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The undermount sink in our recently purchased house has started to pull down from the benchtop, so there is a ~5mm gap and the seal has broken. It's only pulled away from one side but I don't think it will last much longer. It is a manufactured stone benchtop so I'm not sure of the best way to repair it. It seems to have been originally fixed with some kind of thick creamy brown glue that feels soft with some give. Judging by the way the glue has dried with drips running down it was mounted with the bench already in place.

What is the best way to remount the sink? Preferably without removing the entire benchtop first :-)!

EDIT: Added some photos

Under back of sink:

photo from under back of sink

Under front. It hasn't pulled away from here:

goo from front of sink

Back of sink again. This blob didn't even seem to get put on the sink:

back of sink again

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Are there brackets holding the sink in place which have come undone, or was the sink just "glued" in place? Some pictures might help. – Tester101♦ Jun 22 '11 at 15:21
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The brownish goo is likely plumbers putty, and it's there as a sealant not a glue. The sink should be held in place by some type of bracket screwed to the underside of the counter top, not adhesive. – Tester101♦ Jun 22 '11 at 15:26
I couldn't see any brackets, I'll have another look tonight but they could be under the putty so it could require an operation. Will update with details. Thanks! – Ben Scott Jun 22 '11 at 23:15
@Tester101 definitely no brackets and only a blob of putty every foot or so, I'll add some pictures – Ben Scott Jul 7 '11 at 8:30

1 Answer

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An undermount sink needs to be mechanically supported from below, with brackets or some kind of structure that can physically support the weight of sink. Between the water, dishes, maybe even someone leaning on the sink, and the sink itself, we are talking about a load on the order of 100 pounds or more. So definitely far in excess of what an adhesive can support in this layout. In the absence of proper support, the weight of the sink may be resting on your drain pipes, which they are not designed to support. You need to get and install a mechanical support, either brackets (the sink's manufacturer probably makes or recommends some) or a custom-built wood structure to carry its weight. While you're at it, make sure to reseal the edges using a consistent layer of putty or silicone caulk.

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