Resolving black mold, grey fur and general wetness in bathroom floor joists

[Oldman]

I think I need some advise please, I looked up at the outside wall of the ground floor kitchen to see water stains on the wall and ceiling. Ive lived in this house since 1975 and Ive never had a leak upstairs in all that time.
The bathroom directly above has fitted carpet and fitted basin vanity unit with no evidence of water in wrong places, so tonight has been carpet up, floorboards of course go under the vanity unit and toilet so out came the saw. The boards are T & G of 1962 vintage so the cut nails fought back some.
Once I had a long board up I can see staining and black mold around three 8" x 3" joists from the wall back 2ft into the room.
Tomorrows job is to remove the vanity unit and see if its the waste and or a supply pipe leaking, but it must have been doing so for some time I would think to get such a growth.

So, I will of course fix the leak but how to I treat the timbers to remove the mold and fur? Do I let them dry out on their own or force dry in order to rebuild the bathroom before next spring!
I retired 10yrs ago expecting things to get easier, I'm still waiting on that!

 

[Bingy man]

I think I need some advise please, I looked up at the outside wall of the ground floor kitchen to see water stains on the wall and ceiling. Ive lived in this house since 1975 and Ive never had a leak upstairs in all that time.
The bathroom directly above has fitted carpet and fitted basin vanity unit with no evidence of water in wrong places, so tonight has been carpet up, floorboards of course go under the vanity unit and toilet so out came the saw. The boards are T & G of 1962 vintage so the cut nails fought back some.
Once I had a long board up I can see staining and black mold around three 8" x 3" joists from the wall back 2ft into the room.
Tomorrows job is to remove the vanity unit and see if its the waste and or a supply pipe leaking, but it must have been doing so for some time I would think to get such a growth.

So, I will of course fix the leak but how to I treat the timbers to remove the mold and fur? Do I let them dry out on their own or force dry in order to rebuild the bathroom before next spring!
I retired 10yrs ago expecting things to get easier, I'm still waiting on that!

A very small leak that goes unnoticed for years does far more damage than a sudden leak or burst pipe . In the event you don’t find anything leaking inside Make sure all your gutters and any roof valleys are in good order , all external drains are working and not blocked . A good roofer is advisable- Back to inside and check everything use a good light and if necessary run the water in the bath , basin, shower etc . It could be as simple as the seal around the bath or shower . As for the mould then assuming you have corrected the root cause then letting it dry out is key . Leave the problem area exposed if possible ( if safe to do so ) to allow warm / dry air to circulate. Dehumidifier can help the drying process. If the affected timber is sound and not rotten then my choice would be sika 5 star complete x 2 coats to all affected areas. There are others such as everbuild but I prefer sika.

 

[ChaiLatte]

I may be misunderstanding the layout, but is the kitchen under the affected area?

Is it possible that humid air from cooking has found its way there and made the area damp?

Another possibility could be moisture from the air condensing on a cold water supply pipe.

Any place than goes mouldy from humidity needs ventilation as said above, so if the affected area is a dead spot, consider some means of making sure air can circulate.

Are these joists forming the ceiling of the ground floor and floor of the first floor? And are built into the wall? And is the wall an outside wall? It could be that damp is coming in from the end of the joist and progressing along it.

 

[Oldman]

I today stripped the inside of the vanity unit to give myself a better view of the waste and H&C pipework and thought I could see a chalky stain (hard water area) down one of the pipes from an isolation valve. I reached in to get a closer look and found the nut on the cold valve finger tight, I then checked the hot one and that too was loose.
In all the time I have lived here, the one job about 8yrs ago I gave to the plumber was to fit that vanity unit, taps & waste. I always used to do my own work.
I cannot of course say for sure that they got spun on and forgotten or if the rubber seals have both relaxed over time making it feel loose, but I think there is a good chance that this is the cause of the leak.
I am about to spread newspaper in the area as its a good detector of wetness and I will monitor for a few days.
In the mean time I will vacuum out all the debris below floor level and leave the long board out and maybe fit a fan in the void once I remove the surface fungal as I don't want that in the air for others lungs.
Being a bathroom I'm going to have to use low voltage fans on long 12v leads to save anyone getting shocked.

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The old kitchen is directly below yes ChaiLatte but we had a single story extension so the kitchen is more than twice that area now with cooker and extraction well away from this area.
Bingy man thanks for the advice on the treatment I will get this dried out then do that.
The timbers are not rotten as far as I can tell, just doesn't look nice.