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thebadger 05-26-2009 07:01 PM

Help with Granite Install

I found a 25x59" piece of granite about 1 1/2-2" thick to use for my outdoor prep area. I never installed granite but this is my plan...

I'm building a cinderblock wall and plan to pour a 2" thick slab of concrete between the two side walls to support the slab. I'll then set my granite on top of the concrete.

1. Will the 2" slab be enough or overkill? - I do plan to use rebar
2. I was planning on setting the granite on top of the concrete - what do I used to "glue" the granite down. I'm assuming the concrete won't be totally flat so I'm guessing it will install like a big piece of tile.

Anything else to consider? Anything special when handling/setting the granite down? - I don't want it to crack.

Thanks in advance.
aka thebadger

dmun 05-27-2009 03:37 AM

Re: Help with Granite Install
Granite, in a two inch thickness, is really strong, stronger than the two inch concrete you're proposing. (Two inch thick isn't really thick enough to support with rebar, btw)

If it were me, I'd build your two masonry supports a little in from the ends, like the supports for a stone dining room table, then cover the tops with thinset, or mortar, and lower the stone top in place. That's a lot of weight, as you've probably already figured out. You'll need lots of help, or an engine hoist.

thebadger 05-27-2009 07:30 AM

Re: Help with Granite Install

As always thanks! One thing I realized is the slab is only 1 inch thick! Not sure how/if that changes your reco... We bought this slab at a discount place. The first piece "cracked" in half when I was getting it inside of the van (luckily they forgot to have me sign the waiver so they replaced it). I thought granite was a little more "touchy" until it's installed so I was treating it like tile install - hence the slab.

What is the min thickness of concrete I could go with if I still wanted to go that route? Or could I place some steel with a piece of concrete backer board on top.


MAVANO 05-27-2009 07:46 AM

Re: Help with Granite Install
I would go with 3 to 4" concrete with rebar after it sets spread the thin set and level off, if granite is only 1" that is a good backing for it, I would not go with steel bars for center support, rust and all, unless I used stainless

Wiley 05-27-2009 07:54 AM

Re: Help with Granite Install
I have a one inch granite slab as my entry surface with dimensions fairly similiar to your slab. There is what I did and so far it has worked out without problems. I supported the slab all but an overhang of about 1 1/2 inches on a slab that itself over hangs the main support slab. This may be confusing so I would suggest you check out the photos in my thread "Steel Dome Oven".

But regardless if you check out the photos or not, the thing I would suggest is NOT trying to affix the slab to the support. The slab will be fine just resting upon a thin layer of sand and fire clay and be free to expand and contract in response to the heating. And heat it will... and not uniformly, in front of my hearth it will get way too hot to think of resting ones hand upon while near the edges will be close on ambiant temp. Obviously alot of potential for stress and if one attempts to contain it I suspect something would give (ie crack).

Hope this helps,

GianniFocaccia 07-08-2009 10:00 AM

Re: Help with Granite Install

Not sure if you've installed your granite yet, but I'd go with dmun's recommendation. I picked up a DIY outdoor kitchen book the other day that suggested no underlayment needed for an outdoor granite countertop. Just level it on your blocks with thinset and go. I picked up 100sq' of 1 1/4" granite for my outdoor kitchen countertop and island (44"x58" - heavy!) and plan to do just that.


Wiley 07-08-2009 12:17 PM

Re: Help with Granite Install
GianniFocaccia, My granite entrance has been installed and in use for one year this month. So far I have not had any issues with it or my install. On the basis of that I will continue to endorse making the granite entrance "free floating" (as in not permanently attached) as at least one way of addressing the issue that works.
But thanks for the imput.

Lars 07-08-2009 10:11 PM

Re: Help with Granite Install
I would guess that a 1" piece of granite is way too brittle to span any countertop.

Contrary to earlier posts, a 2" concrete slab with 1/2" rebar would actually support quite a bit of weight. I have installed a 2" cantilevered mantle that has been working pretty well for several years. Once the steel is properly embedded in concrete, and you have a granite surface over that, rust is pretty much a non-issue in our lifetimes.

My 2 cents.


ps. Could you possibly support in the center? At that point, I don't think you would ever have a problem. ( i.e. 60" wide with a center wall... at most you are spanning about 24" considering wall thickness, overhang, etc.)

DimTex 07-09-2009 08:05 AM

Re: Help with Granite Install
Just an idea, I recall a granite guy putting ice cubes under the granite counter before putting down the slab. It made it easier to slide it around into final position before setting it, then the ice just melted away.

thebadger 07-12-2009 07:10 PM

Re: Help with Granite Install
1 Attachment(s)
Thanks All!

I actually went with a 2" slab with rebar - for support and to provide an area to attach the stone veneer to. I then used the outdoor mastic and so far so good. I was even able to slide my peel under the pizzas instead of using my "super peels".

I'll keep everyone posted if I have any trouble.


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