Appearance Differences
The most glaring and obvious difference between smooth walls and orange peel walls is the appearance. Smooth walls are just that, smooth and flat, all the way across. You have the option of either painting the walls or placing wallpaper over them. An orange peel wall has a texture that resembles the peel of an orange, for which it is named, and has bumps all over it. You can paint the wall, but you wouldn't wallpaper it. The wallpaper would not only hide the wall's appearance, but the orange peel bumps would be visible all over the wallpaper's surface.
What Shows
The two wall finishes differ also in what minor problems show on each one. With a smooth wall, many imperfections that are left behind from the initial drywalling job can be more easily seen than on a wall with an orange peel texture, which is sometimes the reason why orange peel, or any other texture, is used. If the mud used on the wall is not sanded correctly, you notice it easily on a smooth wall. Also, marks and uneven spots appear clearly on smooth walls. The orange peel texture hides these minor shortcomings. But although the orange peel covers minor imperfections, don't simply cover wall damage such as cracks or holes with texture. Repair these spots before installing the orange peel.
Application Differences
All drywall installations go through the stage of being smooth, whether or not you apply orange peel texture afterwards. Smooth walls are achieved after applying the third layer of drywall mud, using either sandpaper or a drywall sponge. Applying orange peel texture takes more skill and also quickness. After smoothing the wall, apply additional mud that is mixed with water and stirred to the right consistency. Roll the mud onto the wall with a roller or, more commonly, spray it on using a hopper, spray gun and air compressor. These tools are often rented, but you can also purchase each one.
Repair Differences
When damage occurs to smooth walls, repair it and smooth replacement layers of mud onto the walls using the same sanding process with sandpaper or a drywall sponge that is used to install the walls. Repairing a spot on a wall with orange peel texture is more complicated. Unless you remember such things as the exact formula used when mixing the orange peel texture, and the air pressure setting for the spray gun, perfectly matching the surrounding orange peel texture on the rest of the wall is difficult. You match it through trial and error, mixing the drywall mud with water and test spraying it first on a separate surface such as a piece of cardboard.