Question by Guest_9485834: What type of contractor would repair under counter kitchen sinks that have detached from the granite slab underside
Answered by Granitec: I have two kitchen under counter sinks which were glued to the underside of a granite counter top but we're NOT anchored with screws along the sink lip to double secure the attachment of sinks to granite. Now, after much use, seal has become brittle, fallen out leaving sink detached on three sides. It's pretty much being supported by the plumbing work!
you will will want an experienced granite fabricator to drill and epoxy threaded studs into the underside of the counter where he can then attach a clip. You may also be able to use a piece of wood screwed to the sidewall of the inside of the cabinet to hold the lip tight to the stone. Re glueing will result in it falling again
Answered by LCD: My preference - since drilling holes in a countertop outside the factory is iffy, and iffy anyway if less than about 1.5 inches thick, my preference is to hold undermount sinks up using metal strut across the sink bay (from left to right side of countertop usually to support both sides and avoid mounting holes through front face - plus issue of carrying load across the front door openings), and bolting the mounting clips to that. Wood also works - just takes a bit more room as has to be a flat 2x4 or more to provide needed strength to holdup a sink full of water and dishes.
Your sink will have to be taken off and the adhesive cleaned off, then remounted with new adhesive anyway - to get it level and to avoid a small gap between sink and countertop that could let water andgunk get in there and make a nasty slimy mess. Then adding mounting support to actually carry the weight of the sink and what it contains - plus commonly the weight of a garbage disposal on one side. Asking bolts in the countertop to support that, unless underlain by 3/4 plywood, is really asking a lot - and I have seen a lot of countertops with cracks starting at threaded inserts, or total cracking through the bolt holes, so I really recommend NOT supporting the sink/disposal from underhung bolts (or adhesive) only.
If you are going to use this sink before it gets fixed, I would see if I could wedge a couple of pieces of 1x3 or larger wood under the sink to carry the load till it is fixed - because if loose on 3 sides like you say, the plumbing is pretty much holding it up.
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