Varieties
A putty knife can come in a number of variations including:
Flat edged blade and chiseled edged bladeStraight edge and angled edge bladeStiff blade or flexible bladePlastic, carbon steel, stainless steel or brass bladeBlade widths from 3/4" to 6" wide
Spreading and Applying Compounds
Application of a compound is a common use for the generic putty knife. A compound can include any number of paste-like materials such as wood filler or wood putty, base application drywall compound (used in taping drywall joints), spackling paste or other filler materials or even adhesives. The blade edge will typically be straight (versus chiseled) and will tend to be flexible (versus stiff). The most economical version of these knives is made from plastic like polypropylene. Plastic blades are often disposable and do not stand up well to continued use. A better-constructed blade is made from ground and polished carbon steel. However, although the carbon steel is more durable, it may rust if not properly maintained. The premium version of a putty knife blade is made of stainless steel. A well made stainless steel blade knife with a durable nylon or wood handle can last a lifetime. Well made steel blades used for spreading will also have a “hollow ground” feature. That means the blade is ground to be more narrow in the center of the blade and thicker at the handle and leading edge. What this does is allow a good deal of flex in the blade to modulate the pressure being used when spreading material. The blade width will vary according to the use of what is being applied. A narrow blade knife is used in tight space applications and where you are applying a small amount of material. Such applications may include a wood filler to a hole in wood or a joint crack, or a small hole in drywall being filled with spackling compound. Wider blade putty knives are usually used for applications of a lot of material such as drywall compound over a wall patch or applied over a taped drywall joint. Another use of a putty knife is to use it to make a clean paint edge when applying painter’s tape to an edge such as the top of a baseboard when painting a wall. Use a 1-1/2" flex blade putty knife to press the tape firmly to the baseboard and create a knife-edge to the paint line by taking the edge of the putty knife and pressing it simultaneously into the corner of the baseboard and wall and pressing the tape to the baseboard while dragging the knife along the tape on top of the baseboard.
Scraping
Scraping and removing residue is another use of a putty knife. In this usage, however, you will be using a stiff blade (versus flexible) with a chiseled edge (versus flat). You will also want a steel blade instead of a plastic blade. Scraping blades are stiffer than spreading blades so they will not be ground steel (promoting flex). These steel blades will be thicker and more rigid. The chiseled blade edge of the knife should also be angled instead of flat to help get under the paint, dried putty, or other residues more easily. For use in delicate applications and in areas that have volatile fumes, you will want to use a specialty scraper having a brass blade. A well-made scraper will feature a full tang. The metal that makes the blade will run fully through the handle. That way the knife has metal from front to back and allows the knife to be struck lightly with a hammer on the handle to coax the paint or other debris/residue from the material being cleaned.
Specialty Knives
The taping knife is a very wide-spreading knife, 9 to 14 inches wide, used to apply wide swaths of drywall taping compound when feathering a drywall joint. A multi-tool is a rigid scraping tool with a chiseled edge and special cutouts/edges for cleaning paint rollers, scraping open cracks and scraping material.
