Introduction: Replace the Sink in a Cultured Marble Countertop

There are a lot of homes with aging cultured marble countertops in their bathrooms. This material was used extensively in the 1970's and 80's. For the most part it has aged fairly well if it has not been abused. However, the built-in sinks in this substance have the disadvantage of discoloring and cracking around the drain opening. In our home we have five such sinks in varying degree of degeneration that we wanted to repair or replace. After some research we found that the reasonable alternatives were:

1. Replace the entire countertop including the built-in sink.

2. Rejuvenate the whole countertop including the sink.

3. Cut out and remove only the sink portion of the countertop and replace it with a drop-in sink.

We felt that it was a shame to replace these otherwise quite serviceable countertops with some different material, at no small expense, just to remove the sink blemish. We had observed mixed results in rejuvenation attempts in other homes, so we elected to pursue choice number 3. The problem with that option was that we could not find a local craftsman who would do it for us. After investigating the procedure on the net, I elected to do it myself. I have done many home repair projects in the past of much greater difficulty, so this job was not particularly daunting, but I had read that it could be quite messy (with the creation of a large amount of white dust) and that one should make a concerted effort to contain that problem.

My plan was to prepare myself as much as possible and give the project a try. The trial balloon would be to replace the sink in the small countertop in our guest bathroom. The worst case scenario was that if it did not turn out as I had hoped, then I would pay to have a new countertop installed commercially.

Step 1: Do Your Homework

Measure very carefully the size of the old sink opening, because that will help determine the size and shape of the replacement sink. That is to say, the new sink opening will need to be at least as large as the footprint of the present sink while incorporating the faucet openings for that sink. Keep in mind the new sink will have close to a ½-inch external lip around much of the bowl circumference, except in the rear where the lip is much larger to incorporate the faucet set openings.

Step 2: Use a Yardstick and Mark Off the “X and Y Coordinates” of Your Old Sink Drain

Mark the midline and a perpendicular line through the middle of the old drain. This is to help you align the sink cutout template when you are taping it down a few steps later. See photo.

I went to a couple of sink manufacturer websites to look for a sink that suited the dimensions I required. Most sites give you the external dimensions of their sinks and this is good, as far as it goes, because you will need to make sure that you are not crowding the edges of the countertop nor the space in the under-sink cabinet below. However, there is a critical measurement that you also need and that is the size and shape of the actual hole you will cut. This opening must encompass the old sink in its entirety. I found the Kohler site to be easy to navigate, but the actual cutout templates had to be downloaded and then run through a CAD file viewer program in order to see them. (You can find and download free CAD file viewers easily on the net.)

Step 3: Buy Your Sink and Accessories

I ordered our sink from Home Depot online since the actual model and color we wanted were not carried in their stores. The shipping was free. I got the faucet set from a local Lowe's and the drain mechanism was obtained on Amazon.

Step 4: You Will Need a Reciprocating Saw and Angle Grinder

In the past I have never had need for a reciprocating saw, so for this job I bought an inexpensive one at Harbor Freight for $28. A contractor friend said these saws are used more for rough cutting or demolition. But he thought a reciprocating saw would be the best tool for cutting out the sink. I then selected a blade impregnated with carbide grit. It turns out, cutting the cultured marble is fairly easy but slow. You must be patient and apply a firm and constant pressure to the saw grip handle. However, if you push too hard, it slows the saw motor or worse, it can break the blade.

I have read where folks have used jigsaws or routers to cut out a sink from cultured marble. The jigsaw I have does not seem powerful enough and most routers have a wide footplate that might not allow you to get close enough to the backsplash.

I have had an angle grinder for several years which is another 25 dollar tool from Harbor Freight. I don't use it very often, but this one works quite well.

Addendum November 10, 2017:

Rather than try to re-write this Instructable, I am going to add a piece of information that should make your task easier in cutting out the built-in sink. Earlier this year (almost 2 years after I did this project), we had to replace another counter-top that was beyond reconditioning. We hired a highly recommended (and very reasonable) outfit to put in a quartz counter-top. I asked them to just cut the sink openings so I could install the sinks myself, and they had no problem with that.

They were very professional and they brought the counter-top to our driveway and cut the openings there. They explained that it is too risky to cut the openings at their shop and then transport the counter-top, as they may break en route. I watched with great interest as they used an angle grinder with a diamond cove blade. This blade cut that quartz almost like butter and the cove aspect allowed it to easily cut the oval pattern for the sink opening. If I do this project again, I will definitely buy one of those blades. It would greatly shorten the amount of time it took to cut the sink opening and I suspect it would curtail some of the dust. When the installer was cutting the quartz in my driveway, there did not seem to be nearly as much dust as I made in that bathroom.

Step 5: ​Use the Sink Cutout Template Included With the New Sink

The template that comes with the sink has to be cut out (of the large piece of paper on which it is printed) and then taped carefully to the countertop. It would be nice if the location of the new sink's drain opening was on the template but it is not. However, when I went to the installation instructions, there was a drawing that showed that the center of the drain opening was 6 1/8 inches from the top edge of the sink footplate. With a Sharpie I marked that location on the template. (See photo above) It was then easy to align that new line and the existing horizontal line I made earlier on the countertop. The vertical centerline was already drawn on the template and I aligned it with the vertical marks I had made on the countertop.

Next, I used the Sharpie to trace the outline of the template onto the countertop.

Ideally, the new sink drain should be located as close as possible to the position previously occupied by the drain in the old sink. This will make it easier to connect the tailpiece of the new drain with the existing P-Trap without having to introduce any new plumbing or modify the old.

Step 6: ​Cover the Countertop Surface Next to the Template Line With 2-inch Wide Masking Tape

This is to protect that surface from being marred by the footplate of the cutting tool.

Step 7: Remove Everything From Under-sink Cabinet

In fact, now is a good time to remove everything from the bathroom that is not nailed down.

Step 8: Cover Everything in the Bathroom With Plastic Sheeting

This includes the floor. Use towels to keep the dust from going under the door.

Step 9: Protect the Rest of the Countertop

Spread out a couple of towels on the surrounding countertop to prevent doing any damage to that surface.

Step 10: Turn Off the Water to the Sink

This may be easier said than done. In older plumbing you take some risk when you start turning water shut-off valves that are not currently leaking but have not been touched in several years. My preference in this situation is to turn off the water at the street and then turn on the hot and cold water faucets at some nearby sink or bathtub to drain as much water from the lines as possible. Now I can disconnect the water supply lines from the shut-off valves while using a plastic pan to catch the residual water. Next, I screw a brass cap onto both of the shut-off valves which will allow me to then turn the water back on at the street during this project.

Step 11: Remove the Old Faucet Set, Drain Flange and Tailpiece

To remove the old faucet set, the other ends of the flexible water supply lines must first be disconnected from their nipples on the underside of the faucet set. This will allow me to unscrew the mounting nuts on of the faucet assembly. At this point, the faucet set can be lifted out and set aside. Because the space is often very tight behind the sink, I have found it best to use a faucet wrench to remove both the water supply lines and the faucet mounting nuts.

Next, I use a sink wrench to remove the large locknut that holds the sink drain flange against the bottom of the sink. I then loosen the coupling nuts on the P-Trap and remove it. This frees up the tailpiece from below and lets me twist the drain tailpiece and unscrew it from the flange. However, there are many types of sink drains and they may require different methods to remove them.

Step 12: Place Jack Stands and a Piece of Plywood Under the Sink Before You Start Cutting

The sink portion of the countertop is quite heavy and if it dropped as you cut it, it could damage the floor of the sink cabinet or the undersink plumbing. Likewise, it could take out a piece of the countertop if it broke loose prematurely. This is a mandatory step.

Step 13: Put on a Tyvek Suit or Old Jumpsuit, Mask, Cap, and Goggles

I can't emphasize enough how much white powder you are going to create. If you have to leave the bathroom in the middle of this project, you can remove the jumpsuit and leave it there along with its built in booties. Otherwise you will spread white dust all over the house. The goggles or safety glasses are required because you could easily get a piece of the marble embedded in your eye. The mask should be at the very least, a half-face respirator type. You do not want to inhale this material.

Step 14: Cut Out the Old Sink With a Reciprocating Saw by Following the Template Outline

I found the best place to start cutting was in one of the faucet holes and then join the template line from the inside. I made cuts both to the right and to the left. About 70% of the circumference of the sink template covered countertop that is of normal thickness- or about ¾ inch. However, as I cut toward the front of the sink, the material became much thicker because of the built-in overflow channel and just the way the sink was fabricated.

The arrows in the photo above show where I could no longer cut on the surface of the countertop. At that point, I drilled two holes in the sink bowl approximately 3 inches below the surface. I have employed Photoshop on the above photo to better show the locations where I drilled. The black lines show where I connected those holes with each other and then to the surface of the countertop.

I also found that it was easy to start a couple of relaxing cuts across the bowl extending from the faucet holes toward the newly drilled holes in the front of the sink and vice versa. I did not intend to connect these cuts. Then using a hammer, I hit the sides of the bowl allowing me to remove almost 2/3 of the sink bowl by breaking loose moderately large chunks of material (again, see photo above). I found that I did not need to remove all of the thick bowl material in the front of the sink, but instead I used an angle grinder with a 4½-inch metal grinding disk and ground away just enough bowl material to accommodate the new sink.

I did not have a 1-inch masonry drill, so I used a 1-inch spade drill to make the two holes mentioned above. It was surprisingly easy to cut through the material. I could then insert the reciprocating saw blade into the hole on the right and cut upward to join the place where I had stopped cutting on the surface of the vanity. Then I repositioned the saw blade into that drill hole, but turned the blade so that it was perpendicular to the surface of the bowl and cut transversely to the hole on the left. Finally, I cut upward from that hole to the counter surface and what remained of the sink bowl was cut free of the countertop.

Step 15: ​Make Sure the Opening Will Accommodate the Overflow Channel in the Front of the New Sink.

The notch in the front center of the opening is to accommodate the overflow channel which protrudes from the bottom side of the new sink. See photo.

Step 16: Remove the Masking Tape and Clean the Surface Surrounding the Cutout

After removing the tape, clean off the countertop surface surrounding the cutout with some glass cleaner.

Step 17: Attach the Faucet Set to the New Sink

This step is easy to do now, and much more difficult after the sink is installed in the countertop. Install the faucet set on the sink and attach the flexible water supply lines to the faucet set.

Step 18: Install the New Drain Assembly

Use plumber's putty under the flange and Teflon enriched pipe thread compound where the tailpiece mates with the flange.

Step 19: Put the New Sink Into the Opening in the Countertop

Install the new sink into the opening in the countertop and attach the flexible water supply lines to both the hot and cold water shut-off valves.

Step 20: ​Connect the Sink Drain Tailpiece to the P-Trap

If the alignment of these two pipes is not acceptable, then use a flexible tailpiece extension and/or a flexible P-Trap assembly to accommodate any misalignment.

Step 21: Use Silicone Sealant to Seal the New Sink and the Countertop

Use a bead of silicone sealant to seal the seam between the new sink and the countertop. I used a clear type.

Step 22: Test for Leaks

Close the sink drain plug and turn on both the hot and cold water faucet handles to check for leaks in the ingress plumbing and to see if the sink drain is leaking. Next, put a clean dry paper towel on the sink cabinet floor under the P-Trap and open the sink drain. Check for leaks in the egress plumbing. If you find any leaks, address them. Working on older plumbing always runs the risk of damaging it. In my situation, the plumber who installed the old sink had used some unknown pipe thread compound on the plastic threads of the coupling nuts on the P-Trap and I cracked one of them taking it apart. I then had to replace the P-Trap crown pipe in order to install a new coupling nut.

Step 23: ​Clean Up the Dust and Remove the Plastic Sheeting

Even though my wife and I covered up everything with plastic sheeting and plugged up the space under the door, some of the white dust was still able to find its way into the hallway and the nearby den.

Step 24: Conclusion: the New Sink Is Installed and Ready for Use

The new sink is a big improvement over the discolored built-in sink. The $300 we spent on the project was far less than replacing the countertop.

Step 25: Tools and Materials

  1. New drop-in sink
  2. New sink accessories, i.e., drain assembly and faucet set
  3. Safety glasses and a half-face respirator mask
  4. Tyvek suit- get the “bunny suit” that covers your head and feet
  5. Car jack or 2 jack stands to support sink
  6. Piece of plywood to rest sink on. Plywood goes on top of jack or jack stands
  7. Angle grinder with 4½-inch metal grinding wheel
  8. Reciprocating saw with carbide grit blade
  9. Electric drill and 1-inch spade drill bit
  10. Sink wrench
  11. Faucet wrench
  12. Masking tape, 2-inch wide
  13. Plumber's putty
  14. Silicone sealant for sealing sink to countertop
  15. Teflon enriched pipe thread compound

  16. Plastic sheeting to cover floor and EVERYTHING in the bathroom

  17. Shop vacuum
  18. Optional: Flexible P-Trap or tailpiece extension. This may be needed to accommodate the new sink's position if it does not line up well with the old under-sink plumbing
  19. Optional: Female water type (as opposed to the gas type) caps for the water shut-off valves. Use these if either you cannot shut off the valves completely or if the valves are leaking internally. My shut-off valves have 3/8” flare fittings, but some homes may have compression fittings, so get the type of caps that fit your plumbing.