I use whatever mix I want for appearance and strength over a plastic covered mold. This gives the bowl a smooth finish with some small air bubble pits. I pick out any loose edges from the pits and make them large enough to accept the next coat of mix. Then I apply a sloppy mix of one part portland and three parts sand to the inside of the bowl by hand, rubbing it into all of the pores. the next day I repeat the coating if necessary. Wipe off any loose stuff when dry. This seems to hold water well enough. I doubt if it is harmful to birds if it is aged a little before use.

Another option is to imbed a large dinner platter or meat platter in the piece. ths will solve the leakage and harm to birds issue. This also allows you to use a colorful platter. The problem is that birdbath size is limited by platter size. Make one with a half inch deep groove in the bottom to fit over the top rail on your deck railing.

I plan on using mounded sand with plastic wrap over it for my mold. Maybe put a couple nice leaves in there for decoration. I am more worried about the mix being harmful to birds that may drink out of it. (fredw10 I don't have a deck) I plan on making a base for it out of hypertufa using a piece of 4" drain pipe and something larger at the very bottom so it won't tip to easily. Maybe even a larger bowl with drainage attached to the bottom so I can plant in it.

Thanks

Gemfire

You needn't worry about it harming the birds. Concrete is a natural product in itself. I would recommend using the fortifier admix to some degree in your mix. This really helps to seal it (natural concrete sucks up water). You can even use admix for half the water, 1/2 water-1/2 admix.

I make Birdbaths for a living...you're right on track...we want to see pics of the finished product, please.

Happy casting

Kevin

I have never used admix. which one are you using and where do you get it?

It seems to me using a mound of sand would make it difficult to get a uniform shape in the bowl. I have used a large plastic planter tray or even a two inch thick disc of any diameter of blue insulation board covered with a dry cleaner bag for the bowl mold.
For the pedestal I have used a piece of 4in plastic pipe with many drilled one inch holes to help hold the mix. I wedged a piece of wood into the bottom of one end of the pipe then attached it through the bottom of a piece of plywood with a screw. This holds the pipe vertically. Next I split a piece of 8 in dia. cardboard tubing lengthwise and used it to contain the mix as it was built up around the pipe. After setting up, the tube was removed. The outside of the pedestal was, of course smooth, so I added mix by hand to roughen it for the look I wanted. The foot of the pedestal was simply a 4 inch high larger dia portion of the pedestal.
If you like the idea of using a colorful 10 to 12 inch dia platter for the inside of the bowl, it would result in a 14 to 18 inch overall dia piece which could be set on a heavy wire decorative plant stand. I have one about 18 inches tall. I am interested in what you might think of these ideas, and any of your own that I could try. Fred

Fred..The Admix I refer to you can buy at any Home Depot, Lowe's or most Hardware stores carry it. I am not sure of the brand but I buy mine at Lowe's. It is sometimes referred to as Fortifier. It is a polymer liquid. Some people use Elmers glue diluted and that works too.

Gemfire I realized after reading your original post again that you were asking for a recipe, here's mine:

1 part portland
3 parts fine dry sand
admix plus equal amounts of water

You don't have to be exact on the admixture, it is used as an internal sealer for anything holding water, really helps.

Hope I have been of help to you both,

Kevin

Thank you Creteman, that's exactly what I wanted to know. Was wondering if you've ever done anything with pool filter sand? I just dumped one out and the sand looks quite nice so I may try it in one of my projects rather than have it go to waste.

FredW10 I read on an earlier post where people were using mounded sand to get the shape for the bowl of the birdbath. It said to dampen the sand as you mound it so it packs nice and tight. Then put plastic wrap over it. I've looked around for other inexpensive things to use but haven't found the shape and depth I want. I'll be looking for the admix creteman mentioned but might be awhile before I get to the project. Just went back to work after being off 6 months for low back problems and its still awful hot here, don't want to push it. Thanks for the info. Will post pics when I get to the project.

Thanks again,
Happy Hypertuffy,
gemfire