Concrete blocks come in two main types - solid and hollow. On the outside, both look similar. But, they have key differences that matter for construction projects.

Solid concrete blocks are, as the name suggests, solid blocks with no holes. Hollow blocks have open spaces inside them, like squares through the middle. This makes them lighter.

The fact that solid blocks lack inner holes makes them stronger. Their solid shape lets them hold very heavy stacks of brick, stone, or other layers above without crumbling.

Solid blocks often build foundations, load-bearing walls and beam and block flooring. They withstand tons of downward weight. However, solid blocks cost more since they use almost double the concrete mix. And they are heavy, so moving many around a worksite by hand would be tiring work.

Hollow concrete blocks offer useful options where high strength is less crucial. They use less raw concrete, so you save on budgets when purchasing large quantities. Their middle holes make them easier to lift and handle during simple projects like brick fences or small sheds.

Hollow concrete blocks are given grades based on their strength and density:

Grade A blocks (load-bearing) - minimum density of 1,500 kg/m3
Grade B blocks (load-bearing) - density between 1100 kg/m3 and 1500 kg/m3
Grade C blocks (non load-bearing) - density higher than 1,000 kg/m³

For non load-bearing walls grade C works fine. Picking the grade depends on whether the blocks will support heavy loads or divide spaces into rooms.

Solid blocks excel at raw supportive strength but at extra expense. Hollow blocks adequately handle basic jobs if not bearing heavy loads.

You'll have to assess the load, insulation, and affordability levels needed when picking between the two. Also, you could read our post on the differences between concrete blocks and bricks for more information.

Common types of concrete blocks

When starting any construction, you must pick the correct type of concrete blocks to build with. Many kinds exist for different uses.

Standard concrete blocks

The basic rectangular concrete blocks you'll find at most suppliers are considered "standard". They offer durable performance for structural jobs.

Standard blocks work well to make tough lower-level walls and foundations. Layering them builds secure bases. Their solid shape also handles heavy loads if stacked vertically to form partition walls.

As this type of block uses more concrete they will cost more.

Interlocking concrete blocks

This variety stands out thanks to jigsaw-like grooves and sockets along their sides. These allow interlocking blocks to fit together without any bonding effort.

They're useful for retaining walls, patios, and landscape features that shape gardens. No messy mortar troweling speeds projects along. And projects remain reliable since the grid design resists downward shifts over time. Interlocking versions cost more than standard concrete blocks.

Hollow concrete blocks

As mentioned earlier, hollow blocks contain open pockets of space inside rather than a filled solid form. Their inside voids means less cement, reducing budgets when bought for entire jobs.

However, hollow concrete blocks can be reinforced with rebars placed through the cavities along with poured concrete to give a sturdy build. They are also good if you need to run pipes or cables through them.

Hollow blocks are useful in basic barrier walls, room dividers, and sheds. And they offer natural insulation without extra steps, thanks to their air pockets.

Aerated concrete blocks

This is a specialised class of hollow blocks that makes tiny bubbles throughout. It does this by mixing agents that expand when drying, leaving small air pockets.

All that additional air boosts insulation ability without much cost over hollow styles. Aerated blocks help create warmer, eco-friendly spaces. You'll find them perfect for a heated garage or basement conversion project.

Specialised concrete blocks

In modern construction, some concrete blocks have properties that make them good for certain building jobs. For example, soundproof concrete blocks have improved acoustic properties, when compared to a standard concrete block. This helps to reduce the noise from neighbours or busy roads.

Other concrete blocks are fire-resistant. This means they can handle very hot temperatures from flames for longer. Normal concrete crumbles after a short time in fires.

Insulation concrete blocks help prevent heat from easily transferring through walls. Tiny bubbles get trapped throughout while the wet cement mixture dries. This way, cold outside air has trouble reaching interior rooms.

Eco-friendly concrete blocks

Many builders now want to help protect the planet with greener choices. Some companies make concrete blocks by recycling old building pieces instead of only using fresh cement.

For example, recycled aggregates and fly ash can be used in the cement mix. You can also find recycled concrete blocks, which use crushed waste concrete from demolished buildings - a great way to stop usable waste going in to landfil. This saves using as much new sand and gravel as possible.

Which concrete blocks to use

Picking the best concrete blocks starts with your exact building goal. For good reasons, certain kinds work better for homes, large stores, or industries.

You may consider three main factors: the project requirements, structural needs, and budget constraints.

For smaller rooms in homes or garages, hollow blocks offer affordable dividing walls. The block's durable rectangles work great in framing interior rooms on single floors.

Warehouses and shopping centres supporting roofs covering great wide spaces can't risk weak walls from hollow gaps. You can use concrete blocks or rugged interlocking edges. This can help to carry ceiling beams safely.

You can reinforce blocks to construct a larger block of flats or office towers. This should form a robust central spine. When people live above ground level, strengthened blocks withstand the cumulative sideways forces tall structures face daily.

How many concrete blocks do I need?

Figuring out the exact number of concrete blocks needed to complete all walls and sections in a building project requires you to follow key quantity calculation steps:

Step 1: Accurately measure space layouts

Use an architectural drawing or take measurements of all the areas. This includes main perimeter walls, outlining overall rooms, and interior divider walls. Note measurements in basic length x width. For example, "Living Room - 24 ft length x 16 ft width."

Step 2: Calculate total linear wall footage

Add together all the room measurements for individual concrete block walls from the first step. Combine the exterior and interior wall lengths to get the total linear footage of the amount that needs blocks. This provides the baseline quantity requirements.

Step 3: Subtract openings

Think about windows or doors to be placed in planned walls. Deduct the horizontal widths of these openings from the linear wall measurements since blocks won't be used at those void spots.

Step 4: Multiply by block height

To translate from linear horizontal footage to blocks required, multiply the total updated lineal footage by the actual block height in inches. Now, you have the preliminary full block amount with openings subtracted.

Step 5: Add extras as a buffer

You can add 10% onto the modified quantity to receive overage for odd leftover pieces. Also, add on five extra blocks for any spontaneous cracking issues.

Also, we recommend you read our guide about testing bricks quality, so you'll have a standard you work with.

Innovative concrete block technologies

New technologies are making exciting upgrades to concrete blocks. This is why you must stay updated with the industry's trade news and advice.

One example is self-healing blocks. They have special properties that let them fix their cracks. Tiny tubes inside the cement release adhesive liquids if the material starts splitting. The adhesive patches things back up by itself. This could prolong the life of bricks and blocks in the future.

3D printing is also starting to customise concrete blocks. Printers are now using digital models to layer cement in ways nearly impossible by hand before.

Unique and curvy-block shapes get created on demand right at build locations too. Transporting stacks of blocks from factories may fade away in the near future.

While most buildings still rely on regular blocks, technologies like these might help in the future. You get to stay ahead in all of these if you know these modern methods of construction.

Concrete blocks: FAQs

What are the categories of concrete blocks?

There are two main categories of concrete blocks. The first is hollow blocks with internal spaces or holes, making them lighter and easier to work with. These types of blocks are popular for walls and fences. The second category is solid blocks. These blocks are fully dense and without holes, offering maximum strength and stability.

What are 4-inch concrete blocks used for?

4-inch concrete blocks are used for interior, non-load-bearing walls to separate rooms within a building. They are also used for garden and retaining walls, and their smaller size aids in building curved landscaping features.

What are the strongest concrete blocks?

Solid precast concrete blocks are the strongest concrete blocks. They offer the highest compressive strength and load-bearing capabilities, followed by interlocking blocks.

Disclaimer: The information contained on this page is intended as an overall introduction and is not intended as specific advice from a qualified professional. Travis Perkins aims to avoid, but accepts no liability, in the case that any information stated is out of date.

Types of Concrete Blocks Used in Construction

Solid concrete blocks vs hollow concrete blocks