A great many of us have turned to baking our own bread while under quarantine. We’ve learned how to make our own sourdough starter, boil our own bagels and fry our own doughnuts. So if there’s one thing we’ve all learned while performing this newfound hobby, it’s that a good crust is key to a good pastry.
Unfortunately the exact opposite is true when it comes to concrete. “Crusting” of concrete happens when the very top layer of concrete hardens prematurely, giving the impression that the concrete is ready to finish when in fact the layer just below is still soft. If a concrete crew attempts to start finishing operations, the soft jelly-like concrete underneath can bulge out, producing wavy or cracked surfaces. It’s typically caused by “differential stiffening” within the concrete placement. Basically the top layer gets hard way faster than the rest of the placement.
If you, for some absurd reason, want crusted concrete. I included a recipe below.
Recipe for Crusted Concrete:
1 cup of temperature difference between subgrade and the concrete
2 TBSP’s of wind, sun or other environmental factors that might prematurely dry the concrete
2 dashes of Concrete Mix designs that inherently reduce bleedwater rate (air entrainment, silica fume, high cement content).
Bake in the sun and wind.
In order to avoid concrete crusting, try to eliminate the factors that cause differential stiffening. Keep your subgrades closer to ambient temperatures through heating blankets. Use a fog spray to keep the surface humidity relatively high. Spray a monomolecular film like Euclid’s Eucobar on the surface to prevent rapid evaporation of bleedwater.
With this advice in mind, in the coming months we’ll hopefully only see crusts on people’s Instagram pretzels.