What is hollow brick?
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Most brick contain cores — holes in the interior of the brick units that became commonplace when manufacturers embraced extruding rather than molding brick. Cores reduce the mass of the brick and make production, shipping, and installation more efficient, generally without diminishment of brick’s many beneficial physical properties.
“Ah,” you say, “so brick with cores are hollow brick.” If only it were that easy. Even “solid brick”, by industry standards, usually contain cores, leaving one to wonder what on earth is meant by “hollow brick.” What it really comes down to is the degree of hollow-ness.
Solid brick can contain voids (holes/cores) no greater than 25% of the unit’s bed area. Bed area is the flat surface on which mortar is typically applied to create a “bed” for brick to be laid on top of it. Hollow brick are defined as having greater than 25% and at most 60% percent void areas. Large void areas typical of hollow brick are often called “cells” rather than “cores.”
So, why use use hollow brick?
Hollow brick can often cost less to buy, ship, and install because of its lighter weight.
Lighter weight allows for thicker units to be used, making structural single-wythe walls possible — a single width of brick can provide both structural support and facade finish.
Hollow brick lends itself well to reinforcement within its cells, making it useful in a great variety of applications.
Hollow brick retains much of the compressive strength of solid brick, and only slightly less sound resistance.
If hollow brick is so great, why would anyone choose solid brick? Well, there are some drawbacks that might make hollow brick a less advantageous choice, depending on the application.
Hollow brick masonry without reinforcement has less flexural tensile strength than solid brick when the same mortar is used, probably due to the reduced mortar bed area and the quickened curing of the mortar.
Single-wythe hollow brick masonry relies entirely on its thickness and mass as a barrier to rain and moisture. Because it incorporates no secondary form of penetrative water management (as would solid brick veneer construction with its internal air space and flashings), careful detailing and good construction practices are essential.
There are many design, construction, and building code details to consider when using hollow brick. Fortunately, the Brick Industry Association has a complete Technical Note full of “solid” advice on the topic.
