Fired perforated clay bricks with one or more holes (cavities) through the thickness of the brick with the area of cavities in excess of 25% of the volume. The holes can be seen from above after the brick has been laid.

Fired Clay Hollow Bricks 1.JPG

Fired clay hollow bricks, Iran (A. Charleson)

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Fired clay hollow bricks with vertical perforations, Peru (S. Brzev)