Leveling an undermount cast-iron sink

9 years ago

We're installing a cast iron sink. Countertop is 5/8" plywood (now) with (eventually) 3/4" granite above it. We're trying to make the top of the sink flush with the top of the plywood.

We're using 1" plywood on the left and right sides of the cabinets to be the main support, but have installed the rails for fine-leveling if necessary (see photo in next post).

The problem is that, although the countertop is level, the top of the sink isn't completely square/flat - if 3 corners are flush with the plywood, 1 corner is a little bit high (maybe 1/16 to 1/8"). Or if we lower everything, we can get 1 or 2 corners flush with the plywood, but 2 or 3 corners will be 1/8" BELOW the plywood.

So my question is, what is the best compromise? Can the granite countertop handle a 1/8" "bump" from one corner of the sink? Or is it better to have everything at or below the level of the top of the plywood, and have whatever glue/sealant the countertop installer uses close the gap. Or is there something I'm missing?

Thanks,
Fred

This post was edited by yonkiman on Tue, Sep 16, 14 at 13:48

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Comments (4)

Fred Hamilton
Original Author
9 years ago
Here's how we're supporting/tweaking the sink:
snoonyb
9 years ago
Interesting.
I've not used the support brackets in the manner you are employing them.

Those that I use are sufficient to support the weight of the sink, on their own, and are installed front to back, thereby eliminating any risk of interfering with the sink fixtures. (There is a large nut on the basket strainer, which needs to be tightened, and that for a disposal, is even larger in diameter).

If your hope is to eliminate the need for caulking at the intersection granite slab and the sink rail. You'll be hard pressed to find and installer who will warranty the installation, without a waiver.

So, hold the sink as even or below the level of the plywood.
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Fori
9 years ago
Is the top of the sink just not level? Can you return it and get a flatter one? It looks like it is a drop-in sink, not one intended to be undermounted, so maybe QC is relaxed on how flat the top is and you'll have to check all the boxes for the best one.
PRO
Joseph Corlett, LLC
9 years ago
yonkiman:

Place a 4' level (minimum) in an "x" pattern over your sink opening. It should read level in diagonal directions also. Judging by the knots in your plywood, it's not as flat as cabinet grade plywood would be. I'm betting your sink is flat and your substrate isn't.