mould on walls

[sijaysee]

hi
im having big problems at the moment with
black mould on our mainly upstairs walls which face
the elements.

house is constrcted out of solid 9" concrete block

so there is no insulation.

i recently laid new loft insulation and wonder if
this could have made the problem worse.

i am thinking about bording these walls with
gyproc thermaline plus which is basically a
sheet of plasterboard with a slab of insulation
stuck to it

do you think this is a good idea and what
would be the best way of fixing the boards to
the skimmed walls?

the house is naturally pretty cold but do you think
that opening windows a bit would help the situation

cheers

 

[JerryM]

black mold is normally a result of condensation which is sorted by heat or vent.

try to work out what's causing the condensation (cooking or showering) and then try to counter it by opening a window wide afterwards or getting an extract. alternatively leave a window open on trickle for a good part of the day or night.

i don't think the boarding is a good idea as the route cause has not been sorted.

i don't believe the loft insulation has anything to do with it unless a vapour barrier was put underneath the insulation.

 

[sijaysee]

you dont think boarding is a good idea?
only the council are doing just that to all
the houses on our road that they still own

only difference is that they are cladding the outside
of the houses and then plastering straight over the
insulation with a special render

i would have thought that insulating the inside is
pretty much as good as that

all the houses that i know of that are constructed
of solid 9" concrete block suffer from really bad
condensation because the walls are so cold to the touch

 

[JerryM]

Mould is caused by dampness. dampness is caused by condensation, penetrating and rising damp. the general rule is to find the cause in that order then sort.

mould is usually a fair bet to be caused by condensation - and most modern living habits cause it in bucket loads (windows shut, much cooking and showering).

it's not always caused by condensation though. on one house it had mould only upstairs and mainly close to the windows. it was found that the gap between the window frames and wall had not been sealed. foam and mastic sorted.

as your mould is upstairs (as well as some down stairs) then i feel safe to rule out rising damp.

condensation needs to be ruled out. it occurs when moist air reaches cold walls and the water in the air then condenses and the wall becomes wet. the only sure way is to get a relative humidity meter and thermometer and work out what's called dew point (when the water condenses).

noting the potential for wrong diagnosis without instrument the question is do you feel that the moisture (from the living in the house) has increased during the period when the mould became apparent? alternatively clean off the mould increase the ventilation and see if this sorts it.

if it's not condensation then it’s penetrating damp (especially given the solid wall ie no cavity). applying insulation and boarding alone will not sort long term as the moisture from outside travelling through the wall will get into the insulation and travel into the plasterboard.

the cladding is an ideal solution as it's aimed at the cause ie stopping rain penetrating the external surface of the wall. rendering the outside wall is also an alternative.

if nothing is done externally then the inside walls need to stop the water leaving the internal surface of the solid brick wall before it gets to any insulation or plasterboard. This is complicated by the existence of the timber 1st floor which needs to remain dry. By placing some form of vapour barrier on the inside walls will cause the penetrated damp to “move” elsewhere as it will no longer be able to evaporate off the inside walls of the house. The direction is likely to be downwards which is ok if it doesn’t end up reaching the 1st floor timbers.

The special render is likely to be a waterproof equivalent to plaster. But the overall solution is dependent on the outside cladding to stop the water in the 1st place.

I can’t really see a good solution without the external cladding or render. Fitting the insulated boarding stands a chance of working but there’s no guarantee that the mould won’t be back. Fitting a vapour would stop the mould but there is a risk to the floor joists depending on how much damp is coming through. The vapour barrier could make things worse in terms of condensation as moisture can’t pass in either direction.

This must be a common problem and possibly more info on the net would help. I think you might be best initially contacting you local building control office for guidance. I always find them very helpful. This is one that I would have to get technical support on.

 

[sijaysee]

thanks for your very in-depth reply.
we are planning a large extension in the near
future so will probably do something to the other walls
to match in then i.e re render and waterproof

until then i am going to clad the internal walls