(Written in February, 1997)

by Jim Heaphy

In recent years, the majority of solid surface sinks have been installed using the seam undermount technique. This style of sink installation offers many benefits - the transition between sink and countertop is smooth and sanitary, there is no lip on the surface of the countertop, and it is unique to solid surface countertops. The result is a look that is functional, distinctive and difficult or impossible to achieve with other sink or countertop materials. Because solid surface materials are so durable, such an installation will give many, many years of service in almost all cases. However, solid surface sinks are not actually indestructible. Occasionally, one will fail, and then a difficult repair must be completed.

Possible causes of a failure are many. I replaced one sink that cracked when a house painter, a man of substantial size, was standing on the countertop. This gentleman lost his footing, and plunged his foot with full weight into the sink, cracking it. In another case, a heavy cast iron skillet fell from a pot rack into the sink. Occasionally, a sink will fail for no known reason - or the customer may be deliberately vague in discussing the incident.

I always warn the homeowner that replacement of a seam undermounted solid surface kitchen sink is an exceptionally dusty, noisy, lengthy operation, and I pledge to clean up completely after myself when I am done. I begin by removing all items from the countertop, and by emptying the contents of the sink cabinet and any adjoining cabinets. I seal off the tops of nearby cabinets doors and drawers with painter's masking tape to minimize dust infiltration, and hang light plastic drop cloths over any furniture, appliances or cabinets likely to be heavily dusted.

I then disconnect the plumbing, keeping careful track of washers, screws and other small parts. I note the locations of all accessories, such as soap dispensers, filtered water spigots, dishwasher air gaps, and the like. One time, I hurriedly disassembled an unusual garbage disposal mount without paying close attention to the various parts. It took me hours to figure out how to put it back together, so now I observe carefully where every part belongs, so that I can put it back together with a minimum of problems at the end of the day.

Once the plumbing is disconnected, the next challenge is to remove the damaged sink, using a router and a special bowl removal bit. These bits look like small saw blades with four teeth, mounted on a 1/2" shaft and fitted with a ball bearing pilot wheel. These bits are available from Velepec and several other manufacturers. I recommend the largest diameter bit you can find - a 3-5/8" diameter cutter which makes a kerf 1-1/8" deep. This large bit is especially useful when removing a sink mounted close to the wall or the backsplash. The router should be a powerful 3 horsepower variable speed plunge unit, operated at the lowest possible speed with such a large diameter bit.

During removal, the old sink must be supported, so that it does not snap loose before being cut cleanly away. This could break off a chunk of the countertop. I use a jack sitting on a platform of the appropriate height to support the sink.
When routing, it is useful to run a shop vacuum with the hose taped up through the drain hole of the sink. Although this will not pick up all the dust, it will get some and help keep the bulk of the dust in or near the sink.

I begin by making an initial cut about 1/16" or so below the original glue line. This first router cut is strenuous, and I don't want to worry too much about slight rocking or irregularities in the cut. Once the old sink has been removed, I raise the router, carefully adjusting it to trim right at the glue line, and make one or more final trim passes.

There are several problems that may be encountered when removing a sink. As mentioned earlier, sometimes a sink is mounted much closer to the wall than you might like. You will be able to cut all the way through the flange at the front and the sides, but only partially at the back. In this case, I leave the jack in place, and use a reciprocating saw to cut the back of the sink well below the glue line, freeing up the old sink. Once the old sink is out, other tools, such as a die grinder, a narrow belt sander and a random orbit sander can be used to remove what is left of the old sink flange. Trim gradually and carefully to the old glue line.

Another common problem occurs when a large sink has been shoehorned into a small cabinet. In such cases, it may be necessary to cut the old sink into several pieces in order to get it out. It may then be necessary to cut away part of the support structure below the countertop, or cut holes in the sink cabinet side panels in order to maneuver the new sink into position. Reducing the flange width of the new sink slightly can sometimes be the key to success.

When two sinks have been mounted next to one another to create a custom double sink, it can sometimes be difficult to run the router on the level down the narrow rib dividing the two sinks. In this case, a sheet of plywood can be cut, with an opening corresponding to the opening of the damaged sink. This will cover the undamaged sink, and create a wide, flat surface on which the router can travel.

When a solid surface sink is seam undermounted beneath a solid surface countertop, the installation is usually completed in the shop, with the countertop upside down on the workbench. In this method, gravity is working to the fabricator's benefit. However, when a sink is replaced beneath a countertop remaining in place, gravity is working against the installer. Another complication is that the countertop already has a hole the exact size of the sink opening. The replaced sink must be positioned with much more accuracy than in the case of a new installation.

I begin by dry fitting the new sink beneath the countertop, holding it in place with the jack. Inspect the joint between the sink and the countertop, and sand both surfaces as needed to create a good fit. Move the sink into its optimal position, centered in the opening as accurately as possible. Now, I apply four long pieces of masking tape on the flat surface of the countertop, folded several inches down into the sink. Using a razor blade, I then trim the tape 1/4" away from the seam on each side. These pieces of tape are used for visual alignment of the sink once the adhesive has been applied. I then apply continuous strips of aluminum tape around the top vertical edge of the sink. These strips are folded down below the flange level in order to prevent the joint adhesive from dripping into the sink. After cleaning the surfaces to be seamed with denatured alcohol, I lower the sink slightly and insert three shims made of 1/4" thick solid surface material, creating a gap to allow adhesive to be applied. I then mix the adhesive, apply it liberally to the sink flange, remove the three shims, add three blobs of adhesive where the shims were, and raise the sink into position with the jack. I sight down each of the strips of alignment tape as I tighten up the sink, ensuring that it is centered as closely as possible. I then inspect the glue line carefully, adding adhesive wherever gaps are visible.

Once the adhesive has cured, I remove the jack and the tape, and rout off the excess with a bowl trimming bit. Because it is unlikely that the sink will be centered exactly, a substantial amount of sanding is required to produce a consistent, smooth finish all around the sink opening.

I then reconnect the plumbing, using plumber's putty and pipe compound as needed to eliminate drips. A massive cleanup effort follows, to restore the kitchen to how it looked when I arrived that morning.

It is a strenuous and exacting job - definitely a full day's work. The results, however, are well worth the careful effort, and the customer is always delighted with the outcome.