No not really, I do it in the garage so as not to have any wind or sun on them to make them cure faster, beside they aren't thick enough to worry about it. Now if you are going to make them for high traffic areas where they would be used constantly then I would add chicken wire and make them thicker. Mine are really just for decorations even though I do use them to step on in the garden. Besides the mortar is made to dry quickly.
