As a licensed Florida Building contractor, I just repaired a sink undermounted to a residential granite countertop. I got the work because of a sharp-eyed home inspector and thought I’d return the favor by letting other inspectors know what to look for. The consequences for missing the symptoms can be economically painful for home buyers and catastrophic for countertops.
Too often granite fabricators reinforce sink cut outs at the shop with cold steel rods imbedded in polyester (cheap) instead of stainless steel, carbon fiber, or fiberglass rods imbedded into epoxy (expensive), which is much more water resistant.
They compound future problems by attaching sinks to the stone with polyester on a wood shim or stone scrap spanning the sink flange and stone bottom. They may use inadequate amounts of caulk or improper caulk or both. Even the sink clips imbedded into the stone can be inadequate support because there isn’t enough room to fit them between the sink and the cabinet front where they are most critically needed. They rust and fail.
Home inspectors should not be able to push a scraper between an undermount sink flange and the bottom of the stone. A topical application of silicone is an inadequate fix. The sink must be removed, the flange and granite cleaned, and the sink re-siliconed and mounted with a strap method such as the Hercules Universal Sink Harness or the Sink Strap. These act as a truss and turn one of the weakest areas into one of the strongest.
I’ve reinstalled over 50 sinks that have fallen, but these people were the lucky ones. ($300.00) The unlucky have their sink continue to leak in place until they call complaining of a 12" long or so crack at the front sink rail parallel with the sink. The leaking sink flange has dumped enough water to penetrate the polyester and rust the rod. The oxidizing rod expands and splits the stone. No stone is stronger than rust. The sink, cabinet front, and rod must be removed and the crack adhered with color match adhesive, clamped, ground and polished. ($700.00-$1,600.00) If they’ve really waited, it’s apron front sink time ($2,400.00-$3,500.00). Top replacement is the alternative.
I’ve attached before and after pictures of recent repairs.
Thank you for the post Joseph. I appreciate you taking the time to share it with us.
I found your post very informative. I’m actually having new countertops made for my home now. I’m going to have 2 undermount sinks installed. I’m going to spec the mounting hardware as I’ve already had to remount a food prep sink that detached several years ago
Many installers don’t fasten the sink at all. They just dado the plywood substrate and lay the sink in the dado. The only thing “fastening” the sink to the granite is caulk.
Plywood underlayment is used on 2cm stone with a built-up front edge and is a regional thing, predominantly out west. Everyone else seems to fabricate and install 3cm with no underlayment.
Besides a rusting sink clip, there isn’t a whole lot of damage from underneath to show.
Since I’m new here, I didn’t want to come off as a spammer, but I do write professionally for an online countertop magazine. Here is a link to a column with more pictures and explanations on this issue: http://www.countertopiq.com/2016/03/04/curing-countertop-cancer/
Thank you Joseph.
I see a fair amount of stone countertops, but I’m sure not nearly as much as others in more metropolitan areas. I like to be as thorough as possible, and have not yet seen the problems as you have posted. I have always suspected these issues to exist, just haven’t seen it. Thanks for the link. (Since I asked for more info, it isn’t spam). Appreciate your taking the time to assist members of this association and industry. Jeff
