Plastic laminate (commonly called Formica, a brand name) is just about the toughest material in the home. Still, it's not indestructible, and people often ask how to repair laminate kitchen counters.
If your counters are old and generally worn over a large area, the best repair is to recover them. While the job is not particularly difficult, it does require a wide variety of skills new to most homeowners: disconnecting the plumbing to your sink and removing it; cutting, applying and trimming the laminate; replacing and reconnecting the sink and, perhaps, adding trim.
All that adds up to a lot of work, which is why most people just call a kitchen contractor. But not even a contractor can do the job if you have postformed counters. These are the type with backsplash and a slight lip along the front edge molded right in. These curves makes recovering impossible. If you have postformed countertops, repair will require replacement of the whole top, not just the covering.
A lot of people ask if dull, worn laminate can be painted. The answer is yes, but don't expect it to look like new. No matter how careful you are, it will still look like a painted counter. If you do decide to paint, do it right. Clean the counters thoroughly, then sand them well with 120 grit sandpaper. Use an epoxy paint for best wear and adhesion.
If damage is localized -- a gouge or burn, say -- you may be able to make a spot repair. Making a good patch is a bit tricky, so try to get around the problem whenever you can. One trick is to permanently mount an attractive wooden cutting board over the damage. Here's how:
Run a bead of clear silicone caulk around the perimeter of the bottom of the board. Then squiggle a few beads of the silicone across the center of the board. Place it in position and press down. The perimeter bead of caulk should squeeze out around the edges of the board. That's good. Wipe it away and let the board sit undisturbed for at least 12 hours. The silicone will cement the board in place and prevent dirt and spills from slipping beneath the board. If at any time you decide you don't want the board mounted in place you can remove it by carefully prying it off the counter.
Patching. This will require a piece of laminate large enough to cover the damaged area. A few warnings before you start. Locating a piece of laminate to match your exisisting countertop may be difficult. Colors can vary slightly from one production run to another, so even solid colors may not match perfectly. Matching patterns and woodgrains is even tricker. With that warning, let's proceed:
From your piece of new laminate, cut a square of rectangular patch large enough to cover the damaged area completely. File or sandpaper the edges straight and smooth. Place the patch directly over the damage and secure it with a piece of double-faced carpet tape so it won't skid.
Holding it firmly in place with your left hand, scribe around it with a sharp utility knife, preferably one with replaceable blades. Cut right into the laminate on your counter-top. You will probably have to scribe around the patch a dozen or more times before you cut through the old laminate. Change to a fresh blade now and then for faster, cleaner results.
When you finally cut through the old laminate, carefully lift off the patch. Then chisel away the damaged section of laminate. Check the patch for a good fit. If you are satisfied, glue the patch in place with contact cement. If not, cut a new patch slightly oversize. Sand or file its edges a bit at a time until it fits. Then cement it in place.