How to make the perfect sandcastle, according to science

Summer vacation is here and no trip to the coast is complete without building a huge sandcastle that other beachgoers envy.

But as any vacationer knows, there’s nothing more frustrating than being halfway through your majestic creation when it collapses in a heap.

Fortunately, a British researcher has now provided a few tips on how to get the “perfect sandcastle,” according to science, and make it stand proud for hours.

Professor Matthew Bennett, a sedimentologist at Bournemouth University, suggests using an 8:1 ratio of sand to water and using jagged shell fragments in the mix.

He also says to use a simple round bucket – not a square bucket or one with turrets – which help keep the mixture compact – and provide you with the sturdy building blocks to build a mighty sand fort.

“Whether we prefer water sports or relaxing with a good book, the humble sandcastle is often a seaside must,” said Professor Bennett.

“The modest castle with perfect towers, battlements and moat is okay, but it’s the huge castles that break the beach horizon that inspire awe and wonder in passers-by.”

The first step is choosing the right sand, and the academic says that “angular” grains of sand help build a strong sand castle because they can interlock, just like a wall of bricks.

Circular grains, on the other hand, tend to slide against each other and are therefore a poorer choice – although it can be difficult to tell the difference with the naked eye.

If you’re not sure, incorporating small jagged shell fragments into the mix can help augment this interlocking formation and give the castle more structural integrity.

When you start building your sandcastle, the best approach is to collect shovelfuls of dry sand, as you need to control the amount of water that goes into it.

Professor Bennett advises sand castle builders to add one part water to every eight parts sand – meaning that for every bucket you fill during construction, it should be about 12 percent water.

An 8:1 ratio of sand to water is perfect because it provides just the right amount of surface tension – the force that causes water molecules to be attracted to each other.

Too little water and the surface tension can’t keep the grains of sand together, but too much water and the water turns into a lubricant, causing the castle to collapse and begin to flow with the water.

8:1 is the sweet spot between a castle that crumbles like a fruit topping (not enough water) and a castle that flows like a muddy landslide (too much water).

‘The water film between individual grains of sand gives sand its strength,’ says Professor Bennett.

“Too much and it smears one grain over another, but just right and it binds them tightly.”

For this reason, it’s important to mix thoroughly, make sure each grain of sand is water-coated, and pack the bucket to tighten the tiny water bridges that hold the grains together.

Following these steps should allow one bucket full of your mixture to support the weight of another, helping to create the biggest fortress on the beach.

Weather can affect the sturdiness of your structure where the slightest wind can blow it over, so you may want to opt for remote edges of the beach, perhaps sheltered by natural rock promontories.

Professor Bennett was part of a 2004 study comparing sand from the 10 most popular beaches in the UK.

The red sands of Torquay in Devon were the best for castle building, followed by Bridlington second and Bournemouth, Great Yarmouth and Tenby third.

Unfortunately, some famous beaches in the UK, including Brighton Beach, are useless for building sand castles for one simple reason: they have stones instead.