One method to build a sand castle is by using a soft packing technique in which wet sand is accumulated into a pile. Holes are poked into the pile and filled with water. The wet sand pile is stabilized by tamping, then castle features are formed into it.
Use a shovel or bucket to collect sand into a large pile, then use the long end of a shovel to create deep holes into the pile. Use a bucket or cupped hands to add an amount of water that is equal to the amount of sand in the pile. Distribute the water into the sand pile by pouring into the holes and then stomping on or tamping the sand to compact it, while also allowing excess water to drain.
Create a base of compacted sand approximately 2 to 3 feet in diameter. Ensure the sand pile is kept moist to allow it to compact sufficiently before carving into it. If the castle is being built on a beach, a water hole can be dug to gain access to a convenient and self-replenishing water supply.
A sand castle is created from a moist sand pile by carving features, such as castle towers, walls, bridges and archways, into it. Use a smoothing tool, such as a paint scraper, trowel or putty knife, to carve out and form the tallest features of the sand castle first. Work downward along the pile while sculpting the castle’s features.