Oh, absolutely-you can't do a whole drywall project with just one size. It's like trying to bake a cake with only a spoon-you need different tools for different steps. Let me walk you through why different sizes matter, based on my experience.
First, the 4-inch or 6-inch knife: This is for the "prep work." Use it to fill nail holes, patch small dents, or get into tight corners (like where the wall meets the ceiling). Small blades are easy to control, so you don't smear compound everywhere when you're working on tiny spots. I use my 4-inch knife every time I hang pictures-fill the nail hole, smooth it out, and it's invisible after painting.
Next, the 8-inch or 10-inch knife: This is your "taping workhorse." It's perfect for the first two coats of compound on main seams (the gaps between drywall panels). The size is just right-wide enough to spread a thin layer of compound along the seam and press the drywall tape down evenly, but small enough to maneuver without making a mess. I use a 10-inch for taping-one smooth pass, and the tape is stuck tight with no bubbles. Tried using a 6-inch for this once? Took twice as long, and the seams were lumpy.
Then, the 12-inch or 14-inch knife: This is for the "final coat" and smooth finish. As I mentioned earlier, wide blades let you feather the compound over a large area, so the seams disappear. Without a 12-inch+ knife, you'll never get that smooth, professional look. I always use a 12-inch for the final coat-it covers the seam wide enough, and the flexibility (if it's carbon steel) helps with smoothing.
Here's the thing: If you only have one size, you'll end up rushing, making mistakes, and spending more time fixing them. I started with just a 10-inch knife, and my first drywall project looked terrible-nail holes were visible, seams were lumpy, and I had to sand for hours. Once I got a 4-inch and 12-inch, everything got easier. So yes, you need different sizes-they each have a job to do.
taping knife from hanke tools
