These photos show a 10-hole brick cored with 22%, 30%, and 34% void; and a 3-hole unit cored with 25%, 32%, and 35% void.
These photos show a 10-hole brick cored with 22%, 30%, and 34% void; and a 3-hole unit cored with 25%, 32%, and 35% void.

Several years ago, brick manufacturers began providing “hollow” brick for buildings that typically utilized “solid” units. These hollow brick had coring with greater than 25% of the gross bed area of the unit. This demand for change began rather slowly, but has increased each year.

Today, brick manufacturers provide large quantities of units cored more than 25% and less than 30%. In fact, more than 3 billion brick cored over 25% have been sold in the past five years for applications that typically used “solid.” These higher void brick are currently sold as Hollow Brick, conforming to ASTM C652.

To help the masonry community adapt to this important trend, a task group of the ASTM committee that monitors the brick standard was created to consider an increase in permissible void area for facing units. The current proposal permits a 5% increase in allowable void, which means that the cross-sectional area of a solid brick which is currently 75% could be reduced to 70%.

This change was not arbitrary. The 5% increase in void permits the industry to benefit from the change without requiring major alterations to current production or installation methods. At the same time, a thorough industry testing program has indicated that brick manufactured with a full 30% void area retain the physical properties currently required within the industry for solid brick.

When this change was first proposed, there was some confusion regarding its scope. The proposed change relates to void alone, and does not include any alterations to face shell thickness, which will remain at no less than ¾-in. from any face. The coring configuration remains at the option of each manufacturer. For a variety of reasons, not all brick are currently cored to the current maximum allowable 25%, nor will all brick be cored to 30% if this proposal is accepted.

The proposed change aids the masonry industry in several ways. Less material is used to make the brick, thereby extending material reserves. This factor is important today since acquiring, zoning, and permitting land for mining is very difficult. Many areas near manufacturing sites with brick-making material are close to already developed commercial and residential projects.

The use of less material also reduces the quantity of fuel required to make brick, as well as lowering the pollutants resulting from firing the material. Shipping costs of lighter brick, as well as the expense of supporting such units in the wall, are also significantly reduced. The proposal is possible because brick-making technology has advanced since the inception of the physical and performance requirements introduced decades earlier. Brick manufactured today may perform better than units produced when the C216 standard requirements were first introduced. And research suggests that brick made today with 5% less material may perform as well as, or even better than, units made in the 1930s with 10% more material.

Several concerns were raised when this proposal was introduced to the masonry industry in technical committees.

Why make a change since ASTM 652 already exists?

While there is a hollow brick standard already in place, the masonry community has historically used C652 for reinforced applications with face shell bedding, rather than for facing applications using full mortar bedding. Even now, some producers are concerned about the use of hollow brick in masonry applications.

This concern is magnified by owners and designers who believe they would receive significantly less performance by using “hollow” brick. Much of this concern can be attributed to C652 having two classifications based on void area, up to 40% and up to 60%. The proposal recognizes that for facing applications where units will not be grouted, a lower allowable void area may be appropriate to achieve full mortar bedding.