# Is a full sub top needed for granite?



## Wendel17 (Apr 20, 2009)

Hey all. A friend of mine asked me to do a bathroom vanety for him and he's getting a top done for it. It'll be 70"x30"x24".

It's going to have two door cabinets on either side under the sinks, and a bank of drawers in the middle. I'm still in the design stage, so I'm thinking of doing three sections.

My question is do I need a full sub top? Or would 3 or 4" supports front and back be strong enough? This would leave clearance for the sinks...but since I've never really worked with granite, I'm worried it may not be enough.


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## Pirate (Jul 23, 2009)

My bil, who has a big granite shop, told me, to put a plywood "sub top" on the cabinets, before the granite.


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## knotscott (Nov 8, 2007)

Full support is a sure bet.


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## Wendel17 (Apr 20, 2009)

Thanks for the replies. I was leaning that way, but I'm glad I can come here for some decent advice


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## J Thomas (Aug 14, 2012)

Dittos on the full top!! Granite tops are heavy as hell & expensive to replace if you get a crack in it. 
I'd over frame the support structure in good shape.
Look at it as cheap insurance!!
Best luck with it.
..Jon..


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## Wendel17 (Apr 20, 2009)

J Thomas said:


> Dittos on the full top!! Granite tops are heavy as hell & expensive to replace if you get a crack in it.
> I'd over frame the support structure in good shape.
> Look at it as cheap insurance!!
> Best luck with it.
> ..Jon..


Thanks. I'm planning on rabbets all the way around the tops of the cabinets to hide my fasteners anyways, and I,m thinking this will take the weight as well. 

From the scetch my buddy gave me, it looks like there's 1 1/2" x 1 1/2" solid on the corners and fronts of the dividers so I'll probably double up the gables in the middle.

I'll try and post some pics soon so it's easier to see.


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## Steve Neul (Sep 2, 2011)

The weight of a granite top is going to be supported around the parameter of the cabinet. Having plywood floating in the center is going to do very little. The only benefit of having a subtop is keeping the granite people from dripping epoxy on the inside of the cabinet. 

Off the subject, if your neighbor has soft close drawer guides for the drawers in the cabinet, I would remove the hardware before the granite people cut the sink hole. The granite dust will reek havoc on soft close drawer guides.


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## cabinetman (Jul 5, 2007)

I *always* use ¾" plywood under granite, marble, and solid surface composites like Corian. While those are fairly robust, they can crack. I have two methods for using plywood. If the top is going to be a single layer with no build up edge, I'll cut the plywood to be an inset arrangement where the top of the plywood ends up flush with the top of the ends and the front rail/faceframe. The granite can then just be laid on some tabs of Polysemseal adhesive caulk.

If the top has a build up edge, I make the plywood the exact size of the outer edge of the cabinet. Then the top can sit over the plywood and the front edge will cover the plywood edge.

There are several reasons for using plywood.

*Reason #1:* If the plywood is cut properly and square, when installed it will square the cabinet.

*Reason #2:* The piece of plywood can be used as a pattern template by drawing the cabinet below it in detail, i.e., the ends, the front rail, and the back and the recess, and the rabbet the back sits into. Once drawn out, and the cabinet is assembled, it should fit the drawing perfectly.

*Reason #3:* In making the plywood temolate, any holes like for faucet assemblies, or the sink hole can be made. Then the plywood can be sent to the granite shop as a pattern to cut the holes. Notes should be made right on the top pointing to the edges where the granite will align itself on the plywood. The granite will be larger than the plywood, so indications where, how much, and which direction the overages will be. If there will be a build up edge, I allow a small gap, like ⅛" for some wiggle room between the back edge of the granite edge and the face of the cabinet, for alignment.

*Reason #4:* Having a plywood template gives you a support to transport the granite safely.









 







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## Dave66 (Apr 6, 2012)

I would make that vanity in sections with dust frames at the top of each section. The dust frames in the sink section(s) would be sized to allow installation of the sink(s) and faucets.

When the sections are in place, I glue and screw a 1/2" ply top over the whole thing covering the perimeter to stiffen the whole assembly. If the granite gets a built up front edge, that will cover the edge of the ply. If it doesn't, I make a trim piece that will go on after the top is installed.


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## Wendel17 (Apr 20, 2009)

I love this forum! So many good ideas! I knew I could count on you guys..

Cabinetman: I never even thought of using the sub top as a means for transport. Thanks very much. 

Dave66: I'm not quite sure what you mean by dust frames. Maybe I know it as something else? I'm curious now.


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## TylerJones (Dec 4, 2011)

I guess I'm in the minority here with Steve, the plywood really isn't going to do much except make the cabinets look cheap if you can see the exposed edge. If not then all you've done is wasted time and materials. A well built cabinet forms a grid of vertical panels to support the granite, a big piece of ply laid on top doesn't add any load bearing capacity. IMO if the box isn't square after you have attached the back and the face frame, you have bigger issues than worrying about a plywood sub-top. Lastly, I have to wonder if the solid ply under the granite wouldn't be asking for moisture/mold issues.


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## ryan50hrl (Jun 30, 2012)

I agree there's no need for a solid piece. Run stringers front to back on edge in a few places and call it a day.


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## Leo G (Oct 16, 2006)

None of my kitchen cabinets or vanities every had a plywood top and the granite people have never questioned or asked for one. Most of the granite that gets installed here is 3cm (1 3/16") and is tough stuff. If you have an overhang up to 10" they won't ask for support. But beyond 10" they ask for brackets or corbels to support the overhang weight. 

Never had a problem with a top. The perimeter is the supporting structure and it generally goes to the floor.


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## Steve Neul (Sep 2, 2011)

TylerJones said:


> I guess I'm in the minority here with Steve, the plywood really isn't going to do much except make the cabinets look cheap if you can see the exposed edge. If not then all you've done is wasted time and materials. A well built cabinet forms a grid of vertical panels to support the granite, a big piece of ply laid on top doesn't add any load bearing capacity. IMO if the box isn't square after you have attached the back and the face frame, you have bigger issues than worrying about a plywood sub-top. Lastly, I have to wonder if the solid ply under the granite wouldn't be asking for moisture/mold issues.


 When formica countertops became unfashionable I started subcontract the granite work. Each time I change granite companies they tell me they prefer not to have a sub-top so that is what I give them. Any company I've ever used has installed the counter top without the sink hole and cut it in the house on the cabinet to make sure they had it in the correct position.


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## cabinetman (Jul 5, 2007)

Steve Neul said:


> When formica countertops became unfashionable I started subcontract the granite work. Each time I change granite companies they tell me they prefer not to have a sub-top so that is what I give them. Any company I've ever used has installed the counter top without the sink hole and cut it in the house on the cabinet to make sure they had it in the correct position.


Maybe they didn't trust your templates.









 







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## Steve Neul (Sep 2, 2011)

cabinetman said:


> Maybe they didn't trust your templates.
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Any fabricator worth a grain of salt wouldn't trust anybodies templates other then their own. I wouldn't trust anyone else’s templates or even measurements for my work. It goes beyond templates though. A sink hole takes so much material out of the center of counter top I wouldn't carry a Formica top with a sink hole already cut. It's too easy to break.


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## cabinetman (Jul 5, 2007)

Steve Neul said:


> Any fabricator worth a grain of salt wouldn't trust anybodies templates other then their own. I wouldn't trust anyone else’s templates or even measurements for my work. It goes beyond templates though. A sink hole takes so much material out of the center of counter top I wouldn't carry a Formica top with a sink hole already cut. It's too easy to break.


I trust my templates. It can get transported on the template...it will be lighter too.:laughing:









 







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## Steve Neul (Sep 2, 2011)

cabinetman said:


> I trust my templates. It can get transported on the template...it will be lighter too.:laughing:
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I just can't picture carrying a granite counter top with the sink hole cut in it to a jobsite even crated and get it out and set in on the cabinet without breaking it. I get cold chills just thinking about it. :laughing: I do though trust my own templates too.


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## cabinetman (Jul 5, 2007)

Steve Neul said:


> I just can't picture carrying a granite counter top with the sink hole cut in it to a jobsite even crated and get it out and set in on the cabinet without breaking it. I get cold chills just thinking about it. :laughing: I do though trust my own templates too.


Nothing gives me cold chills.











 







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## Trav (May 30, 2011)

I vote no solid tops as well. When I get to a job it is rare that the cabinets are level front to back and side to side. I think it is just a difference in tolerances. What is level to the cabinet install crew is not always what I consider level. I like the eggs to stay on the counter. So if your solid top is not level the granite will get shimmed. You don't fully glue the top down so the granite is still not supported anywhere except where it makes contact. Most natural stone tops can take very little deflection without breaking it varies by the type of stone, but in all cases that I know of it is less than what 3/4 plywood top would move if I push firmly down on it. Properly installed natural stone tops will be perfectly fine without the solid top. The only thing that should break it is abuse. So hey electrician use a ladder not my top to hang that light! ;^)


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## firehawkmph (Apr 26, 2008)

Steve Neul said:


> I just can't picture carrying a granite counter top with the sink hole cut in it to a jobsite even crated and get it out and set in on the cabinet without breaking it. I get cold chills just thinking about it. :laughing: I do though trust my own templates too.


Hey Steve,
I install a lot of kitchen and bath cabinets. We have a local,well established granit shop do our granite tops. I had them make me a top for a 5' vanity for my own house and cut the sink hole. I took it home in my van, up on edge during transport. I carried it in myself and set it in place with no problems. I will admit, it was a bit heavy.
Mike Hawkins


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## Leo G (Oct 16, 2006)

Ttharp said:


> I vote no solid tops as well. When I get to a job it is rare that the cabinets are level front to back and side to side. I think it is just a difference in tolerances. What is level to the cabinet install crew is not always what I consider level. I like the eggs to stay on the counter. So if your solid top is not level the granite will get shimmed. You don't fully glue the top down so the granite is still not supported anywhere except where it makes contact. Most natural stone tops can take very little deflection without breaking it varies by the type of stone, but in all cases that I know of it is less than what 3/4 plywood top would move if I push firmly down on it. Properly installed natural stone tops will be perfectly fine without the solid top. The only thing that should break it is abuse. So hey electrician use a ladder not my top to hang that light! ;^)


Countertop guys love me. Straight, flat, true, level and in plane for all connecting cabinets. The last countertop guy stayed a bit after he was done to make sure that I knew that he was impressed with the cabinet install. I was kind of flabbergasted that he was impressed. I just figured that installing cabinets you need to know that they need to be level and in plane. He says hardly ever does he find a job that he isn't putting shims on the cabinets and leaving gaps between because the cabinets aren't true.


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## Dave66 (Apr 6, 2012)

> I'm not quite sure what you mean by dust frames


Dust frames are simply rectangles that fit in the rabbets at the top of the cabinet carcass. I make them from 3" strips of scrap ply, join them with pocket screws and put them in. They cut down on the cab weight, save a bit of material, and give me easy access to screw the back to the wall.


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## Wendel17 (Apr 20, 2009)

Dave66 said:


> Dust frames are simply rectangles that fit in the rabbets at the top of the cabinet carcass. I make them from 3" strips of scrap ply, join them with pocket screws and put them in. They cut down on the cab weight, save a bit of material, and give me easy access to screw the back to the wall.


Jeez...now i feel stupid :'( 
I know what you mean now. This is how I usually do my cabinets as well. I've done this instead of a full back for sink cabinets as well to give room for plumbing. Saves me from cutting holes in the back, but still leaves something to screw to the wall.


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## Wendel17 (Apr 20, 2009)

Ttharp said:


> I vote no solid tops as well. When I get to a job it is rare that the cabinets are level front to back and side to side. I think it is just a difference in tolerances. What is level to the cabinet install crew is not always what I consider level. I like the eggs to stay on the counter. So if your solid top is not level the granite will get shimmed. You don't fully glue the top down so the granite is still not supported anywhere except where it makes contact. Most natural stone tops can take very little deflection without breaking it varies by the type of stone, but in all cases that I know of it is less than what 3/4 plywood top would move if I push firmly down on it. Properly installed natural stone tops will be perfectly fine without the solid top. The only thing that should break it is abuse. So hey electrician use a ladder not my top to hang that light! ;^)


I've always assumed a level cabinet was a must..if the cabinet itself is not level, to me that means something's not square. Floors are a different story. I've always levelled my cabinets before the top goes on.


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## cabinetman (Jul 5, 2007)

Danno said:


> I've always assumed a level cabinet was a must..if the cabinet itself is not level, to me that means something's not square.


The cabinet could be square but not level.









 







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## Wendel17 (Apr 20, 2009)

cabinetman said:


> The cabinet could be square but not level.
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That's what I mean...you would build the cabinet square and level it to the space, no?


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## cabinetman (Jul 5, 2007)

Danno said:


> That's what I mean...you would build the cabinet square and level it to the space, no?


Yep...that's the method. It can be done by having a loose toe kick, which would in essence be a framework, like an enclosed ladder. That frame can be leveled with shims and the cabinet box will sit on top. If need be aditional leveling can be by shimming between the toe kick and the cabinet.

Or if there is a fixed toe kick, or no toe kick per se, to shim under the cabinet to get it level.









 







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## Wendel17 (Apr 20, 2009)

cabinetman said:


> Yep...that's the method. It can be done by having a loose toe kick, which would in essence be a framework, like an enclosed ladder. That frame can be leveled with shims and the cabinet box will sit on top. If need be aditional leveling can be by shimming between the toe kick and the cabinet.
> 
> Or if there is a fixed toe kick, or no toe kick per se, to shim under the cabinet to get it level.
> 
> ...


I did the loose kick in my kitchen. It sure looks nicer to have it all flush to the floors.


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## cabinetman (Jul 5, 2007)

Danno said:


> I did the loose kick in my kitchen. It sure looks nicer to have it all flush to the floors.


It could be if the toe kick was left a bit tall/high, and was scribed to the floor to level the cabinet.









 







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## Wendel17 (Apr 20, 2009)

cabinetman said:


> It could be if the toe kick was left a bit tall/high, and was scribed to the floor to level the cabinet.
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Yep. Exactly what I did ;-)


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## Dave66 (Apr 6, 2012)

> you would build the cabinet square and level it to the space, no?


Absolutely. The "target" height of the base cabinets countertop is 36". I make my base carcasses 31" high and use a 4" ladder-type framework to get the toe kick. The 1/2" ply and 1/2" thick countertop bring things to 36".

During installation, I find the high spot in the floor and snap level lines at 4" and 36". I make the ladder on site and level it to the lower line as well as square it with the flooring. Screws, nails, glue and shims hold everything in place. Getting a ladder level and square is far easier than wrestling with a bunch of cab bases. When the ladder is in, I can just sit the bases in place and screw them together and into the wall. The upper line gives me a second check on the height.

Working from the high spot is the key to a good job. Starting anywhere else will turn into a colossal PITA! - lol

When the bases are in, 1/2" ply goes on and the countertop folks make their templates.

At final trimout, the toekicks get covered with whatever is being used for a baseboard. If it's a tile floor, the tile guy does it. If it's a wood floor, I'll rip strips of the flooring to make the base.


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## Pirate (Jul 23, 2009)

Steve Neul said:


> I just can't picture carrying a granite counter top with the sink hole cut in it to a jobsite even crated and get it out and set in on the cabinet without breaking it. I get cold chills just thinking about it. :laughing: I do though trust my own templates too.



My bil made 2 small countertops for us. 1 was with a double kitchen sink cut out. There was only 5" on 1 side of the cutout, and 6" on the other side.

Both tops were transported 2800 miles in a travel trailer, by my fil, to our house, and installed, by me (no granite experience) with no issues. 
Lucky I guess!


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## Steve Neul (Sep 2, 2011)

Pirate said:


> My bil made 2 small countertops for us. 1 was with a double kitchen sink cut out. There was only 5" on 1 side of the cutout, and 6" on the other side.
> 
> Both tops were transported 2800 miles in a travel trailer, by my fil, to our house, and installed, by me (no granite experience) with no issues.
> Lucky I guess!


 Well a granite counter top is expensive and in a kitchen the tops are often 8' to 10' long. With a sink cutout there normally isn't but a couple of inches at from and back and is easily broken. It's just safer to cut the sink hole after being glued to the cabinet.


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