The single most important aspect (out of many very important aspects) of a marble topped vanity is the seemingly simple responsibility of the vanity to provide a rigid support structure for the marble top. Without the necessary support structure, the heavy marble top will not be adequately supported and may crack under its own weight.

In the stone and tile world the amount of give allowed under a piece of stone is called deflection. And when you're using a natural stone product, your deflection is only allowed to be L/720 (complicated calculation of dead load + live load and the amount of allowed flex), lest you risk some cracking.

This need for minimal deflection has been a major challenge in our quest to convert an antique store find into a suitable vanity for our bathroom.

This is the point in a project where I get into my own head. I essentially cripple myself with thoughts on how I can make this work. Rather than jumping in and trying things out, I make excuses for why I shouldn't work on the project and instead obsess about how to properly accomplish what I need to accomplish.

This is my process, no matter how infuriating and counter productive it tends to be. It insights fury and threats of "hiring someone to just get the damn thing done" from my better half, and side-eye skepticism from the pets in our home. The thing is, as inconvenient and ridiculous as it is, this is my hideous personality and it seems to work for me. Ugh.

After sufficient deliberation in the vacant corners of my brain where I often become all too distracted by the dust bunnies and tumbleweed ideas I uncover (I haven't built that automatic door opener for the bedroom yet, maybe I should do that first), I came up with an adequate solution for support that should alter the structure of the vanity to offer sufficient support for our future marble top.

It's difficult to see the issues from the earlier photos, but there are issues with this vanity that makes this a difficult proposition right from the start. If you'll notice, the weight of the buffet top is carried across the width by that single small center support piece. Well, that support doesn't really offer any support at all. It's too small, it's actually cut too short, and the lower horizontal piece has warped down over the years. Any support it once offered is long gone. Add to it that the actual weight would be carried out to the sides of the center drawers (in the lower section of the vanity), and you've got yourself a nearly impossible engineering problem given the current set up.

Once I started to take apart the whole thing I noticed other issues. The pieces to support the front and back are undersized and give a lot when placed under pressure. There are also essentially no center support elements. Pretty much the only thing holding any top in place are actually the four small corner posts. Given that the vanity's unsupported span is about 48", and we want to put two sinks in the marble, we'd surely be looking at cracks as soon as we set our toothbrushes down on the beautiful vanity top for the first time.

To resolve these issues I first had to start by taking things apart. At this point I've realized that almost every project I ever begin will typically "start by taking things apart." It's now part of my DNA, similar to the fact that I will always need to breathe air, over analyze every situation, and perpetually piss off my wife with projects that take years to complete because I always have to "start by taking things apart." Cheers.

I removed both the back and front support pieces of the cabinet so I could get better access to the interior structure. Once removed I used a tried and true trick of up-cycle renovators that has been an old standby since the earliest civilizations, I added a bunch of wood to it.

Don't believe me? Do poke around in the ancient pyramids of Giza. I guarantee that one of the ancient Egyptians, whose job it was to get one of those giant stones all of the way to the top of that damn pyramid, got it all of the way up there only to realize that it was just a bit too small. Do you think he took that stone all of the way back down? No, he didn't, because that's ridiculous. Instead, he probably got someone to bring a piece of pallet wood or some other scrap up there is shoved it into place, then made some snide comment like "Who cares? The Pharaoh will never know this is here. Besides, do you really think this house will be standing in 100 years? No way."

Sorry, I drifted there for a second. Got caught up in one of those dusty brain corners.

I started with a large 1x8 length of poplar that I screwed and glued to the back of the vanity, anchoring it into the legs that do much of the "heavy lift support" of the whole thing. This also allowed me to ensure the whole vanity was square. A byproduct of the fact it was all built with nails, glue, and rail and stile joinery, meant that the whole thing was a bit wobbly. This addition of structure for the upper support has also meant that we'll be fixing the wobbly.

Once the back piece was applied we were in much better shape already. The length and size of the piece of poplar meant that we'll have nearly sufficient support along the whole back of the piece of marble, especially in the critical weak areas in the middle of the sinks.

The next focus of my efforts were on the sides. The rail and stiles had already failed a bit here as the glue had aged, so there was a little bit too much give in the sides. using the same 1x8" popular I ripped it down a bit and glued & screwed them to the front and back support legs, then also glued & screwed them to the new back support piece. Once these two pieces were in we were looking really good!

Next up, I had to focus on the front support element, which was actually one of the main reasons for my obsessive delay on this project. The buffet had two upper drawers, but we will be putting in two undermount sinks and drastically reducing the capacity of those upper drawers.

Having lived in our narrow and storage-light house for some 11 plus years, the thought of losing out on potential storage is one of those things that makes my spouse's eye twitch as she slowly loses control and bursts into a mixture of tears and volcanic rage. To say she appreciates storage is a bit of an understatement. And my suggestion that we'd need to get rid of those two upper drawers in exchange for the support necessary to keep our marble topped vanity from crumbling beneath the weight of her hairdryer was met with something slightly less than enthusiasm. In fact, I believe she said something like "Not an option," "Nope," or just a blank stare that began to turn me to stone. Really, we can just assume any one of those realistic responses actually happened and move on.

Rather than face the wrath of Mecha-Wendy, I devised a plan to sure up the front of our set up but allowing us to maintain some minor lean out type drawer assembly for things like tooth brushes and other small items.

Like the back, I began by screwing a piece of 1x2" poplar as a horizontal element. This is also the demarkation for the front of the sink once all will be said and done. Though in improvement, this small piece of lumber isn't nearly enough to offer sufficient support, so there was still a lot to be done.

I then ripped down the original front piece of lumber that I had removed from the front of the buffet. I made it fit in the gap between the front and the new piece of wood, glued, and then screwed through from the back of the new piece. This did quite a bit to stiffen up the wood.

We were getting closer, but the main thing I noticed was the lack of any center support. If I could add some center support items it would likely be enough to solidly support the marble by both supporting the center of the stone and making the front piece of wood more rigid. One final thing I wanted to do was to make this center support rest not on the unsupported lower section of the upper buffet drawer, but instead distribute the weight out onto the sides of the drawer supports.

To accomplish this I ripped a center piece of wood to the height I'd need, then notched it in several places to accept the cross support pieces.

I also grabbed a piece of 4/4 material (actual 1" thickness) and cut it just long enough to span the two lower support areas. This piece of wood will act as the bridge piece that will distribute any weight brought down through the center piece out to the supporting pieces. Those supporting pieces then transfer weight down to the base of the cabinet and into the ground. Essentially, I created a carry beam where any weight of the stone will ultimately travel.

The final piece I had to apply was the center facia component. The original piece was never the right size, as I believe it was actually cut short, and didn't quite fit right. This didn't look terrible when it was stained, but once the piece is painted, the gaps and change in size would have stood out. I took a new piece of wood and cut it to the same width as the old. 

Then, measuring carefully, I cut it to the correct height.

Then I cut a dado in the back of that piece so I could apply it to the center piece in a glued up and sturdy manner. I had also cut some pocket holes in the center piece so I could sink a few screws from the back and hide the fact they are there.

A few good smacks with the mallet to get the piece in place and it was looking good.

After it was all said and done the top portion of the vanity is about as sound as it's going to be. I think you could have a party up there and not get any significant sag. And given how long it's taken me to get to this point, I might just have to have a little party up there. I might even invite Wendy (though she'll just point out how long things are taking).

I still want to add some structure to the bottom of the vanity, cut some holes for the plumbing, and also cut an inch or two off of the bottom before we can call it ready for paint, but this level of progress is very encouraging.

What do you think? Is this sufficient for our vanity stone? I'm thinking maybe I need a few more corner pieces to help out, but I'm also thinking it's getting to just be pure overkill.