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Retaining walls that go up without mortar.

You stack or lock concrete modules

RETAINING WALLS have been used for centuries to create level garden spaces on hillsides. Homeowners have a choice of three basic wall-building materials--wood, stone, or concrete--but until recently, the prospect of working with concrete scared away even the most handy of homeowners, since it required assembling forms, bending reinforcing bar, pouring footings, and other messy, labor-intensive tasks.

Now, a number of new systems for building concrete retaining walls have been developed with the owner-builder in mind--and you don't have to mix a single bag of concrete.

You build these walls with precast concrete modules that stack or lock together in various ways. They are ideal for building low retaining walls (from 3 to 4 feet tall) and raised planting beds.

Some of the systems can be used to construct much taller retaining walls, but they require more complex techniques and prior consultation with a soils engineer and local building department.

Invariably, the modular concrete walls will be compared with those made of wood or stone. If you look only at the cost per square foot, the concrete walls cost slightly more. Unlike wood, however, concrete won't rot, and the same modules can be used to make straight or curving lines. They require less skill and experience to build than fitted stone ones.

Most of these modular (sometimes called segmental) walls are considered "gravity" retaining walls because they rely on the weight of the concrete to hold back the mass of soil behind them.

PINS, LIPS, AND FRICTION

The precast modules come in a variety of sizes, weights, shapes, surface textures, and colors. There are three basic categories of modules, each distinguished by how the blocks connect with one another. Some blocks can be stacked vertically, but most are designed to create a slight offset that steps each course back into the hill or retained soil in small increments, usually 1/2 to 4 inches per level.

Lips. To establish the setback and resist outward pushing forces, various manufacturers cast lips into the fronts or backs of their blocks. One maker uses blocks with a slot-and-key cast in the center. If you're just interested in making low garden retaining walls or small raised planters, you'll find that there are a number of styles in this category that are relatively lightweight (in the 19- to 25-pound range).

Pins. To interlock blocks on two levels, several manufacturers employ sturdy fiberglass or steel pins or clips that fit in holes or grooves or attach to the back wall of the blocks. The pins join a top block to two lower ones, helping establish the setback and resist the forward push.

Friction. If you want a more unusual-looking wall, consider a friction-style design. This style has the most diversity of shapes, ranging from bevel-sided O-rings to diamond faces to zigzag profiles. In many instances, the design allows you to create pockets for plant material. The modules' shapes, weight, and frictional resistance combine with backfilled material to resist forward push.

AVAILABILITY AND CONSTRUCTION

The availability of concrete modules varies widely. Many of the major manufacturers license regional production, and what you're apt to find at landscape or building supply stores or home centers depends on regional distribution. The modules are heavy and costly to ship long distances.

Once you've decided on the style of block you want, determine the square footage of the wall you plan on building. Because the modules vary in size, you will need a different number of blocks per square foot depending on the style you choose. Expect costs to run $4 to $8 per square foot.

Each manufacturer's literature can help you design a wall using its system. None require concrete footing, but you do need to dig a shallow trench and fill it with gravel to form a well-draining, level base. Usually, the bottom course of modules is partially buried to help resist forward movement. Some blocks have hollows cast in them, which should be filled with gravel to reduce side-to-side movement and add to the wall's weight. To reduce hydrostatic pressure and assist draining of water, you should also backfill with gravel up to the height of the wall and 6 to 12 inches behind it.

Building these walls is hard work. Surface textures are rough, so heavy leather gloves are a must. The blocks weigh anywhere from 19 to more than 100 pounds apiece, and even a modest-size wall means lots of lifting and shoveling.

For taller walls or for retaining soils that have a heavy clay composition, you can add reinforcing layers of "geogrid," which is made of a synthetic mesh such as polyester. As you build the walls, you need to backfill constantly with gravel or soil. The geogrid is trapped between periodic courses of blocks, lies flat on the backfilled gravel or soil, and then is covered with more gravel or soil. Friction and weight make the wall and soil mass act as a single unit.

SOURCES

The following list covers the three main categories of retaining wall systems. Call the manufacturers for product literature and to see if they have distributors in your region of the West.

LIP SYSTEMS

Allan Block Retaining Walls, (800) 279-5309.

Anchor Wall Systems, (800) 473-4452.

Keystone Retaining Wall Systems (Garden Wall), (800) 747-8971.

Risi Stone Systems, (416) 882-5898.

Rockwood Retaining Walls (E-Z Wall, Rockwood Classic), (800) 535-2375.

Versa-Lok Retaining Wall Systems (Handy-Stone), (612) 770-3166.

PIN SYSTEMS

Innovative Concrete Design (StoneWall Select), (414) 962-4065.

Keystone Retaining Wall Systems, (800) 747-8971.

Rockwood (Rockwood Supreme), (800) 535-2375.

Versa-Lok Retaining Wall Systems, (612) 770-3166.

FRICTION SYSTEMS

Gravity Retaining Walls (Secura-slope, Triangolo), (800) 472-8489.

Hokanson Building Block Co. (Earthstone), (916) 452-5233.

Loffel Retaining Walls (Yardstone), (619) 931-6541.

Peterson Precast Concrete Products (Sta-Bil System), (509) 427-5677.
COPYRIGHT 1993 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Author:Whiteley, Peter O.
Publication:Sunset
Date:Jun 1, 1993
Words:957
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