Can the newer laminates be applied over old but, still good (not chipped, blistered or peeling) laminate?
I had the square edge laminate counter tops in every kitchen in my building.
I found it easiest to pry the old laminate off the existing plywood tops,
then use lacquer thinner to remove the old contact cement,
then install a prefab top over the existing plywood.
And, I've done a total of 20 counter tops that way.
Sometimes, a bit of the old plywood will come up with the old plastic laminate, but the new top is 5/8 inch thick and so it doesn't need support under every square centimeter.
Whatever you do, PAINT the cut edges of your prefab laminate counter tops (and any particle board that may come into contact with water) with a high gloss alkyd paint or boiled linseed oil. The idea is to prevent water from being absorbed into the particle board to prevent it from swelling and the laminate coming loose from it as a result.
I paint:
1. the cut edge for the sink hole, the holes for the kitchen faucet and the
underside of the counter top in the sink area,
2. the back side of the front bullnose and the first 3 or for inches of the underside of the counter top behind it,
3. the particle board edge that butts up to any wall at the end of the counter top and both cut (mitered) edges in "L" shaped counter tops.
(I laminate the exposed edge of the installed countertop.)
This is especially important in the sink area, along the front of the top where water may drip off and in front of any dishwasher. The steam from the dishwasher will otherwise condense on the cool particle board (when the dish washer door is opened) and the condensate absorbed into the wood.
Welcome to "Installing plastic laminate counter tops 101":
Also, the people that install plastic laminate counter tops need to take an evening course in "Basic Thinking" cuz they're doing it wrong. If you watch an installer, he'll throw the top on the cabinet and immediately scribe the shape of the back wall onto the top of the 4" backsplash so that when he cuts along that scribe mark, the back splash fits perfectly to the back wall.
A better way is to put a board behind the front bullnose of the counter top and push the counter top against the cabinet until that board is sandwiched between them. NOW scribe the shape of the back wall onto the top of the 4" backsplash, and cut along the scribe mark. The counter top will fit just as well to the back wall, but now the front of the counter top is ALSO parallel to the front of the cabinet.
Also, when doing an "L" or "U" shaped counter top, don't try to accomodate back walls that aren't at a 90 degree angle by mitering the tops at different angles. The reason why is that the length of the kerf on each side of the miter will be different, so you won't be able to get the two tops to meet properly at both the front and the back. A better gameplan is to miter your corners at 45 degrees and use the 5/8 of an inch you have on your backsplash to make the tops fit properly to the walls. But, before doing that, it's a good idea to cut some wide pieces of cardboard at a 45 degree angle and see how well the cardboard fits on the cabinets. That will tell you whether the 5/8 of wiggle room you have in cutting your backsplashes to fit against the wall will be sufficient to accomodate any screwiness in your walls.
If you have to miter the tops at an angle different than 45 degrees cuz the walls are really out of whack and you just can't make the tops fit otherwise, make sure both mating tops are mitered at the same angle to keep the kerf length the same. Like both at 44 degrees or both at 46 degrees, for example. Cutting one at 44 degrees and one at 46 degrees will give you a 90 degree angle, but the kerfs will be of different lengths, and that's a problem you won't be able to overcome.