Sand Sculpture Festival 2010, Blankenberge, Belgium

Construction
Sand grains will not stick together unless the sand is reasonably fine. While dry sand is loose, wet sand is adherent if the proper amounts of sand and water are used in the mixture. The reason for this is that water forms little ‘bridges’ between the grains of sand when it is damp due to the forces of surface tension. However if too much water is added the water fills the spaces between the grains, breaking down the bridges and thus lowering the surface tension, resulting in the sand being able to flow more easily and the structure collapsing. According to the BBC TV programme Coast, the ideal ratio is eight parts dry sand to one part water, (though this may depend on the type of sand).
When the sand dries out or gets wet, the shape of a structure may change and "landslides" are common. Furthermore, the mixture of fine (mostly sharper) and coarse sand granules is very important to achieve good "sand construction" results. Fine granules which have been rounded by the natural influences of seas, rivers or fluvials, in turn negatively influence the bonding between the individual granules as they more easily slide past each other. Research is thus necessary to find the most suitable sand to achieve an optimal, landslide-free construction.