How to Build a Retaining WallNovember 4, 2016
Today we came across a helpful “how to” article on retaining walls and their construction. It was on the website of Alabama-based Total Landscape Care magazine. We are very grateful to them for permission to reproduce parts of it here. You’ll find the original, expanded article by following this link .
You will need:
Wall Caps – of solid, flat material. Most blocks are designed to be used in curved or straight walls.
Interlocking Blocks – These come come in a variety of sizes, colours and designs. Some use pins to lock to the course below; others have a built-in tongue and groove system.
Gravel Backfill – a barrier behind the wall, lined in fabric and filled with gravel, to create an area for water collection and movement.
Landscaping Fabric – helps keep the voids in the gravel from packing with silt.
Topsoil – Leave room above the gravel backfill for topsoil. You can use the top course of blocks and/or the wall cap as edging.
Drainage Pipe – perforated pipe, which allows water to enter along the length of the wall, reduces pressure on the wall structure.
Compacted Gravel Base – A trench with up to 6 inches (150mm) of compacted gravel creates a solid base for the first row of blocks.
1. Lay out the wall
Use a string line for straight walls or a garden hose for curved walls, and mark out a layout line on the ground with marking paint.
2. Dig for a levelling pad
Starting at the end of the wall that is lowest in elevation, dig a trench with a bottom that is 1 foot below grade. Make sure the trench is nearly level in both directions.
TIP : If you find keeping your trench level is getting more than two-blocks deep, you can make steps in the trench that are equal to the height of the blocks you will be using.
3. Add and compact a gravel base
Add up to 6″ (150mm) of 3/4″ (20mm) gravel. Compact with a tamper or wacker plate.
4. Set the first row of blocks
Lay the first course. Use a 4-foot level to straighten several blocks at once, end-to-end and side-to-side.
5. Lay the drainpipe
Connect enough perforated pipe to reach the length of the wall. Wrap the pipe in landscaping fabric and position it just behind the first course of blocks. Slightly raise the end away from the desired pipe exit for positive water flow.
6. Add additional courses
Break up the vertical lines by centering the first block of a new course over a joint line of the course beneath.
With the second course in place, backfill the first course with gravel. This backfill gravel should not have any sand mixed in. 3/4″ (20mm) is ideal because water must pass through it. Continue adding rows and backfilling until your wall has reached its desired height.
8. Top it off
Wrap landscaping fabric over the gravel backfill and trim the fabric. Add topsoil as desired.
Your local builder’s merchant will be able to supply you with all of the materials listed in this article. They’re there to help you build!