Mold problem in new shower

[jlrossi]

We finished our new master bath shower about 4 months ago. We are having a mold problem on the bench and floor in the shower. There is a fan installed in the main bathroom, but water appears to sit on the tile and grout for most of the day. Also, a towel used after we shower remains moist until the next day.

We were anal about waterproofing and used 3 coats of redgaurd on the walls over backerboard and a membrane system over backerboard on and around the bench. The floor was done with pre-slope cement, then a shower pan, then a final slope with cement before tile was installed.

The mold is prevelant on the floor and parts of the bench. It has not moved up the main walls. We used a standard sanded grout and sealed three times prior to using the shower. My wife insisted on using vinegar to clean the shower and I have heard that may have ruined the sealer. I have thought about cleaning with a bleach solution and resealing to see if that does anything.

The local tile store recommends removing all grout and redoing with an epoxy grout (which my tile guys hate) or some new liquid that you mix with the grout to eliminate the need to seal it. I was also thinking of installing a fan inside of the shower to see if that would do anything. I am attaching numerous pictures. The shower is 8' X 4', so I would like to avoid redoing the grout at all cost.





I appreciate any thoughts on a remedy.

Thanks,

Joe

[cx]

Welcome, Joe.

Several possibilities.

Do you know that the pre-slope under your pan liner was at least 1/4" per foot of run all the way to the far corner(s) of the shower?

Do you know that some sort of protection was used in the areas of the drain weep holes to prevent the final deck mud from clogging those holes?

Do you have a similar slope in the top of your bench?

Do you know that your bathroom exhaust fan is adequately sized for your room? Do you run the fan adequately after each shower use, like 30 minutes or more?

Do you always eat all your vegetables like your mom told you?

Do you have similar mold around the drain area?

[Houston Remodeler]

7- was bagged, powdered thinset used or pre-mixed in a bucket?

[jlrossi]

We hired someone to do the pan, but I was not thrilled with his work. I know he used the plastic guides to ensure the final cement had an appropriate slope. I did not see these on the pre-slope before he installed the liner.

The bench definately has the 1/4" per foot slope.

Not sure on the weep holes. Is there a way to see if they are functioning properly?

The exhaust is a NuTone HD80NT which is rated for rooms up to 75sf. My bathroom is 68sf and we run the fan for about an hour after showering. The ceiling in the shower is about 6 inches lower than the rest of the bathroom. Was thinking maybe I need a separate fan inside of the shower...

There is no mold near the drain. Only within about 10 inches from the walls.

Of course I eat my veggies. Mom taught me well...

[jlrossi]

I believe it was thinset that was mixed with water... Not positive though.

[Kman]

I believe there's more going on there than an exhaust fan can handle. There's either some mastic involved, pre-mixed grout, or some "flat spots/back falling" that is causing the shower to hold water.

The level of mold is more consistent with a shower that is several years old, not four months.

What kind of backer was used?

[Houston Remodeler]

If a bucket of latex / mastic was used, then you'll have mold in a few months. I'd be tempted to remove the grout in some of the bad areas and look for thinset or mastic between the tiles or pop a tile off and check.

[jlrossi]

There was no mastic or pre-mixed grout. Your last thought on "flat spots or back falling" has me wondering... I remember that the final cement floor that the tile was adhered to had a few areas that were not smoothed perfectly. There may be a few areas that could "puddle". Would this cause the mold? Short of tearing out the floor and redoing it, is there any other solution? This does not explain the mold on the bench as there was no areas that could puddle on the bench.

We used backerboard with 3 coats of redgaurd on the walls and backerboard with a membrane system (sold at floor & decor, but cant remember the name).

The guys a F&D recommended taking out all of the grout and drying the area, then reinstalling an expoxy grout. Any thoughts on this proposed solution?

[jlrossi]

Definate that bagged thinset was used to install the tiles.

[Kman]

Exactly what was the backer board that was used?

[lou432]

How about contaminants in the water or in the grout?? the whole thing looks fishy to me ?? sporadic mold on horizontal & vertical ?? one area is spotted black & clean grout in between ,then others is solid black lines then clean grout, makes me think ? is it on the surface of the grout or just below the surface the the mold is growing ? Mold needs food ,usually organic in nature so I would scratch some of the moldy grout & see if its all the way thru or can it be removes with a bit of grout removal ??? Just my thoughts as I read this thread !

[Kman]

You don't happen to have any pics of the work in progress, do you?

While the tile over the bench has a proper slope, do you know if the bench itself is sloped? If the top of the bench was flat before the tile was installed, it will hold water.

There's some reason that your shower is holding water and therefore growing mold. The sealer is of no consequence as it adds nothing to the waterproofing. However, I would not use vinegar to clean the shower as it will in fact strip the sealer.

[Scott_V]

Joe, where do you live? It sounds like you have too much ambient humidity for the shower to dry fast enough to prevent mold. You mentioned the tile and grout remain wet for an extended time after showering, and that your towel doesn't dry out. Have you tried leaving your shower door open after showering to improve air circulation over the tile surfaces? Perhaps replacing the grout with epoxy grout will solve the mold problem. Until you figure out the root cause, try this every week or so to prevent mold:

[Davy]

First off, you should be able to have regular grout that doesn't grow mold. You shouldn't have to go to epoxy grout. There were a couple things mentioned that rings a bell to me. Possible clogged weepholes and keeping the door shut after showering. You want to keep the door open.

[Scott_V]

How would clogged weep holes cause mold on a horizontal wall?