Request advice re. problem with undermount vanity basin


Hi all: Request advice re. problem I've encountered while replacing faucet in bathroom vanity. The valves and spout are mounted in the countertop, and the basin in front of them is an undermount variety. I removed the basin for easy access to the faucet hardware, but when replacing the basin after installing the new fixtures, I discovered that the rubber/metal washer that's under the counter and at the base of the new spout apparently has a larger diameter than the one it replaced, and it prevents the flange around the top of the undermount basin from snugging up against the underside of the counter. There's insufficient space to move the basin forward, so the only option would seem to be, if possible, to remove a semi-circle of material approx. 2" across and 1" deep from the basin flange in order for the same to be able to clear the spout washer. Would appreciate any advice whether it's possible to do so without cracking/ruining the basin and, if so, best method and tool(s) to use. Also any ideas for alternative work-around. Would like to keep the new hardware if I can and would rather not buy a new basin. Thanks for your replies!
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It's probably better to use the old mounting washers against the new fixture. Or you could grind or nibble a section off the new mounting washer. I would be a little cautious about modifying the mounting ring for the lavatory. Any cutting or grinding is asking for deformity and a poor fit, and those flanges are not easy to find.
Happy modeming, Bill
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The old mounting hardware was so badly corroded that I had to cut it off in order to remove the old fixture. But I share your concern about the basin, and may give your second suggestion a try. Thanks!

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Just curious...wouldn't it be easier to complete your project if you removed the entire countertop and re-engineered the installation with better fitting harware? That is a common practice in plumbing work. HTH
Joe
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I guess it depends on how you define "easier"!! :), although a variation on your suggestion did solve the problem. I enlarged the existing spout mounting hole in the counter by grinding out about 1/3" of material on it's rear side, thus enabling the spout to be mounted far-enough back and away from the basin so that the basin's flange now cleared the spout's undercounter mounting hardware. The resulting, enlarged spout mounting hole in the counter was still small enough to be entirely covered by the new spout's decorative countertop flange. Thanks for putting me on to the idea!
wrote:

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Had similar issues replacing faucets on pedestal sinks. If you don't have to remove much material from the new washer...go for it.
If you need to remove a substantial amount of the washer consider getting a thicker thicker washer & modify it.
The basin system works now, I would suggest not messing with it.
Cheer Bob
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