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Articles by Jim Heaphy
for Kitchen & Bath Design News

Cooktop Cutout Quality is of Critical Importance - May 1995

Two years ago, I established my own business, specializing in repairing solid surface countertops. Since then, I've seen hundreds of problems with solid surface countertop installations, and successfully repaired a wide variety of failures. Indeed, the reparability of solid surface materials, and the fact that the manufacturer's warranty will cover many such repairs, are among the main selling points of these materials.

Unfortunately, many of the problems that homeowners encounter with solid surface countertops are due to errors in the fabrication and installation process. Fabricators must be scrupulous in following all of the current policies and procedures recommended by the manufacturer in order to minimize failures and ensure that the manufacturer will pay all valid warranty claims. Based on my experience, I believe that the most common area of fabrication and installation problems is the cooktop cutout. I believe that warranty claims could be reduced significantly if every fabricator and installer took special care to ensure that every cooktop cutout was done in strict accordance with the standards established by the manufacturers. In this column, I will review the cooktop cutout requirements of the leading manufacturer of solid surface materials. Although the general principles are common within the industry, be sure to follow the specific requirements for the brand of solid surface material you are working with.

Before making the actual cooktop cutout, consider the support structure beneath the countertop. Solid surface countertops should never be installed over a solid plywood or particle board subtop. Instead, they should always be supported by an open perimeter framework, usually consisting of strips of plywood a couple of inches wide, running on top of the cabinet edges. If at all possible, cabinets with solid tops should have most of the top surface area removed to allow free air circulation beneath the countertop. There must be a level, structurally sound framework around the perimeter of the cooktop. After the cutout is completed, the inside edge of this framework should be no closer than 1" and no farther away than 3" to the edge of the cooktop cutout. If it is too far away, it will not provide sufficient structural support. If it is closer than 1" to the edge of the cutout, it will act as an insulator, capturing excessive heat at the edge of the cutout. It is essential to have free air circulation from below, to help dissipate this heat.

If the cooktop fits tightly into the opening, too much heat can be transferred to the edge of the cutout. Additionally, the cooktop itself will expand when heated, exerting pressure against the edge of the cutout. Clearance of at least 1/8" all the way around will solve this problem. When laying out the size and position of the cutout, the opening should be at least 1/8" oversized on all four sides. Cutout dimensions shown on the cooktop manufacturer's installation instruction sheets are often not large enough for cutouts in solid surface materials, and should be considered a starting guideline for laying out the size of the cutout, rather than the final word.

When solid surface materials crack, it is often at an inside corner. The general principle is that a smoothly radiused inside corner is much more crack resistant than a square inside corner, and that a larger radius is better than a small one. Some models of cooktops have stamped metal housings with large rounded corners and wide flanges. With this type of cooktop, it is both easy and advisable to create a very large large corner radius. Other cooktops have sheet metal housings with sharp, square corners and narrow flanges. This type of cooktop requires greater care in laying out the radius at each corner to make it as large as possible. With careful planning, though, any cooktop now on the market can be installed with a reasonably large cutout corner radius.

Gas and solid disk electric cooktops should be installed using the high-strength cutout procedure. This procedure is also appropriate when customers do lots of canning, candy-making, deep fat frying or other demanding cooking operations. I recommend it for all cooktops, whether required by the manufacturer or not. Install 6" X 6" solid surface reinforcing blocks on the underside of the cutout at each corner, using a consistent coating of joint adhesive over the entire bonding surface of the block. These blocks should be beveled at a 45ΓΈ angle on two perpendicular edges, and these edges should be the ones that meet the cutout on the underside. The radius of each inside corner should also be increased using the technique of flaring the corners out to within 1/8" of the outside edge of the flange. This flared corner technique will triple the corner radius possible with any given cooktop, and this is an important benefit.

The countertop cutout itself should be machined cleanly and smoothly with a router. The top and bottom square edges of the cutout should be rounded over with a sander or a small diameter quarter-round router bit, and all edges should then be sanded to eliminate any tooling marks, to at least 150 grit or finer.

Then, aluminum heat conductive tape must be installed properly. This tape helps dissipate excess heat when the cooktop is in use. The tape should be applied to the vertical edges of the perimeter of the cutout, dangling into the opening. Do not wrap this tape up under the edge of the cutout. Apply enough tape to the top horizontal surface of the cutout perimeter that excess tape will show when the cooktop is first placed into position.

Center the cooktop in the cutout, so that there is equal clearance on all four sides. Do not secure the cooktop with screws driven into the solid surface material. Clamps or other fasteners should be set snugly, but not over tightened. Place a shim where any pointed fastener contacts the solid surface material.

Once the cooktop has been positioned, use a sharp utility knife to score the aluminum tape flush with the edge of the flange of the cooktop. Don't bear down hard enough to score the countertop itself. Peel off any excess tape, and the cooktop cutout process is now complete.

Following these procedures with care will prevent the vast majority of customer complaints regarding cracks starting at cooktop cutouts.
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