You can also remove desired areas by selecting the area you want removed press and hold down the alt key - click the left mouse button on the selected area, and move the selection to an area the same size with no defects - copy and paste that area - anchor the selection - this creates a new layer with your copied area -move the piece over the desired area you want to cover.This works very well for even patterned areas many times.It keeps the area the same texture and color of the original as you are copying areas of the original to cover the defects.
You can also use this method to add sketches to another on one layer.You may have to make the canvas bigger though - Image/Canvas size - this gives you a bigger area to work with.
Sort of like stamping out a copy of the selection with the colors or patterns you want, and covering the effected area.