Formica Counter Top

Heavy duty Liquid Nails and something heavy on top of it while it cures. A weight, or dumbell, etc.

Rig something to apply pressure while the glue sets. Me, I'd use a 2x4 (maybe more than one) from an opposite wall and a couple of shims. Maybe some supports to hold up the 20-foot long 2x4 concoction. It only has to work for an hour or so.

Suppose the opposite wall is ten feet away. Two 2x4s, held together by a couple of C-Clamps can give you the length need to bridge the glue-area to the opposite wall.

Probably should run a thin line of silicone caulk on the seam, or keep water off of it. I have the same problem with a very old counter in bathroom. I painted the exposed particle board and put sil. caulk over it. It doesn't seem to take much water to start particle board expanding, so no seam should be allowed lengthy standing water. I used to have a kitchen countertop that sloped ever so slightly lower toward the back, so that spills could run and collect under stuff standing on the back of the counter. Eventually caused the mitered seam on the corner to start bulging.

If you've got C clamps, why not clamp one of the boards to the fron lip of the counter, and thus avoid having 2x4s across your room? Out of curiosity, is the substrate under the formica plywood, press-board, or wood?

You are quite right. However, most Formica is bonded to 'crumble board' and once water damage occurs, no amount of gluing will save your counter top. Odds are you need to shop for a replacement and soon. If your budget is adequate, consider having a cabinet shop make you a new countertop. If you ask them to use a high quality plywood it will last for many years. This is typically how commercial installations are done. One advantage is that the whole top is far more dimensionally stable so unusual designs (and heavy sinks) can be accommodated with no worries about butt seams springing leaks. HTH

Joe