Innovation No. 28 of 77 in the book
Mortar
Gypsum mortar used to bind stone blocks
- When
- c. 2500 BCE
- Dynasty
- 4th Dynasty
- Era
- Old Kingdom
The pyramids at Giza, built around 2500 BCE, are held with the world’s first widely-used mortar — millions of tonnes of it.
Egyptians burned gypsum rock and mixed it into a paste that set hard between the blocks. It wasn’t mainly glue: it worked as a lubricant, letting masons slide multi-tonne stones into a snug fit.
Whole industries of quarrying, burning and hauling grew up just to supply it.
The stuff that binds the modern built world starts with Egyptian gypsum.
Laboratory analysis of the mortar between the Giza blocks shows a consistent mix of burnt gypsum, sand and other natural minerals — the same recipe, batch after batch. Neolithic builders had occasionally used mud or lime slurries before this, so the first is industrial scale rather than the idea itself. Excavations of kiln sites near Giza have turned up the pits where raw gypsum was roasted, the earliest known manufacturing plant built to supply a construction project.
Frequently Asked Questions
If it wasn't glue, what was it doing?
Acting as a lubricant. Masons floated multi-tonne casing blocks into position on a bed of wet gypsum rather than setting them down precisely from above, then let it harden around the joint.
How tight were the joints?
On the Great Pyramid's outer casing, under a fiftieth of an inch — too narrow to slide a razor blade into. That fit is a consequence of the mortar, not of lifting accuracy.