Cinder Block Wall Guide: How Block Walls Are Built

A cinder block wall is built from hollow concrete blocks laid in mortar on a concrete footing, with steel and grout in the cells where the wall needs strength. Block walls are a good choice for retaining soil, for a structural wall behind a stone or stucco finish, and for a plain, solid garden or privacy wall. They are less suited to a wall that has to look good with no finish at all, unless you choose an architectural block.

Most of what decides whether a block wall lasts in Massachusetts happens below ground: a footing below the frost depth, drainage behind any wall that holds back soil, and reinforcement sized for the job.

Cinder block vs. concrete block

True cinder blocks were made with coal cinders as the aggregate. Almost all blocks sold today are concrete masonry units, or CMU, made with sand and gravel. People still call them cinder blocks, and the terms are used for the same thing.

Block types and sizes

• Standard 8-inch block: the common hollow block used for foundations and structural walls.
• 4-inch and 6-inch block: thinner units for partitions, low garden walls and backing behind veneer.
• 12-inch block: wider units for taller or more heavily loaded walls.
• Corner, half and end blocks: shaped units so corners and wall ends finish cleanly.
• Bond beam and lintel blocks: blocks with a channel for horizontal steel, used at the top of walls and over openings.
• Architectural block: split-face, ground-face or colored block meant to be seen, so it needs no other finish.
• Cap blocks: solid units that close the top of the wall and shed water.

Segmental retaining wall block, from makers such as Unilock and Techo-Bloc, is a different system: solid units stacked without mortar, often with geogrid in the soil behind. Our post on building a retaining wall on a slope covers that method.

Retaining wall or freestanding garden wall?

Decide this first, because the two are built differently.

• Freestanding garden or privacy wall: has soil at the same level on both sides. It needs a footing below frost depth and reinforcement against wind and impact, but no drainage system behind it.
• Retaining wall: holds back soil that is higher on one side. Wet soil pushes hard, so the wall needs more reinforcement, a drainage layer and pipe behind it, and weep holes or another way for water to get out.

How a block wall is built

1. Plan, permit and call Dig Safe. Check with your town building department about permits; taller retaining walls, and walls holding up a driveway or slope, generally need an engineered design under the Massachusetts building code. Before digging, call Dig Safe, which requires 72 hours' notice in Massachusetts, not counting weekends and holidays.
2. Dig and pour the footing. The footing is a reinforced concrete strip wider than the wall, set below the frost depth your town requires so the wall does not heave in winter. Vertical rebar is set in the footing where the wall cells will be reinforced.
3. Lay the first course. The first course goes on a full bed of mortar and must be dead level. Every error here shows up at the top.
4. Build up in running bond. Each course overlaps the joints below by half a block. Corners are built first and the courses between are laid to a string line. Horizontal joint reinforcement goes in at intervals set by the design.
5. Grout the reinforced cells. Cells with rebar are filled solid with grout. Retaining walls typically have more of them.
6. Drain and protect the back of a retaining wall. The soil side gets a damp-proof coating, a layer of clean crushed stone, and a perforated pipe at the base that carries water to daylight. Our post on retaining wall drainage covers this.
7. Cap and finish. A cap block or stone cap keeps water out of the cells. The face can be left as architectural block, parged or stuccoed, or faced with stone or brick veneer.

Building a garden wall with block

For a low garden wall, the steps are the same at a smaller scale: a footing below frost depth, a level first course, running bond, and a cap that sheds water. Backfill against a garden retaining wall with crushed stone rather than the clay that comes out of the hole, and leave a way for water to drain. A natural stone cap or a stone veneer face makes a block wall look much less utilitarian.

What drives the cost of a block wall

We do not publish prices, because every wall is different. These are the things that move the number:

• Height and length, and whether it retains soil.
• Footing depth and size, which depend on frost depth and soil.
• Reinforcement and grout, and whether an engineer's design is needed.
• Drainage behind a retaining wall.
• The finish: plain block, architectural block, stucco, or stone or brick veneer and caps.
• Access for equipment, removal of an old wall, and ledge or poor soil.
• Permits.

Our retaining wall cost guide goes through these factors in more depth.

When to call a mason

A short garden wall on flat ground is within reach of a skilled DIYer. Call a mason for any wall that retains soil, carries a load such as a driveway or pool deck, stands near a property line or walkway, or needs a permit. On the Billerica pool job shown above, a block wall holds up a raised deck; you can see more of that project on our Billerica pool deck page. For new walls of any kind, see our retaining walls page, and for foundation walls, foundation and bulkhead repair.

Common questions

Is a cinder block wall strong enough for a retaining wall?

Yes, when it sits on a proper footing, has steel and grout in the cells, and has drainage behind it. An unreinforced block wall with no drainage is one of the most common retaining wall failures.

Do block walls need a footing in Massachusetts?

Yes. Without a footing below frost depth, the wall moves with the ground each winter and cracks along the mortar joints.

Can I make a block wall look better?

Use architectural split-face block, or finish standard block with stucco, a stone or brick veneer, and a stone cap.

Mortared block or segmental block for a retaining wall?

Both work. Mortared, reinforced block takes up less room behind the wall and suits a wall that is part of a structure, such as a raised deck. Segmental block is faster to build, flexes slightly with frost, and comes in finished faces, but taller walls need geogrid in the soil behind.

Thinking about a block wall for a slope, a raised patio or a pool area? Gerrior Masonry is a family-owned company in Woburn, MA with over 30 years in masonry and hardscaping. We are fully insured, our work is guaranteed, and owner Joseph Gerrior oversees projects. Request a free estimate or call (781) 933-4157.