Building a concrete or cement wall out of cinder blocks gives your home and yard privacy, and the final product has a low-maintenance durability that can last for decades.
While wood fences are popular for their economy and easy buildability, concrete or cement walls can provide more privacy and even a greater degree of soundproofing. Because masonry materials last not just years but decades, a well-built concrete or cement wall can be a long-term asset to your home.
Basics of Building a Cinder Block or Concrete Wall
You can build an entire concrete wall with just concrete masonry units (CMUs), often called concrete blocks or cinder blocks. Mortar is the glue that holds them together below and to the sides.
Concrete or cinder blocks are 16 inches long, 8 inches high, and 8 inches wide. The blocks are hollow in the center. A concrete web separates this area into two, smaller hollow sections.
All concrete walls need to rest on concrete footings for stability. Some concrete walls need 1/2-inch metal reinforcing bar (or, rebar) to be run vertically and horizontally through them.
When to Build a Cinder Block or Concrete Block Wall
Digging the trench for the cinder block wall's concrete footing and curing the mortar are the only weather-dependent parts of this project. If the ground is frozen, you will not be able to dig by hand, and extreme cold can affect the curing process of the mortar. Otherwise, the wall can be built at any time of year, in nearly any condition.
Estimating Number of Blocks
Calculate the necessary cinder blocks by square feet. The typical cinder block is 8 by 16 inches, meaning that a cinder block covers an area of 1.125 square feet. The total cinder blocks needed will be 1.125 times the area of the wall, but be sure to subtract the openings such as windows, doors or any other architectural feature. The wall area is calculated by height times its length.
Remember to add five percent to account for waste or any material that will be damaged. When completing the estimate, make sure you have also included some material that will be needed as fillers that might be required when the height or wall-to-wall dimensions are not according to plan.
Permits and Codes
Free-standing concrete block walls may require permitting. Check with your local building department to determine if a permit is required. Even if the wall is exempt from permitting in your area, it may still require zoning approval. Check with your local planning department for zoning requirements.
This cinder block wall is non-load bearing, so it is used for privacy or as a decorative element and not as walls of a structure, such as a garage. If the wall were built to load-bearing specifications or even as a free-standing wall, alternating centers of the cinder blocks may need vertical rebar or a ladder mesh reinforcement running from the top of the wall to the bottom of the concrete footing.
Some of the cavities may need to be filled with either mortar or concrete. You may also need to run horizontal rebar the length of the wall, between every third course of blocks.
Discuss your intended concrete block wall with your local permitting department for information about rebar or reinforcement requirements.
Working with masonry materials is labor-intensive, so take frequent breaks and stay hydrated. Keep your back straight and use your legs when lifting. Wear heavy-duty gloves when handling the concrete blocks. When pouring mortar or concrete or for any other activity that creates dust, wear breathing protection.
Consult a structural engineer to design the footing including where to install the vertical reinforcement, which usually is placed every 24 inches. Normally a foundation wall with seven rows of blocks will be 24 inches wide and 12 inches deep and should have a footing 30 inches below grade. Remember to build a leveled footing where the cinder block will be placed.
Equipment / Tools
- 75 cinder blocks, 16 inches x 8 inches x 8 inches
- 3 bags of mortar
- 3/8-inch scrap plywood
- 8 concrete cap blocks, 8 inches x 16 inches
- Trenching shovel or trenching machine
- Mixing tub
- Chalk snap line
- Garden hose and sprayer
- Bubble level
- Clean bucket
- Mason's string line
The poured concrete footing should be twice the width of the intended concrete wall. So, for an 8-inch-wide cinder block, the footing should be at least 16 inches wide. Use only high-strength concrete for building the concrete wall footing.
With a trenching machine or a trenching shovel, dig down below the frost level for your area. If your area experiences freezing temperatures, building above the frost line will result in frost heave, a condition where expanding soil causes structures built on top to move and sometimes fail.
Fill the trench with concrete until it is just below the frost level. If rebar is required, prior to pouring the concrete, you will need to set up the rebar so that the concrete can be poured around it. Wait two or three days for the concrete to cure. The thickness of the footing will vary based on where the frost level is and how deep you dug your trench, but it should be a minimum of eight inches thick.
Snap Chalk Line
With the chalk line and an assistant, first snap a chalk line down the center of the intended placement of the bottom row of concrete blocks. Then snap two more lines: one on each side of the intended bottom row of blocks.
Establish Two Leads
Dry-fit one full-size block between the lines. Add a 3/8-inch spacer of plywood at the end to represent the mortar that will eventually be filled in there. Continue dry-fitting the course until you reach the end. Mark the locations of the two end blocks, or leads, then remove them.
Use high-strength mason's mortar mix for setting the blocks. Mix up the mortar in a motorized mixer or in a masonry tub, using the amount of water specified on the package. Test the mortar with the trowel by picking up some mortar, then holding the trowel to the side. If most of the mortar remains on the trowel, the ideal consistency has been achieved.
Lay Mortar Base
With the garden hose and sprayer, lightly moisten the footing. Using the two outer chalk lines as reference marks, lay two rows of mortar, each row about 1 inch high by 1/2 inch wide. One 80 pound bag of mortar mix will lay a course of about 12 to 14 standard-size concrete blocks.
Lay Cinder Block Leads
Press the cinder block for the first lead down onto the lines of mortar. The holes should be facing vertically. Do the same for the other lead at the far end of the wall.
Press firmly, but not so hard as to extrude the mortar from the sides. Check on all sides with the bubble level. Most adjustments can be made by tapping the block with the handle of the trowel. For more force, tap the block with a rubber mallet or by placing a piece of scrap two-by-four against the block and tapping with a hammer.
Fill Bottom Course
Continue the entire bottom course, often checking for level and plumb by laying the bubble level along the top and sides of the blocks. Maintain the 3/8-inch distance between each block. Before laying a block, butter the side of it with the trowel so that it will stick against the adjacent block.
Set Closure Block
The last open space in a course will be filled with a closure block. Butter each side of the closure block and set it straight down. If there is any extra space between joints, fill it with mortar.
Start Second Course
The second course begins with two half-sized 8-inch blocks, one at each end of the wall.
Similar to the lines of mortar that were laid on the footing, lay mortar on top of the bottom row of blocks. Just lay the mortar along the two outer ridges of the blocks but not on the center web. Press the two end 8-inch blocks into place, checking for level and plumb with the bubble level.
Continue Second Course
Run a mason's string line along the tops of the 8-inch blocks on the second course. This will help each row maintain uniform height and straightness.
The remaining blocks on the second course should be full size. Lay them in a brickwork pattern so that joints fall in the center of lower blocks. This running bond helps the wall gain strength and greater lateral stability.
Continue building the remaining courses.
Remove Excess Mortar in Joints
Every so often, when the mortar between the joints becomes putty-like or stiff enough to imprint your finger, run the jointing tool between the blocks to smooth out the mortar.
Add Cap Blocks
When the wall has reached its full height, add mortar to the top of the blocks. Install the cap blocks, alternating across joints.
When to Call a Pro
Due to the large quantity of concrete required for the footing, you may want to have a concrete professional pour the footing and set the rebar.