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.



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



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?

[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

[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.

[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.

[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?

[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.