As unsexy as it sounds, a new set of equations may be the secret to 3-D printing for construction.

The problem: Firms like 3D Printhuset have tried printing buildings out of concrete on-site, but it can take a long time and the machines have a habit of breaking down.

All about timing: Specifically, the timing for drying concrete. If the lower layers don’t dry fully before the next are added, they buckle under the weight. You don’t want wonky walls.

The solution:  These equations, developed by Akke Suiker from the Eindhoven University of Technology, tell you how much material is needed and how long it needs to dry between layers. Time to fire up the concrete printer.