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Articles by Jim Heaphy
for Kitchen & Bath Design News

Common Fabrication Errors Lead To Countertop Failures - May 1994


Last fall, I went into business for myself, specializing in inspecting and repairing problem solid surface countertop installations. After ten years of selling new countertops, it is an interesting change to concentrate on repairing those that have failed. It has given me the opportunity to see firsthand on a daily basis what happens all too often when fabricators and installers let quality standards slip. It has also fortified my own commitment to high quality workmanship, which has been the theme of this column from its beginning.

In recent months, I have had the opportunity to inspect sixty kitchen countertop installations. In most of these cases, I have been able to repair the damage, although a few of the situations have been so serious that the countertops needed to be replaced. Some interesting patterns have emerged that reinforce the importance of following the manufacturer's fabrication and installation requirements to the letter.

In over 90% of the cases I've seen, the complaint involves a crack of some sort. In most of the other cases, the complaint involves new installations with workmanship so poor that future cracks are almost inevitable unless the shortcomings are corrected.

The most common problem I've seen, occurring in about 40% of the cases, is one or more cracks originating at a cooking appliance. Nearly 80% of these involve drop-in cooktops, although freestanding ranges and slide-in ranges are also involved occasionally.

As soon as the cooktop or range is removed, the problems that caused the crack are almost always apparent. Usually, the cutout is just barely large enough to allow installation of the appliance. When cooking takes place, the appliance expands, pressing against the edge of the cutout. Heat transfers rapidly to the countertop, leading to an increased risk of overheating. The proper procedure is to oversize the cutout at least 1/8" on all sides, to isolate the countertop as much as possible from the heat source. If the flange is wide enough, it is wise to oversize the cutout even more than 1/8" on all sides.

In many cases, the cooktop cutout has been made by drilling the four corners, and cutting the straight sections with either a circular saw or a saber saw. Often, there is no sign that the edges of the cutout have been sanded. This results in an unacceptably jagged edge that is likely to crack under stress. The proper procedure is to machine the cutout with a router guided by a template. The edges should then be rounded over to a radius of at least 1/16", and all surfaces should be sanded smooth, using 150 grit or finer abrasives.

It is important to have continuous wood supports beneath the perimeter of the cooktop cutout, within 3" of the opening. However, these supports should be kept at least 1" away from the edge of the cutout. If the wood supports extend right up to the edge of the underside of the cutout, they will act as insulators and inhibit the dissipation of excess heat. In many cases, I find that these wood supports just below the edge of the cutout have contributed to the crack and complicate the repair process. When I repair a crack, I try whenever possible to add a solid surface reinforcing strip or block beneath the cracked area. This is hard to do if a wood support extends right up to the edge of the cutout.

In almost every cooktop cutout crack I've seen, the required aluminum conductive tape is either missing or applied incorrectly. This aluminum tape helps move excess heat away from the area of the operating burners, spreading heat around the perimeter of the cutout. When installed properly, the tape covers the entire horizontal surface below the flange, the vertical surface of the cutout, and dangles into the opening below. It therefore acts like a radiator vane, shedding excess heat into the air below the cooktop. When the tape is present, it often does not extend out to the edge of the flange, or is wrapped up underneath the countertop. Another common error is to substitute a lighter gauge of cheaper aluminum tape, which is therefore less effective as a heat conductor. In one case, an installer used duct tape, which is not a conductive tape, and an 18" long crack resulted.

One discouraging trend is that in over 40% of the cooktop cracks that I've seen, there was an unsuccessful previous repair attempt. This leads me to believe that cooktop cracks are especially difficult to repair with assurance that the same problem will not develop again. However, I tend to be more thorough in my repair efforts then previous repair people have been - I always enlarge the corner radii, round over all edges and sand all surfaces smooth, and add reinforcing blocks in the corners whenever this is practical. I install new aluminum tape properly. Therefore, I hope that I will be able to achieve a higher success rate.

The second most common failure I've seen, accounting for 25% of the cases, is the seam separation - a straight crack that follows a seam on the horizontal countertop surface. The causes of this type of failure may not always be as glaringly obvious as in the case of the cooktop cracks, but certain problems do show up over and over. These seams should always have some sort of continuous reinforcement beneath them. In the past, this might have been a strip of plywood. Current standards call for a second layer of solid surface material beneath the seam, fastened with a layer of joint adhesive. When I look at the underside of a seam that has failed, often I find no seam support at all, and I can see gaps and voids where adhesive has leaked out of the seam. Such a seam may look fine on the top surface just after installation, but is much more likely to fail later on.

Seam location is also important. It is poor practice to locate a seam directly into an inside corner, which is an area of increased stress. Instead, the offset seam method should be used, moving the seam at least 1" away from the inside corner. Care should also be taken when locating a seam near or through a heat source. Seams above dishwashers and undercounter ovens and through cooktops should be avoided if possible, and assembled with great caution and adequate reinforcements if they are absolutely necessary. Edge buildup pieces that are not properly fitted to one another can also contribute to seam failures. These pieces should be of the same depth, and should be cut square and well-filled with adhesive where they butt into one another.

The good news about seam separations is that it appears that repairs are successful in most cases. I've yet to see a second repair required of a straightforward seam failure.

As already mentioned, inside corners are well-known as a potential problem area. Over 20% of the problems I've seen involve cracks originating at inside corners. The general rule is to create the largest radius possible at each inside corner, consistent with the kitchen design. At the front edge, 1/2" is now considered the minimum acceptable radius. This principle applies not only to the inside corners where the front edges of sections of "L" and "U" shaped countertops come together. It is also important when a countertop wraps around the corner of a wall into a greenhouse window, for example. If this corner is cut square, a crack can start that is particularly difficult to repair. It isn't possible to maneuver a router all the way to the wall where such a crack starts, and it is very difficult to reinforce this type of repair from below.

So far, about 25% of the inside corner cracks that I've seen involve a second crack that has previously been repaired. Therefore the success rate seems to fall somewhare between the excellent results seen with seam separations, and the more mixed results seen with cooktop cutout cracks.

A poor quality countertop support structure is a factor that frequently contributes to failures. At one extreme, I've seen quite a few tops installed over solid underlayment, which are often overglued. Portable heat-producing appliances, such as electric frying pans, can then more easily overheat the countertop, because the solid underlayment acts as an insulating blanket below the top. The result is often an audible bang as the top cracks while the homeowner is cooking. Customers should be provided with trivets made from cutouts for their portable cooking devices. These trivets will help prevent cracks, and can be used as color-matching patch material if a crack should occur.

At the other extreme, I've seen tops installed on a flimsy and poorly leveled hodgepodge of shims and loose blocks. This lack of continuous, flat perimeter support can lead to seam separations or inside corner cracks due to shearing stresses. The proper way to install solid surface countertops is on a continuous, sound, flat perimeter support structure of wood strips that exposes most of the underside of the tops to free air circulation. The tops should be attached with a flexibe adhesive used sparingly. Silicone sealant is the best. This allows for slight expansion and contraction due to temperature changes, without creating excessive stresses in the countertop.

In about 90% of the cases I've seen, the overall appearance of the countertops before the problem occurred was good. Usually, the tops are accurately sized, nicely finished, and fitted neatly to the walls. Decorative edges most often look fine. The home owner has no inkling of a problem until they notice a crack. From this, I conclude that most fabricators have the skills to produce good-looking installations that will be accepted by the customers as visually pleasing. It doesn't take any greater skill level to fabricate and install the tops in a structurally sound fashion at the same time. Instead, it is a matter of training, personal responsibility, quality control, and pride in the hidden aspects of one's workmanship. These are essential to long-term success in this line of work.
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