Purchase or find limestone on your property and crush it up into small, 3-inch (7.62 cm) pieces with a sledgehammer. You can tell if the stone is limestone if it fizzles or cracks when you put vinegar on it.  Industrial grade limestone companies use mechanical crushers or hammer mills to crush the limestone. You can also buy limestone-based Portland cement online, at hardware stores, or at home and gardening centers instead of making it yourself. Preheat the kiln and put your limestone into it. Let the kiln heat the limestone for 3 to 4 hours at 2,700°F (1482.2°C). Use a high-temperature kiln thermometer to determine the level of heat in the kiln. Make sure to wear a respirator and goggles when heating the limestone because it will let off a harmful gas. Let the limestone cool for an hour or two before handling it. Point a fan towards the stone to speed up the cooling process. Wear thick rubber gloves when handling the limestone. Transport the limestone to a wheelbarrow and then use a shovel to break up the limestone pieces until it turns into a fine dust.

Summary:
Crush limestone into 3-inch (7.62 cm) pieces. Put the limestone in a kiln and raise the heat to 2,700°F (1482.2°C). Crumble up the pieces of heated limestone once it cools.