Step 1: Mixing Grey Matter Concrete
Measure your water in a separate container. Approximately 100ml for every 1 kg of Grey Matter. An accurate amount of water is extremely important and will have a direct correlation with the final strength. Depending on the natural humidity of the region you're in you may need to add more or less water to achieve the perfect mix consistency.
Measure out the amount of concrete for your casting into a mixing bucket.
Slowly add water. Mix your concrete and water together to achieve the texture of cookie dough, stir until no dry concrete remains. Let mix rest for 5 minutes. Stir one final time. The ideal mix consistency can be measured by feel. Grey Matter should act like a ball of dough, if it flows like a milkshake you've added too much water, add dry powder. When in doubt err on the side of dry, you can always spritz in a bit more water.