How to make a perfect sandcastle

Now summer seems to finally be here, we thought we’d get the sand table out and start playing. We tried to make sandcastles with the dry sand, which didn’t work at all. They just collapsed.

Can you think why this is? What could you add to make the sand more ‘sticky’?

We added a little bit of water, which made the sandcastles slightly better, but still not great.

We kept adding water until we could make an almost perfect sandcastle. It took several attempts to get the right combination of sand and water.

Too much water and the sandcastles fell apart and stuck to the inside of our bucket. Too little water and the sand just flowed out. We found that if we could squeeze the sand into a ball in our hands and it stayed together it made a good sandcastle.

How to make the perfect sandcastle

Sandcastle sand to water ratio

According to PBS the magic sand to water ratio is one bucket of water to 8 buckets of sand!

We put this theory to the test and it worked really well! The sand was sticky, but not too sticky…almost perfect!

Why does water make sand stick together?

You should have noticed that wet sand is much stickier than dry sand. This is because the water forms tiny bridges between the grains of sand which holds them together. This is due to the surface tension of the water. If too much water is added, water fills the space between the grains of sand and the bridges break down.

Read more about the physics of sand on Live Science.

More Science Activities using Sand

Use sand to filter water in this easy activity.

Make a volcano eruption using sand.

Or, try one of our 50 Summer Science Activities.

The BEST sandcastle sand to water ratio