How do I extend outlets after installing a backsplash?
If your problem is that the thickness of the back splash material has caused the electrical boxes to become recessed you may need to use electrical box extenders. These come in a number of styles depending on the type of electrical boxes you have. There are options for metal or plastic boxes for starters. Other factors would be amount of extension needed and whether you are dealing with a single width type box or a wider type.
Here is an example of a metal box extender that works in a telescopic manner to accommodate just the amount of extension that you require.

If you're in an area that follows National Electrical Code (NEC), the boxes cannot be set back more than 1/4&quot; (6 mm). If the backsplash has caused the boxes to be set back more than this, you'll have to use extenders to bring the box out to the proper depth.

National Electrical Code 2011
ARTICLE 314 Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures
II. Installation
314.20 In Wall or Ceiling. In walls or ceilings with a surface of concrete, tile, gypsum, plaster, or other noncombustible material, boxes employing a flush-type cover or faceplate shall be installed so that the front edge of the box, plaster ring, extension ring, or listed extender will not be set back of the finished surface more than 6 mm (1⁄4 in.).
In walls and ceilings constructed of wood or other combustible surface material, boxes, plaster rings, extension rings, or listed extenders shall be flush with the finished surface or project therefrom.

If the box is less than 1/4&quot; from the finished surface, you can use as many spacers as needed to mount the receptacle in such a way that the yoke is held rigidly at the finished surface.