I have a newly built (seven months) shower and during the construction the tile installer applied a paint on membrane over the mortar bed of the shower pan along with the walls just ahead of laying tile. A PVC type liner had already been installed over the pre-slope and flood tested for 24 hours. The drain assembly has the plastic ring style weep holes from the noble company. When I saw it at the time of install it seemed like a thorough detail that would make the shower more water tight. However, working on a second bathroom I ran across commentary about this very situation and the possibility of creating a mold problem. What are the telltale signs of a problem? Would it be advisable to remove the tile from the floor of the shower and scrape off the membrane? I am certain that the shower is constructed to a high standard in all other respects. I have recently noticed faint odor in that bathroom which seems to be coming from the drain but have no idea if that is an indication of mold.
Shower pan construction and mold problems.
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Jadnashua
Retired Defense Industry Engineer xxx
It's best to avoid sandwiching the deckmud between waterproofing...if any moisture gets there, it will be hard for it to get out. That being said, if you don't see problems, it may not create issues. Probably the first sign of a problem would be the grout staying wet long after the shower, usually starting around the drain and potentially spreading out from there.
IMHO, a much better way to build a shower these days is to forget the conventional liner and use a surface waterproofing method which, generally, requires a compatible drain. Then, the entire waterproofing for the entire shower is the surface right underneath the tile so there's so much less that can possibly get wet. IF you flood test it, you should be golden. It's not as easy as you might think to get a perfect painted on waterproofing layer. It does work if done right. It's just easier, I think, to get one with a sheet verses a liquid.
IMHO, a much better way to build a shower these days is to forget the conventional liner and use a surface waterproofing method which, generally, requires a compatible drain. Then, the entire waterproofing for the entire shower is the surface right underneath the tile so there's so much less that can possibly get wet. IF you flood test it, you should be golden. It's not as easy as you might think to get a perfect painted on waterproofing layer. It does work if done right. It's just easier, I think, to get one with a sheet verses a liquid.
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Thanks for the reply. I am very fastidious about always wiping down my shower immediately after use with a cotton cloth and the grout joints were filled with Mapei Flexcolor CQ so the grout is well sealed. All that to say there is never any standing water in the pan following use. The tiles are 1" square and the grout always seems to be completely dry in fairly short order. Nonetheless, I want to be cautious about mold.
Jadnashua
Retired Defense Industry Engineer xxx
Mold requires three components:
- moisture
- food
- the spores themselves
Eliminate any one and mold will not grow. Of the three, about the only thing you can't control is the spores, as they are nearly universal unless you live in a clean room. You're working on the moisture issue, and regular cleaning should minimize any food source.
One symptom of a saturated shower pan is the grout discoloring, but also, starting to smell like a swamp.
FWIW, grout sealer doesn't really 'seal' things. It does make it take longer for staining effects to penetrate, but it won't prevent moisture or stains unless you clean up a spill fairly quickly. IOW, it gives you a bit more time, but it doesn't prevent it from happening, if you don't.
- moisture
- food
- the spores themselves
Eliminate any one and mold will not grow. Of the three, about the only thing you can't control is the spores, as they are nearly universal unless you live in a clean room. You're working on the moisture issue, and regular cleaning should minimize any food source.
One symptom of a saturated shower pan is the grout discoloring, but also, starting to smell like a swamp.
FWIW, grout sealer doesn't really 'seal' things. It does make it take longer for staining effects to penetrate, but it won't prevent moisture or stains unless you clean up a spill fairly quickly. IOW, it gives you a bit more time, but it doesn't prevent it from happening, if you don't.
For future knowledge, if the pan does become saturated can I simply remove most of the field tile in the pan, remove the brush on membrane and let the pan dry out? I know that my liner is secure so I'd rather take on a fix that's minimally invasive. It's a beautiful tile job and I would want to act ahead of needing any major demolition. The 1" tile would seem to work in my favor in that regard. The shower pan measures 36x60 so I could easily leave a perimeter of 1" tile and expose most of the pan.
Jadnashua
Retired Defense Industry Engineer xxx
Is there a preslope so that the liner is actually sloped? If so, I suppose that might work, but removing tile isn't always all that easy without damaging the mudbed. If there isn't a preslope, things WILL start to accumulate moisture down there. It could start in a few weeks, and it could take a few years, but it will happen unless the shower is not used often.
Yes, the liner is sloped. It's a cloraloy liner on a noble pre-slope. This situation is disheartening because the shower is otherwise bomb proof and the extra layer of waterproofing on the floor was an impulse move. It's the same application as for the walls which is probably not sufficient as a liner. I have a construction background, did a ton of research, but made the mistake of thinking more would be better.
Some images of the shower floor with some closeups of the grout. There is some discoloration but I think that's just water staining from the area where you stand in the shower. The grout does not feel wet after an hour or so.
Jadnashua
Retired Defense Industry Engineer xxx
There's a huge amount of lousy information everywhere. Your best resources are respected, well-established product manufacturers and the TCNA handbook (updated annually) when it comes to doing something with tile. Only if you're in the business, and have the resources to experiment and test should you consider 'rolling your own' method. Those people that say "I've been doing it like this for ages and never had a problem" should raise a big red flag. First, they rarely look back at their previous installations past a year, and second, products and methods are constantly evolving, so what was done even last month is not always the best or even still correct way to do it based on the latest research and products out there.
Jadnashua
Retired Defense Industry Engineer xxx
Leave it unless you notice a problem. Being in AZ may be an advantage in that your relative humidity level is probably low, so evaporation will be faster than say in Southern FL.
FWIW, next time, consider that it's never a great idea to use two waterproofing layers, sandwiching something that can get wet...limiting the path for escape. I know the initial thought that if one layer is good, two must be better is there, but first thoughts aren't always right! In the USA, the TCNA handbook is the bible on how to build a shower that will work. Multiple methods described in there. Choose one, and follow it. Trying to combine multiple ones is problematic.
FWIW, next time, consider that it's never a great idea to use two waterproofing layers, sandwiching something that can get wet...limiting the path for escape. I know the initial thought that if one layer is good, two must be better is there, but first thoughts aren't always right! In the USA, the TCNA handbook is the bible on how to build a shower that will work. Multiple methods described in there. Choose one, and follow it. Trying to combine multiple ones is problematic.
Thanks. Our relative humidity only gets above 60% during the monsoon season and that's only for short periods of time. The rest of the year it hovers in the single digits and teens. The shower is generally dry within an hour.
johyd
New Member
In my opinion, homeowners should not solve such problems on their own, they should first call specialists to remove it, and then the cleaning company. In my opinion, only professionals should be engaged in removing mold. Well, you can remove it with hydrogen peroxide or a special detergent and it will give visible results. In addition, you shouldn't do this without a respiratory mask. And this is not enough to completely eliminate mold. I think that the main thing is to identify the cause of mold and eliminate it, so in such cases.
Well, I am sorry but what was on your mind when you actually decided to sandwich the the deckmud between waterproofing?! You must have been out of your mind at that moment. That is a pretty stupid mistake, as long as even a single drop of water gets in there, it is over, you get mold, and a ton of other problems. After you fix it, I would recommend you to go for crawl space encapsulation, trust me it is also very efficient in avoiding mold. If you do not know anything about it, you can read this guide https://ratslab.com/crawl-space-encapsulation-complete-guide/ , after you read it, you might be able to do this job by yourself.
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