For as long as humans have built with stone and mortar, lime has served as the quiet mediator between old walls and new repairs. Now, researchers have found that a small addition of finely ground biochar — charred plant matter rich in carbon — can make natural hydraulic lime both stronger and more capable of drawing greenhouse gases from the air, offering heritage conservators and sustainable builders a material that honors the past while addressing the pressures of the present. The discovery, published in the journal Biochar X, suggests that ancient building traditions and modern climate conc