Leaky bathroom window and mold after 5 years

Good day everyone,

I have a problem that more or less burdens us...

Well, we moved into a rental apartment.
Great location, great landlord, everything really great.

The bathroom was renovated 5 years ago, including a new window.

Now we noticed the following:

- There is always moisture on the silicone seal on the bathroom window sill. Even if we always wipe it away, a few hours later it is there again, although we always ventilate after showering/bathing.

- As a result, some black mold has taken hold there, which we cannot get rid of like this.

- Right in front of the window/window sill is the bathtub... when sitting in it, you can feel a "draft" on the neck.

- Remedy with Tesamoll brought nothing, the sealing lips are now tight and it still drafts.
Taping these small openings also did not help.

Judging by the outdoor sensor of the weather station, the window sill is below 17 degrees and over 70% humidity (closed window and no one showered shortly before).

If you place the device in the middle of the room, the temperature rises, humidity decreases.
Don't be surprised, I actually just wanted to know how far the sensor reaches ;)

The landlord wanted to address the problem, which is very unpleasant for me because all the beautiful tiles would have to be removed if the foaming in the frame is not tight.
Above all, I find the landlords (a couple) very likeable and human, and it was unpleasant for him too... and above all annoying :-/

But especially: how does the warranty look after 5 years?
The seal is tight, the window probably too... so poor workmanship just now becoming apparent?

So... we need help to possibly look where the fault lies beforehand :-/

What to do? What else is noticeable: in the small bathroom (measuring 3x4 meters) it is unusually cold in the morning (weather side).
There are no blinds to pull down there either... :-/

I would be happy if anyone had tips.
Thank you in advance,

Regards,
Daenni

Hello again... even though I’m a bit surprised that apparently nobody knows this problem...?
Or is this the wrong forum? Hm...

Yesterday I was out with the laser thermostat...

Bottom edge/silicone joint of the bathroom window (still on the windowsill) a proud 8.5 degrees Celsius.
Other rooms (including) kitchen at the same spot about 14 degrees Celsius.

So something down there must be leaking, right?

Greetings and thanks

Daenni

Hello Daenni,

obviously, the lower sealing was really not installed during the installation of the window, this was already a generally accepted rule of technology 5 years ago and must be installed. Whether this constitutes a hidden defect must be answered by a lawyer, as I cannot and may not make any legal statements.

To make the window truly permanently sealed, an outer vapor diffusion open and an inner vapor diffusion tight installation must be carried out, this is usually installed within the sealing level to the masonry in a window.

To properly carry out repairs now, the window would actually have to be removed and then properly reinstalled, but the tiles will probably be damaged in the process if there are still any, then I would have it done this way; if not, there is an alternative. There are so-called finishing strips that can be mounted inside and outside.

Your description still makes me somewhat suspicious because the temperatures are very conspicuous; there could certainly also be a thermal bridge present, this should be checked, it is best to do this with a thermal camera.

The temperature should never fall below 12.6 °C because from this temperature mold formation is almost unavoidable. If mold is now present, the sealing should at least be completely removed and treated with a mold-killing agent (Isopropanol or hydrogen peroxide) and a new sealing should be installed.

Hope to have helped you

Hello Andreas,

thank you very much for the response.
Well, the landlord apparently spoke with a building biologist who was involved in the planning back then.

Her statement: mold is always present everywhere (apparently more where there are windowsills, which still seems logical to me).
Also, the fact that this silicone joint molds is nothing new and "harmless"... well.

Then she said that the temperature difference is also normal because it is a stoneware windowsill and these insulate less.
Options: remove the windowsill and install a new windowsill made of plastic.

That we have all windowsills made of stone here shouldn’t really matter :rolleyes:
So in my view, this explanation is nonsense.

As I already mentioned above, I measured the temperature and it also seemed very strange to me that with the same window sizes and the same windowsills there is a temperature difference of 6-7 degrees behind them. Even if it is the weather side... the room is 3x4 meters large, has a heater that can be set to level 5 out of 5 and it is still cold... so we'll see.

What is positive, however:
the landlord really did not base himself completely on her statement (he was already here today even though he could only inspect on Sunday) because it is really drafty. And in addition, there is no draft and no moisture in the apartment below (where his son lives).
His option: remove tiles, then see and possibly redo.

I would call this a defect here. Not towards the landlord (he is really making an effort), but with regard to the building biologist (who knows from afar that the mold is not harmful) and towards the window construction company that apparently forgot something.

By the way, the facade was completely "blown out(?)" back then... so it should insulate well.

Let’s see how it goes.

First of all, many thanks to you!

Regards,

Daenni

Hello,

you are absolutely right, what the lady is saying is nonsense.

Mold can only develop where there is moisture above 70%, and that is where the temperature drops below 12.6 °C, because that is where the usual room climate begins to condense.

Hello Andreas,

just for your information... in case you're interested ;)

Tomorrow the gentlemen from the window construction company are coming.
We were able to wipe this lower silicone joint dry about 4-5 times daily throughout the whole winter because the condensation water settled there.

Let's see what the gentlemen say tomorrow.
Very unfortunate overall, since it’s once again above + degrees and the temperature of the windowsill is therefore already over 10 degrees and no longer around 8 degrees.
The windowsill is thus only "damp" but no longer wet.
Tomorrow we’ll see further.. I’m curious.

Regards and many thanks to you.

Daniel