For the base mould, I'm using a plastic cup and for the inner mould, I'm using a yakult bottle. Thanks to my son Jules who loves Yakult to bits and drinks a bottle every other day. So I kept most of his Yakult bottles for this DIY project.
Above: Here's how they look like...all set to dry. As our Singapore weather is rather humid, mine took about 4 days to be fully dried out.
Here's how they look after we pried them out from the moulds.
i actually like the "bubbles" at the bottom of the tealight holders. I read online that if you do not like the bubbles effect, you will need to tap the concrete mixture when it's settling in the cup/mould to remove the air bubbles.