You can spray or roll joint compound as a texture, but you need a blade to finish seams.
Joint compound, called "mud" in the industry, is a plaster-like gypsum product that builders use for finishing and texturing drywall. It comes in different weights. The heavier ones are suitable for taping seams while the lighter ones are more appropriate for top-coating and texturing. In addition, a setting-type, called hot mud, is available for applications that require extra strength and resistance to cracking. Mudding techniques vary with the mud type and according to whether you're taping or texturing. Does this Spark an idea?
Taping Seams
Whether you use taping compound or all-purpose joint compound, the technique for taping seams is the same. With a 4- or 6-inch blade, you spread the mud generously along the seam in a strip slightly wider than the drywall tape, then lay the tape on top and scrape over it with the blade to remove the excess. If the tape bubbles up, it usually means there's not enough mud. Some builders prefer to let the tape dry before top-coating, but others recommend spreading another coat immediately to shorten the time needed for finishing. It's largely a matter of preference.
Finishing
The care and skill you apply to top-coating the seams and covering screw holes determines the final appearance of the wall. You should apply at least two top coats, using either all-purpose joint compound or topping compound, and apply each coat with a progressively wider blade so the edges gradually feather into the wall. Professionals often use a 10- to 12-inch blade for the final coat. Apply the mud generously and scrape it in long, straight strokes. Let each coat dry before you apply the next, and keep the wall free of dirt and dried mud so you won't create tracks when you scrape.
Texturing
Many texturing patterns can be made with joint compound. You can thin it down and spray it to make a mottled or eggshell pattern, or you can apply the thinned mud with a roller for a similar effect. You can also spread topping compound at full strength with a blade and make swirl patterns or knife edges. One of the most common patterns is called "knock-down." To do it, apply blotches of mud to the wall by spraying or with a blade, then use the blade to scrape the tops flat to create the texture.
Using Hot Mud
Because it sets quickly, hot mud is more difficult to use than regular joint compound, but its superior strength is desirable on joints that are prone to cracking and damage. After you mix hot mud, you have a limited time to apply it before it becomes unworkable, so you should mix only what you need and work quickly. Apply it like the non-setting variety, but scrape carefully to ensure there are no ridges or high areas. While regular joint compound is easy to sand, hot mud isn't, and any mistakes you make while using it will be difficult to correct.
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