How to Dry Lay Retaining Walls for Terraces and Landscaping

The ancient Romans used concrete to build bridges, buildings and retaining walls. Many of these structures still exist. Concrete is a preferred building material even today, but maybe not for retaining walls. The problem is that concrete needs to be engineered for stresses in situ, or in position. Over time conditions may change–the supporting earth may recede, heave, or wash out. This causes engineered concrete structures to move out of position and fall, crack, or otherwise lose integrity. The structure is no longer in situ. An excellent way to combat this problem with retaining walls is to use an even older method known as dry laid construction. Dry laid construction is nothing more than laying stones, blocks, or other materials on top of each other with no mortar or other adhesive material.

The advantages of dry laid retaining walls are:

Cost effective. Rocks, blocks and other materials are available almost anywhere. Any medium or larger city will have several manufacturers of well engineered blocks. Big box lumber yards carry the engineered blocks.

Easy to do. Even kids can stack blocks. There is no time frame or deadline for completing a wall. It can be done as you have time and money.

The wall can move with the surrounding earth. This means you will never have cracks or damages that can’t easily be repaired. Dry laid walls that have crumbled after hundreds of years can be brought back to new condition time after time.

The materials and patterns can enhance the beauty of the plot. Colors, textures and patterns are available to please anyone.

Here’s how you do it with engineered blocks:

Dig a trench following the contours of your future retaining wall. The trench should be level, wide and deep enough to lay your base block on an initial two inch layer of sand and gravel. I use simple 4 X 8 X 16 inch concrete blocks for base blocks. The top of the base blocks should be two inches below expected finish grade. If your land slopes a lot you simply step up, or down, with the base blocks as needed.

Engineered blocks are shaped with a step on the bottom which helps maintain the proper lean to the wall and adds strength and integrity. With rock or stone blocks you need to manually maintain the lean. Lay the blocks with a staggered joint pattern. After two or three layers add gravel behind the blocks to aid water drainage. Gravel alone is enough for short walls. For higher walls you may consider adding PVC pipe with holes designed for septic tank drainage fields. Cover the pipe with several inches of gravel. Lay geo-textile material (heavy paper) over the gravel so dirt doesn’t filter down and clog the gravel. The paper will eventually rot out but the backfill will have hardened enough so it won’t be a problem.

Continue laying up the blocks and backfill as necessary. You can compact the dirt as you go or allow rain and time to do it for you if you are laying the wall slowly. This is what I do because of time or money–maybe because I’m lazy.

Depending on the design of the blocks you may add a topping block when you’ve reached the desired height. That’s it. You’re done!

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