You must seal the area between a sink's drain body and the actual sink surface. Otherwise water will leak out between the two and begin dripping under the sink. Some plumbers and installers favor plumber's putty for installing drains, while others lean toward the more modern waterproof material called silicone caulk.
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A clay-like substance called plumber's putty is the most popular choice for sealing sink drains, but you can also use silicone caulk.
Most Popular: Plumber’s Putty
Plumber's putty comes in containers ranging from small to large tubs, which you may choose from depending on how much plumbing installation work you are doing. Plumber's putty literally is a putty, similar to the clay you may have played with as a child. You can form the putty into a variety of shapes, just like clay. And like clay, the putty dries and hardens after it is out of its container long enough.
A seal made with plumber's putty may fail down the road if the putty becomes brittle and it cracks apart, allowing water to pass through the seal.
Plumber's Putty Installation
When you are installing a sink drain and decide to use plumber's putty, you must wrap the putty around the sink's drain opening before you install the drain body. To do this, you must roll the putty between the palms of your hands until the putty becomes a long rope. You wrap the rope around the drain opening, tearing off any of the rope that overlaps the rest.
The drain body goes on top of the putty, and as you tighten the nut on the bottom of the drain body, some of the putty squishes out from between the drain body and the sink itself, which you must wipe away before it hardens.
Alternative: Silicone Caulk
Silicone caulk comes in a tube, with some allowing you to squeeze the caulk out by hand while others require the use of a caulk gun. Silicone caulk is a clear substance and it is fairly fluid when it first comes out of the tube. After about an hour of exposure to the air, the caulk begins to form a skin. Once the silicone caulk fully cures, it becomes hard but not to the point of becoming brittle.
Because silicone caulk does not become waterproof until it fully cures, it's not a typical choice for sealing a sink drain. If you do choose to use caulk, take care to purchase 100% silicone caulk, not acrylic, latex, polyblend, or sanded varieties, which are not up to the task of coming into constant contact with water. Like plumber's putty, silicone caulk won't last forever and will eventually break down and require replacement.
Silicone Caulk Installation
With silicone caulk, you must apply an even amount either to the underside of the sink's drain assembly and to the sink immediately around the drain hole opening. Like the plumber's putty, some silicone caulk may squeeze out from between the drain body and the sink, which you must wipe off before it hardens. To remove hardened silicone caulk, you must purchase a caulk softener solution at a hardware or home improvement store.