"...a 24" x 24" marble inset within the wood"

"He had routed out the area where the marble was going to go in the maple"

"The marble will be permanently fixed in place in the wood."

The arrangement you're describing is problematic at best, regardless of who does the installation. Wood shrinks and expands with seasonal humidity changes, while the marble remains a constant size. I don't know what sort of fixative your guy was planning to use to 'permanently fix' the marble to the wood, but you can't use any rigid adhesive to attach a sheet of stone to butcherblock and expect it to stay adhered for long. The moisture content of interior woodwork typically fluctuates around 3% over the course of the year, in most areas. In hard maple this translates to as much as a 1/4" difference in size over a 24" wide area.

If you cut a recess that neatly fits the stone in the humid part of the year then that stone will prevent the wood from shrinking during the dry part of the year, which will in turn split the wood. If you fit the stone into the wood during the dry season then gaps will open up around the stone as the wood expands in humid weather.

You could, conceivably, cut the recess for the stone intentionally oversize and fill the joint with silicone caulk, but the caulk would be difficult to keep clean and have to be redone more frequently than you'd probably like.

What it comes down to is that I think your original plan is a bad one. You can recess a piece of marble into a butcherblock IF room is left for the wood to shrink and expand independently of the stone, and if the piece of stone is light enough to be easily and frequently lifted out of the recess so you can clean around it. With such a large piece of stone as you are using, it's just not going to be a happy situation. Blame it on the guy who's doing the work, for not steering you clear of these problems, if you like, but I would rethink the whole idea. I'd probably look for a small, independent area of countertop that can be made entirely out of marble.

It should be left loose and removeable. If it is bonded to the wood the marble will surely crack. The wood has already bowed once, if it continues to move with the marble affixed, there you go.
Maybe if it is attached via an isolation membrane such as Schluter Ditra it would not crack. How thick is the marble and the wood?
Casey

Many thanks for your responses--they are very, very helpful. In answers to your questions and to clarify a couple of things:

1. The wood is being reordered from John Boos since the first "slab" was so bowed. Hopefully the 2nd piece will be properly constructed to avoid that issue again.
2. The marble is 2 cm and the maple is 1-1/2 inches.
3. The countertop fabricator had told me he was planning on mounting the marble to "backer board" before he affixed it into his routed out area.--is that the same kind of thing as Schluter Ditra or is that something different?

I definitely don't want to leave it loose and removable--it's just too big of a piece of marble to clean very easily and then if God forbid it broke, I'd have a big recessed area in my wood that wouldn't look so great!

I got the idea from a kitchen magazine but I have no idea how it was affixed to the wood without causing a problem. I don't want the potential of it causing problems though with expansion and contraction of the wood, so maybe I should just let it be a great idea in a magazine and leave it at that :(

Ditra is a different sort of product from the backer board. "Backer board" is a loose enough term that I could easily guess wrong what he means by it. Ditra is intended for tile installations (for which I've used it a few times), and I doubt it would accommodate the amount of movement a butcherblock counter is prone to.

The fact that he's planning to attach this to a backer board makes me wonder whether I misunderstand what you're attempting. The marble, without any backer, is about half the thickness of the butcherblock. Are you recessing the stone just far enough that it's flush with the surface of the wood, or are you cutting a 24" square hole all the way through the butcherblock so that the marble is supported more directly by the cabinets? Is the recessed marble completely surrounded by butcherblock, or does the stone extend all the way to one side or corner of the island?

Hi Jon1270,

I can't thank you enough for helping me make sense of all this. Here are the answers to your questions:

1. What he did in the original piece of wood is cut the stone just far enough for the marble (and backer board) to fit in the hole and be flush with the surface of the wood. So the backer board would have essentially been adhered to the wood at the bottom of the "hole" he created.

2. Yes, the recessed marble would have been completely surrounded by butcherblock on all 4 sides.

Do these answers make the whole setup even more precarious in your mind?

Thanks for clarifying. "Backer board" often means a cement-based sheet product meant for mounting tile on, but he might just mean a piece of plywood. Either way, I'm not sure what purpose it would serve here. All of the problems with this idea stem from the fact that the butcherblock will expand and contract with the seasons while the marble remains a constant size. This means you can't glue the two together and expect them to stay stuck. You also can't fit stone tightly into a recess in the butcherblock and expect it to stay tightly fitted. Putting another rigid material such as plywood or tile backer between them doesn't change anything.

Gluing any rigid material, be it a backerboard or the stone itself, to the butcherblock over a large area is a bad idea. Period. The glue will come loose and/or the butcherblock will develop cracks to accommodate its inevitable shrinkage and expansion. For the stone to be completely surrounded by the wood, the recess MUST be oversized, leaving a gap along the two edges where the grain of the wood runs parallel to the edge of the stone. If it's an end-grain butcherblock then there must be a gap all the way around. Such a gap will rapidly collect debris (flour, bits of fudge, whatever), and water spilled across the countertop would sit in the groove as if it were a clogged gutter, get trapped under the stone, soak into the wood and probably do some damage. You could, as I mentioned earlier, make the hole oversize and fill the gap with a soft rubbery material (silicone caulk), but I think this could create maintenance issues that I wouldn't feel good about.

A simpler, less risky alternative to Plan A would be to cut the recess all the way over to one of the long edges of the countertop so that one of the marble's edges (nicely polished, of course) is visible, and just sit the stone there loose. A 24" square piece of 2cm marble should weigh something like 45 pounds, which is heavy enough that it won't slide out of its pocket accidentally but light enough to move for occasional cleaning underneath.

Simpler still is to install a normal butcherblock countertop and just leave the slab or marble sitting on top of it.

[begin rant] I should confess, though it's not directly relevant to the woodworking part of this, that I'm skeptical that marble is all that necessary for pastry making. I know it's useful for sticky confectionery stuff like fudge and caramel that starts out warm and needs to cool, but I've watched Julia Child roll out her pie dough on a floured wood counter, and I do it myself on a large wood cutting board. I Googled a bit to see if I could find a convincing explanation of why marble would be a superior surface, but I failed. The only explanation I found was that marble is supposed to be "cool," which, if true, would make sense in terms of not melting the fats you've cut into the dough -- but this claim is bunk unless you keep the stone in the refrigerator. Marble sitting out in the room is at room temperature, just like everything else. It feels cool because room temperature is typically lower than body temperature, its got a lot of mass and is a good thermal conductor so it can suck up a fair bit of body heat fairly quickly. For the same reasons, though, if you were a sentient slab of chilled pie dough, that slab of marble would actually feel warmer than a wood surface would because the marble would be warmer than you were, and would be able to rapidly conduct its heat into you. [/rant over]

jon1270,

Many, many thanks for all your help. I have actually decided to go with marble for the entire island now. Since the inset didn't make good sense structurally and I really love the look of marble more than the wood, I decided to take the plunge with it. I'm hoping Santa will bring me a nice maple cutting board for Christmas to use in the new kitchen on top of the marble :)

Someone should have called Boos to ask them. The answer probably would have been "you're on your own" but you would have had an answer. Maple can have major seasonal expansion and contraction, and cutting a big hole in the center only partway would have weakened the resistance to bowing, and possibly made it more likely to split.

I'm always skeptical to follow ideas from magazine shoots. They look pretty. Practical things don't always make for pretty photography. The marble island with a good cutting board or two is probably the right way to go.

Wow, this is an old post, but so still so helpful to me. Great thanks to the people who asked and answered. I have a question of the same ilk. I would like to install a wood countertop in my kitchen with an apron front sink that will be undermounted. I want a way to try to protect the wood around the sink right where it "meets" the sink. I envision the wood and the sink being flush to one another. I had fantasized about switching to marble as an inch or two perimeter, but the above explanations have educated me. How have others solved the problem of wood countertops where they meet the sink? I have one other question. I am still not 100% convinveed that I want the apron front look. I assume that I can take that sink (it is not the Kohler Whitehaven with the rounded overlay edges) and use it as a trafitional undermount with cabinet doors all the way up. How much space do I need in front and back of it? And if I wanted to change to an apron front view at some point would the apron be damaged from haivng been covered by the cabinet? Naturally I realize that the cabinet would have to changed if I one day went to the apron front look.