I have under the counter mounted sink and it is bowing in the middle; there are gaps around the edges. They did not use clips and I have no idea how to fix it.
first what type of material is the counter top ? particle board or granite . are you looking for a quick fix ? they sell under counter clips any local plumbing supply . make sure its clean and dry predrill small holes not to deep , apply clear silicone then install clips . not too much silicone and wipe off excess with damp rag on inside of sink
When joining an under mount sink to a hard surface counter top the natural choice is two-part epoxy.
This extremely strong adhesive will hold between 3,000 and 4,000 pounds per square inch.
The important steps to your repair include:
1) Remove any loose debris from the sink or the underside of the counter top; 2) Thoroughly mix equal amounts of the two parts, blending back and forth until the two colors appear as one; 3) Spread a generous amount of epoxy between the sink and counter top, being careful that it will not squeeze out on the sink side; 4) Use a lift or hydraulic jack against a board to lift and hold the sink in position immediately after applying epoxy; and 5) Leave the lift in place overnight ... even though most epoxies dry in less than 20-minutes.
NOTE: Do not use your tools to mix epoxy.
Use a paint stir stick or pop cycle stick.
And, mix on top of cardboard or a paper plate ... something you can throw away.
FINALLY: Should you accidentally squeeze epoxy onto the sink, use tee shirt material to wipe while the epoxy is still a thick paste ... it will be almost impossible to remove after cure.
Your best approach is to apply epoxy away from the inside edge, so you will not have this problem.