It’s sand. Who knew there was so much info on sand. Especially the kind that works best for great sandcastles. Well, good thing you stopped by today. Read on, then impress your friends and family this weekend.  :)))))

Now that I hold the title of “grandpa”, I get to do all sorts of fun things with the grandchildren. Silly hide and seek, playing with toys, and taking them to fun places.  In my neighborhood, I have access to one of our beloved Metroparks, Huntington Beach.  Jackie and I love taking the kidos down there, splashing in the waves, watching sunsets and of course playing in the sand. I get to lug the gear – towels, blankets, chairs, sunscreen, snacks, and of course I had to bring some shovels and pails and molds to make shapes.  We have been constructing sand “castles” since the girls were able to stand – one of our ladies actually learned to walk on the beach!  The majority of our structures had to also have an elaborate moat for protection.  Little water, little sand, and presto, a castle. I have to say once finished with the castles,  their next choice would be to bury me in sand!  That did make for a nice nap!   My curiosity got to me back at the office, to learn a bit more about why the sand sticks sometimes, and crumbles other times.  I went online and found this cool article written by Joseph Scalia – Associate Professor of Civil and Environmental Engineering, Colorado State University (to understand why some sandcastles are tall and have intricate structures while others are nearly shapeless lumps of sand, it helps to have a background in geotechnical engineering). I also found some amazing designs from beaches all over – must say WAY more than my pail domes. Thanks to and YouTube for the info and song.


  • The size of particles, or grains, also determines the way sand looks and feels. The smallest sand grains have a texture almost like powdered sugar. The largest grains are more like the size of small dry lentils.
  • Most sand will work for building a sandcastle, but the best sand has two characteristics: grains of sand in several different sizes and grains with angular or rough edges.
  • Sand grains that are more angular, with sharp corners on them, lock together better, making the sandcastle stronger. It’s the same reason a pile of angular wooden blocks will stay in a pile, but a pile of marbles will go everywhere.
  • This is also why, surprisingly, the best sand for sandcastles is not typically found on an island or a coastal beach. More angular grains of sand are usually found closer to mountains, their geologic source. These sand grains have not yet had their edges rounded off by wind and water. Professional sandcastle builders will go so far as to import river sand for their creations.
  • Water is key – Without water, sand just forms a pile. Too much water and sand flows like liquid. But between dry sand and saturated sand lies a wide range of moisture levels that enable sandcastle construction.
  • Water is cohesive, meaning that water likes to stick to water. But water also sticks to or climbs up certain surfaces. Look at a half-full glass of water and you will see the water going up the insides of the glass a little. This tiny power struggle is what makes sandcastles possible.
  • If the glass were much skinnier, like a straw, the water would rise higher and have more surface tension. The narrower the straw, the higher the water would rise. This phenomenon is called capillarity (think celery stalk).
  • Water behaves the same way in wet sand. The pores, or spaces, between the sand grains are like a bunch of very tiny straws. Water forms tiny bridges between the grains. The water in these bridges is under tension, pulling the grains together by a force we geotechnical engineers call suction stress.
  • Just enough water – The quantity of water in the sand controls the size and strength of the water bridges. Too little water equals little bridges between the sand grains. More water, and the size and number of bridges grows, increasing the suction holding the sand grains together. The result is perfect sandcastle sand.
  • Too much water, though, and the suction is too weak to hold the sand together.  A general rule of thumb for building great sandcastles is one part water for every eight parts dry sand. Under ideal conditions in a laboratory, though, with dense sand and zero evaporation, one part water for every one hundred parts dry sand can produce wonders. At a beach, sand with the right moisture level is near the high tide line when the tide is low.
  • Incidentally, salt from seawater can also be a boon for sandcastle stability. Capillary forces hold sand grains together initially, but capillary water will eventually evaporate, particularly on a windy day. When sea water dries up, salt is left behind. Since the seawater was forming bridges between the grains, the salt crystallizes at these points of contact. In this way, salt can keep a sandcastle standing long after the sand has dried. But be careful not to disturb the salt-bonded sand; it’s brittle and collapsible.
  • To build a strong sandcastle, compact sand and a little water as tightly as you can. I prefer to create a dense mound and then scoop and carve away to reveal the art within. You can also compact the sand into buckets, cups or other molds, and build from the ground up. Just be sure to get the sand dense and place the mold on a compacted foundation. Hands make for both a great compaction and carving tool, but a shovel or a seashell will allow for more precision.

Have fun, and don’t be afraid to get sandy!

Oh, and check this out before you go:
5 cool sandcastles in the making





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