manageable areas.
Set the row of concrete-block on top of the first row. Space the block so the end of the block on the bottom row will be at the halfway point of the block on top of it. When concrete retaining wall blocks are Staggered like this it allows the wall to be stronger.
Use a wet saw to cut concrete-blocks as you go to make them fit.
Fill in the area behind the concrete-block with crushed stone. Crushed stone helps with drainage and takes away a lot of the pressure that is put on the retaining wall.
Continue to mortar the top, put concrete-blocks in place, add stone behind the wall until you reach the height you want your retaining wall to be.
The top row is a finish block the will look nice on top of your wall. Mortar your finish block to the top of your wall in the same manner you added courses to the retaining wall.