New Delta faucet install; won't stop leaking under base

[justjudy63]

I am installing a new Delta bathroom faucet, single handle. The big plastic seal that the faucet sits on has a square hole in the center. No matter how I line it up with the round center hole in the sink, water leaks through the square.

The old faucet (also Delta, but 40 years old) had only a very small hole in the center of the seal, so there was plenty of surface around it to seal with the sink. I am baffled as to why this has a large square hole, and how I can get it to seal properly.

Attached is a photo looking up under the sink.

 

[TomFOhio]

Is the water coming out of the hole underneath while you have the faucet running?? If so then you have
a leak under the base plate. If it leaks only if you splash water around the faucet then the seal is not
on properly

 

[havasu]

If this is a new faucet and it is leaking when you turn turn it on, you have a defective unit. Take it back.

 

[Mr_David]

Like tom said. Those thin nylon seals suck if it only leaks when you splash water on base.

I stuff a good wad of plumbers putty inside the base of faucet then install the nylon seal with a 1/4" diameter string of putty around the edge.
The wad inside the base helps back up the silly thin seal from the rolled string of putty pushing up and distorting the seal.

If you have granite or stone countertop make sure you use stain free putty. Regular putty has an oil base and will leach out and stain the stone

 

[justjudy63]

No longer leaking! The nuts under the mounting washers were not tight enough, apparently. The faucet instructions said to run the faucet for a full minute without the aerator, which made the water go in all directions. I think that's how the water got under the base. Once I removed the faucet, dried it out, and reinstalled with the nuts tightened better, no more leaks. Thanks for the pointers!

 

[havasu]

Thanks for posting your resolution.