Keystone walls are retaining walls made out of unique concrete blocks that are designed to fit into each other. This makes it easier to build a concrete wall, since ordinary concrete blocks made from flash ash stack poorly and require cement and rebar to provide enough strength for a retaining wall. Keystone materials help save a step or two in the installation process, while also providing the look of a layered concrete brick wall.
With enough Keystone blocks at hand to build the wall, start by preparing the ground. Remove all plants and roots. Excavate the base trench and fill it with 6 inches of granular fill, such as 3/4-inch well-compacted crushed stone. Deeper trenches are needed for below-grade placement of Keystone blocks. Include room in the trench for a drainage zone. If the project is a large one, you may be able to use a concrete leveling pad. Building on an incline requires a stepped base with sections that rise up the height of one block. The first row of blocks is the trickiest, because they need to be perfectly level. Set the receiving pin holes down so that the pinholes themselves face up.
Each Keystone concrete block should have paired holes. The Keystone package comes with reinforced fiberglass pins designed to create a setback for new courses as you build the walls higher. You can place pins in either the front or the back of the blocks, depending on how vertical you want the wall to be. The further back the pins are, the more stepped or terraced the wall will look.
After the pins are installed in the first course, fill in any empty spaces with crushed stone or other well-draining granular materials. Include extra filler behind the course to provide room for drainage. Behind the drain zone, use soils to create more backflow. Do not use pea gravel. The other courses go on top of the first, fitting into the fiberglass pins. Repeat the steps for the filler materials, drainage and backflow as the wall rises.
When you have reached the last layer of your wall, you need to install the Keystone cap units, smaller face blocks that fit over the last course. Keystone sells a construction adhesive you can use to bond the caps to the underlying unit. Finish the grade with a plastic soil cap or drainage swale so that surface water does not flow directly into the wall.