Slab building is a handbuilding technique that starts from a flat sheet of clay, rolled to an even thickness, then cut to a template and assembled into a form, in much the way flat cardboard is cut and folded into a box. It suits geometric, architectural, and tile-like forms particularly well, and is one of the more straightforward handbuilding methods to plan out in advance, since a piece can be sketched flat before it is ever cut.
Clay is rolled flat with a rolling pin, guided by a pair of wooden strips (thickness guides) laid on either side to keep the sheet an even depth, typically a quarter to a half inch for most functional work, or run through a mechanical slab roller for a larger or more consistent sheet. Rolling on or under a canvas cloth keeps the clay from sticking to the work surface or the rolling pin, and is standard practice rather than an occasional aid. Once the slab reaches an even, leather-hard-adjacent stiffness (firm enough to hold a cut edge, still soft enough to bend gently), pieces are cut to a paper or cardboard template and assembled: edges to be joined are scored and slipped, then pressed together and reinforced with a thin coil of soft clay pressed into the interior seam. Curved forms are made by draping a slab over a rounded form (a hump mold) or into a shallow depression (a drape or slump mold) and letting it firm up before removal, rather than folding flat panels at an angle.
Slab-built seams are a common weak point if the two edges being joined have dried to noticeably different stiffness, so slabs are typically kept covered and worked with soon after rolling rather than left to stiffen unevenly before assembly. Because the walls start out perfectly flat, slab building is the natural fit for boxes, planters, architectural forms, and tiles, where wheel throwing and the other handbuilding methods would fight the material to get a comparably flat, straight-edged result. Soft supports, such as foam blocks, rolled towels, or crumpled newspaper, are commonly used to hold a slab-built form in its intended shape while the joins firm up enough to be self-supporting.