18 May 2008

Nothing accidental about this - - a functional, quick, and (relatively) easy retainer wall can be built using concrete blocks and flat steel bars (no concrete mixing, no rebar, no mortar).

This project started when I found myself with a pile of “extra” dirt following a few landscape changes. After thinking about the situation, it seemed that using the dirt to create a small “raised garden” was a good idea. Of course, a raised garden requires some sort of retainer wall to keep everything in place. Having recently suffered “sticker shock” after hiring a contractor to construct a similar retainer wall as a foundation for a fence, I decided to be kind to my bank account by doing it myself. Turns out this decision provided several hours of satisfying activity in the garden in addition to being financially sound.

The concrete blocks I’m talking about look something like this:

Concrete blocks come in a variety of sizes. I used two sizes:
[1] About sixteen inches long x eight inches wide x eight inches high
[2] About sixteen inches long x four inches wide x eight inches high

Where I need a two-block-high retainer, I use the 16 x 8 x 8 blocks as a “foundation”, then stacked 16 x 4 x 8 blocks on top, like so:

Notice that there is a small “lip” on the front of the wall, and a larger “lip” on the back side of the wall. The small lip in the front of the wall served to disguise any small misalignment of the blocks. The blocks can, of course, be mounted flush, without the lip, if you so desire.

The building of the two-block-high retainer goes something like this:

(1) The 16 x 8 x 8 blocks were laid on solid, level ground.

(2) After the foundation blocks are in place, lined up, and squared up, the holes in the blocks are filled with tamped dirt.

(3) Remove any “excess” dirt from the top of the blocks so the upper blocks can be added.
(4) Place the 16 x 8 x 4 blocks on top of the foundation blocks.

(5) Two steel bars are driven into the ground inside the rear wall of the 16 x 8 x 4 blocks.

These steel bars are ready made in various lengths, and can be found at lumber yards and hardware stores. The bars are used when building forms for pouring concrete, but here they are being used to “nail” the retainer wall to the ground so it will not move when dirt is placed behind the wall. These “ready-made” steel bars have become a bit pricey lately. Mine were “leftovers” from some concrete work that was done a couple years ago. Sometimes, you can find them reasonable priced at garage sales, but that could take months.

The steel bars I used are twenty-four inches long, an inch and a half wide, and about three-sixteenths of an inch thick. The dirt in my yard is pretty solid stuff, so the 24-inch bars are more than adequate to hold the blocks. If your dirt is sandy, or has a lot of organic material in it, longer bars should be used.

Does it meet building code. Darned if I know (didn’t ask, so nobody could tell me “no”).

Does it work? Definitely.

NOTE: Probably not a good idea to use this method for a retainer more than two concrete blocks high.

Here is a photo of the wall under construction:

As you can see, one of the steel bars is in place, ready to be driven into the earth to hold the blocks in place. Once all the bars are driven, the openings on the blocks are filled with tamped dirt. Concrete covers for the blocks are available to hide the openings, but I did not consider them to be necessary.

The retainer wall has been completed, dirt has been placed behind the wall, and a few plants have been put in place.

I will post an update when the plants are mature and ready for prime time showing.