Clay is a fine-grained natural rock or soil material that combines one or more clay minerals with traces of metal oxides and organic matter. Clays are plastic due to their water content and become hard, brittle and non–plastic upon drying or firing.
Many artists won't work with natural clay because it cracks and often falls apart. But there are ways to minimize the cracking problem by applying a thin layer of foaming glue to the surface. Using rubber gloves, you can apply the glue to the surface of the clay immediately after you finish sculpting with it. By using a minimal amount of glue and rubbing it lightly and uniformly across the clay surface, you can create a shell casing around the clay. Because the clay dries slowly and the glue quickly, it will form a hard outer layer within a few hours. The precaution is though that you need to watch the foaming glue for at least 20 minutes. If the glue foams to high, you need to use your finger to gently deflate it again. Once it hardens, you will have no further troubles with it raising and your clay should remain firmly encased while it dries. Cracking can be virtually eliminated leaving your original sculpted shape.
In the photo you can see the yellowish white of the glue beginning to foam around the base of the ruined tower structure. In this case I want some cracking to occur higher up, so I've left most of it exposed to natural drying. But I don't want the bast to fracture or large chunks to break off. Gluing the base allows a lower protective shell to form. Once dried (usually 2 hours) I can paint over both the clay and the glue further reinforcing and minimizing the cracking.
You will want to give the clay at least 2 days to do a total surface drying before working more closely with the piece.
If you do a partial glue casing where some clay is exposed, and you encounter severe cracking after drying it should terminate at the shell. You can use a clear jell glue to fill the cracks. I suggest GO2 glue by Loctite. Whatever you use make sure that it is both clear when dry and that it is not a liquid like a basic super glue. This just drips through the crack. Using a gel glue lets you fill the cracks cleanly and wipe away the excess. Once dry you can again paint over it and the crack will for the most part disappear. Dry time is about an hour with GO2 glue. Others may vary.
Keep in mind that you can also use the foaming glue to create texture on the clay. After letting it set about 5 minutes you rake it with something as simple as a plastic fork or use a dry sponge on it and it will retain the pattern. This may take some experimenting to get the hang of the best time to texturize. If you do it too soon it will melt back and refoam. If you do it too late it will be too hard to be of use to you. But with a little playing around its pretty easy to get the hang of.
As an example, the cliffs in this photo were built with clay stretched over styrofoam. This traditionally wouldn't work because the clay would just break off of the foam as it dried. But by applying an overlay of foaming glue and working with the texture to create a rock looking surface, there was no cracking and the sculpture is solid enough that it can be hung on a wall and won't budge. I even applied natural small rocks embedded in the glue before it dried to add to the natural feel of the cliffs.
SO the advantages of using these techniques means that you can use clay as a medium without having to heat it in a kiln. Natural Clay is great for so many things and if you can overcome the cracking problem the possibilities are endless.
One word of warning! With any glues, please be careful. This should not be attempted with the bare hand or a utensil. Use rubber gloves and allow your finger to work over the clay gently. Utensils can gouge.
Have fun and feel free to share your questions or experiences!