Cutting Sink Cut-Out in Granite

[illuminance]

I have done a number of formica countertop installations, but am trying my hand at granite next week. Its a relatively straightforward installation in that there is no "L" counter, just a straight 9' slab.
I have read conflicting info on the web, and want to make sure I get it right. I am going to install a self-rimming sink (22" x 21"), and want to know if the granite should be laid down over the plywood and secured and then cut the cut-out, or should the cut-out be cut BEFORE laying the granite down on the plywood? Seems to make sense to cut the granite after its installed to avoid moving a somewhat weakened piece that could crack. So...put the granite in place and cut my opening, or cut the sink opening first?
Thanks!
Charlie

 

[Geniescience]

dust management

this must be a new house being built. No way should that much dust get into a lived in house.

david

 

[Sponsor]

 

[Statjunk]

As I was reading your post I was thinking the same thing. It is a very very dusty job.

I've got a question for you. How much are you paying for the granite if you are installing it yourself? What is the thickness?

I found a website on the internet that sells direct to consumer granite. I was pretty surprised.

Tom

 

[hj]

sink

Most sinks in granite tops are undermounted which would make it impossible to cut after the top is installed. I do not know anyone who would attempt to cut and install a granite top without adequate experience and training. Even professionals have to replace the tops occassionally due to errors.

 

[Statjunk]

HJ,

I agree with you that most granite installation are below mount. I think it would look strange to see an above mount on a granite top.

Tom

 

[Jadnashua]

Cutting a hole for a sink in a slab weakens it significantly. If there are any veins or weak spots it can be very dicey. The fabricator that made my counterpieces charges $300 to cut and polish a sink hole for an undermount. They do the majority of work on a huge CNC machine so there is very little stress on the slab, but it also sprays water all over the place.

An undermount doesn't require the precision or polishing, but unless you have the ability to cut it wet, it will be very messy. Not sure what to tell you...

 

[Prashster]

Not sure why yr laying the granite on plywood. On my counters, it goes right on the cab tops. Am I missing something?

I agree that you should just have someone do the install for you.

 

[Jadnashua]

3cm stuff is strong enough to not need anything, but slabs are also available in 2cm and sometimes even thinner which survives better with support.

 

[illuminance]

thanks for all of the replies. First off, there is no one living in the house presently. It is completely empty. Dust cleans up. The granite is probably about 3/4" thick. I presonally have seen self-rimming sinks over granite and they have looked fine. With a self-rimming sink, it will cover up slight imperfections in the cuts, as there is about 1/2" overlap by the sink lip.
You know, I had never done formica. And then I did it. I had never refinished hardwood floors. And then I did it. I had never stuffed a BUICK V6 INTO A TRIUMPH TR7, but then I did it. I like to try, I like to learn, I like to grow. So, if I mess up a 9' slab of granite (which is only $130!), then maybe I learn something. If I used an expert everytime I had not done something before...then I would not know how to do anything myself. Isnt this supposed to be a DIY forum?
I was trying to find out from others if they did the sink cut-out with the granite already on top of the cabinetry, or if they cut it out and then laid it on top.

 

[Frenchie]

Isnt this supposed to be a DIY forum?
I was trying to find out from others if they did the sink cut-out with the granite already on top of the cabinetry, or if they cut it out and then laid it on top.

...and the answer was: we get it cut by the manufacturer. Why the mini-rant?


That TR7 project sounds like a hoot!

 

[Jadnashua]

You'll need diamond tools, and when cutting support it very well - the stress from the cutting and vibration can be deadly to a slab. At 3/4", it sounds like a nominal 2cm slab, and yes, it is best to support it underneath on a counter with a layer of ply. Make sure that things are VERY flat or it will eventually crack at any high point. Cutting granite dry means a fair amount of heat buildup as well, which can mess things up.

 

[Statjunk]

a 9' slab of granite (which is only $130!), .

Man is that dirt cheap! The 3/4" thickness will be working against you though. Becareful not to crack it. Granit is strong but will break easily along a certain areas where it is weak.

Did you get it from the internet?

Tom

 

[PEW]

Remember, granite dust can be deadly and expect a lot of it.

Also, don't forget to metal rod the front to provide additional support for the thin edge. No sharp corners.

I have seen it done once. Would never happen in any property I own.

 

[Geniescience]

so, for the record, and just so someone says it, I'll say it: in the context you have described, if I were in your shoes, I'd cut it on the spot as fully supported as possible and not expect to move it ever again because it risks cracking more than anything else, and I'd not worry about the mess.

david

 

[Mean jeans]

Just wondered if you ever did cut and polish your sink cutout yourself and how did it come out? I have the same philosophy regarding doing things everyone says I should leave to "experts". I mean just how can you learn anything if you dont try it at least once? There's a first time doing anything for everyone. I hope you did it and it came out awesome. Please let me know because I'm considering the same thing.

 

[hj]

quote from Jdnashua; An undermount doesn't require the precision or polishing,

he is not using an undermount sink, but if he were it WOULD need "precision and polishing". A top mount sink does not need to have the cut polished. The reason for a plywood underlay is to make the granite appear thicker with a "bullnose" edge on the front.