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How to Install Sinks, Cooktops and Overhang Supports

In this section we’re going to cover the following aspects of installing solid surface materials:

  • Installing Solid Surface Undermount Sinks
  • Installing Stainless Steel, Granite, or Porcelain Undermount Sinks
  • Installing Cooktops
  • Countertop Installation and Support

INSTALLING SOLID SURFACE UNDERMOUNT SINKS

Beyond aesthetics, there are functional benefits to having a solid surface undermount sink, versus a top mounted (or drop-in sink.) Undermount sinks are easier to clean and keep hygienic since the barrier around the sink, like the lip for a top mounted sink, is no longer there. Additionally, the seam between the sink and the top is bacteria, stain and water resistant because it is a hardened resin like the rest of the non-porous sink and countertop.

The first step to installing a solid surface undermount sink is to turn the solid surface sheet upside down and locate the place where the sink is to be placed. Then, position the bowl on the surface and use hot melt glue to fasten positioning blocks around the sink to aid in alignment during gluing. Drill a 1-1/4” hole in the top, in-line with the sinkhole, so that you can insert an all-thread rod. The rod, along with nuts and wood blocks (that act like large washers), are used to place a moderate and even amount of pressure on the sink for gluing. (See Figure 10)


 Clamping Sink Bowl to Underside of Counter Surface

Carefully remove the sink from it’s marked location. Scuff the undersurface of the top where the sink will sit and the top flange of the sink bowl with 80 grit sandpaper. Clean both surfaces with denatured alcohol. Use a flat sanding block to ensure you don’t round-over the inside edge of the sink when sanding. (See Figure 11)

 

Preparing Bonding Surfaces

The goal, when gluing a sink in place, is to have the glue line appear perfectly flat. In almost all instances the countertop is true (flat). In these cases, where the rim of the sink is perfectly true, then the glue line will be flat and you can use the adhesive color recommended by the manufacturer for the countertop or the sink.

If the rim of the sink is not perfectly true (flat), then use the adhesive color that is recommended by the manufacturer for the sink.  That way, the uneven sink rim will not show, since the adhesive which matches the sink will effectively “disappear” from view. In essence, the adhesive will create a self-leveling effect. The only line that will show will be where the sink matching adhesive meets the underside of the flat countertop, making the glue line appear flat.

This can seem simple enough, however, it is often difficult to find adhesive that matches a sink. Therefore, make sure you sand the sink rim true.  Once it is true, then the adhesive matching the countertop can be used. If you do not sand the sink rim flat and go ahead and use the countertop matching adhesive, then an uneven appearing junction between the sink and top can occur.

Next, apply two beads of adhesive to the sink rim; one near the inside edge, making sure there will be squeeze-out all the way around, and the other near the outside edge. Carefully position the sink inside the area of the positioning blocks.

Place the all-thread rod in place with wood blocks and tighten it until you see adhesive squeezing out all around. Even though you won’t be able to see it, you will want to apply enough adhesive so it squeezes in around the inside as well. Do not over tighten as this will “starve” and weaken the seam. Allow the squeeze-out to harden for about 30 minutes or until it is hard to the touch.

Turn the countertop over so the top is facing up. Two different router bits will be used to remove the material from within the bowl opening and provide the edge to the sink. The first is a ½” 2 Straight-Flute bit with a large nylon bearing at the bottom. The bearing has a larger diameter than the bit which will position the cutting edge of the bit back from the inside wall of the sink. This bit will cut away the top and will leave a lip around the inside edge of the sink that will be removed by the second bit. (See Figure 12)

Routing Out Sink Opening

[Figure 12: Routing Out Sink Opening]  

Next, use a Roundover bit with a nylon bottom bearing. This bit will cut a small amount from the edge of countertop and the sink, including the protruding squeeze-out. Position the bit, up and down, so the bearing rides below the seam squeeze-out and the top of the cutting edge clears the countertop surface. (See Figure 13) Pay attention to the router bit rotation to avoid any chatter (vibration or wobbling of the bit due to the high-speed rotation.)

 

Routing the Finished Sink Opening 

Make sure the bevel angle of the Roundover bit is suitable for the bevel angle of the sink. The angle of the sink wall may change as you move around the sink. There may be a slight ridge left in some places after routing. This is expected and can be sanded away with a random orbit sander and 180 grit sandpaper, followed by 280 grit sandpaper.

Always make sure the bearings on the router bits are new or functioning perfectly. Otherwise it may disintegrate and result in a gouged sink surface.

Finally, finish sanding the rounded surface with a random orbit sander and a soft thick backing pad. The pad allows the sandpaper surface to flex and easily follow the rounded edge.

INSTALLING A STAINLESS STEEL, GRANITE OR PORCELAIN UNDERMOUNT SINK

Stainless steel, granite and porcelain sinks are often installed so the edge of the countertop extends beyond the inside edge of the sink. In some ways this is an easier install than an undermount, solid surface sink, but the procedures are very similar.

Follow the steps above, but in place of the solid surface adhesive use 100% silicone (often labeled silicone sealant or silicone caulk) and metal sink mounting brackets. Glue the metal sink mounting brackets to the underside of the top and clamp the bowl in place. Leave the sink brackets in place after the silicone sets for extra support. This type of sink mounting bracket doesn’t require drilling or inserts.

The next step is to remove the countertop material from within the bowl. Before gluing the bowl, place a strip of tape ¼” down from the inside top edge of the sink. This is to protect against any markings that might be left by the nylon bearing as it runs against the surface. Once the bowl is taped and glued in place, use the Straight-Flute router bit (as above) to remove the excess countertop material. This will leave the edge of the countertop nearly flush with the inside of the sink or extend it beyond the edge of the sink by a small amount. You can control how far the top extends into the sink by changing the size of the nylon bearing.

If you aren’t comfortable with this approach you can create a plywood template. Most manufacturers supply a template pattern, but it may not allow for the overhang. If they didn’t include one with the purchase of the sink, you can create one out of cardboard that provides the correct overhang and use it to cut an opening in the piece of plywood. Make sure the plywood template has the correct shape and has smooth edges for the top mounted bearing on the router to run against. You are now ready to position the template and make the router cut.

Attaching Mounting Brackets

[Figure 14: Attaching Mounting Brackets]

The last step for installing a stainless steel, granite, or porcelain undermount sink is to create the round over for the edge of the top. A small radius Roundover bit is used to create the round top edge. Alternatively, if the edge is left square, a slight rounding can be done with a sander or sanding block. Figure 15 shows three undermount configuration options for the top overhang, including a rounding option.

Undermount Options

[Figure 15: Undermount Options]

INSTALLING COOKTOPS

Heat emanating from cooktops can create an expansion and contraction issue with your solid surface countertop. This is especially true at the corners of the cooktop cutout opening.

Most cooktops come with a pattern to indicate the size of the opening needed. However, make sure to allow for ¼” space around the edge of the actual glass range top when you cut the opening (not including the decorative finish ring) to account for potential expansion and contraction. Be especially careful not to cut away too much material at the corners . The cutout can be made with a jigsaw, but using the router and template method is preferred. If you use a jigsaw it’s essential to remove all the tooth marks left by the blade with sandpaper. Otherwise, the tooth mark impressions can create stress points and become an initiation point for cracking.

The edges of the opening should be taped with aluminum-backed insulated tape to help with expansion caused by heat from the cooktop. Tape the entire inside edge of the cook top opening with 9 mil heat reflective tape. Apply two layers of aluminum tape in the corners and do not wrap the tape under the surface (See Figure 16.)

Cooktop Layout and Taping

[Figure 16: Cooktop Layout and Taping]

All four corners should be reinforced with 5” square blocks that have rounded edges. The inside corners of the countertop must have a minimum ¼” radius, as seen in Figure 17. All of these steps are designed to prevent cracking of the countertop due to repeated heating and cooling associated with use of the range top. Lastly, trim the aluminum tape so that it is not visible from the top surface.

Reinforcing the Cooktop Cutout Corners

[Figure 17: Reinforcing the Cooktop Cutout Corners]

COUNTERTOP SUPPORT AND INSTALLATION

Solid surface tops that are ½” thick need support in two different locations. First, any overhang of more than six inches needs support. Second, the portion of the top that is above the cabinets needs support.

Figure 18 shows three options of overhang support when the overhang is over 6” and up to 12”. Figure 19a shows an option for wooden strip support for the portion of the top that is directly above the cabinets. Figure 19b shows an option for steel structure support of countertops over 12” and over extended overhangs.

Overhangs like those found on a wall pass through, and eating bars of more than 6”, but less than 12”, can be supported with wood or metal corbels. They can also be supported by a relatively new product called a COUNTERBalance™ CounterPlate™. An appealing feature of the CounterPlate™ is that it is only about 3/8” tall and doesn’t get in the way of knees like corbels can. They are also out of sight and fast and easy to install (See Figure 18, far right frame.)

Supporting Counter Overhang

[Figure 18: Supporting Counter Overhang]

Large island overhangs up to 18” can be supported with large corbels, a welded steel frame of 16 gauge 1”x2” rectangular steel tubing, or a series of COUNTERBalance™ IslandBrackets™.  The IslandBracket™, like the CounterPlate™, does not get in the way of knees, are out of sight and fast and easy to install. The IslandBracket™ is 1-1/2” x 1-1/2” and shaped like a “T” when looking at it from the end (See Figures 19a and 19b.) The welded steel frame option can take on any shape or dimension needed. However, it does require welding without heat warping and must be painted. Corbels can be a good option as they come in all shapes and sizes and can add a decorative flair.

COUNTERBalance™ IslandBracket™

[Figure 19a, COUNTERBalance™ IslandBracket™]

Supporting the Extended Overhang

[Figure 19b: Supporting the Extended Overhang]

The portion of the countertop that resides directly over the cabinets is supported by 2” wide plywood strips every 12 inches (strips are used instead of solid sheets of plywood so the countertop can dissipate heat or cold on the underside.)  They are there mostly to provide spacing, so they can be either ¾” or 1” thick. The strips can be affixed to the top of the cabinets, as shown in Figure 19a. Hold the countertop in place using thumb sized dabs of silicone sealant placed on the strips about every 12”. Alternatively, the strips can be affixed under the surface of the top with the dabs of silicone sealant. Then, the top (with the strips attached) can be affixed to the cabinet tops with dabs of silicone sealant. Silicone sealant is used to allow for expansion and contraction of the top.  If you place the countertop on top of the cabinets without these ¾” to 1” spacers, the 1” dropped edge on the front of the countertop could prevent the drawers near the top of the cabinets from opening.