What is a Cement Block?

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  • Written By: Lou Paun
  • Edited By: Jay Garcia
  • Last Modified Date: 17 January 2020
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A cement block may also be called a concrete block, a foundation block, or a concrete masonry unit (CMU). It is also known as a breeze block, a cinder block, or a clinker block. These blocks are made with a mixture of Portland cement, aggregate, and water. The standard size is listed as 8 inches x 8 inches x 16 inches (20 cm x 20 cm x 41 cm) in the US and 44 cm x 21.5 cm x 10 cm (17.3 inches x 8.5 inches x 3.9 inches) in the UK, although the blocks are actually a bit smaller to allow room for mortar joints. Some cement block companies will make other sizes upon request.

The most common aggregate for cement blocks is a mixture of sand and gravel. This is mixed as a rather dry, low-slump mix that results in a hard, durable cement block. Aerated concrete can be used to make blocks that are lighter in weight but still very strong.

Industrial wastes are sometimes used as aggregate, but the cement blocks will be lower in density and therefore less durable. Cinder blocks, called breeze blocks in the UK, have cinders in the aggregate, and clinker blocks have clinkers. These blocks have less compressive strength and are not suitable for foundation work.


The first cement block was manufactured in 1882. Concrete blocks are now manufactured with a machine that molds the wet concrete mix into standard shapes. The blocks are cured inside a special chamber at high temperatures. They are then stored to dry completely.

Most concrete blocks are manufactured with hollow chambers. This makes the block a bit lighter weight and easier to handle. More important, the hollow chambers make it possible to drive reinforcing bars vertically through the wall, giving it added strength. The chambers are then filled with wet concrete, which dries to create a strong wall with great thermal properties.

Because threading the open chambers of a cement block over rebar that has already been driven into place is a slow process, a special kind of concrete block has been developed to make the procedure faster. These open-ended blocks are often called speed blocks, and they are shaped like the letter H. Instead of being lowered onto the wall from above, these blocks can be edged between the reinforcing bars and slipped into place. This makes the job far less time-consuming.

Cement block construction is often considered an eco-friendly building material. Cement blocks are durable, but they are not very portable. Most concrete blocks are manufactured within 50 miles (80.5 km) of the building site, and most are made from local materials.


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Post 4

@lighth0se33 – I generally use cement blocks to hold something down so that the wind won't blow it away or gravity won't take it down. I have an above-ground swimming pool in my backyard, and whenever I have to refill it with the garden hose, I place a cement block on top of the hose where it rests on the the top of the ladder.

If I don't weight it down with something substantial, the water pressure will cause the hose to fly out of the pool and flop all around. I've tried using boards before, but a cement block is the only thing heavy enough to secure it.

Cement blocks are heavy! I usually roll them along the ground to wherever I'm going, because I can't carry them for more than a few feet.

Post 3

My dad and I always used the terms “concrete block” and “cement block” interchangeably. We knew they were the same thing, and we had heard both terms used so much that we just went with whatever rolled off our tongues at that moment.

We used concrete blocks mostly to hold things up. I remember when my dad hit part of the big rosebush with the lawnmower and it drooped over to one side. We put concrete blocks along the base of it, and they were able to support the drooping section and make it look as though nothing had happened to it.

Post 2

Never stick your fingers into the holes of cement blocks without examining them first. My cousin did this, and he got bitten by a black widow spider.

Spiders like to hang out in dark places like this. Also, if you have a pile of cement blocks, then it also might be a good hiding spot for snakes.

Post 1

I have a friend who lives in a cement block house. Before I met her, I never knew that entire houses could be built out of these blocks.

I suppose it's a pretty durable structure, considering that concrete is tough. However, she can't really hang things on the walls, unless she uses some sort of adhesive.

She told me that if her house had been made of something else, she might have done some remodeling and added a few windows. However, she feels like she is stuck with the current layout.

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