Do you really need solid blocks for that wall?

COMMENT | APOLLO BUREGYEYA | Allow me to take you back to class today. No assignments. Just a group discussion.

Seventeen (17) bags of cement give us 680 hollow blocks, each measuring 200 × 200 × 400 mm, with a compressive strength of 3.5 MPa. Yes, 3.5 megapascals. In wall-building terms, that is already strong, already functional, and more than what your wall will ever need.

But some clients still insist, “I only use solid blocks.”
Alright then, let’s entertain that.

To make 680 solid blocks of the same size, you need double the cement, 34 bags, just to reach 7.5 MPa.

That’s double the cost,
double the pressure on your budget,
and zero added value,
unless you are building a basement for those honouring EPS tickets. You know them. Those unpatriotic citizens.

Now let’s put on our engineering helmets.

Take a typical residential house wall, 3 meters high. That gives us about 15 courses of blockwork. We are wishing away the mortar joints.

Each course, per meter of wall, takes 2.5 blocks. The block is 400 mm long, so you only fit 2.5 blocks in one metre, assuming we ignore mortar joints.

So we have:

15 × 2.5 = 37.5 blocks per metre of wall

Assume each block weighs 35 kg (a conservative estimate for a solid block since most solid blocks weigh just below 30kg).

Then:

37.5 × 35 = 1,312.5 kg

Now double that to include roof load:

1,312.5 × 2 = 2,625 kg

This is the maximum dead weight acting at the base of 1 metre of wall, that most critical point of a continuous vertical wall.

The cross-sectional area of the wall is:
200 mm = 0.2 m
So: 1 m × 0.2 m = 0.2 m²

Now apply Senior Two Physics:
Stress = Force ÷ Area
Stress = 2,625 ÷ 0.2 = 13,125 kg/m² = 0.13 MPa

Yes, just 0.13 MPa. That’s the actual stress your block needs to handle.
And remember, if we used 15 kg for a typical hollow block, that light weight thing with holes in the middle, the stress would be much lower.

So, now that you know we need only 0.13 MPa stress, why are we chasing 7.5 MPa?

By now, you understand why the traditional soil blocks perform well in walls, and they contain zero cement.

In fact, in over 20 years of engineering practice, I have never seen a building collapse because of weak walls. So, this obsession with strength is not about structure. The real concern is durability.

We want blocks that do not disintegrate under rain, sun, and time. That is why we insist on a minimum cement content to ensure the block lasts. And a solid block of 7.5MPa has a lower cement mix ratio compared to a hollow block of 3.5MPa. Strength has much to do with the quantity of materials in a unit volume. And when you combine that with Eco Concrete Ltd ’s industrial-scale machines, you get a product that is strong enough, durable enough, and gives your money 20% more mileage on your building walls.

Do You Really Need Solid Blocks for That Wall?
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Allow me to take you back to class today. No assignments. Just a group discussion.

17 bags of cement give us 680 hollow blocks, each measuring 200 × 200 × 400 mm, with a compressive strength of 3.5 MPa. Yes, 3.5 megapascals.… pic.twitter.com/8qKmKNwa5J

— Buregyeya Apollo (@ApolloBuregyeya) June 12, 2025

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The writer is an engineer, entrepreneur and industrialist. THIS COMMENT WAS ADAPTED FROM X @ApolloBuregyeya