The Hidden Engineering of Blocks In Our Buildings

My heart leans towards explaining some civil engineering today. In past editions, I spoke about the wonders of concrete and of particular types of foundation. Today, let’s talk about concrete blocks.

Throughout my childhood, I am not sure I saw solid blocks. Well, there are kerbs but because they are not 6 or 9 inches, they are not the ones I am referring to.

That’s why I still remember the first time I noticed the difference.

It was during my NYSC year, posted to a project at the State House Clinic, Asokoro. I was watching the trucks pull in, the laborers unload, and the bricklayers arrange them in neat, dusty stacks. That’s when I spotted something odd. Some of the blocks had gaping holes in them. As usual, hollow and light-looking. And then there were others heavy, compact, and solid.

“What’s the difference?” I asked one of the workers.

As someone only there for his daily wage, he was not interested in chitchat, or maybe he didn’t know. Doesn’t he just do as he is told? So, he shrugged, and so began my quiet curiosity.

It wasn’t until a few days later, during one of those slow afternoons on site, that I got my answer from Mr. Paul, an elderly, weathered project manager with decades of experience under his hard hat and a calm patience that only time can teach. If there was anyone to learn from, it was him.

Sitting under the shade of a scantily-finished temporary site structure, he leaned in and explained the logic behind the bricks of our buildings.

Hollow blocks, he made me realize, are not just a cost-saving trick. They’re the backbone of modern construction. At first glance, they seem weaker. After all, they’re filled with air. But that’s precisely the point. Those cavities make them lighter, easier to transport, and quicker to lay. They’re larger than solid blocks too, which means fewer are needed for the same stretch of wall.

“And yet,” Mr. Paul added with a smile, “don’t be fooled. Once we fill those cavities with concrete and steel rods, they become just as strong as any solid block.”

That blew my mind, apparently from my deficient earlier education. I had assumed strength came only from mass. But in engineering, strength is often about smart design. Mark Miodonik’s book I am currently reading shows how thin sheets of graphene can have more strength than far bigger materials. It’s all in the design.

So, hollow blocks can be really strong depending on what you add to it. But in itself, hollow blocks bring structure, speed, and even comfort. The air inside them acts like a buffer; keeping rooms cooler in the heat, warmer when it’s cold, and muting outside noise.

“They make buildings smarter,” Mr. Paul said, tapping one of the blocks with his pen. “And cheaper too.”

It turns out one of the reasons he used the word ‘smart’ is because they make the lives of electricians and plumbers much easier. No need to cut long chases into walls; the cables and pipes can be threaded right through the existing hollows. Efficiency, once again, built into the design.

That doesn’t mean solid blocks are out of fashion, though. Mr. Paul was quick to point that out too.

“There are places you don’t play around with,” he said. “Foundations. Pillars. High-load walls. That’s where solid, or as you can also call them, blind, blocks come in.”

These blocks are dense, heavy, and uncompromising. They’re used when the structure needs to absorb serious stress, like under machines in industrial buildings, or in places where vibrations could be an issue. They also block sound better, making them ideal for certain walls and enclosed spaces.

But they come with trade-offs. They’re more expensive to move, harder to lift, and slower to work with. That’s why you won’t see them in every wall, they’re used deliberately, where it counts most.

Apparently, it’s for these reasons that in places I had not seen solid blocks being used, nine-inch hollow blocks are used in foundations. They’re chosen because they offer a balance between cost, handling, weight, and strength. And for them to have the strength of solid blocks, they are almost always filled with concrete and steel rebar. This filling process gives them the compressive and structural strength needed to support loads.

By the time Mr. Paul finished explaining, I was seeing the site differently. Every stack of blocks, every wall going up, it wasn’t just bricks and mortar anymore. It was strategy. Balance. Engineering. Hollow blocks for speed, lightness, and insulation. Solid blocks for strength and support. A dance between materials, guided by experience and the laws of physics.

I invite you to join me in the book I am reading called “Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World”. It will make it such that the next time you walk past a building site, you will be forced to take a moment and look closely at the blocks. It will make you see a story in them, not just of cement and sand, but of choices made to build smarter, stronger, and better.

Civil engineering is such quiet brilliance.