[Rjcsjc62]

I have never tried doing this, but I feel like you are opening up a can of worms.

With a drop in sink, the hole that is cut can be imperfect to the tolerence of the size of the sink's flange. The cut doesnt even need to be straight, the cut is completely covered up by the sink itself.

What you are counting on here is, that the builder made a cut specifically for a certain size sink, and for whatever reason just put in a drop-in sink.

If the edges arent finished, or the penetration doesnt line up perfectly with an undermount sink, then your undermount sink will look far worse than the drop in sink that is there now.

However, if the conditions are perfect and you have a hole that suits a specific undermount, the install isn't too tough.

You need a block of wood longer than the width of the sink set on top of the counter, drop a rod through the centre of the wood through the outlet of the sink, and through another block of wood, that is bigger than the sink's outlet. Add some PL-400, or some kind of heavy duty adhesive to the undermount's flange and tighten the two blocks of wood until the sink is firmly in place. Leave overnight, then remove the lumber and rod.

Any silicone from the drop in sink install that is left on the top of the granite would be easily removable. It should just be a caulking, or some kind of sealant, and not really an adhesive.