What to Consider When Buying a Taping Knife

a Taping Knife on a wood table with a red instrument and white object next to it

A taping knife is used to apply joint compound or drywall mud. Since there are a variety of taping knives to choose from, it is important to consider what knife or knives best suit your project. Read on to learn about various types of taping knives and their different applications.

Drywall and Taping Knives

Taping knives are used with drywall. Drywall is gypsum board or wallboard. It is also commonly known as sheetrock. It is comprised of a gypsum core, with smooth paper attached to the finish side and coarse paper on the back side. Drywall comes in thicknesses of 5/8-inch, ½-inch, 3/8-inch and ¼-inch.

Taping knives are used to fill holes or gaps in drywall and to fill joints in between using pieces of drywall tape. Taping knives are constructed of wood, metal, rubber and plastic handles. At the end of the handle a thin sheet of metal, known as the blade, extends outward. The blades are made of carbon steel, blue steel or stainless steel. There are small taping knifes and large ones. Sizes can vary from 3 inches to 14 inches. Some of the more popular sizes for general drywall work are the 6-inch, 8-inch and 10-inch taping knives. There are also corner taping knives, also known as drywall corner trowels. These knives are shaped at a 90-degree or right angle in the middle for use on the inside corners of drywall.


When wallboard or sheetrock is installed, there are gaps in between the adjoining boards. Drywall mud and tape fills these gaps and keeps them from cracking and coming apart. Drywall mud is applied to the seam or joint with the knife and a layer of tape is applied over the top. An additional layer of mud is then applied over the top of the tape. This insures the seam or joint is sealed and allows for light sanding and finishing when the drywall mud is dry.

The Right Knife

Most 4-inch, 6-inch and 8-inch taping knives are used for applying drywall mud to gaps or holes and for taping. They are also used to remove excess drywall mud. The 12-inch taping knife is used for feathering areas where a wall or ceiling may be sloped or uneven. The larger surface of the 12-inch knife allows for a gradual transition in the surface so sloping is less noticeable. Corner taping knives or trowels are used on inside corner areas where tape needs to be applied. The right angles of the corner taping knife press mud and tape into both sides of the corner at once and give an even, more consistent edge.


Keeping your drywall taping knives clean will preserve their life. Drywall taping knives are cleaned with water and elbow grease. Allowing drywall mud or joint compound to harden on the knife will make it difficult to clean. It may impair its use until all the hardened mud is removed. It can also cause rust to form on the metal of the knife.