I would not cover the disintegrating marble with anything as you have no idea if the problem will progress and make anything you put over it less than useless. As this is in a condo you have to be aware that things you do...and don't do...could affect your neighbors. So a disintegrating shower should be fixed and even brought to the attention of the condo board in case it is a bigger issue like water quality.

That has nothing to do with the water and everything to do with acidic bathroom cleaners being used. Its textbook, in fact.

verbo, except it does have to do w/water because you can see how the stone is darker and wet in some spots. Limestone sucks up water like no ones business. (should never be used in a shower)

If it was strictly acidic cleaners, the other wall tiles would have had the same issue. only the portions that get water soaked during showers have the crumbling effect.( and, if was just cleaner, like you think it is, the entire surface of the stone would be ruined w/etch marks and streaks, especially after 20 years. I know this because I used to have travertine in my shower a long time ago. Not mine, but when improper cleaners are used, streaks and etching will look like this:

The actual cause of the crumbling is repeated water absorption

Limestone is extremely durable. It does, however, absorb water and, since it is a carbonate rock, it is highly reactive when exposed to acids or even mildly acidic rain water, and it can suffer substantial deterioration.

Cleaners could have contributed, but 100% its the constant water absorption that caused it to crumble.

Marble showers require more careful cleaning than the people using them. (Worse than the stupid plexi that's all the rage now.)

If this repair/replace is going to be a financial burden on you, I understand why you may have been looking for a simpler, quicker and cheaper solution than ripping it all out and starting over. However, If anyone else in the condo has this same material in their showers, it might need to be looked into, and the HOA might need to take on some of the responsibility for solving the issue.

Why on earth would any condo board ”need” to assume any responsibility for a privately owned and maintained residence? That is absurd. The condo owns and maintains the common areas, and building infrastructure. They have jack to do with someone’s choice of a limestone shower and their vhoice of Lime away being used to clean it with. Do you expect your municipality to assume responsibility for the rusty orange stains in your sink from the iron in the water?

When that stone is dried out and it's assured there is no leaking behind the wall, since there is no way the stone will become wet if it's covered in Corian, it can no longer fail from moisture. It's a safe bet that the valves are stubbed out far enough to allow a 1/4" or 1/2" wall thickness addition. And if they're not not, no big deal. Chip out the stone and reset the valves.

There's way too much "tear it out and start over" attitude here. It's actually kind of lazy. Demolition is easy; diagnosing and problem solving is not. Just because someone was foolish enough to specify and install an inappropriate natural stone for the application doesn't mean there aren't creative cost effective solutions to make amends. My solid surface solution is one and I'd guarantee this installation if I did it.

IMO bonding anything onto this crumbling CaCO3 would go against one of the basics of tile setting and construction ie you need to build on a known structurally solid base. It might not keep crumbling; maybe some thinset or epoxy will stabilize it, but even so, as a homeowner I would not want to hang Corian on it. With such dramatic damage I would insist on seeing what was going on behind the wall.

Not only that, but what happens to the shower pan when u add another 1/2” onto the walls ? Its a janky solution. Maybe even hillbilly. Not like you at all Joseph.

Homeowners Insurance is the place to call. A. The stone is inhaling water. But where is it going. Somewhere after the stone.
A pro needs to locate problem in behind something leaking into this area. What is above? No I am not crazy. I have seen a similar situation and tbere was a deck above and gutters. And water coming in for years.
So one never knows.
Get an inspector and your insurance can be informed 
Than find a reputable local Architect to solve the problem

Is there a bathroom on the other side  -shower ? Is this line of bathrooms for the building all in this area?
Condo call now. There may be others. Take some out and look behind

Whatever you decide to do you are wrong in your interpretation of the condo rules.

Please dont call your insurance company about this. they probably wont cover it and your home will just get blacklisted for future coverage even if a claim isnt made.

Homeowners/Renters insurance provides coverage for sudden, unexpected, catastrophic events. This is a wear-and-tear/maintenance issue, just like a rotting deck, a deteriorating roof, etc. Don't bother making a call to your insurance company.

I have to disagree calling your insurance company is why you pay insurance. Blacklist you for a call and help , never heard of this. And this is not a decision we make. Insurance firms can help
.

I know people who have used insurance for non-catastrophic things and have been cancelled - then it's nearly impossible to get insurance from a new company. Cancelled and you're blacklisted by insurance companies. One person I know had to go to Lloyd's of London for several years to get any insurance and it was $$$$. Save your insurance for catastrophes, carry a high deductible to save on premiums and pay for the lower cost fixes yourself.

Coco, it’s not an insurance claim. There is no leak. It’s continual water absorption that has eroded away at the tiles. Plain and simple.

Let’s just say u do report it to insurance and say it’s a leak. They send their leak detector people out. The leak detector people say there is no leak. But guess what? You now have a claim against your policy. Your rates will increase for the next three years. The exact same scenario happened to me except it was a pipe in the slab in my floor. Didn’t even use them to get it fixed. Just because we called and they sent out a leak detector, we got hosed. ( no pun intended)

But all that aside, this is not a leak, not a catastrophe and nothing that falls under homeowners.
It’s a case of the owner failing to upkeep the natural stone tiles in the shower over 20 years.

Can we just retire this post now? The tiles need to be removed and the shower redone. On the homeowners dime, not the insurance company.
That’s all there is.

Joseph, if there is nothing going on with the walls with crumbling tile, why would the rest of the tiles be intact? It seems unlikely that the one or two walls would have received inferior tile and the rest got something different.

"Homeowners Insurance is the place to call."

Poor design, application, material choices and neglect are not insurance claims. period.

Oh Olychick--your commnet made me smile AND feel a bit better! I now know I'm not the only Houzzer that notices such unkind and snobbish comments.

Now--carry on! (but kindly, please)

Its funny, I coached LL softball when my girls were little. We had to learn a few strategies to talk to the kids. One was what was called a ”criticism sandwich” you start with a positive, slide in any critique but end with a positive statement. It worked like a charm on all of those girls, and it works on most grown people. There are many posters on here that only know the criticism and hold the bread if you know what i mean.

Let's face it - EVERY PRO - has said something mean to an OP!!!!!!!!!!!!

Except Flo!!!

She is never condescending.

Ladies It is the job to voice an honest opinion.

Mine is an acceptable response .I will still say the client should have an inspection. Call a pro in to see what is going on. This is a photo no x-ray and no knowledge of when built, by who or where.

Get all the assistance you can.

Thank you for being pros and accepting answers that can be agreed or not agreed with . The responsibility is to be straightforward.

Call an engineer or Architect and find problem. One cannot repair without knowing what or why it needs the repair

Thank you all for having an intelligent conversation.

There is no reason the Corian panels can't be hung mechanically instead of with adhesive. That avoids the expense, mess, noise, and risk of demolition. Y'all are way over-thinking this. And over-spending.

i actually think the crumbling marble looks beautiful, like a cliffside. I also understand that you probably need to gut the shower. Hopefully you get some good professional, in person advice and your board understands this (TBH I never understood why people who choose to live close to other people complain about the noise of everyday living and maintainence… it’s what we sign up for when we decide to share walls, etc., with other people).

I like the look of crumbling marble too!

Many buildings are built by developers with one mind. Cost Sell one should be low, one high 
90% of the buildings, the builder purchases floors, cabinets, doors, heating air ,parking , cages for storage, etc. If this is 20 years old owners problem. But what if the entire line had problems? Was the stone the problem? I have no knowledge of this building , the date the plumbing went in or if there are multiple leaks and where are they going. 
If you lived on the other side would you want to know what was happening. Is this area covered in mold. Built when?
An area near where I am the pile for sewage from home to street a problem by developer. 
They must replace. This is generally a homeowner bill and can get very heavy 
Making decisions based on a photo is not a smart move.
This event is over from my point of view. They need to get in a pro, find problem, notify others if affected and stand up to what is happening.
That is how I see this. I understand others have a different viewpoint. We are allowed to a forum is that. .Thank you

Eli When did this happen?

It happened over time, trust me.

@Coco @Joseph

about 4 years ago there was a tiny speck the size of a quarter which we thought was a bad little piece of tile. We then rented the condo out for 3 years and all this happened then.

@JosephI really appreciate your effort at vosualizing a plan B which is exactly what I hoped to get.

I was just looking for a simpler solution than tearing down if at all possible... the neighbor is an old lady with a husband who is very ill. I would like to spare them if possible. That does not mean I am getting ready to cover up mold and destroy everyone in the building 😂. I thought just maybe you had seen this before and could help.

We are just getting the condo back now, for those that want to know "how we could possible ignore it and let it get so bad".

And @Beth no, I am not "angry because it is not going my way" .No I am not "shooting the messenger".

I just appreciate ideas and a solution rather than uninformed attacks from different people about my many and varied hypothetical sins. And as stated before Beth I appreciate your ideas.

The obvious first thing to do is remove the valve handles and escutcheons in order to hopefully get an idea of what is behind the tile...how the shower was built. Along with ordering a moisture meter as suggested above.

After removing the valve parts and getting an idea of how large the cavity and access is, an endoscope might be helpful. (Known as snake inspection cameras/ camera probes--either an attachment for a phone or a stand alone tool.)

IMO, Joe's suggestion of Corian sheets is reasonable. (But knowing the moisture levels is critical before proceeding.) .

The challenge of using a solid surface cover-up is the aesthetics of pulling it all together and looking pleasing & intentional.

Factored with the cost--material, installation, possible need for a plumber to reset the control valves, removing the glass, replacing the glass or part of the glass (will a new panel match the existing?) That vs cost of tearout and rebuild.

Do you intend to live with the solution or will this unit be a rental again?

ETA: Keep in mind that this a 20 year old shower. Is it worth a costly bandaid fix?

@ci_lantro

Thanks for the valuable suggestions, and yes, apparetly either route will be quite expensive,

Intend to live here now....
Thanks

Eli, please come back to this thread and let us know what solution you decide on.

Even post some demo/ progress photos if so inclined. I know this is an awful mess for you to deal with. But an interesting conundrum for the rest of us. We will all learn from this.

Which shower wall/ walls are common walls with the neighbors?

Another thought--since you said the neighbors are elderly--per chance they wear hearing aids? If so, the noise from demo may be less bothersome for them than you imagine since they have some control over what they hear?? And the worst of the noise, demolition, should happen in the space of only one day or part of one day. Do talk to them about the project--maybe even show them the problem. They may well be more understanding & tolerant than you anticipate.

update, especially @ cilantro who asked gor follow up!
After your many valuable ideas, we first let it dry out unused for a month. Crumbling did not go on, so we fugured we were right about humidity not behind but lack of sealer on top.
Had the bad area demolished and replaced with tile. Everything behind the marble was perfectly dry.
Will attach the demo and the end result

My pictures won't post I will keep trying

This is the after, still not managing to post the demo. We only replaced the two bad walls. Gave the remaining part in the shower three coats with an impregnating sealer with that will keep it fine

demo
yikes, not letting me post from my pic album...any ideas? the little icon does not react to take me to the photo library...only the camera icon works

Still need to install new vessel sink and faucet.

The reason we kept the part of the wall it was OK it's because right before demolition we noticed that the crumbled part Changed color when wet so it was absorbing water and that piece of wall did not. Conclusion - that part had been sealed, the rest probably not. We gave it more miracle sealer 511 and water rolls right off it. Now we know to keep doing it.

demo- took a screenshot from my phone screen since I could not post the pic.

demo

Thank you for the follow up. You did a great job of melding the new with the old. Very nice!

I agree; it looks really nice now.

@cilantro and @olychick, thank you! Means a lot that you like it!

Waterproofing is non existent.

@ABC
I know,

but with that sealant it has lasted 20 years in the shower just fine with absolutely no precautions, so figure it should last longer than me with another couple coats.

Of ooursewe intend to squeegee now that we know what the issue was.

Thanks

That is not how that works. That is now how any of that works.

At ABC not sure what you mean exactly, what you suggest doing or not doing st this point?
of course I am not an expert, but it is too late now....we will have to see how it holds up.
Thanks