Cinder Blocks: a cinderella story

What is a cinder block? It conjures an image: 8 inch by 8 inch by 16 inch rectangular cube, with two or three core holes. Grey and dull, solid and regular, straight walls and square corners: as American as WalMart.

Actual cinder blocks are pretty cool. You can’t get them any more. They used to be made from the cinders which were a waste product of burning coal. Coal combustion is now done much more efficiently, and doesn’t create large cinders but a very fine fly ash. No more cinders, no more cinder blocks.

Around 1910 coal cumbustion produced cinders, and few places burned more coal than Pittsburgh, Pennsylvania. A brick mason from Pittsburgh named Francis Straub realized the potential of this large volume waste product, and experimented with cinders and cement. This led to the discovery of material mix designs for cinder block in 1913.

Cinder blocks are lightweight, insulate, and nails can be driven into them. Mr. Straub had many challengers to his technology, and fought several patent infringement cases on his invention. The crux of the decision on his case was that if you could drive a nail into a block, it was a cinder block: it was his patent, and nobody else could make block like that.

Mr. Straub would show up at competitors he suspected of infringing on his patent, and try to drive a nail into one of their blocks. If he could drive a nail, he would collect royalties or shut them down, or both.

Around 1936 the United States made a decision to streamline construction and manufacturing by making all construction materials based on a modular coordination of design. It was decided to base all construction materials on a 4 inch cube volumetric grid, so that all materials were designed to fit within this grid; everything from sheets of plywood to 2”x4”s, to windows and doors. The block industry settled on the 8’x8”x16” design which we’re so familiar with today.

Eventually coal combustion became more efficient, and cinder blocks were no longer made. The term stuck though, so today people still refer to concrete blocks as cinder blocks. Today the fly ash from coal combustion is used as a pozzolanic material in concrete, creating a higher strength concrete. They are more dense and you can’t drive a nail into them.

“Cinder block” is practically a cultural icon, it is so ubiquitous and familiar. There are musicians calling themselves ‘cinder block’, and certain crude urban interpretations have been applied to the term. All thanks to Francis Straub from Pittsburgh, circa 1913.