How to Build a Block Fence Above Three Feet

Preliminary Planning

• Unlike shorter block fences, tall ones require special planning to ensure they are securely built and not in danger of toppling over during construction or over time. Before you begin work, check if you need a permit or permission to build this type of fence and make sure you follow any relevant codes. Contact utility companies to check whether or not it's safe to dig where you plan to install the fence. Alternatively, call 811, a nationwide service that will notify your utilities companies to come out and mark the underground lines, cables and pipes that run through your yard so you can safely avoid them. Call several days in advance of when you plan to begin the project.

Firm Foundations

• A block fence more than 3 feet tall requires a substantial foundation to support its weight and hold it steady for all the years it stands. Pour a solid concrete foundation that is at least twice the width and twice the depth of the width of the blocks you'll use to build the fence. For example, create a foundation that is 16 inches deep and 16 inches wide to support blocks with a width of 8 inches. Don't start building for three days after pouring the foundation to ensure the foundation has time to harden properly.

Mortar Mixtures

• Because the mortar is what holds the tall fence's blocks together, it's crucial you mix it to the proper consistency and apply the mortar correctly. Anything less puts the stability of the wall in jeopardy. Always follow the mixing instructions on the mortar package and check the consistency by holding a mortar-filled trowel at a 90-degree angle to ensure the mortar adheres to the trowel in that position. The thickness of the mortar between blocks should be a consistent depth of 3/8 inch when complete.

Fence Construction

• Construct the fence by laying one layer of concrete blocks at a time. Secure them to the foundation with a layer of mortar, laying a level along the blocks after installing four in a row. Use a rubber mallet to gently tap the blocks before the mortar dries to level them, if necessary. When starting the second row, begin with a block that's been cut in half. Place the solid edge facing the outer end of the wall. This creates a staggered effect that allows the blocks to overlap. Continue the construction of the wall in this matter until finished.

Structural Stability

• To provide stability for a tall fence, insert 1/4-inch steel reinforcing bars 6 inches into the foundation horizontally and extend them to the top of the fence. Place one bar in each alternating masonry core for maximum strength. When the concrete blocks have centers larger than 4 inches wide, or for added stability in blocks with smaller centers, fill each with fill grout poured around the reinforcing bars. Level the fill grout off when you reach the top row to create a solid top to the fence.