Putty knives and drywall taping knives both have handles and flat blades, and while you can occasionally use them for similar tasks, you can't always substitute one for the other. Putty knives, so named because they allow you to spread putty into depressions without using your fingers, are smaller than drywall taping knives. Taping knives, depending upon their sizes, have different purposes, but both types of knives can save you time and labor.
Putty knives are generally lightweight, with blade widths that vary from 1.5 inches up to 4 inches. The handles are short, about a palm's width, making the knife simple to grasp and control in tight spots. Putty knife blades may be rigid with a beveled edge for scraping or slightly flexible for spreading putty or spackling. Putty knives with metal and stainless steel blades have a permanent place in the toolbox and workshop. But for quick jobs, you can purchase inexpensive, disposable plastic putty knives.
Drywall Taping Knives
Drywall taping knives are the tools of the trade for drywall contractors, who usually have at least half a dozen of these trowel-like knives for applying and smoothing joint compound. A 6-inch drywall knife is handy for scooping up wet joint compound and smoothing it into the seams between drywall panels. The larger knives are reserved for feathering the wet compound out over a wider area, which makes the seams less visible after finishing and painting the wall. Standard widths of drywall taping blades start at 6 inches and run up to 14 inches.
Both putty knives and drywall taping knives are valuable for scraping. Rigid putty knife blades, especially beveled blades, slip easily beneath loose and peeling paint, scraping it away from siding, porch rails and decking before repainting. Drywall blades are useful for scraping bits of dried joint compound from taped walls or for removing old wallpaper.
Drywall taping knives are used almost exclusively on walls during the mudding process. When repairing and retaping small areas, however, such as a narrow strip of wall between a door frame and the corner of a room, a drywall-taping blade may be too wide. In limited spots like this, putty knives come to the rescue, smoothing compound, filling cracks and scraping away thin strips of wallpaper.