Mold in shower drain

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prusakolep

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Feb 11, 2022
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Location
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I have a strong moldy smell from a shower drain in a newly built house. I have cleaned the drain multiple times with baking soda and vinegar, bleach, drano, and the moldy smell is returning. The plumber came out and all they did is fish out a tiny amount of hair from the p-trap but that did not change anything (there was no problems with slow drainage, but very strong smell). I took a look in the drain and I saw that there is quite a bit of what appears excess gray ABS glue, and there appears to be mold growing on that excess glue - see picture below. Somehow the plumber missed this?

Question: why is this happening, and what is the proper remedy? The house is under warranty, so I want this fixed properly, but the plumber the builder is sending me is not fixing the problem. Is it as simple as removing the excess glue from the ABS pipe surface? And I am puzzled why a glue used for drain pipes would be susceptible to mold growth. Is this a wrong type of glue by any chance?

Thanks!

1644605815770.jpeg
 
Welcome.
The black fittings are ABS, not PVC, and could you post a more panoramic view, because if the white material is the mold, it appears as also existing beyond the drain.

Is there an operating exhaust vent, that is left on, for a period, after the shower is used?
 
Yes, the pipe is black ABS (I edited my post, initially said it was PVC). The grey part is the glue that was applied and what I think is mold is the dark stain on the grey glue. There was originally more excess glue and I peeled some of it off - it came off easily and it was rubbery.

We have not been using the fan much, but the space is large and well ventilated. And while extra ventilation may help - this is definitely not the root cause of the mold. We've been living in many houses before and never had problems with mold growing in the shower drain despite not using the fan much ever before. There is no trace of mold (visible) anywhere else in the shower enclosure or in the house. There is definitely something funky with this particular drain.
 
let me say this about humidity in bath rooms, Bathroom are suppose by code to have a forced air exhaust system . but most people go to have a shower turn on the fan have a shower then walk out the door and turn off the fan, WRONG.
what you should have is a exhaust fan with a humidistat controlling it.
So you go in have you shower when the humidity rises the fan turn on and runs, you leave the fan continues to run for about 20 minutes until the humidity drop to normal.
this is why so many people have mold problems in bathrooms.
 
Also, in your sequence of events, you hadn't mentioned that there was a notification, too the plumber, regarding the mold appearance on the excess adhesive, which might be a point of interest.

In my experience all the ABS adhesives, were black, in color.

Warm air will, in capacity, contain more moisture, and if you leave the door open, after the shower is used, there will be greater air circulation, Also if there is a humidity control within your comfort heating system, an adjustment there may be an option.
 
Bill/Snooby - I hear your insistence on ventilation and leaving the fan on. However, I have to tell you that I have never been going out of my way to do this, and without revealing my age online, let's just say I have many years experience with that. In the past I never had problems with mold in the shower drain, at least not to the point that it would be so obvious that it would reek when you open the shower door. This is the first time I am experiencing this issue, and I am especially puzzled because this is a new construction house. The shower cabin is open above with a 9 ft ceiling - a 3 ft opening. It's low humidity in the house with the heating running, and the heating ventilates the space very well. I suspect that there may be something wrong with how the drain is installed, and I am asking for help with answering that question. So let's leave the ventilation question aside, and if you can share your thoughts with me whether/what could be the issue with the drain installation, that would be very helpful for me. So far with one visit from the builder's plumber they did not see any issues with the drain itself, and I am wondering if they are overlooking something or intentionally avoiding providing warranty service. If you don't think there is anything wrong with the installation of the drain - please say so, I am here to hear opinions from other forum members.

When the plumber visited I did not have the picture I posted earlier, I will share it with them next time they visit.
 
Thank you.
We're just here sharing our multiple years of experiences, with you, as steps in the process of elimination.

As I shared, the color of the ABS adhesive I'm familiar with, is black, so you might inquire, of the plumber, of the brand of adhesive used, if he knows, and then investigate if that product is prone to being a supporter of mold.

I'm 80+, with 45yrs in the trades.
 
I have been following along and you have been given some good solid advice so far.



I have wonder if the source of the smell is coming from that small amount of mold or whatever it is that shows around the drainpipe and the glue joining it. I have seen many times worse without the type of smells you are describing.



Without really being there to investigate it is hard to say what a source could be. You said you have been using bleach on it with no luck and I would think that would stop it dead for at least a week or so.



Do you hear any kind of grueling when other water sources are run. I have seen situations where when someone runs say a washing machine that it causes some back pressure because of poor venting and a trap will burp sewer gas past the trap.

I really don’t know but that amount of smell from that amount of mold if it is mold is hard for me to equate.
 
Thanks. I am quite certain that there is no burping of gas past the p-trap, I would definitely have paid attention to gurgling sounds like that. Bleach did in fact stop the smell for about a week, so that suggests the drain is indeed the source of the smell. Last night I pulled out my black light, and it turns out the dark color on the glue may not in fact be mold, or at least not live at the moment - it did not glow at all in the black light. The smell is still there, less at the moment, as I had just done a round of cleanup.

I appreciate all the feedback. I will continue to work with the plumber and the builder and will report back whatever I find out. If this proves hard to eradicate, I may call a mold specialist. This really smells too bad just to be plain surface mold, but I can't pinpoint it. There are no signs of any water leaks in the drain. The ceiling of the floor below looks perfectly fine.
 
Not septic, new construction by major builder in an urban area. I've been in Seattle area for 15 years, lived mostly in one previous house, had the same exact shower routine, and the previous house shower was definitely less airy. It is one thing to see surface mold, and it's another thing to have a very strong odor. I am concerned about the strong odor and no mold that I can see.
 
Are you sure it's coming from the drain? Have you checked the attic to see if you have water stains on the decking or rafters? Have you checked the exterior walls that may be close to your bath to see if any flashing is missing or damaged?
 
prusakolep said:
Not septic, new construction by major builder in an urban area. I've been in Seattle area for 15 years, lived mostly in one previous house, had the same exact shower routine, and the previous house shower was definitely less airy. It is one thing to see surface mold, and it's another thing to have a very strong odor. I am concerned about the strong odor and no mold that I can see.
Click to expand...

Ok, so you know the difference between "Everything molds" like I'm talking about and your situation. I lived in the West Sound for close to 30 years, more rural, but never had an internal plumbing mold issue.

I'm drawing a blank, other than talking to your neighbors to see if they have such issues? If there is a massive mold problem in the sewer system?
 
Spicoli43 said:
I'm drawing a blank, other than talking to your neighbors to see if they have such issues? If there is a massive mold problem in the sewer system?
Click to expand...
If theres water level in the trap, any fumes from the sewer should be prevented from coming back in the house. I think there might be other factors contributing to the smell. In my career, I've found walls leaking, pipe boots, roofs, even plumbing pvc joints on soil stacks that wasn't glued causing hidden leaks. Anything and everything could be the source.
 
oldognewtrick said:
If theres water level in the trap, any fumes from the sewer should be prevented from coming back in the house. I think there might be other factors contributing to the smell.
Click to expand...

I have only experienced that with my introduction to septic when the trap dried out and I got the septic gas. That was easy to remedy of course. If I was him, I would call the City and have them do an inspection, since he pays for it anyway.
 
Tape the drain off 100% for a couple days and see if the smell goes away.
 
If I put my nose at the drain, it is very obvious that the drain is where the smell is coming from. And if I treat the drain with bleach, I can make the smell go away for about a week. It is definitely coming from the drain. And given that the bleach is temporarily curing it, it indicates it's not a problem of gas coming back through the trap.

I will check with my neighbors, they have the same builder and same environment.

Thanks everyone for responses, I see that this is quite unusual...
 
Sounds like you have ruled out everything possible except that that little bit of reoccurring mold that can’t be killed only slowed down for a week at the most.



If that is the case the only solution is to find something that will kill the mold or remove the shower drain and tail pipe and build a new one with different glues that hopefully mold can’t feed on.



What is below the shower? Is it an unfinished basement or finished ceilings?



If a ceiling your builder needs to open it and rip out what is there and put in new.

Sorry we were not more help.



 
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