You won't need any reinforcement in that column mold, I've made lots and never reinforced any of them. I've used hardware cloth for the basins, and used up old bits of chicken wire too. The basin is pretty substantial though, So I've made lots with no reinforcement too and never had any issues. I have added some fibre reinforcements in the mix though sometimes.
Good luck and happy casting,
Cindy

I don't think that PVC pipe would work as reinforcement as it is far too flexible, but I don't know.

Any experts?

I have used plastic pipe in birdbath pedestals for two reasons. First, if you use a 3 inch dia pipe it will reduce the weight of the piece. Second, extension of the pipe an inch or two above the top of the pedestal can serve as the connection with the bowl. I have drilled one inch holes in the pipe for the mix to be forced into for a good grip on the pipe. you can also use a cylinder of hardware cloth around the pipe for strength. Any of these things will work. Or, you can make a solid pedestal without anything inside. I use a piece of a black nursery pot around the stem of the pedestal to retain the mix until it sets up.

Hi all!
From everything that I've been learning here in the past year, the pedestal of the birdbath should be heavier than the actual bird bath; this too maintain good support above. I suppose if one has a hollow pedestal and it appears to be light-weight one could fill it with heavy sand or small rocks. just my 2cents..Wendy

Anything that works for the maker is good. It's common sense that the pedestal can't be allowed to tip over. The diameter of the base needs to be large enough to prevent that.