Concrete block: types, strength and how to read the data sheet

In Mexico, concrete block is regulated by NMX-C-404-ONNCCE-2012, "Masonry – Blocks, structural clay or concrete units – Specifications and test methods," in force since February 11, 2013. Before buying, the first distinction to make is whether the block is structural or facade-grade, and whether it is hollow or solid, because each combination serves a different role on site.

Key facts

• NMX-C-404-ONNCCE-2012 has regulated structural concrete block in Mexico since February 11, 2013.
• Block is classified by function into structural or facade-grade, and by shape into hollow or solid.
• Structural block is part of a wall's load-bearing system; facade block is mainly a finish.
• Each block line's size and strength are declared by the manufacturer in its data sheet.
• Promotora Server, part of Grupo Server, manufactures structural and facade concrete block, and concrete brick.

What is structural block and how does it differ from facade block?

Structural block is designed to be part of a wall's load-bearing system: it carries structural weight in addition to dividing space. Its manufacturing and quality testing are oriented toward meeting the requirements NMX-C-404-ONNCCE-2012 sets for structural use.

Facade block, by contrast, serves mainly a finish and cladding function on the visible face of the wall. It may carry textures or a stone-face pattern, and its structural demands are lower because it is not always part of the load-bearing system. The choice between the two depends on the wall's use, not aesthetic preference alone: using facade block where a project calls for structural block compromises the element's load-bearing capacity.

What is the difference between hollow and solid block?

Hollow block has one or more internal cavities, which reduce its weight and the amount of material per unit, and also make it easier to run electrical or plumbing lines through the wall. It is the most common type in partition walls and much of residential construction.

Solid block has no such cavities, or a much lower percentage of voids. Carrying more material per unit, it tends to be heavier, and in applications that call for more mass or strength per unit, it is the option specified. NMX-C-404-ONNCCE-2012 covers test methods for both hollow and solid units, and each manufacturer states in its data sheet which category its product falls under.

In both cases, block is manufactured with stone aggregate —sand and gravel— that must in turn meet NMX-C-111-ONNCCE-2018, the standard governing aggregates for hydraulic concrete in Mexico. Block made with out-of-spec aggregate can perform differently than its data sheet states, whether it is hollow or solid.

What size is a concrete block?

A concrete block's dimensions are not a single figure for the whole market: each manufacturer produces different lines, with different widths, heights and lengths, depending on the intended use. NMX-C-404-ONNCCE-2012 does not set one mandatory dimension; instead, it defines the test methods and quality specifications each unit must meet, regardless of its exact size.

That is why the right way to learn a block's dimensions before buying is to check the manufacturer's data sheet, where the dimensions of each product line — structural or facade, hollow or solid — are specified along with evidence that it meets the standard.

Comparing dimensions between two manufacturers without checking each one's data sheet can lead to project calculation errors: two units that look the same size at a glance can have different wall thickness or internal proportions, which affects both how much mortar the job consumes and the wall's structural behavior.

What should you require in a block's data sheet?

Before buying block for a project, it is worth requiring that the manufacturer's data sheet state, at minimum, four things: whether the block is structural or facade-grade, whether it is hollow or solid, that it complies with NMX-C-404-ONNCCE-2012, and that this claim is backed by evidence of quality testing.

A manufacturer that cannot show that information, or that offers only a generic figure without specifying the product line, does not let you verify that the block is suitable for structural use. The table below summarizes what to ask by criterion.

It is worth requesting that data sheet before buying, not after: switching block halfway through a project because it was not verified in time as structural or facade-grade means demolishing and redoing work already finished, a cost that a first review of a document the manufacturer should be able to provide without difficulty would have avoided.

How does Grupo Server help?

Promotora Server, a Grupo Server company founded in 1982, manufactures structural and facade concrete block, along with concrete brick and eco-friendly pavers. It is the group's company dedicated to producing construction materials, distinct from Triturados Gramol, which produces stone aggregates.

You can review Promotora Server's profile, browse the group's construction section, or write in through the contact form to request a specific block's data sheet.