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The Greener View: Retaining Walls

Jeff Rugg on

Q: Everyone in my subdivision uses man-made blocks for the retaining walls they installed on the sloping parts of their yards. I do not like the look of these concrete blocks and want to use natural stones, but I do not want to mortar them in place. How do I build such a wall?

A: The first step in wall building is to measure how long and how tall the wall will be. If you keep the walls to a maximum of 3 feet tall, you will be able to keep the stones to about the size of a large pumpkin. This is important because a stone that is 1 foot thick, tall and wide will weigh around 100 pounds.

Instead of one tall retaining wall, it is easier and safer to make smaller walls and terrace the land in between them. The terrace may only need to be 1 foot wide so there is just enough room to plant perennials in it.

For natural stone walls less than 3 feet tall, dig a trench for the wall so the first row of boulders can be installed at least halfway in the ground. The trench also must be deep enough to have a minimum 6-inch layer of gravel compacted in the trench first. The wall should be built with the biggest stones on the bottom layers, the medium ones in the middle and the smallest stones on top.

Keep the trench gravel flat and level so the base course of large stones is level. This is the hardest row to install on any wall. Once the base course is in, the rest of the wall goes up easily. The second course, and all higher ones, needs to be set back into the hillside a couple of inches for each foot of wall height. Pour a few inches of gravel behind the wall stones as it goes up, and use a weed barrier cloth behind the gravel to keep the retained soil from washing into the gravel.

Do not allow the seams and cracks between wall stones to run very far without having a rock block the path of the seam. A good wall-building rule is that one rock should sit on two, and two rocks should sit on one. Anyone can just stack a pile of rocks up, but it takes effort to make the wall attractive and strong.

You should be able to walk on the wall stones as the wall is being built. If they are not stable while it is going up, the wall will not be stable afterward. Remember, kids love to walk on the top of walls, so make it a safe walk. Use big or long rocks turned sideways into the hillside to act as anchors that stabilize the wall.

 

One of the nice things about a natural wall like this is that there are spaces between the rocks. This allows the wall to flex with any frost action or gentle earthquakes. Because the gravel pore spaces stay open with the weed barrier cloth protection, water drains freely from behind the wall. The reason many mortared walls tip over is that the soil behind the wall expands when wet and pushes on the wall. After the soil dries, there is no counteracting pressure to push the wall back into place. Even if the wall only bows out one-hundredth of an inch, after one hundred rains, the wall has moved an inch.

If possible, leave out a rock here and there so that a plant can be installed in the wall. It is easier to plant them as you build the wall, but they can be planted afterward, too. Just lay the plant on its side, spread out the roots, spread soil over them and make sure the branches spread out between the stones. Many ground covers, perennials and vines will soften the look of a cold stone wall.

The cost of stones tends to be low, but the shipping and handling adds to the cost. Pretty stones from far away tend to cost more than any stones from close by. Irregularly shaped rocks are easier to build with than rounded ones.

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Email questions to Jeff Rugg at info@greenerview.com. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

 

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