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Need a New Kitchen Sink? 11 Pitfalls of Sink Replacement

Common problems that could turn your project into a nightmare—and how to avoid them

how to install a kitchen sinkFamily Handyman

Replacing a kitchen sink and faucet is a quick way to give your kitchen a new look, but there are potential plumbing and installation problems to watch out for. This article explains how to avoid the ten most common.

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Got your eye on a deeper new kitchen sink? Measure the tailpiece first!

Measure the tailpiece for buying a new kitchen sink

You can choose a new sink with a deeper basin than the existing sink has, but if it hangs down too low, it won’t drain properly and you’ll have to lower the sanitary tee connection in the drain line inside the wall. You’ll definitely want to avoid this task if the connection is metal and ends up being behind base cabinets. Plastic pipe is easier—if you can get to it easily. The actual tee connection may be several studs over from where the waste arm enters the wall.

Measure the sink tailpiece between the basket strainer and the tee. That measurement is the extra depth that can be added to the sink bowl without lowering the drainpipe going into the wall. Also be aware that a new disposer may have a lower drainpipe than your existing one—but it can’t be lower than the tee. If the disposer drainpipe will be too low, consider a sink with different depth bowls. You’ll have a deep bowl for dishes and a shallow one for the disposer.

New Kitchen Sink: Make sure the new sink will cover the old hole

Check the cutout size before installing new kitchen sink

A sink that’s too small for the countertop opening will leave ugly gaps along the sides (or even fall right through the hole!). Before removing the existing sink, measure the opening from underneath. Measure all four sides because the cutout may not be square. Pay special attention to the corners. Contractors often cut them at 90-degree angles (instead of rounding them off) because it’s faster.

Take the measurements with you when buying the new sink and make sure it’ll cover the opening, including any square corners. If you can’t find a sink that’ll fit, buy a larger one and enlarge the opening.

New Kitchen Sink: Swollen countertops spell trouble

Check for water stains

Leaks around a sink rim can soak the particleboard under a plastic laminate countertop. A little water damage is normal and won’t interfere with your new sink. But severe swelling will prevent the new sink from sitting flat on the countertop. And crumbling particleboard won’t provide a solid base for the clips that fasten the sink to the countertop.

Look at the countertop surface around the sink. Check for bulges or areas where the laminate has loosened from the particleboard. Then look at the countertop from under the sink for areas that are too spongy to support sink clips or support the sink itself. If you find any of these problems, replace the countertop.

New Kitchen Sink: Seal with caulk, not putty

Use the right sealant when installing new kitchen sink

Plumber’s putty has long been the standard sealant for sink baskets and sometimes even sink rims. The problem with putty is that it eventually dries out, cracks and causes leaks. Worse, it can damage some plastics, including some of the plastics used to make sinks. Avoid drips and disasters by using a silicone caulk instead.

Use a kitchen-and-bath 100 percent silicone that requires solvent cleanup—sold at home centers. Apply a bead around the sink opening when you set in the sink and around the drain opening when you set the disposer drain and basket strainer. Wipe away excess caulk.

Seal basket strainer

Seal around the drain opening with silicone caulk instead of plumber’s putty when you set the disposer drain and basket strainer. Wipe away excess caulk.

Remove a self-rimming cast iron sink

Wedge the sink

Lay a flat board across the cabinet bottom. Then angle a 2×4 between the sink basins and the board. Tap it so it pushes up against the sink bottom.

Cut and shim

Slice through the caulk with a utility knife if possible. If the caulk is too hard to cut, use a putty knife like a chisel to cut through the caulk. To lift the sink, tap in shims as you go. Then cut along the front edge of the sink and up the opposite side.

Self-rimming cast iron sinks are held in place with caulk. If you’re replacing the sink but keeping the laminate countertop, you’ll have to cut through the caulk. That can be tricky, especially if the caulk has hardened.

You’ll need lots of patience and these items: shims, a few feet of 2×4, a stiff putty knife and a heavy-duty solid-blade utility knife.

Wedge a 2×4 between the sink bottom and the floor of the cabinet to create slight upward force. Then cut the caulk. If the caulk is too hard to cut, hammer an old putty knife through the caulk, driving it toward the sink a section at a time.

Once you’ve cut the back corners, sides and front, tilt the sink up and cut the remaining caulk from the underside of the sink. Lift out the sink and clean the caulk residue from the laminate.

Remove ALL the old caulk

Use caulk remover

The caulk around your new sink is all that’ll stand between your countertop and water damage. For a lasting, watertight bond with the countertop, you have to completely remove the old caulk.

Remove the old sink, then scrape off the caulk (or plumber’s putty) with a putty knife. Apply a caulk remover (sold at home centers) to stubborn caulk. Let the caulk remover sit for a couple of hours, then scrape off the softened caulk. Finally, use rubbing alcohol or nail polish remover to wipe off residue, and then clean the surface with a sponge and water.

Get the gunk out

Flush out sediment

Working on the water lines always shakes sediment loose. The last thing you want is for these deposits to clog your new faucet. Avoid this problem by purging the lines before hooking up the new supply lines.

Once the entire project is complete and the new supply lines are attached to the faucet, fasten the old supply lines to the shutoff valves. Next, turn the water all the way on for a full minute to wash away any debris in the lines. Then attach the new lines to the shutoff valves. After three days, take the aerator off the faucet and rinse away any sediment that has seeped through.

Make sure you have enough holes

Match faucet to sink openings

Most sinks have three holes for the faucet and a fourth for an accessory, such as a sprayer or a soap dispenser. But some faucets require only one or two holes, and you may not want enough accessories to use the rest. You can buy plugs for unused holes, but they usually don’t match the sink. If the sink doesn’t have enough holes, cutting an extra hole in stainless steel or cast iron is often difficult or impossible.

To avoid these hassles, choose the faucet and accessories first, then buy a sink with a matching number of holes. Some sinks have “knockouts” that you can drill to provide extra holes. You can also special-order a sink with the number of holes you need.

Trash all the old parts

Replace the entire waste assembly

Resist the temptation to save a few bucks by reusing the old drainpipes. The threads are probably corroded and won’t form a tight connection. A new drain assembly is easier to install and less likely to leak.

Instead of shopping for each individual part for the drain, buy a kit at a home center that has everything you need. A sink kit includes drainpipes, fittings, shutoff valves, supply lines and new basket strainers.

Test the shutoff valves first

Replace leaky valves

If the shutoff valves under your sink don’t work or you don’t have any, you’ll have to turn off the water supply to the entire house while replacing the sink. This could cause domestic strife, especially if the job turns into a half day or longer project, so make sure the valves work before going to the home center.

To test the valves, close them and turn on the faucet. The faucet may drip for a minute or two, but if the drip continues, the shutoff valves are leaking. Repair or replace old valves. If you’re buying new ones, use quarter-turn balltype shutoff valves. They’re more reliable and less likely to leak at the packing nut.

Rusty old pipe? Cheat!

Solve tough problems with couplings

Corroded steel drainpipes are a bear to work with, since the slip nuts are almost impossible to loosen or retighten. You can easily bypass those rusty old threads by adding a section of plastic pipe.

If the slip nut attached to the drainpipe in the wall won’t come off, spray on WD-40 and try a bigger wrench. If that doesn’t work, cut off the drainpipe with a hacksaw (save as much of the threaded area as possible). Then buy a plastic trap adapter, a transition coupling and a piece of plastic pipe (PVC or ABS) and cement (sold at home centers). Cement the adapter to a 4-in. section of pipe, then place the coupler over the other end of the pipe and over the steel drainpipe.

Required Tools for this How to Install a Kitchen Sink Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • 4-in-1 screwdriver
  • Adjustable wrench
  • Bucket
  • Caulk gun
  • Cordless drill
  • Flashlight
  • Hacksaw
  • Jigsaw
  • Pipe wrench
  • Plumbers tape
  • Putty knife
  • Rags
  • Safety glasses
  • Slip joint pliers
  • Soldering torch
  • Utility knife

Required Materials for this How to Install a Kitchen Sink Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

  • Caulk remover
  • Drain assembly
  • Pipe joint compound
  • Shutoffs
  • Silicone caulk
  • Transition coupling