I get this question a lot so I thought I would post it. In my opinion removing old formica and trying to reuse the old top is not practicle for several reasons.
1. It is time consuming and somewhat expensive.
2. There is some danger involved as you are going to work with a highly flammable solvent.
3. By the time you figure your material cost and time you will find that a ready made top is not that much more money, less mess and a whole lot quicker.
If you decide to give it a try make sure that there are no open flames or pilot lights, no smoking, plenty of fresh air and protect your eyes and skin with safety goggles and apply skin cream to exposed skin. Use solvent resistant rubber gloves.
Still want to try it? OK lets get started.
Several thin putty or narrow spackle knives
Safety glasses and rubber gloves
Shim shingles, available at most home bldg supply centers
3-4 pcs of wood 1/2-3/4" thick, 3-4' long
Lots of newspaper to stand the countertop on and absorb the mess.
A fresh water supply nearby for accidential contact with exposed skin as the lacquer thinner will Burn.
Avoid working in direct sun or in a heavy breeze but make sure you have PLENTY of fresh air!!
Turn OFF any and all pilot lights and no open flames or smoking.
When finished soak all rags, newspaper, wood etc in water and allow to dry before disposing. If contained in a closed trashcan or bucket they can burst into flames (spontaneous combustion)
Remove the old top and stand it on edge. Take a thin putty knife or spackle knife and work it into the crack where the formica meets the wood. Once you have the knife inserted a little pour a little lacquer thinner into the crack. The lacquer thinner will soften the adhesive and you can start working the knife in deeper a little at a time. As the glue loosens you start driving in thin wedges of wood, shim shingles are good for this as they are tapered from real thin to about 1/4" thick. As the crack opens keep adding more thinner and drive the shims in until you can start inserting pieces of longer thin wood up to 1/2" thick and as long as the countertop is wide so that they reach the bottom. Try to work the whole edge evenly so as to keep a nice pocket for the thinner. Leave the outside edges intact until the very end.
Once the formica is removed you need to scrape off as much old adhesive as possible and smooth out the surface as any globs or builtup areas of adhesive will show through the new formica. Patch any gouges, sand smooth and then apply the new Formica as per my instructions Here
Next time you Paint You Can also INSULATE!