View Full Version : need help with installation of undermount kitchen sink

01-16-2009, 04:19 PM
here's the situation. i currently have an old formica countertop. i am planning cover it with marble tile (12" x 12"). i want to sandwich the undermount sink between existing formica and new marble tile. do i need to grind the bottom of the tiles that will surround the new sink since the flange of the sink will be higher than the existing formica, OR, should i cut out the formica to make the sink flange flush with the other formica surface? :confused:

Lee Tanner
01-16-2009, 04:54 PM
My brother is a title setter and I have help him some, we have not done this while I was helping, but it seems to me it would be easier to cut the counter top.

master plumber mark
01-16-2009, 05:30 PM
I really want to see pictures of the finished product....

the easy way to keep from makeing a total mess
out of it would be to forget about the under mount sink
and install a nice normal SS sink on top of your finished marble ........

01-16-2009, 05:32 PM
A recipe for disaster...most formica is set over partical board which, when it gets wet swells up and will tear up your stone tile; plus, while a good modified thinset will stick to nearly anything, formica isn't a great idea as it could delaminate from the backing.

There are ways to do an undermount sink with tile. The better way is probably to use something like Rondec from www.schluter.com (http://www.schluter.com). Another method is to mount the flange on top of the counter substrate, then tile over it. Making the edges look good is a little tough, but doable. Marble, at least some of them, can be shaped with sandpaper and a grinder. You would get a better result with a profiling bit, then you can polish it with sandpaper...wet/dry paper works and is available in very fine grits. Diamond pads will last longer, but cost more. Many formica counters have rounded edges, which will also give you grief with tile. They also make tile-in sinks, with square corners (much easier to tile to) that are designed to be tiled in and flush with the counter. The worst junction is the sink to counter...any moisture in there will often cause the counter to delaminate, swell, and ruin the overall result.

Check out www.johnbridge.com (http://www.johnbridge.com) for some tiling help, pictures, and ideas.

01-18-2009, 08:39 AM
well guys having a variety of suggestions from you i think i go with the topmount. i didn't take into consideration that the particle board could/would swell. as for the de-lamination....i'll take my chances. my counter has has squared edges so there's no problem there. also i plan to butt the tiles to each other without grout lines. is that a problem? i do have another question though. what do i edge the front edge and top of slash panel with? i've seen wood trim but i'm afraid it will deteriorate when it gets wet. need more help

01-18-2009, 05:45 PM
You don't need a very big grout joint, but you DO need one. A kitchen counter is often going to get stuff spilled on it. Guess where it will end up? In the gaps between the tile. You'll never get it out. Think of stale beer, milk, etc...it will be nasty. A regular grout will be helped by a sealer, but you could go with an epoxy grout, which is nearly impervious to everything.

The formica and tile will expand and contract at different rates, so it's a tossup whether a good modified thinset will hold it indefinately. You'd have better luck with something like cbu installed, but it must be anchored with screws, which will give you a path for moisture to the partical board underneath. If you put some cbu down, then used some RedGard on it, you'd waterproof it. Apply liberally around the sink opening, too to protect the edges.

Check out www.johnbridge.com (http://www.johnbridge.com) for help with tiling.

01-20-2009, 01:39 PM
DO NOT tile over formica countertop. That is an absolute no no. It's not that much work to rip it up and screw in a 3/4" plywood. Then thinset 1/4" cbu and screw down with cbu screws. Use a good quality thinset and then use epoxy grout. I never worked with epoxy grout. I heard it's very tuff to work with. Read directions carefully and do a practice run on some scrap tiles.

You don't have to put a space if the tile is beveled on top. The 1/16" bevel placing two tiles together will give you a grout joint. If you are going to butt tiles you have to work perfectly square as there is no room for error. Also tuffer to make an overall flat appearance.

Note: Some colored marbles such as green marble require epoxy thinset or you take the chance of the tile warping.

Schluter systems makes a nice countertop edging profile.

01-20-2009, 04:39 PM
An epoxy grout MIGHT stick in the microbevel, but a traditional cement based grout will not. It won't last long...even a 1/32" gap is enough, but the smaller the gap, the harder it is to mash the grout in between the tile. If you don't, it will not last, especially on a countertop. Can you picture a thread of cement 1/32" thick - no strength unless is has some contact area - there's none in the microbevel. WIth stone, 1/16" joint is fairly common. If you choose a grout color that blends with the tile and don't overwash it, it should end up flush with the tile after installation. For professional tile help, check out www.johnbridge.com (http://www.johnbridge.com).

An epoxy grout is made up of the plastic binders and a colored sand like material (sometimes, it is sand). The hardest part of using an epoxy grout is cleaning up properly...if you don't do it well, you'll end up with a sticky, splotchy layer on the top of the tile. Also, the color filler can scratch a highly polished , soft stone tile just like sanded grout can. That is why people use unsanded with most stones, but also keep in mind, an unsanded grout can't be used in joints bigger than 1/8"...it shrinks more than sanded grout (epoxy grout doesn't shrink appreciably) and will usually crack.

01-21-2009, 06:40 AM

For tiled countertops, do you think someone should use epoxy grout or regular unsanded grout.

My thinking was all the small food particles and smashed food will work it's way into unsanded cement grout and stain it, even with a good sealer.

With epoxy, it doesn't absorb anything.

01-21-2009, 06:52 PM
There are millions of tiled counters out there using cementious grout...nobody really knows how long an epoxy grout will last. Probably longer than you need it, but cement can too. Liquids can penetrate standard grout, but if sealed well and you clean up rather than letting things sit, it can look good a long time. Older epoxy grouts could yellow a little, but the newer ones seem to be less prone to this. I guess it might depend on the color chosen...I was going to go with a really light colored grout, I'd lean more towards epoxy; if it was dark, it's a toss-up. Epoxy will cost more. Installation isn't really harder, but you must be meticulous with cleanup procedures, or it can make a real mess. If you have a textured tile, cleanup is harder.

01-23-2009, 04:46 AM
SInce the existing sink is already installed in a cutout in the countertop, what do you plan on setting it on, or holding it up, before you install the new tile over it? You might as well just leave it and the rim in place and then tile over the rim so only the sink is exposed.

01-23-2009, 05:02 AM
Sounds bad all around. Definitely go top mount. I wouldn't tile over formica for any money. And definitely use a grout line.

I would go epoxy.