My grandfather made garden sculpture and I have a number of his old cast pieces, but not the original molds. I have experimented with latex mold making using sculpty clay and roma plastina, but I would like to try and make molds from these concrete sculptures. The works are fairly small and seem suitable to the latex method. Do I have to coat the sculptures with shellac (I'd rather not) or can I just layer the latex directly on to the concrete? Any suggestions on the best way to do this would be appreciated.

Concrete is a porous surface so you will need to use some kind of sealer. The good news is that you have a bunch of choices, for example one mold-making material manufacturer writes, "Suitable sealers include shellac, paste wax, and petroleum jelly thinned with mineral spirits. Smooth-on SuperSeal™ is a non-intrusive sealer that does not interfere with surface detail and can be removed with warm water."

Thanks Bear, I'll give the least instrusive a try and go from there.