How to Choose Modular Concrete Block

Sorting out the options

Modular concrete blocks for retaining walls and garden projects are available in a huge range of styles and prices. This article surveys the choices and explains the options.

By the DIY experts of The Family Handyman Magazine

Overview

Walk around most residential neighborhoods and you'll find concrete block retaining and garden walls dotting the landscape. No longer just holding back earth, stabilizing slopes and preventing erosion, modern concrete block walls define pathways, create borders for outdoor “rooms” and serve as focal points in featureless yards.

Building a block wall is a significant investment of time (if you do it yourself) and money (whether you do it yourself or pay someone to do it). Shopping for modular block can be confusing because of the many colors, textures, shapes, styles and stacking systems available. This article will help you sort through your options and discuss what you need to know before you shop so you can buy the right block for your garden or retaining wall.

In a nutshell

  • The more expensive the block, the more it will look like natural stone.
  • Each block system will accommodate curves, steps, corners, caps and setbacks differently. Your wall's requirements will help narrow your options.
  • When you shop, take along a sketch of the wall's height, length, radius of inside and outside curves, and specific features. Then you'll have everything you need to choose the material and narrow down prices on one trip.
  • Even if you plan to hire a pro, shop around to see actual walls rather than depending on contractors' pictures to imagine how yours will look.
  • Home centers carry some systems, but you'll find the widest variety of options at landscape suppliers.

What Kind of Wall Do You Get For Your Buck?

Top of the line: $11 to $15 per sq. ft.
The most expensive block offers the greatest flexibility in design potential, styles, colors and wall size. Big “wow” factor.

Mid range: $9 to$10 per sq. ft.
Mid-priced block is good for highly visible walls where function is still the primary concern. It offers a high-end look and feel and is available in many colors and styles.

Least expensive: $4 to $8 per sq. ft.
These easy-to-install blocks are often used for garden walls. They're available in a limited number of styles and colors.

Top of the line Top of the line: $11 to $15 per sq. ft.
Mid range

Photo courtesy of VERSA-LOK

Mid range: $9 to$10 per sq. ft.
Least expensive

Photo courtesy of KEYSTONE

Least expensive: $4 to $8 per sq. ft.
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What's the wall's purpose?

A freestanding garden wall 3 ft. or less in height that serves a more decorative function gives you more flexibility with the size, style and type of block you choose. Most manufacturers offer a wide variety of styles in two or three basic sizes. The garden wall size is the most common. These relatively small blocks (about 12 in. long x 4 in. high) are lightweight (less than 25 lbs.) and work best for accent walls around the yard and garden up to about 30 in. high. All four sides are finished and they have special blocks for columns, corners and ends.

Retaining walls, because they're load-bearing and slope into a hill slightly, require larger blocks and beefier connections. These blocks are 16 to 18 in. long x 6 to 8 in. high and weigh 50 to 75 lbs. Big walls usually entail excavating and moving tons of soil and gravel as well as the heavy block itself. These walls can be daunting to do yourself, so think it through before you unknowingly dedicate a whole summer to the task. Most systems are engineered to handle heights up to 4 ft. Retaining walls above that height must be designed or approved by a licensed engineer.

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What kind of look do you want?

Do you want the block to blend with your property's existing features or to inject something new into the landscape? Although specific shapes, colors and textures vary by region, almost every manufacturer produces four main styles (see photos).

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What are your wall's requirements?

The details of your project will help you decide on a block system. Different block systems are suited to different project requirements. For example, all block systems have limits as to how tight a curve they can form without being cut. Systems also vary in how they handle corners, setbacks, cap blocks, columns and steps.

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What's your budget?

The cost of block is only a piece of the total project budget. If you're using a contractor, you'll obviously pay labor costs. A good rule of thumb for a contractor-built wall is to double the materials price—in other words, half labor, half materials. Make sure to agree on the front end whether your contractor will provide final grading and resodding (or will leave your yard a total disaster). Will the driveway be repaired? Wheel ruts fixed? Topsoil included? These details often account for why one bid is significantly higher or lower than another.

If you plan to build your own wall, beware. There's a lot of heavy work, including tons of fill and footing material to get delivered and moved. Also consider the tools you'll need to rent and other additional costs:

  • Delivery charges for materials. Don't wreck your back or your vehicle. Block is heavy, even the garden wall variety. Pay the extra charge to place your materials exactly where you want them.
  • Skid steer rental ($200 per day). Keep in mind that using heavy machinery will damage your yard, so you need to add in the costs of grading and resodding as well.
  • A block splitter costs $90 per day. You can also have the landscape yard split the blocks for you.
  • Plate compactor rental ($50 per day). It's crucial to compact your footing material or you'll have a sagging, crooked wall in the future.
  • Other materials such as “compactable gravel” for the base, drainage layer material and drain tile.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Tape measure
  • Line level
  • Level
  • Wheelbarrow
  • Rubber mallet
  • Safety glasses
  • Spade

You'll also need leather gloves, a block splitter, plate compactor, skid steer, sod cutter, and (for large jobs) a skid steer.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Modular concrete block
  • Gravel
  • Sand