Humid rockwool - condensation or window leak?

[Tiboo]

I noticed the rockwool in the wall in my bathroom is pretty humid, particularly below, where it is almost soaked with water (I only can check in a few spots though). Some of the wooden panelling is getting somewhat wet and some mold is appearing here and there (low on the wall). The issue still appears almost a meter away from the window and I don't notice any leaks around that window frame (it also seems correctly sealed from outside as far as I can see of course). Regarding condensation, I can say the shower is only used once every few weeks and the boat is appropriately ventilated and heated in the evening with a wood stove located ~35ft and a few rooms away. (I don't find any leaks in any water pipes by the way). What would you say is going on?

[cuthound]

Is there any water in the cabin bilge? I think there may be as you say the rockwool is wetter towards the bottom. If so check water pipes and shower drains etc for leaks.

 

If there is, and it has reached the bottom of the rockwool, then the insulation will cause it to wick up.

 

Window leaks (and those from high level ventilation) are notoriously difficult to trace because the water often drips someway from the source of the leak. Try using Captain Tolley's Creeping Leak Cure around windows you suspect may be leaking.

 

It is unlikely to be condensation because the insulation should prevent this forming where it is installed, and you would need a lot of condensation to fill the bilge enough to reach the insulation.

[Tony Brooks]

Water leaking between the cabin side and window frame can travel a long way,  especially if your boat has a horizontal board under the gunwale. If the boat trims down by the stern I would suspect the window in front of the wet insulation.

 

Ditto water from leaking roof vents.

 

I would want to ensure the material is not extended below the floor so it can wick bilge water.

[Tiboo]

Ah, sorry, I should have mentioned: there is no water in the bilges (luckily).

Thanks for your helpful comments. Sounds like I should get some of that Captain Tolley's creeping leak cure.

[David Mack]

2 hours ago, cuthound said:

 

 

It is unlikely to be condensation because the insulation should prevent this forming where it is installed

Only if you have a proper vapour barrier on the inside face of the insulation. Without one or, or with an imperfect vapour barrier, water vapour from inside the boat permeates through the rockwool insulation and then condenses on the inside face of the steel shell. 

That's why sprayfoam or cellotex with properly taped joints make better insulation than rockwool or fibreglass wool, as the former are vapour-impermeable.

Edited January 2, 2022 by David Mack

[Quattrodave]

I always thought rockwool was non hygroscopic... not sure where I for that from tho....

[system 4-50]

2 hours ago, Quattrodave said:

I always thought rockwool was non hygroscopic... not sure where I for that from tho....

Rockwool is not hygroscopic, that is a different, chemical process, which would result in it becoming wet itself without necessarily needing to wet surrounding surfaces (though it would if carried to excess).  

Condensation occurs on the metal surrounding surface and then soaks the rockwool which plays a passive role of just failing to prevent the water vapour passing through.  

Edited January 2, 2022 by system 4-50