Yuck, I feel for you--we're facing black mold too, thanks to DD's not-so-smart choices for the last few months...grrr...

A question: do you have an exhaust fan? Well, two questions: how long do you run it during/after the shower?

I am not an expert by any stretch but I think you have an installation problem. If you are getting mold this early, you have an installation failure. Myabe BillV and Mongoct can offer some different advice. If you don't have a vent fan in the bathroom, you should install one. I don't know that this will help much for installation failure but it should help with other mold issues.

Good luck!

Here in Georgia we have a constant mold problem as well--everybody does. I agree with the advice to dry the grout line immediately.

I have allergic asthma, allergic to 5 different groups of molds. And we currently have baths with tiled shower surrounds. Yes, we've upgraded our exhaust fans and use them, on a timer. Also have a whole-house HRV. Nothing works except drying those grout lines.

BTW, you do NOT have to kill the mold, you only have to remove it (like an insect from your house--don't have to kill it before escorting it out). And if you don't remove it, even IF you've killed it, the remaining mold spores can contribute to airway irritation, whether your household is allergic or not. I can't tolerate the fumes from anything that kills mold anyway. So I just use a mild cleanser and brush to remove it; rinse well, take brush outside and give it a quick soak in hydrogen peroxide, regular strength.

Mold, beyond its health problems, leaves ugly stains even when removed. And whether dead or live when removed. Hydrogen peroxide, if safe for your marble, will remove recent/not too entrenched stains. But not real well. The only thing I've found for the stains is chlorine bleach.

Sealing our grout did not help but very briefly.

Silicone caulk/grout actually makes the problem worse. Because it remains flexible (its great benefit), it allows water, then mold growth, behind it. And it is transparent so you can see the lovely mold through it. So, I've abandoned the silicone that was supposed to be the best.

You don't want to know my permanent solution because it is not popular or stylish. For anyone who does want to know it, here it is: buy a one-piece acrylic (not regular fiberglass, it's too fragile) bathtub or shower or tub/shower combination "module" which has its own ceiling as well. About $2400. with built-in stainless grab bars from Kohler's Freewill line. Less, without the grab bars, from Lasco. That's all we will ever use in the future. For health reasons, and because I'm getting too old to fight with mold and grout issues.

You might try this product. It is called Concbium mold control. Non-toxic. I read about this in the newspaper the other day. It is susposed to eliminate mold by encapsulating it. Available at Home Depot. Has a link on one page to find a dealer in your area.

Here is a link that might be useful: Concrobium

a really simple solution is 1 part bleach to 2 parts water in a spray bottle.

dgmarie, I found in research that bleach supposedly doesn't kill the spores, it just kills the existing mold...

That Concrobium looks interesting, rjoh--we also found another thing at HD this weekend--by Scotts Liquid Gold, actually--it's the same formula used by professional remediators, just for smaller amounts of space--kills spores as well as the mold (as does, supposedly, a formula posted on the Home Repair board, made of peroxide, white vinegar, and boric acid). (Last week it was PR'd that the SLGD product also kills MRSA, which is a pretty huge claim to make)

I do hope mongo or Bill will see this and address the possible installation-failure issue.

We all know that's it's a moisture thang...there's too much latent moisture in the shower after it's used. It's not drying out fast enough.

Do realize that mold spores are everywhere.

EVERYWHERE!

Kill the mold that shows today with bleach, and residual bleach will prevent new spores from showing themselves for a few days or longer.

But once the bleach has dissipated, new spores will show due the the ever-present moisture.

So...the shower either isn't draining fast enough...too little floor pitch, too deep grout lines (or too deeply tooled caulk) in the corners, a grout line "crevasse" around the wall/floor intersection where water can pool and collect.

Too little moisture vapor removal. Perhaps and improperly sized vent fan, or the duct is improperly routed so the vent has trouble moving air. Or the fan simply isn't being run long enough. Or you have a gasketed door and there it too little makeup air available for the fan to move. An EFI timer switch could help there.

OR the stone wasn't sealed so it's absorbing and holding moisture.

Or the pan or pan preslope was improperly constructed so you have water pooling and saturating your under tile deck mud because it can't flow through the secondary weep holes in the drain.

Enough already!

Lots of solutions, but first we have to now the cause of the problem.

A neighbor had a similar problem in her shower, the easiest solution was to installed an electric Runtal Omnipanel towel warmer. It gave off enough warmth to dry the shower and prevent future mold and mildew growth.

Sorry for your situation.

Mongo