Cement Pot

Hi All

I've made a pot out of pure portland cement (and water). You can see a picture here:
https://drive.google.com/file/d/0BwUfC- ... p=drivesdk
It's a mix of grey and white cement.

It has stainless steel mesh reinforcing inside:
https://drive.google.com/file/d/0BwUfC- ... p=drivesdk

It came out of the mold and all looked fine. Then about a week later i noticed a few cracks, very fine but possibly deep.

Can anyone help by suggesting what to mix with the cement and water to avoid this cracking? Will sand help? And or gravel/crushed stone (concrete)? I've read lime cement is more flexible than portland, so less cracking? Not too concerned about increasing weight a bit.

Any help much appreciated. Obviously this is not really a building project, but thought the expertise of people looking at this forum would be relevant.

Cheers
Byron