Tips for Building A Retaining Wall: Digging and Backfill
Building a sturdy retaining wall requires creating proper drainage around the wall. Failure to
excavate or backfill properly can trap water in the surrounding soil. This can cause cracks in the
concrete or mortar and result in extensive damage over time.
In Massachusetts and New England, it is important to dig deep enough to protect your wall from
heavy frost. Retaining walls built with mortar or concrete need footings that are dug below the
frostline. A non-mortared wall should be built on a gravel filled trench that is also dug below the
Once it is time to backfill around the wall, you should replace the original topsoil with some bank run
gravel or washed stone to promote better drainage. The washed stone that makes up the bank run
gravel measures from 1/4 inch to 6 inches in diameter.
Before adding the gravel, putting down some landscape fabric will create a layer between the
topsoil and gravel to prevent sentiment from mixing in with the gravel. The ends of the fabric
should face downhill to direct water away from the retaining wall. Once the fabric is in place,
began to backfill the bank run gravel in 4-inch layers. Each layer should be graded so that it
slopes downward from the wall at least an inch for every 4 feet. This will give water a place to
drain away from the wall. Be sure to also put down a 4-inch perforated PVC drainpipe at the
base of the wall to aid in drainage.
Backfill one tier at a time as you build the wall. If you do it all at once, the soil and gravel will
not compact enough to prevent a sinkhole from developing or some of the backfill from eroding
away. Tamp down the gravel as you build each tier. When the top tier of the wall is all that
remains, add 6 inches of topsoil behind it and lightly compact the topsoil.
When it is all finished, you will be left with a retaining wall that is equipped to survive the