Space filler is a term used to describe materials that are used to fill in gaps or cracks in walls, floors, and other surfaces. A SHIM is a thin piece of material, usually wood or metal, used to fill small gaps between two objects. Spackle is a type of lightweight plaster used to fill holes and cracks in walls and ceilings. GROUT is a cement-based material used to fill the spaces between tiles. All three materials are commonly used as space fillers.