Before Portland cement (1824), everything was built with lime mortar. The Colosseum, medieval cathedrals, Amish homes.
Recipe
1 part slaked lime + 3 parts sand + water. Mix to thick cream consistency. Better to age lime (putty lime) 3+ months — mortar becomes more workable.
Properties
Breathable: passes moisture, walls don't get damp. Cement seals — moisture builds, brick deteriorates. Flexible: during foundation movement, lime joint bends, cement cracks. Self-healing: micro-cracks seal themselves — CO2 from air reacts with lime, forming calcium carbonate.
Why Not Cement
Cement is harder than brick — under stress the brick breaks, not the joint. Lime is softer — the joint breaks, brick stays whole. Joint repair $10. Brick repair $100+.