Kitchens – change an under mount sink for a drop in

Matt, there is a huge difference between an under mount and a drop in fixture. The first concern is the counter itself. what kind are you using? Some counter tops cannot be used with an under mount sink. The support and sealing of an under mount sink is completely different than a drop in. The holes for the faucet need to be in the counter, not the sink unit, and the edges of the sink unit have to be flat and are usually epoxied and clamped in place while the counter is upside down. If you are very clever, you probably can fit the drop in under the counter, but how are you going to finish the counter edges and drill your fixture holes? They will need to be polished. This is usually a production job, not a DIY unless you give the counter maker an exact template, not something you can simply cut out and do yourself.

I hate to be a wet blanket on this one, but you are not going to like my answer. It will be very difficult to find someone that will attempt to do what you are asking for an in place, already installed granite counter top. Since you have a drop in sink, the cut out is probably not polished and the cut edges are not routed. In the fab shop, they use lasers and computer aided cutting tools to get perfectly shaped holes. Cutting in the field is hardly ever done. The process of attaching the under side bowl is not as difficult as the cutting and polishing, but will require some type of custom support to hold the bowl in place while the epoxy cures.

Depending how large the counter is, it may be cheaper and safer to have it taken out and done at the fab shop.