Are the birdbaths thinner at the edges? Maybe the edges dried out too fast when it was curing.

Thanks for the response. The round bowls seem to crack as opposed to the oval shapes. They are not thin (1"+) at the edges. They all have cracked several weeks after the curing process. I usually cure them for about 7-10 days. On some other sites, they say to never put water in them for the first few days. Why? Is there a detriment to having them too wet in curing? I always thought the more water the better, but maybe that is more for tufa than straight concrete?
Is using a pre-packaged mix any better than me mixing my own?
Thanks for any further advice!

I cure a lot of things in a water bath after the first 24 hour set. I use a plastic muck bucket and a plastic mortar pan for the bath.
Your own mix is better because you know what the portion are and exactly what's in your mix.
Can't tell you why the round are cracking as opposed to the oval shape. Good luck and keep us posted on how it's going.
Is this the original "gardener boy"? There have been quite a few people that use to post here a couple of years ago posting again.
Billie