Kevin M. Padden

AZ School of Rock & KM Padden Consulting

Regardless of how and when we learned about installing undermount sinks, there is definitely a right way, and a wrong way to “install” the sink when we are also installing slab countertops. 

I’m reminded of what my dad always said about having to “go back” out to a finished job for a “call back.” My dad said, and now I say, “Call backs ain’t green backs.” In 99% of the time – this is true.

In all of the years that I have been working in the slab countertop industry, I have seen countless jobs installed by other companies that have issues with the undermount sink actually falling down after the fact. This usually occurs within 1 to 3 years after the date of installation.

100% of the time, the cause of the failure is because the sink was simply glued to the underside of the countertop material—whether the material used was natural stone, engineered stone, or some of the newer “green” products that contain recycled glass and cement.

Regardless of the material that’s used for the countertop, if an undermount sink is glued to the underside of the slab, and allowed to just hang there, time and gravity will work its magic, and eventually, the sink will start to literally “peel” off the stone. The sink will start to sag and a gap will become visible (usually noticed by the customer long after the job has been completed and paid for).

Think about this the next time you want to “silicone” or “bondo” a stainless sink to the underside of the slab countertop you’re installing in a kitchen application: The glue that you use to stick the sink to the underside of the slab has to hold more than just the weight of the empty sink. The plumbing connections usually apply an amount of downward tension or pull on the sink.

Additionally, the weight of water and other heavy items placed into the sink adds to the stress in the glue that’s holding everything up in place. Now add to this the weight of a garbage disposal unit, and you have some significant downward pull on a glue joint that is supposed to hold all this up and keep it tight.

If all of this weight isn’t enough, every time your customer turns on their garbage disposal, they are adding vibration to the equation. No wonder sinks that are installed using silicone or bondo fail!

Remember this as well about “bondo” type products – they are made using polyester glue. Polyester shrinks over time, and will literally release from the material it’s supposed to be bonded to. It can’t penetrate or soak in to the stone or the stainless steel. So, what happens over time, is that the polyester bondo literally shrinks up and lets go of the stone and/or the sink, allowing it to start sagging, and eventually fall down! Using an epoxy glue will solve the “soaking in” issue with natural stones, but won’t fair any better on stainless steel – so why go through an exercise in futility?

Sadly, there are many companies that have the old “that’s the way we’ve always done it” mentality and continue to mount their sinks this way, and then wonder why their customer’s sinks fall.

If you are a fabricator who has been installing your sinks this way, there are much better ways to support sinks that will not allow the sink to sag or fall down over time.

The vast majority of the sinks that I have set have been used in 2cm granite applications where using studs mounted into the stone is not recommended – as 2cm stone is too thin to handle the studs in the stone.
Here are some suggestions for “better than just using silicone or bondo” to support your sinks:

2cm Stone – I always recommend that the sink be supported from underneath, using a cradle-type assembly like Sink Setters, the Sink Undermounter Hercules® System, or even simple wood cleats to hold the sink up. I really like the Sink Setter System – as you can adjust the height of the sink after the stone tops have been set and secured in place. The screw adjusters allow you to achieve a very tight seal between the sink flange and the underside of the stone.

3cm Stone – Since I have had such good results with the Sink Setters, I also would recommend them for all 3cm applications as well, however, you can use stud and/or clip type systems to mount large, as well as, small sinks. Drilling into the underside of 3cm stone is an acceptable technique that is sanctioned by the Marble Institute of America – but only for 3cm or thicker materials.

Braxton-Bragg has a variety of different support systems that you can employ to properly support your sinks from underneath, and they are priced reasonably so you can provide the best finished product for a competitive price.
For a small investment to cover the cost of whatever system you prefer using, you’ll get a better night’s sleep knowing that the sinks you set today will never fall down on the job. That’s priceless!

Until Next Month – Best Regards & Happy Fabricating!

“Using Sink Supports” is a “hands on” topic that is taught each month by Kevin M. Padden from AZ School of Rock. For more information on classes, contact Kevin at 480-309-9422 or online at www.azschoolofrock.com.