Marble dining table help please

[Ollie McDottie]

Hello all. Hope you’re well.

Got a client who want a large table built using a slab of marble she has already for the top. Looking to seat about 8+ people. Legs/base to be built out of white oak.

Table top dimensions 40” x 96”.

My thinking is using a 8/4 white stock for a frame/apron with a a pair of lateral supports across about 30 inches inset from the ends of the apron. I will rabbet a channel on the inside of the apron and inlay thick pieces of mdf or plywood for more surface are for adhesive to attach marble top and further support the weight, which will be 200+ lbs.

She wants very simple legs only on the corners attached only at the top to the apron. Will this be enough to support the weight of the marble and apron? Can’t imagine the table will be lifted if ever moved, so will such an attachment allow for racking were the table dragged/slid?

Any other suggestions for leg attachment? Perhaps an X on the legs to still allow for chairs, improve stability and tie legs together for a more unified stucture, or is that not needed/overkill?

All insights/experience welcome and eagerly sought. Thanks in advance.

[Jamie Buxton]

You're right, a big question is racking when the table is dragged. So how tall are the aprons? The taller the aprons, the stronger that leg joint is.

[Jamie Buxton]

And how thick are the legs? If you just make square cross-section legs from the 8/4 stock, they'll be 1 3/4" square or so. That will look spindly on an eight-foot table. I'd be going for 3" or more.

[Ollie McDottie]

Not sure about height of apron. Waiting to hear back about the height of the seat top to i sure enough leg room underneath apron. And then I’d make the apron and high as possible without making it look weird. But I think even with a 3-4” apron it would be a risk, no?

As for legs, she wants L-shaped legs and wrap the corners. Probably make the legs about 3” on either side of the L.

Just give. The length and width of the table,
I’m not sure how those legs wouldn’t rack.

Has anybody made a table of this span and tabletop weight got some insights?

[John TenEyck]

A 200 lb top is not that heavy. I made a wood top table about that's 42 x 96" earlier this year that weighs about 150 lbs. I used 4-1/2" wide x 1-1/4" aprons, tenoned into the 3-1/2" square legs with inside braces. No bottom stretchers. It's rock solid.

https://lh3.googleusercontent.com/pw/AM-JKLWch1wMj9GxEN9nyCPHbCSwuHv_UVNuU0KzYxe0lVJWKbeKM U8Dd_wxOc3fsKPEsE8HAYMOuSwNUkXE9A57OWMcen3gyDVfctz 6RL36pS9hK9LubTUol2tjSV9otcqFZmgv5GFHLAwoISD2CRKmh Lnltw=w1094-h615-no?authuser=0

Two cross span braces connect the long aprons and are fit into dovetailed slots.

https://lh3.googleusercontent.com/pw/AM-JKLUQ4a_KV5XN4_ty3o7Lcty7xNyBdhbTJXKH3-P05T6Ktm4UL0J83ju1jUAoIOaZLxmgHCKolek0SxSCwmwp7Uld h0sx7oXb4JPi0NDVRQsJZW125chGJbNDMXxZ8IKWm2HY4rfQir FaRm2XxobsS-8a-g=w1094-h615-no?authuser=0

I'm not a fan of the L shaped legs your client wants. They look cheap to me. But if you have to use them I would add some solid blocking at the top to reinforce the leg to apron joints.

John

[johnny means]

A marble top that big will weigh several hundred pounds. Any sagging in the middle will lead to cracking. I would double or even triple up on the support length wise. Cross members will be much less helpful.

[Curt Putnam]

I have a ~ 48" x48"x1" coffee table and it weighs about 200 lbs. From experience, narble will get stained and need to be removed from the table for refinishing. Consider asking the client id she might not prefer an ogee or some other edge shape.

To move the table, it will have to be lifted. A top that heavy will tend to stay put as long as people do not try to hip check it to move it. Surface the top of the wood supports with non-slip material and that top will not move. YMWV

[Ollie McDottie]

A marble top that big will weigh several hundred pounds. Any sagging in the middle will lead to cracking. I would double or even triple up on the support length wise. Cross members will be much less helpful.

Really? I would think that the long arms of the apron would handle the sag. And the inset plywood would further mitigate sag as well as cupping while giving ample area for adhesive. The inside area of the apron will be completely flat and filled in with plywood between the cross members. I agree as much support as possible is needed, but how is length wise different from cross when it’s all going to end up flat top substructure?

[Ollie McDottie]

\
A 200 lb top is not that heavy. I made a wood top table about that's 42 x 96" earlier this year that weighs about 150 lbs. I used 4-1/2" wide x 1-1/4" aprons, tenoned into the 3-1/2" square legs with inside braces. No bottom stretchers. It's rock solid.

https://lh3.googleusercontent.com/pw/AM-JKLWch1wMj9GxEN9nyCPHbCSwuHv_UVNuU0KzYxe0lVJWKbeKM U8Dd_wxOc3fsKPEsE8HAYMOuSwNUkXE9A57OWMcen3gyDVfctz 6RL36pS9hK9LubTUol2tjSV9otcqFZmgv5GFHLAwoISD2CRKmh Lnltw=w1094-h615-no?authuser=0

Two cross span braces connect the long aprons and are fit into dovetailed slots.

https://lh3.googleusercontent.com/pw/AM-JKLUQ4a_KV5XN4_ty3o7Lcty7xNyBdhbTJXKH3-P05T6Ktm4UL0J83ju1jUAoIOaZLxmgHCKolek0SxSCwmwp7Uld h0sx7oXb4JPi0NDVRQsJZW125chGJbNDMXxZ8IKWm2HY4rfQir FaRm2XxobsS-8a-g=w1094-h615-no?authuser=0

I'm not a fan of the L shaped legs your client wants. They look cheap to me. But if you have to use them I would add some solid blocking at the top to reinforce the leg to apron joints.

John



This is great. Thank you.

Yeah, I’m not crazy about the L-shaped legs myself.

Here are pics of the piece she’s trying replicate. Interestingly, it appears to me, and I might just be seeing things, but it really does appear that in one of the pics, the table slightly sags in the middle. Likely just an optical illusion playing up on my anxiety about making this thing proper.

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[johnny means]

Really? I would think that the long arms of the apron would handle the sag. And the inset plywood would further mitigate sag as well as cupping while giving ample area for adhesive. The inside area of the apron will be completely flat and filled in with plywood between the cross members. I agree as much support as possible is needed, but how is length wise different from cross when it’s all going to end up flat top substructure?

Imagine a ladder suspended across a gap. You really wouldn't expect the rungs to flex a whole lot. The plywood substrate would actually add more flexion than it would prevent, seeing as how it wouldn't support it's own weight.

[Bill Dufour]

I would not glue the marble. This makes it easier to move and marble expands different then the wood which can cause cracking. If the top has no wood edge you my have to drill a few holes in the marble and use pegs to hold some cleats so it does not move too much.
Bill D

[Ollie McDottie]

Imagine a ladder suspended across a gap. You really wouldn't expect the rungs to flex a whole lot. The plywood substrate would actually add more flexion than it would prevent, seeing as how it wouldn't support it's own weight.


I see. Excellent analogy. Thank you.

So would you forgo the plywood altogether and use cleats to affix top as another person suggested?

[Gary Ragatz]

I would not glue the marble. This makes it easier to move and marble expands different then the wood which can cause cracking. If the top has no wood edge you my have to drill a few holes in the marble and use pegs to hold some cleats so it does not move too much.
Bill D

I think maybe a thick bead of silicone caulk all along the top of the aprons, allowed to set before the top is put in place would do the job without drilling. That amount of silicone-to-marble contact should prevent the top from sliding, while making it easy to remove if the table needs to be moved.

[John TenEyck]

Granite and marble countertops are attached to kitchen and bath cabinets with silicone and even rigid polyurethane adhesive. As Johnny said, make the aprons beefy and all will be well.

Now about those ugly L shaped legs .....

John

[Joe Jensen]

The key here is not the weight but that stone has zero tolerance for any flex. lean on that top and if there is any flex in the aprons it will crack. I have a desk with stone wing that we work on. Not heavy but I wanted to ensure it won't crack if someone sits on the edge. I ended up putting 8/4 oak planks about 8" wide behind the apron. My apron is only 2 3/4" high but it is only decorative. I looked at doing some steel but it would have had to be very heavy.

[Gary Ragatz]

Since the table is going to be fixed-length, you have lots of flexibility to strengthen the support structure. I think I'd make the aprons pretty thick (maybe 8/4) and create a lattice of solid stock with half-lap joints to span the aprons. Attach the lattice structure to the aprons with mortise/tenon or sliding dovetails. Should be no problem with the top racking

If you're going with the L-shaped legs, I'd take @Jon TenEyck's idea a step further and fill each of the corners with a good-sized triangle of solid stock the same depth as the aprons to provide some extra racking resistance for the legs.

[andrew whicker]

You could laminate carbon fiber (or steel, but that would require hardware) into the apron or apron / leg connection point.

[John TenEyck]

With that in mind maybe a torsion box would be the best approach. Light but very stiff.

John

[johnny means]

I see. Excellent analogy. Thank you.

So would you forgo the plywood altogether and use cleats to affix top as another person suggested?
A couple of dabs of silicone in some key spots is all that's necessary. as said earlier the mass of the top will do most of the work. I'm guessing a top this size would be in the 400 lb range. It really takes a lot to get that moving. I'm also assuming it never gets moved.

[Jamie Buxton]

OP is in Los Angeles -- earthquake country. Along the San Andreas, the major ground motion is usually horizontal.

[Don Stephan]

My suggestion would be first to pay a couple respected marble fabricators to specify how the top should be supported and attached.

If the customer already has the marble who is responsible for getting it on the tabletop and secured? If the marble top is glued to the table will it be possible to move the table out of the house and into another should the desire arise?

[Paul Bent]

Once the marble was positioned, I would silicone a few stops to the underside of the marble and butted (no silicone) against the inside of the framework. Top would be removeable and easy enough to cut off the silicone stops if needed to relocate.

[Curt Putnam]

A true torsion box would provide all the support you need and could be hidden behind decorative aprons. With a nonslip surface that slab will not move.

[Frank Pratt]

I'm not a fan of the L shaped legs your client wants. They look cheap to me. But if you have to use them I would add some solid blocking at the top to reinforce the leg to apron joints.

John

Yikes! I agree, they look really bad.

[Malcolm McLeod]

A marble top that big will weigh several hundred pounds. Any sagging in the middle will lead to cracking. I would double or even triple up on the support length wise. Cross members will be much less helpful.


Once the marble was positioned, I would silicone a few stops to the underside of the marble and butted (no silicone) against the inside of the framework. Top would be removeable and easy enough to cut off the silicone stops if needed to relocate.


A true torsion box would provide all the support you need and could be hidden behind decorative aprons. With a nonslip surface that slab will not move.

My folks did a USAF ~3yr tour in Germany; Italian visit yielded a set of green + black-veined Carrera marble slabs - including a coffee/cocktail-table sized piece. All are relatively thin IMO :: ~25mm. But all have survived to date; this involves their inclusion in several iterations of furniture thru many years.

Highlighted above are some key take-aways:
As surface area increases, the thickness 'ratio' drops for a given thickness and it will crack if not well supported. Lots of good advice above on healthy 'ladder' or torsion box frame. Didn't see it mentioned, but you might look at taller tapered 'keel' - parallel to side apron, but centered - out of range of knees. The tall keel has greater mass-moment of inertia = less flex.

Don't want a wood frame around the edge? My experience is that even smaller pieces (10x20") are heavy enough to stay in place with normal house-hold handling, so hot glue locating blocks to the slab that constrain movement. Just flip the top upside down, place the leg/frame, and glue the blocks touching the aprons, keel, etc. If you go with a torsion box, cut pockets in the top layer of the box to receive the glued-on blocks. Just lift the slab off the frame as needed. Blocks can also be removed easily and allow for re-purposing the slab (maybe a value-add selling point?).

Mr. McDottie might consider how the slab is transported as well. My folks kept the shipping crates in the attic thru several houses and many years; tops were pulled off furniture, individually crated, and shipped separate from the frames to their next house. The largest crate finally got trashed due to very limited storage space, so I just built a new crate to support a recent move. Again, maybe a value-add option?

[Malcolm McLeod]

Imagine a ladder suspended across a gap. You really wouldn't expect the rungs to flex a whole lot. The plywood substrate would actually add more flexion than it would prevent, seeing as how it wouldn't support it's own weight.

Recommend you not ignore the 'rungs' tho'! They serve to unify the rails. A point load gets spread across more of the structure. (In case it's not obvious;)) IMO ditch any plywood except as the top/bottom of a possible torsion box solution.

[Ollie McDottie]

With that in mind maybe a torsion box would be the best approach. Light but very stiff.

John


Thank you all for these excellent insights. Man, this community never lets me down.

So to sum up — no glue needed for top, just a thick bead of silicone on top of apron and/or members of torsion box, allowed to set before putting on the marble slab.

As for apron, looking at about 4” wide either 8/4 or 10/4 stock.

I like the idea of a torsion box. Would I build it out of the same stock at the apron/legs? White oak? That would be quite expensive, perhaps ash or poplar could work as well?

Instead of mortise and tenon, will dominoes suffice for connecting to apron? I’ve never made a torsion box, doesn’t seem terribly difficult, but any and all insights, as always supremely appreciated.

And I’m working on convincing client to go with 3-4” solid square columns for the legs instead of the l-shaped. If I can convince her that it more structurally sound, she will readily opt for it.

[Randall J Cox]

you might want to try and calculate the weight of that top if you know its thickness. I'm sure there are tables out there that give marble weight in cu inches or whatever. It has to be more than 200 lbs. I have a small coffee table with a marble top and the top alone is really heavy. Maybe 65 lbs.

[Prashun Patel]

Throwing this out there... would the client consider a seam in the center of the table for the marble? This will provide stress relief at the expense of aesthetics.

The taller you can make the long aprons, the better the resistance to flex. Shaker trestle tables are able to use quite thick lengthwise supports that are in the center of the table, so they aren't seen and don't interfere with the sitter's knees. This of course means you need a way to catch and transfer that load by the side assemblies vis-a-vis thicker aprons, closer spaced legs, or center supports.

To be honest, when I am in situations where flex is a threat and at odds with the aesthetics, I opt for low profile steel or iron supports. You can use angle irons or i bars or even flat bar stock mounted vertically. If the client will pay and weight is an issue, carbon fiber is an option - but I have not used this for a table, so cannot vouch.

[andrew whicker]

I agree. I Googled it and a 1.5" thick marble slab that is 40" x 96" is 530 lbs. 2" thick is 700 lbs.

[Adam Herman]

great advise.

I would also go with a construction similar to the picture posted earlier. my father and I built a large version of this about 6' x 12' for a model railroad setup. 1.75x 5.5 oak aprons, 5 in sq poplar legs with the corner braces and 3 lags per leg on the diagonal as shown. the top was lighter, but maybe not by much with all the 0-gauge trains, the bridge, buildings, transformers, etc. top was 3/4 baltic with 1x4 oak rails around the edge and a "rung" at each plywood joint. about 11 feet of span between the legs and no sag whatsoever. that table has been around about 20 years now and is still flat as ever, I think it may qualify for some kind of flatness spec like a surface plate.

I think you have a good plan even if the slab weighs more like 400 lbs. I would add a center "truss" of a slightly taller dimension, could be solid or a couple thicknesses of ply glued, and about 3 ladder rungs in the frame. no ply infill, not necessary and does not really add any structure. I think dominos would be great.
I/we often way overthink stuff like this.

[Ollie McDottie]

A big thanks to all of you for your insights. Started project yesterday. Will post pics in a week or two when it’s done. The kindness and helpfulness of the folks on this site never ceases to impress me. You all the best.

[Rob Burch]

I don't think the table I made is as big as the OP was thinking about. Mine has a top about 63" long and maybe 32 wide (intentionally narrow per the wife's instruction since our dining rom is smaller). The top is granite and it is simply "stuck down" with silicone
Frame is red oak.

It has been in service for 3 years with no issues and we have moved it around a few times. No sign of flexing and cracking.


https://i.postimg.cc/CKct3FJG/IMG-2505.jpg (https://postimg.cc/Z9yV3zGn)

https://i.postimg.cc/qRgY09Z9/IMG-2545.jpg (https://postimg.cc/1nhMrYSH)

https://i.postimg.cc/1tTdzJk4/IMG-2549.jpg (https://postimg.cc/1nGBCc5Z)

[Aiden Pettengill]

As someone working in the stone fabrication industry, the most important thing is making sure there is NO sag what so ever. Granite will flex some but marble is very brittle and will snap especially if its 2cm vs 3cm. Experience sucks!:D (I've broken my fair share of slabs!) Not really something you want when marble can run up to $180/sq ft for Calcutta Gold. Nice looking table Rob too!

[Rob Burch]

Thanks Aiden

My wife is pleased with it and she gets the only vote cast. It was the second piece that followed the beverage center you see behind the table.

You know how it goes.....built the beverage center and the minute it was installed..."I want a table to match".

This has now precipitated phase three which is a cabinet re-do. She was not happy with the timeline I was on so she want and had new granite (to match the table and the beverage center) and new backsplash tile. My part is new shaker style doors and a host of new drawers and slide out shelves followed by a re-painting of the cabinets. I am on the clock now.

My solution was different in that I would have started with a sledge hammer and ended up with all new stained wood cabinets. I lost that decision in a landslide on a 1-1 vote.

To the OP.....Did not mean to hijack your thread.

[Ollie McDottie]

As someone working in the stone fabrication industry, the most important thing is making sure there is NO sag what so ever. Granite will flex some but marble is very brittle and will snap especially if its 2cm vs 3cm. Experience sucks!:D (I've broken my fair share of slabs!) Not really something you want when marble can run up to $180/sq ft for Calcutta Gold. Nice looking table Rob too!

Thanks for this. When you say sag, do you mean in the middle or along the edge where the marble might overhang the inset apron by an inch or so? For the middle I'm building a torsion box of sorts to support the weight of the marble. Two supports running the length 12" apart with perpendicular lateral supports between them about every 21".

[Aiden Pettengill]

Thanks for this. When you say sag, do you mean in the middle or along the edge where the marble might overhang the inset apron by an inch or so? For the middle I'm building a torsion box of sorts to support the weight of the marble. Two supports running the length 12" apart with perpendicular lateral supports between them about every 21".

You want to be sure that the bracing and frame won't flex with the weight. From the sounds of it you should have plenty of bracing! So long as there isn't a high spot you should be good. Good luck and share pictures!
Aiden
ps. don't worry about the overhang! With 3cm or 1 1/4" thick stone (measurement systems vary depending on where the slab was cut) you usually can safely overhang 6" without support.

[Ollie McDottie]

A big thanks again to all who jumped on this thread with all of your excellent suggestions. Thought I'd share some pics of the base now that I've finished it. Again, so grateful to this forum and the insights of you fine folks who very much informed my construction. You all the best!!!



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[Tom Bender]

Ollie
You have built a nice ladder frame. It should provide enough support. Just a couple of concerns;

A torsion box would have protected the marble from twisting should the table be placed on an unflat floor or be lifted unevenly. I would not be comfortable with the risk you have created.

The leg to apron joints look suspicious. When the table is dragged those joints could fail catastrophically and crush the dragger.

I would follow advice given to adhere locator strips to the marble with hot melt or silicon.