Tip one: Every good sand sculpture needs a solid base or shape to begin with.

For Christchurch-based pros Asheley Elizabeth and Annette Griffiths, work on the base of their masterpiece started about 6.45am on Friday.

Their company, In Good Form, which specialises in sand sculptures and other artistic installations, was hired by the Banana Boat New Zealand Ocean Swim Series, which had its annual Generation Homes Sand to Surf event at Mount Main Beach on Saturday.

Elizabeth said stage one of any sculpture should involve "pound ups", which was the compacting of sand and water together.

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"It's like a layered cake," she said.

Shovel a few loads of sand into a bucket and fill it with water so the sand is fully immersed, then make mud pies, lots of mud pies, and form your solid base.

Elizabeth and Griffiths used wooden forms to make theirs and it took them about three hours, with the help of some locals.

They then let the sand structure settle, before starting the sculpting.

Elizabeth said it was much easier to carve from a block of hard sand.

Tip two: Always keep your sculpture wet as you work on it.

For Elizabeth and Griffiths, that involved spray bottles and constant monitoring.

They sculpted until dark on Friday night, about 8.30pm, and then returned at 7am on Saturday to finish the job.

Overnight, security watched over the artwork.

By 10.30am on Saturday, the sculpture was complete, just as the first ocean swimmers were crossing the finishing line.

"The body's feeling it a bit at the moment," Elizabeth said with a laugh, having just completed her own endurance event.

The distinctive peak of Mauao, sculpted in great detail, stood strong at the centre, with ocean swimmers, waves, rocks, sponsors and event logos all carved around the sides of the sand mountain.

"If someone wants to take a picture of it, they know where they've been," Elizabeth said, as passersby did exactly that.

Tip three: Have an idea of what you're aiming for, visualise the image in your head, and do the planning and dreaming before you come to the beach.

Elizabeth said she and Griffiths started with some main features and then worked on the smaller details from there, including as many other elements as they could in the time they had.

She said it was their first time working at Mount Main Beach – "we love this place, it's great" – and she hoped the sculpture would stay up for at least a couple of days.

She said it always depended on the weather and the type of sand.

"This is quite granular sand; it doesn't have a lot of silt in it up high on the beach here, so it's quite coarse so it will dry out quite quickly."

Generation Homes also had a competition set up for kids next to the sculpture at Mount Main Beach on Saturday.

"The main sculpture is like a hype event, and they wanted to have the competition just as a parallel for the kids, because once they see this, they just want to get in there," Elizabeth said.

"There's already kids going for it, using our tools, they're opportunists," she added with another laugh.

Tip four: Just have fun.

"That's why we got into it," Elizabeth said.