I have a granite island 54"x38" on a 30x24" base cabinet with 12" overhangs on 3 sides. The granite is a 1.25" thick slab and I am right on the fence of supported vs non-supported overhang from what I have read. I am considering adding some supports although I am alredy following the 2/3rds rule for cantilever 1.25" granite: 24" supported with a 12" overhang front to back and 30" supported with a 12" overhang side to side.
Per recommendations from a previous post, I will be securing the cabinet to a 2x4 box frame which is bolted to the floor to prevent tipping front to back.
The granite will sit on the 3/8" inch furniture board edges which were reinforced with some 3/8" plywood on the inside of the cabinet on 3 sides. The 3rd (back) side will have a finished plywood panel for another 3/8" inch of support. Due to the unbalanced overhang front to back, I planned to put a couple of L brackets on "3rd" side. These will be "hidden" and without gussets. Additionally,I thought of perhaps running 2 steel "strips" across to pick up the two side overhangs (as pictured) since there is no plywood top to the cabinet.
1. Are the steel flatbars required? Or is it overkill to have one or both as pictured?
2. Is 1/4" steel appropriate for the brackets and flatbars? or would there be enough rigidity and support in 1/8" thickness?
3. Does a 3" wide vs 2" wide flatbar provide any greater strength, or is it just surface area contacting the granite at that point
4. The flatbars would sit on the cabinet edges which would be notched out to allow the steel to fit flush (i.e. I hadn't planned on adding a plywood top to the cabinets since it wouldnt have any middle support... is this ok?
5. My plan was to have the 1/4 steel stop 2" short of the edge (so theyd remain hidden), i.e. supporting 10" of the 12" overhang? Would I be ok with supporting only 8" of the 12" overhang?
6. Will the 3/8" cab edge + 3/8" plywood (on part of three sides) as a perimeter edge provide enough of a gluing edge for the granite, or should I add plywood across the top?
Kal72 if it were mine I would install 3/4" ply onto the base. The 3/8" + 3/8" extra laminate is not much to hold the weight of the stone. If you did use 3/4" you could route out a groove in the bottom of the ply on the 54" direction to allow the flatbar to sit flush with the bottom of the ply on the sides. Then do the same on the top to allow the bar to sit flat against the stone the opposite direct to the 38" direction. But I would run the steel from side to side rather than just the 12" space as you are planning on doing on the long side. Decorative Corbels are also an option on the short side but will be visible and may restrict stool options.This message has been edited. Last edited by: redoverfarm,
I planned to install the plywood on the INSIDE of the cabinet as oppposed to the outside, so I wouldn't be covering up the factory-finished side panels. The cabinet has full width drawers so the plywood side panel is hardly visible but with the drawers I can't fit 3/4" ply on the inside without interfering with their operation. I could get 1/2" ply in there instead of the 3/8". Better perhaps?
I also re-read your response, and I am not clear what you are saying about the flat bar?
>"I would run the steel from side to side rather than just the 12" space as you are planning"
Are you suggesting running (a third) flatbar across the L brackets? Or are you suggesting running flatbar perpendicular to the direction I show in my picture?
With "beefed" up side edges, is there any need to put plywod ontop of the cabinet? Structurally, the cab sides will take all the load and I don't particularly want to raise the height of the island particularly since the edge of any plywood would be visible (particularly) on the side that has no overhang
This message has been edited. Last edited by: redoverfarm,
thank you so much for the response. It's crystal clear now. I was trying to avoid the plywood top but now I see what you mean about having steel on the underside and top of the plywood subtop- essentially criss-crossing the steel. The only remaining question is whether I should stick with the 2 long strips on the 54" length (as pictured) and get 2 or 3 strips for the 38" width (2 along edges and one in the middle)
My granite has no edge detail, so it won't conceal the plywood subtop, if I stop the plywood 1-2" from the edge of the granite it won't be so noticeable, but on the side with the drawers I would think the edge it would be very noticeable, perhaps I could bevel the edge to make it less so?
We've built islands like this many times and build them much like redoverfarm suggests. We usually cut the three sides of the cabinet away from the face down by 3/4" and install 3/4" birch plywood. Cut the plywood back several inches from the edge and laminate a birch strip to cover the plys. If the overhang is large enough, we'll route in a channel to hold some steel or do a double layer of plywood with steel laminated inside in channels. Steel and plywood are all joined with Gorilla glue.
For a 12" overhang, your steel should be enough, or one layer of plywood will be enough.
Jaybee: If I go with 1/4" steel without plywood and route a channel in the cabinet edge will it be rigid enough to extend not only for the overhang, but also to span the interior cabinet base of 30? Seems like I have some choice. The best thing about the plywood subtop with steel is that I can use steel in both directions and forget the L brackets. The bad part about the plywood subtop is the extra little bit of height and exposed plywood edge (particularly on the front side where you are opening a cutlery drawer.)This message has been edited. Last edited by: kal72,
Your 1/4" flat steel will be strong enough to support the top - provided you can keep it from flexing. To do this, you use the steel to support the top and the top to keep the steel from flexing.
Go ahead and cut 1/4" notches in the cabinet back and sides and if you have the ability, partial notches in the front. When you install the top, put silicon on top of the sides of the cabinet as well as the top of all the steel. This will bond the steel to the top and keep the steel from flexing across the width of the cabinet.
If you really want to make it strong you can get someone to weld all the steel so that it's on one plane (but frankly, this is a bit of overkill). Another way to avoid overlapping the steel yet keep things strong is to install the steel in a modified "W" pattern - where the steel pieces flair out from a central point near the front / middle part of the island cabinet with legs running out the sides, corners and middle.
Finally, I know you are liking the steel idea but don't discount doing this in plywood. With steel, you are still going to have 5 to 7 steel fingers visible underneath the top. Plywood can be stained the color of the cabinetry or painted a neutral color to match the underside of the granite. Plywood is easier to work with compared to steel. Plywood will give 100% support to the granite and plywood is probably cheaper - depending on your source for steel.
BTW - stock steel at places like Lowe's or HD is way overpriced. You can buy the same stuff at a steel fab shop for 1/10th the price.
The steel is much more hidden on the underside - 5 to 7, 1/4 " thick "fingers" vs 3/4 inch plywood running the perimeter of the island. I am worried about concealing that plywood since I don't have an edge on the granite that would conceal the 3/4 inch ply. I guess I could leave the plywood edge flush with the drawer side edge and paint the ply edge the cabinet color on that edge only. I could perhaps bevel or router the edge on the overhang sides and paint it the granite color.
The top of the top drawers instead of just clearing the underside of the island top would now be 3/4" below the counter top.
The difference is that you do not conceal the plywood - rather you trim it smooth and paint/stain it so that it's a decorative feature of the cabinet/ countertop combination. The plywood doesn't have to be flush or even close to the edge as you can make the plywood edge profile follow that of the granite top, just inset 4" to 6".
I'm not trying to talk you out of the steel as both plans will work for support. I've just done this many times and have found the plywood method to be cleaner looking from the bottom along with the other benefits mentioned above.
Kal here is what you can use on the edge of the ply. Just use a iron to activate the glue. Simple process. It comes in a multitude of colors and sizes. I am sure you can find something that either matches the granite or the wood cabinet shade. Remember it may not be an exact match but being it is under the edge and is shadowed I doubt you will be able to tell that it is not an exact match.
Thanks for the patience and all the responses. I really havent done anything like this before so I appreciate you explaining everything so well.
Plywood it is! Since I was planning on spending over $100 on two L brackets that are no longer required (http://www.federalbrace.com/Freedom_Hidden_Countertop_Brackets_ppsqo_VHV22927YTW_VHV119YTW_VHV6YTW_VHV22927YTW.aspx), I think I will put a few steel flatbars in routed channels in the plywood (got a quote from a metal fab shop -indeed much cheaper tha big box!
If I was concerned about the extra 3/4" of height of the counter top, in theory I imagine I could take 3/4 inch off the bottom of the cabinet base. Does anyone ever do that?
My cabinet is a painted antique white, I need to match the color and paint the back plywood panel and some base moulding, so I will paint the edge of the subtop and set it back 2-3 inches from the granite edge. On the front edge (where the granite overhang is only 1") the subtop edge will be more visible so thats where it would be good to use the banding, so that you dont see the end grain of the plywood. I assume I can install this banding after the fact if I dont like the look of the painted edge?
Should I route or bevel the 3 seating area edges of the plywood subtop so its smooth against the thighs? (yes I just said , "smooth against the thighs" in a DIY discussion board). I guess this would prevent me from using the edge banding on those sides unless the edge banding can attach to a slightly routed edge. I figure I could round the corners a bit too, even though the granite is "square".
Any finishing tips appreciated!
I love the idea of cutting the three sides down, I will do that. I can only cut down 3/8 inch until I reach the top of those corner cross brace pieces, but that would reduce the front-side exposure of the subtop to 3/8". Or can I just cut those corner supports off since the plywood top will provide the same if not better support?
Cut the corner supports off - as you say, once you install the plywood they are not doing anything anyway.
You can also add a small ledger to the front side to support the underside of the plywood at the front. It can't be a big ledger, but even a 3/4" x 3/4" glued in place will do the trick.This message has been edited. Last edited by: Jaybee,
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