Granite Top Supports
Granite Top Supports TIPS
- Granite can crack if you bend it
- Plate steel is ideal but heavy
- Decorative thin cabinet will work
- Custom panel matching cabinets
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DEAR TIM: My husband and I are just about at the end of an arduous and stressful kitchen remodel. Originally in the planning phase, the general contractor said we didn’t need a support under a long peninsula countertop made with solid granite. Now the field construction manager feels very uncomfortable with the 50 inches of unsupported granite that spans between a cabinet and two decorative posts at the end of the peninsula. I like the clean look we have now with no supports. How would you solve this problem? What suggestions do you have? Linda H., Broomfield, CO
DEAR LINDA: I’d like to think that you’ve come to the right place for advice because I’m cross trained in a few disciplines that converge in this situation. I feel we can solve your conundrum and keep everyone happy. But with most things, there’s going to have to be some compromise.
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Geologist Builder Tim!
My college degree happens to be in geology and granite is by far my most favorite rock of all. I love everything about granite, most of all the varied colors and crystals you can get. Believe it or not, my house is built on what’s considered to be the most attractive rock in all of New England, the Meredith Porphyritic Granite.
This is the Meredith Porphyritic Granite next to my driveway. You can't see the huge orthoclase feldspar crystals in this wide view, but they're there! © 2016 Tim Carter
This stunning bedrock contains massive white feldspar crystals, some the size of giant cocktail shrimp, in a fine-grained black matrix. I have a huge block of this ledge exposed right next to my driveway.
I cut this rectangle using my diamond wet saw. It started out as a baseball-sized piece of the Meredith Porphyritic Granite. You can see the monster orthoclase feldspar crystals and the shiny mica too. © 2017 Tim Carter
Form vs Function
I’ve had discussions like yours with quite a few customers that focused on form versus function. That’s what we’re dealing with here. You mentioned that you’re attracted to the clean look of the current top with nothing underneath it. I respect that, but function is paramount in my mind.
My decades of job site experience cause me to look at situations like this differently. The vision I have in my head is not quite unlike the classic movie and play Scrooge where the main character gets to look into the future.
I see in your future a party at your house attended by quite a few teenagers and one of them decides to sit on the countertop at the center of the unsupported span! I also see some painter standing on the top because he’s too lazy to move his ladder. Both visions end up with large chunks of granite on your gorgeous hardwood kitchen floor.
This granite top is doomed for failure the moment someone decides to sit on it unless a support is put underneath it. © 2016 Linda Hewing Perpetual license to publish it granted to Tim Carter - AsktheBuilder.com by Linda
Granite is Strong One Way
You probably think that granite is extremely strong, after all, it’s granite! Just about every stone product, including artificial stone like concrete, is very strong in compression. This means if you squeeze it it requires thousands of pounds of force per square inch to cause a crack.
While your granite has great compressive strength, it’s very weak in tension. Tension is the opposite of compression. A stone is subjected to tension when it’s stretched. If you were to load the center of your granite peninsula countertop right now with a given amount of weight, the bottom of the granite starts to stretch or pull apart.
While I can’t say exactly what the tensile strength of your granite top is for its current thickness, it’s usually only ten percent of what it exhibits in compression. The bottom line is that your granite top could crack and tumble to the kitchen floor with as little as 100 or 150 pounds that’s loaded at the center of the 50-inch span.
Here's another view of Linda's countertop. That's a wide expanse of unsupported granite. How many pounds of weight loaded in the center do you feel it will take to crack the top? Enter your guess in the comments below. ©2016 Linda Hewing - Perpetual license to publish it granted to Tim Carter - AsktheBuilder.com by Linda
Repair Scenario?
I often talked to my customers about cost. What would it cost to replace a broken countertop? Would it be possible a year or two down the road to get a matching piece of granite? Remember, granite is a natural product and the colors, crystal structure, etc. can vary in the quarry. You may not even be able to get a matching slab six months from now much less two years from now.
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I feel you need to install a support that runs down the center of the peninsula. It can be very narrow and provide the necessary bracing to prevent failure when someone loads the center of the top.
Support Options
Here are a few options that popped into my mind. I’m sure that a kitchen designer might have some additional ideas swirling about in her/his head.
You can purchase a thin sheet, no more than 1/8-inch thick, of plate steel that would be epoxied to the underside of the granite. It should really rest on the cabinet and the two legs supporting the granite. The steel doesn't have to extend to the edge of the granite top. It can be just 18 inches wide and do the job. After it's installed and the epoxy is cured, paint it a color that's close to the primary color of the top - or just flat black.
Tingler Trick?
A more complex solution was suggested by a friend of mine, Robert Tingler. He thought it could be a good idea to install a small steel beam down the center of the underside of the granite. It needs support at each end and it likely may be visible. This is my least-favorite option not because it won't work, but it's hard to incorporate into the cabinet and the two post supports at the end of the peninsula.
Nagler's Notion
Tim Nagler happened across this column after it was published. Here's how he'd solve the problem. "To keep the open look (your suggestions did not do this) why not support the top with two steel angles running parallel to the length. A 1" x 1 1/2" angle would be invisible to someone over 5'-0" tall if the angle were back as little as six inches from the edge."
The simplest idea is to have a custom panel made that’s about an inch or so thick that matches the look of the two end posts at the corners of the peninsula. I see from the photo you provided there’s a recessed flat area in between the thicker material at the corners. This would provide you with the maximum space under the top in case you thought about putting low stools at the counter.
If you’re willing to give up a little more legroom space you can have a thin cabinet made that has glass doors on both sides. I see in your one photo that the cabinet facing your front door has glass doors so that you can see what’s in the cabinet. You might display decorative items in this narrow cabinet under the granite. With glass on both sides you’ll be able to see through and it would help preserve that clean look you like.
You might also have a narrow open bookcase installed under the granite. Many books are just six or eight inches deep and this would not take up too much space. The bookcase wouldn’t have to be packed full of cookbooks and if you do this, once again, there will be open space that helps satisfy your desire to keep the look sleek and simple.
You’ll not lose a moment of sleep once you have support under that granite. My vote, in case it counts, is to go with the thin cabinet with the glass doors. I’d put a bunch of my colorful granite rock samples in it!
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Column 1175
100 pounds could crack the granite
Since the openness of the space under the granite is important to the homeowner, could you just put a 2 x 4 down the center of the granite, ending at a cross piece between the two legs? This construction would be nearly invisible unless your line of sight was below the level of the granite countertop.
modulus of elasticity is MUCH higher in the granite than the 2x4. Therefore, the granite will carry all the load until it cracks, then the 2x4 will carry load. Won't work. The center needs to be supported with something very rigid, like a stainless pillar going to the floor.
Another strong but shallow support system could consist of something like 3x3 steel angles run from the inside corners of the two posts to the end of the cabinet. If inset from the edge by the width of the posts and painted black to match the countertop color, I think they would be quite unobtrusive and stronger and stiffer than wooden supports.
How about a black painted steel I-beam or 2 glued to the bottom of the slab? Maybe only 1" or 1.5" might do the trick & be virtually invisible?
I like Tim's suggestion about the smaller end cabinet with glass doors. While the countertop appears balanced (viewing) on the kitchen side, it looks awkward (in the photo) from the living area.
Adding the extra cabinet space would bring balance to the space on both sides as well as form and functionality. If necessary, additional steel/iron plates could be added under the granite slab to reinforce it - although I would still never suggest someone (except a cat maybe) sit or stand on the granite slab for anything.
I have addressed this problem of and unsupported granite slab counter top by using a 1/8 to 3/16 inch steel plate (depend on span length) that spans from the cabinet to the support legs and the full width. This thin steel plate can be painted make it a little narrow than the slab and it will not be seen and will more than take the possible load applied to the counter top
First off, I am surprised that the Granite installer did it that way! Was there a warranty givin? And second off, myself, personally, I would have fired the kitchen designer for doing such a bad design! Just my 2 cents here!
3 inch channel with 1x4 hiding it painted same color as legs would support and look pleasing to thr eye as well.
275 pounds static weight and I agree with response #8 from "Bill".
I'd rather have cabinets underneath it anyways....this way it is ugly.....and a person can always use cabinet space....wish I had more....and I love the Granite.....don't have it, because they would never put it in apts.when they build apts. for Seniors, they put the cheapest things in them that they can and charge us big rent......wish I had kept my house now.....but not in the area where I lived tho......reason for moving.....they wouldn't even give us a dishwasher....said Seniors don't need them, when I asked the mgr.....ticked me off.....how rude.....
The "clean lines" don't work aesthetically, because it doesn't work structurally. Form follows function. One of the most basic tenants of architecture. Classical forms were generated and fine tuned over centuries and have become empirically pleasing to the eye as a result.
If this were purely modern in detail and material, many more options are opened up. But because this is based in a Craftsman or Shaker style, the forms need to follow that style. It would look more pleasing and correct, and in turn, more structurally sound, with more structure underneath, with profiles proportioned and scaled properly, while allowing for internal structure.
The posts at the end are too bulking, visually, against the slenderness of the granite. They are also placed at the very end, which looks odd. I'd be happy to generate some visual alternatives, but I'd imagine this has long since been solved.
Thank you. This is very helpful. Would the same be true of a quartz peninsula, or is quartz harder than granite?
Maybe. Quartz is one of the primary minerals in granite. Check with the manufacturer.