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Recipe for 16-foot-tall sandcastles revealed

AP / Mel Evans

In this file photo, Chuck Feld of West Chester, Pa., works on his sand art during a sandcastle contest in New Jersey. New research shows that just a dash of water is all that's needed to hold together the sand grains.

Just in time for the dog days of summer, scientists have revealed the winning formula for sturdy, sky-piercing sandcastles. The secret ingredient is a dash of water.

Daniel Bonn, a physicist at the University of Amsterdam in the Netherlands, and colleagues explain that water is necessary to form capillary forces that help sand grains bridge, or stick together.

While we all know that some water is necessary to turn the dry sand between our toes into suitable building material, the new research shows that just 1 percent water by volume is the perfect amount.

Less surprising, the team also found the wider the base, the higher a sandcastle can reach into the sky before buckling under its own weight.

Using the optimum mixture of water and base, sandcastles reaching 16 feet high are possible, according to the research published Thursday in Scientific Reports

Pakpour et al / Scientific Reports

Using commercially available hydrophobic sand, it is possible to build an underwater sandcastle.

What’s more, the team found that even taller sandcastles are possible when using water-repellant sand (yes, there is such a thing) and building the structures underwater. 

“In this case the air and not the water ‘wets’ the grains and we can simply interchange water and air, which does not change the bridge force,” the team reports. 

“This makes it possible to build underwater sandcastles, which are even more spectacular than normal ones."

In case you’re wondering why university scientists are spending their time building sandcastles, they say their research has practical importance to civil engineers dealing with soil mechanics.
