Mysterious damp coming from somewhere unidentified

pieroabcd

Hi,
last week i've bought a  house in Havering and almost moved in (still waiting for the furniture).
As soon as I entered the house I noticed something strange: the wall that during my viewings was dry and clean now had some infloscerence/bubble, there was some strange smell of closed that I didn't notice in December and there's a visible repaint that has also faded away.
During my two viewings in November and December that wall (that was the original external wall before the kitchen extension was built) was dry and without bubbles, the damp meter didn't report anything strange, while now it reports humidity in the range 60-70% almost everywhere in the corner.
I've removed the laminate floors in the area. They were dry and I noticed that the underlay was wet, even though not soaking.
The hardwood boards at the base were completely dry and the damp meter reported humidity in the range 7-12% almost everywhere, except in a narrow strip at the corner where it read 20-22%. In spite of this the boards are completely solid, no sign whatsoever of sponginess, weakening or of mould. I've even passsed the sandpaper on the wettest area and I haven't noticed any sign of deterioration. The part at the corner shows a perfectly square black spot, but I assume that it must be due to some old stove lied there for ages before the area was covered by the current laminate.

Since I intend to replace that flooring with solid wood, today the worker has removed one of the hardwood boards to inspect the area below. The joists are in very good conditions, barely humid at all at the touch, the kind of humidity that is unavoidable underground. Same for the bricks all around. This seems to rule out broken pipes. In the meantime the heating system was up and tap water was flowing: no signs of water leak.

Any idea where should I search to identify the source of this damp? The only things that I can think of are
- the kitchen extension has a flat roof that maybe leaks in the area that connects it to this wet wall? Even so, I've poured a bucket of water over the roof and I haven't noticed anything getting to the wall, nor dripping inside
- on the back wall there's a crack in the external plaster (that doesn't extend to the bricks, as far as I can see). Could it be leaking water to the wall? I intend to plaster it with some appropriate filler. Do I need to seek approval from the Council? Being at the back I imagine that I don't need to.
- I don't know if the water pipes (on the vertical) were closed when the chimney breasts were removed. Maybe the water is entering from there and not evaporating?

Thanks for any idea.

theartfullodger

Ensure all trickle vents open, any windows on v slight opened, heating on low. 

Then see how it is after a week.

I had a house with terrible mould and damp.  Did as above for 2 weeks (terrible..) - no problems thereafter.  Even painted over dried mould with white emulsion, sorted, stated pristine. (Not recommended)

NornIronRose

I had what sounded almost exactly like this. Turned out to be the cold water feed pipe at the back of the washing machine on the other side of the kitchen had a slow dribble. Had been running under the tiling and underfloor heating for a while.  
As the bubbling was coming up on what would have been the original outside wall, I was thinking all sorts. 

FreeBear

NornIronRose said: I had what sounded almost exactly like this. Turned out to be the cold water feed pipe at the back of the washing machine on the other side of the kitchen had a slow dribble. Had been running under the tiling and underfloor heating for a while.

Another area that does crop up from time to time is central heating pipes running through concrete floors. The cement eats away at copper and eventually causes pinhole leaks to occur. Very difficult to trace the exact location of the leak, and very disruptive & messy work to fix.

RelievedSheff

Is it just condensation if the house has been left unheated and unventilated ?

pieroabcd

The house must have been used until the completion day because the heating was still turning on in the morning. 

As for the concrete, when I inspected the joists I didn't see any concrete, that left my quite shocked because I imagined to find a foundation in the form of a concrete slab at the bottom.
Hopefully it's there but hidden from sight.

On the other wall (in a symmetric position) there's the cloakroom with the washing machine. That is the only thing that I couldn't test because I don't have it yet, but maybe there's some pipework that leads here? I don't know.

LHW99

Did something with water in break in that area just before completion? such as a fish tank or similar?

pieroabcd

No fish tank, but I'm beginning to wonder if they haven't poured water when cleaning

pieroabcd

Update: today I've removed a nail from the wall and a big chunk of paint has literally peeled off.
I've removed as much as I could with incredible ease, literally like dead skin.
Tha part of wall is actually covered by plasterboard and it's definitely wet at the touch.
Now I'm wondering if that paint can have prevented the plasterboard from drying out and if -now that it's naked- it will dry out better (and maybe in depth)?
I hope that I won't have to replace the whole plasterboard, too. 

FreeBear

If plasterboard (and gypsum plaster) remains damp for any length of time, it turns to mush. You may be OK depending on how long the wall was damp.. I'd suggest starting a savings pot to fund repairs & minor renovations as you redecorate.

pieroabcd

FreeBear said:

If plasterboard (and gypsum plaster) remains damp for any length of time, it turns to mush. You may be OK depending on how long the wall was damp.. I'd suggest starting a savings pot to fund repairs & minor renovations as you redecorate.

That is a life long habit 😉

It feels still solid, but I don't know in what condition it's inside 
I think that it must have been wet for no more than 5 months. In December it didn't feel wet and there were no bubbles on the wall