Hello.

I have a 1940s house, so even though it has cavity walls (I'm still learning about all this) can cement rendering cause dampness on internal walls?

My kitchen and extension's external walls are rendering. One part is "hollow" though it was fixed and the dampness is more noticeable after rain. Also both rooms have a concrete floor.

Thank you.

Ed.

On 02/11/12 21:26, wrote:
Hello.

I have a 1940s house, so even though it has cavity walls (I'm still
learning about all this) can cement rendering cause dampness on
internal walls?

My kitchen and extension's external walls are rendering. One part is
"hollow" though it was fixed and the dampness is more noticeable
after rain. Also both rooms have a concrete floor.


where is the dampness showing up?

Thank you.

Ed.



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Nov 2, 9:26*pm, wrote:
Hello.

I have a 1940s house, so even though it has cavity walls (I'm still learning about all this) can cement rendering cause dampness on internal walls?

My kitchen and extension's external walls are rendering. One part is "hollow" though it was fixed and the dampness is more noticeable after rain. Also both rooms have a concrete floor.

Thank you.

Ed.

If your walls are cavity, the only way damp can penetrate is if the
cavity is bridged in some way (rubble/cement droppings etc.) ie some
constructional defect
Condensation is more likely.

Determining the source/cause of damp needs experience.
More info/pix needed.

If you tap on rendering and it sounds hollow it is an indication that
it has become detached/"unstuck" from the wall. However this in itself
should not cause damp to penetrate a cavity wall.
At some point it will fall off/get much worse & have to be fixed.
Probably caused by frost action.

On 02/11/12 21:26, wrote:
Hello.

I have a 1940s house, so even though it has cavity walls (I'm still learning about all this) can cement rendering cause dampness on internal walls?

My kitchen and extension's external walls are rendering. One part is "hollow" though it was fixed and the dampness is more noticeable after rain. Also both rooms have a concrete floor.

You don't say where the damp is. If it's at the bottom couple of feet of
the wall I'd suspect that the damp proof course has been bridged on the
outside by soil piling up or, in my case, by somebody plastering the
inside wall all the way to the floor (and with the wrong kind of plaster
too).

If it's higher than that is it the upper floor? If so suspect a roof or
guttering leak or, as others have said, condensation caused by lack of
ventilation.

We need more details.

Another Dave

wrote:
Hello.

I have a 1940s house, so even though it has cavity walls (I'm still
learning about all this) can cement rendering cause dampness on
internal walls?

No, damp is caused by water getting in, either by tracking across the cavity
if it's been breached, or by a failed DPC


My kitchen and extension's external walls are rendering. One part is
"hollow" though it was fixed and the dampness is more noticeable
after rain. Also both rooms have a concrete floor.

If it's 'hollow', it's not been fixed, otherwise it wouldn't be hollow.

Where does the external render finish at the bottom? - it needs to be above
the DPC not below it.

You may need to hack off the hollow render and do it again, also you need to
check the internal plaster that it's not all the way down to the concrete.

More information required for a proper diagnosis

Hi all,

thanks for the replies.

The damp is in the inside of the external walls but also in the dividing wall.

It goes up about 4 feet.

The plaster seems to stop about an inch above the floor.

I say it's *in* the walls. The bricks are actually damp.

There's no radiator in the kitchen but I had one put in the extension. It seems to dry out the wall until it rains again.

It could be that the DPC has been bridged but I can't even see a DPC to be honest. The bricks were painted black. The paint had peeled about below where the patch of hollow render is.

Could it be a water course under the extension?

Thanks again all.

And to add, the render finishes about 2 feet above the ground and is curved outwards, which I assume is to stop rain dropping inward.

On Nov 3, 7:07*pm, wrote:
Hi all,

thanks for the replies.

The damp is in the inside of the external walls but also in the dividing wall.

It goes up about 4 feet.

The plaster seems to stop about an inch above the floor.

I say it's *in* the walls. The bricks are actually damp.

There's no radiator in the kitchen but I had one put in the extension. It seems to dry out the wall until it rains again.

It could be that the DPC has been bridged but I can't even see a DPC to be honest. The bricks were painted black. The paint had peeled about below where the patch of hollow render is.

Could it be a water course under the extension?

Thanks again all.

If an internal wall is damp that points to either a massive
temperature/humidity difference between the two sides of the wall or
faulty damp proof course.
What sort ofDPC is fitted?
If it is the felt it is probably OK If slate/engineering bricks it
might not be.

On Friday, November 2, 2012 9:26:17 PM UTC, wrote:

Hello.
I have a 1940s house, so even though it has cavity walls (I'm still learning about all this) can cement rendering cause dampness on internal walls?
My kitchen and extension's external walls are rendering. One part is "hollow" though it was fixed and the dampness is more noticeable after rain. Also both rooms have a concrete floor.
Thank you.
Ed.


Hi all,
thanks for the replies.
The damp is in the inside of the external walls but also in the dividing wall.
It goes up about 4 feet.
The plaster seems to stop about an inch above the floor.
I say it's *in* the walls. The bricks are actually damp.
There's no radiator in the kitchen but I had one put in the extension. It seems to dry out the wall until it rains again.
It could be that the DPC has been bridged but I can't even see a DPC to be honest. The bricks were painted black. The paint had peeled about below where the patch of hollow render is.
Could it be a water course under the extension?
Thanks again all.


And to add, the render finishes about 2 feet above the ground and is curved outwards, which I assume is to stop rain dropping inward.


The most likely cause is condensation, caused primarily by too high an interior RH. This type of thing is often misdiagosed as rising damp, which although it exists, is unusual. The solution is normally to address interior sources of dampness, eg showers without adequate ventilation, hob cooking on excessively high heat, drying clothes indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior, since interior RH is higher on average. Thus evaporation of water from the exterior of the wall is necessary to avoid dampness. You mentioned a black paint, if you mean bitumen on the exterior then this can gradually cause damp problems by preventing evaporation. Painted cement render can occasionally too in walls that are borderline in terms of how they handle damp, but that's not likely to apply to a cavity wall. Are you sure they're cavity walls, as everything you describe is a lot more likely to occur with non-cavity walls?


NT

On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

Hello. I have a 1940s house, so even though it has cavity walls
(I'm still learning about all this) can cement rendering cause
dampness on internal walls? My kitchen and extension's external
walls are rendering. One part is "hollow" though it was fixed and
the dampness is more noticeable after rain. Also both rooms have a
concrete floor. Thank you. Ed.


Hi all, thanks for the replies. The damp is in the inside of the
external walls but also in the dividing wall. It goes up about 4
feet. The plaster seems to stop about an inch above the floor. I
say it's *in* the walls. The bricks are actually damp. There's no
radiator in the kitchen but I had one put in the extension. It
seems to dry out the wall until it rains again. It could be that
the DPC has been bridged but I can't even see a DPC to be honest.
The bricks were painted black. The paint had peeled about below
where the patch of hollow render is. Could it be a water course
under the extension? Thanks again all.


And to add, the render finishes about 2 feet above the ground and
is curved outwards, which I assume is to stop rain dropping
inward.


The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?


NT


Thank you for that glimpse into 1950s Britain before central heating was
the norm

On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

Hello. I have a 1940s house, so even though it has cavity walls
(I'm still learning about all this) can cement rendering cause
dampness on internal walls? My kitchen and extension's external
walls are rendering. One part is "hollow" though it was fixed and
the dampness is more noticeable after rain. Also both rooms have a
concrete floor. Thank you. Ed.


Hi all, thanks for the replies. The damp is in the inside of the
external walls but also in the dividing wall. It goes up about 4
feet. The plaster seems to stop about an inch above the floor. I
say it's *in* the walls. The bricks are actually damp. There's no
radiator in the kitchen but I had one put in the extension. It
seems to dry out the wall until it rains again. It could be that
the DPC has been bridged but I can't even see a DPC to be honest.
The bricks were painted black. The paint had peeled about below
where the patch of hollow render is. Could it be a water course
under the extension? Thanks again all.


And to add, the render finishes about 2 feet above the ground and
is curved outwards, which I assume is to stop rain dropping
inward.


The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?


NT

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

Hello. I have a 1940s house, so even though it has cavity walls
(I'm still learning about all this) can cement rendering cause
dampness on internal walls? My kitchen and extension's external
walls are rendering. One part is "hollow" though it was fixed and
the dampness is more noticeable after rain. Also both rooms have a
concrete floor. Thank you. Ed.


Hi all, thanks for the replies. The damp is in the inside of the
external walls but also in the dividing wall. It goes up about 4
feet. The plaster seems to stop about an inch above the floor. I
say it's *in* the walls. The bricks are actually damp. There's no
radiator in the kitchen but I had one put in the extension. It
seems to dry out the wall until it rains again. It could be that
the DPC has been bridged but I can't even see a DPC to be honest.
The bricks were painted black. The paint had peeled about below
where the patch of hollow render is. Could it be a water course
under the extension? Thanks again all.


And to add, the render finishes about 2 feet above the ground and
is curved outwards, which I assume is to stop rain dropping
inward.


The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?


NT

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

On 04/11/2012 12:17, stuart noble wrote:

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Probably lives in Scotland. :-)

http://www.bbc.co.uk/news/uk-scotland-20176376

--
Rod

On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a small extent out through walls.


NT

On 04/11/2012 09:03, wrote:


The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?


NT

RH is all about water vapour.

If the interior water vapour is going through the wall then there is no
evaporation at the outside.

If that water vapour is condensing in or on the wall, that is a
different matter.

--
Rod

On 04/11/2012 12:39, wrote:
On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a small extent out through walls.


NT

The warm air indoors is quite able to carry a bit of extra moisture, so
it doesn't go anywhere. In fact, in what I would term a normal household
there is more danger of low rh than high but, if you're not going to
maintain a temperature fit for human habitation, then there won't be
much difference between inside and out. No way to live though

On Sunday, November 4, 2012 2:07:35 PM UTC, stuart noble wrote:
On 04/11/2012 12:39, wrote:
On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:


The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a small extent out through walls.

The warm air indoors is quite able to carry a bit of extra moisture,
yes

so it doesn't go anywhere.

People keep breathing, washing and cooking, so water keeps being put into the interior air. If it really went nowhere, it would condense out and flood the house. Its pretty obvious it goes somewhere.


In fact, in what I would term a normal household
there is more danger of low rh than high but,

In some cases yes, in some the reverse.


if you're not going to
maintain a temperature fit for human habitation, then there won't be
much difference between inside and out. No way to live though

Unheated houses have higher indoor RH than out because of the constant supply of water vapour from breathing, washing and cooking.

Seriously you need to get this figured out beore you can understand how damp works.


NT

On 04/11/2012 14:51, wrote:
On Sunday, November 4, 2012 2:07:35 PM UTC, stuart noble wrote:
On 04/11/2012 12:39, wrote:
On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble
wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:


The most likely cause is condensation, caused primarily
by too high an interior RH. This type of thing is often
misdiagosed as rising damp, which although it exists, is
unusual. The solution is normally to address interior
sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying
clothes indoors, unvented gas heating, inadequate
ventilation in rooms etc.

The gradual movement of water vapour is from interior to
exterior, since interior RH is higher on average. Thus
evaporation of water from the exterior of the wall is
necessary to avoid dampness. You mentioned a black paint,
if you mean bitumen on the exterior then this can
gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that
are borderline in terms of how they handle damp, but
that's not likely to apply to a cavity wall. Are you sure
they're cavity walls, as everything you describe is a lot
more likely to occur with non-cavity walls?

Thank you for that glimpse into 1950s Britain before
central heating was the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher
than outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all
put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a
small extent out through walls.

The warm air indoors is quite able to carry a bit of extra
moisture,
yes

so it doesn't go anywhere.

People keep breathing, washing and cooking, so water keeps being put
into the interior air. If it really went nowhere, it would condense
out and flood the house. Its pretty obvious it goes somewhere.


In fact, in what I would term a normal household there is more
danger of low rh than high but,

In some cases yes, in some the reverse.


if you're not going to maintain a temperature fit for human
habitation, then there won't be much difference between inside and
out. No way to live though

Unheated houses have higher indoor RH than out because of the
constant supply of water vapour from breathing, washing and cooking.

Seriously you need to get this figured out beore you can understand
how damp works.


NT

All I need to figure out is why you appear to be living in the land that
time forgot.

wrote:
Hi all,

thanks for the replies.

The damp is in the inside of the external walls but also in the
dividing wall.

I know you know where the dividing wall is but I don't, the dividing wall
between what?



It goes up about 4 feet.


rising damp

The plaster seems to stop about an inch above the floor.


you'd be wise to knock off another inch or two

I say it's *in* the walls. The bricks are actually damp.


Then it needs a dampcourse, you can DIY, providing you know how to drill a
hole

There's no radiator in the kitchen but I had one put in the
extension. It seems to dry out the wall until it rains again.

It could be that the DPC has been bridged but I can't even see a DPC
to be honest. The bricks were painted black. The paint had peeled
about below where the patch of hollow render is.

Water is getting behind this patch of hollow render, and running down, which
has caused the paint to peel.

The DPC is the level of your internal floor


Could it be a water course under the extension?

No

Sorry, the dividing wall is between the kitchen and the extension, both have the concrete floors.

I had a chemical DPC done by a plasterer a few years back.

On Sunday, November 4, 2012 5:32:13 PM UTC, stuart noble wrote:
On 04/11/2012 14:51, wrote:
On Sunday, November 4, 2012 2:07:35 PM UTC, stuart noble wrote:
On 04/11/2012 12:39, wrote:
On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble
wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:


The most likely cause is condensation, caused primarily
by too high an interior RH. This type of thing is often
misdiagosed as rising damp, which although it exists, is
unusual. The solution is normally to address interior
sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying
clothes indoors, unvented gas heating, inadequate
ventilation in rooms etc.

The gradual movement of water vapour is from interior to
exterior, since interior RH is higher on average. Thus
evaporation of water from the exterior of the wall is
necessary to avoid dampness. You mentioned a black paint,
if you mean bitumen on the exterior then this can
gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that
are borderline in terms of how they handle damp, but
that's not likely to apply to a cavity wall. Are you sure
they're cavity walls, as everything you describe is a lot
more likely to occur with non-cavity walls?

Thank you for that glimpse into 1950s Britain before
central heating was the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher
than outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all
put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a
small extent out through walls.

The warm air indoors is quite able to carry a bit of extra
moisture,
yes

so it doesn't go anywhere.

People keep breathing, washing and cooking, so water keeps being put
into the interior air. If it really went nowhere, it would condense
out and flood the house. Its pretty obvious it goes somewhere.


In fact, in what I would term a normal household there is more
danger of low rh than high but,

In some cases yes, in some the reverse.


if you're not going to maintain a temperature fit for human
habitation, then there won't be much difference between inside and
out. No way to live though

Unheated houses have higher indoor RH than out because of the
constant supply of water vapour from breathing, washing and cooking.

Seriously you need to get this figured out beore you can understand
how damp works.
a

NT

All I need to figure out is why you appear to be living in the land that
time forgot.

That's one lousy answer. Or are you really claiming the basics of physics have changed lately

On Nov 4, 12:17*pm, stuart noble wrote:
On 04/11/2012 12:07, wrote:







On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

Hello. I have a 1940s house, so even though it has cavity walls
(I'm still learning about all this) can cement rendering cause
dampness on internal walls? My kitchen and extension's external
walls are rendering. One part is "hollow" though it was fixed and
the dampness is more noticeable after rain. Also both rooms have a
concrete floor. Thank you. Ed.

Hi all, thanks for the replies. The damp is in the inside of the
external walls but also in the dividing wall. It goes up about 4
feet. The plaster seems to stop about an inch above the floor. I
say it's *in* the walls. The bricks are actually damp. There's no
radiator in the kitchen but I had one put in the extension. It
seems to dry out the wall until it rains again. It could be that
the DPC has been bridged but I can't even see a DPC to be honest.
The bricks were painted black. The paint had peeled about below
where the patch of hollow render is. Could it be a water course
under the extension? Thanks again all.

And to add, the render finishes about 2 feet above the ground and
is curved outwards, which I assume is to stop rain dropping
inward.

The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?

NT

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Showers kitchen and bath rooms of course. When the warm damp air
encounters a cold surface, it condenses.

On Nov 4, 2:07*pm, stuart noble wrote:
On 04/11/2012 12:39, wrote:







On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a small extent out through walls.

NT

The warm air indoors is quite able to carry a bit of extra moisture, so
it doesn't go anywhere. In fact, in what I would term a normal household
there is more danger of low rh than high but, if you're not going to
maintain a temperature fit for human habitation, then there won't be
much difference between inside and out. No way to live though

Clearly a topic you have zero knowledge about.

On Nov 4, 10:52*pm, wrote:
Sorry, the dividing wall is between the kitchen and the extension, both have the concrete floors.

I had a chemical DPC done by a plasterer a few years back.

It is very likely condensation especially if it is worse on the
kitchen side and the extension is a cold room..
I'm surprised you don't also have condensation on the outer wall(s)
of the kitchen but some surfaces don't show it or maybe are insulated.

Do you have a cooker hood to take away cooking vapours?
If not, that is the likely cause of your troubles.
The chemical DPC should be good if properly done.

On 05/11/2012 08:10, harry wrote:
On Nov 4, 12:17 pm, stuart noble wrote:


Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Showers kitchen and bath rooms of course. When the warm damp air
encounters a cold surface, it condenses.

"Normally" seem to imply an ongoing, more-or-less permanent state of
affairs. Our kitchen and bathroom might transiently have RH towards the
high end - but very rapidly reduce - we do have opening windows! Hence
ours are not running in condensation, are not coated in black mould, etc.

--
Rod

On 05/11/2012 02:27, wrote:
On Sunday, November 4, 2012 5:32:13 PM UTC, stuart noble wrote:
On 04/11/2012 14:51, wrote:
On Sunday, November 4, 2012 2:07:35 PM UTC, stuart noble wrote:
On 04/11/2012 12:39, wrote:
On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble
wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:


The most likely cause is condensation, caused primarily
by too high an interior RH. This type of thing is often
misdiagosed as rising damp, which although it exists, is
unusual. The solution is normally to address interior
sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying
clothes indoors, unvented gas heating, inadequate
ventilation in rooms etc.

The gradual movement of water vapour is from interior to
exterior, since interior RH is higher on average. Thus
evaporation of water from the exterior of the wall is
necessary to avoid dampness. You mentioned a black paint,
if you mean bitumen on the exterior then this can
gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that
are borderline in terms of how they handle damp, but
that's not likely to apply to a cavity wall. Are you sure
they're cavity walls, as everything you describe is a lot
more likely to occur with non-cavity walls?

Thank you for that glimpse into 1950s Britain before
central heating was the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher
than outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all
put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a
small extent out through walls.

The warm air indoors is quite able to carry a bit of extra
moisture,
yes

so it doesn't go anywhere.

People keep breathing, washing and cooking, so water keeps being put
into the interior air. If it really went nowhere, it would condense
out and flood the house. Its pretty obvious it goes somewhere.


In fact, in what I would term a normal household there is more
danger of low rh than high but,

In some cases yes, in some the reverse.


if you're not going to maintain a temperature fit for human
habitation, then there won't be much difference between inside and
out. No way to live though

Unheated houses have higher indoor RH than out because of the
constant supply of water vapour from breathing, washing and cooking.

Seriously you need to get this figured out beore you can understand
how damp works.
a

NT

All I need to figure out is why you appear to be living in the land that
time forgot.

That's one lousy answer. Or are you really claiming the basics of physics have changed lately


We have insulation and central heating these days. That is what has
changed. Breathing, washing and cooking just aren't a problem in the
modern home.

On 05/11/2012 08:12, harry wrote:
On Nov 4, 2:07 pm, stuart noble wrote:
On 04/11/2012 12:39, wrote:







On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a small extent out through walls.

NT

The warm air indoors is quite able to carry a bit of extra moisture, so
it doesn't go anywhere. In fact, in what I would term a normal household
there is more danger of low rh than high but, if you're not going to
maintain a temperature fit for human habitation, then there won't be
much difference between inside and out. No way to live though

Clearly a topic you have zero knowledge about.

Turn your heating on, Harry. You know it makes sense!

On 05/11/2012 08:23, polygonum wrote:
On 05/11/2012 08:10, harry wrote:
On Nov 4, 12:17 pm, stuart noble wrote:


Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Showers kitchen and bath rooms of course. When the warm damp air
encounters a cold surface, it condenses.

"Normally" seem to imply an ongoing, more-or-less permanent state of
affairs. Our kitchen and bathroom might transiently have RH towards the
high end - but very rapidly reduce - we do have opening windows! Hence
ours are not running in condensation, are not coated in black mould, etc.


Well exactly. What's so complicated about that?
You get rid of condensation either by ventilation or by raising the air
temperature so that it can carry more moisture (i.e. it dries) or, shock
horror, a combination of both. Yes it hurts to have the windows open and
the boiler on but it's not for long.

On Monday, November 5, 2012 9:35:32 AM UTC, stuart noble wrote:
On 05/11/2012 02:27, wrote:
On Sunday, November 4, 2012 5:32:13 PM UTC, stuart noble wrote:
On 04/11/2012 14:51, wrote:
On Sunday, November 4, 2012 2:07:35 PM UTC, stuart noble wrote:
On 04/11/2012 12:39, wrote:
On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble
wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:


The most likely cause is condensation, caused primarily
by too high an interior RH. This type of thing is often
misdiagosed as rising damp, which although it exists, is
unusual. The solution is normally to address interior
sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying
clothes indoors, unvented gas heating, inadequate
ventilation in rooms etc.

The gradual movement of water vapour is from interior to
exterior, since interior RH is higher on average. Thus
evaporation of water from the exterior of the wall is
necessary to avoid dampness. You mentioned a black paint,
if you mean bitumen on the exterior then this can
gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that
are borderline in terms of how they handle damp, but
that's not likely to apply to a cavity wall. Are you sure
they're cavity walls, as everything you describe is a lot
more likely to occur with non-cavity walls?

Thank you for that glimpse into 1950s Britain before
central heating was the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher
than outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all
put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a
small extent out through walls.

The warm air indoors is quite able to carry a bit of extra
moisture,
yes

so it doesn't go anywhere.

People keep breathing, washing and cooking, so water keeps being put
into the interior air. If it really went nowhere, it would condense
out and flood the house. Its pretty obvious it goes somewhere.


In fact, in what I would term a normal household there is more
danger of low rh than high but,

In some cases yes, in some the reverse.


if you're not going to maintain a temperature fit for human
habitation, then there won't be much difference between inside and
out. No way to live though

Unheated houses have higher indoor RH than out because of the
constant supply of water vapour from breathing, washing and cooking.

Seriously you need to get this figured out beore you can understand
how damp works.

All I need to figure out is why you appear to be living in the land that
time forgot.

That's one lousy answer. Or are you really claiming the basics of physics have changed lately

We have insulation and central heating these days. That is what has
changed.

Indeed, which doesnt change the above one iota.

Breathing, washing and cooking just aren't a problem in the
modern home.

AFAIK they've never been a problem in any home. Excess water vapour however is in some old houses that have been wrongly modified and are now borderline in terms of how they handle water vapour.


NT

On Monday, November 5, 2012 9:48:27 AM UTC, stuart noble wrote:
On 05/11/2012 08:23, polygonum wrote:
On 05/11/2012 08:10, harry wrote:
On Nov 4, 12:17 pm, stuart noble wrote:


Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Showers kitchen and bath rooms of course. When the warm damp air
encounters a cold surface, it condenses.

"Normally" seem to imply an ongoing, more-or-less permanent state of
affairs. Our kitchen and bathroom might transiently have RH towards the
high end - but very rapidly reduce - we do have opening windows! Hence
ours are not running in condensation, are not coated in black mould, etc.

Well exactly. What's so complicated about that?

Nothing. It seems to confuse increased RH with condensation & mould. Condensation only happens where RH locally reaches 100%. Mould only happens where condensation happens so much the wall is too damp over time.


You get rid of condensation either by ventilation or by raising the air
temperature so that it can carry more moisture (i.e. it dries) or, shock
horror, a combination of both. Yes it hurts to have the windows open and
the boiler on but it's not for long.

Most of the time such meaures aren't being taken, and water vapour is being put into the air all the time a house is occupied. Heating enables it to carry more water vapour, but obviously that alone wouldnt keep it dry for long, there is then ventilation which replaces interior air with greater vapour content with outdoor air with lower water vapour content.

In walls without a VB, you also have higher water vapour content on one side than the other, so the vapour slowly migrates through the walls from inside to outside.

Its basic physics.

Most of the time such meaures aren't being taken, and water vapour is
being put into the air all the time a house is occupied. Heating
enables it to carry more water vapour, but obviously that alone
wouldnt keep it dry for long,

Obviously it would. With the thermostat at 20 degs the air will carry
more water than you can produce by breathing and cooking. That is
precisely why it isn't a problem for normal people in normal houses.

It's interesting that tropical hardwoods grown where the RH is damned
near 100% dry out too quickly when they are felled. It's all about
temperature

there is then ventilation which
replaces interior air with greater vapour content with outdoor air
with lower water vapour content.

How much vapour content there is, in or out, depends on temperature. You
can't just say that the interior has a higher vapour content.


In walls without a VB, you also have higher water vapour content on
one side than the other, so the vapour slowly migrates through the
walls from inside to outside.

Its basic physics.


Fortunately the average housewife knows perfectly well how to keep a
house dry and healthy without your in-depth knowledge of physics.

You continue to adopt this high handed and patronising attitude to
anyone that disagrees with you, which I don't find at all constructive

wrote:
Sorry, the dividing wall is between the kitchen and the extension,
both have the concrete floors.

I had a chemical DPC done by a plasterer a few years back.

In which case the horizontal row of holes must still be visible both inside
and outside the house?
If not then they are plastered over inside and rendered over outside - they
should not be covered, they can be filled in, but the brick that has been
injected should be visible (provided you've removed the skirting boards)

I think it needs injecting again, the rendering and internal plaster
completely removing and fresh render applied inside and out, stopping
*above* the DPC in both cases....chances are he's used browning or other
similar inappropriate plaster internally.

I assume the dividing wall was once an external wall prior to the extension
being built?

On Monday, November 5, 2012 6:08:08 PM UTC, stuart noble wrote:


Most of the time such meaures aren't being taken, and water vapour is
being put into the air all the time a house is occupied. Heating
enables it to carry more water vapour, but obviously that alone
wouldnt keep it dry for long,

Obviously it would. With the thermostat at 20 degs the air will carry
more water than you can produce by breathing and cooking. That is
precisely why it isn't a problem for normal people in normal houses.

Even if heating increased vapour carrying ability by 10 or 100x, the amount of water vapour it can carry is always finite. But the addition of vapour to the air by living is endless. Its patently obvious that air can't carry an endless amount of vapour, so heat alone doesn't resolve things.


there is then ventilation which
replaces interior air with greater vapour content with outdoor air
with lower water vapour content.

How much vapour content there is, in or out, depends on temperature.

Yes

You
can't just say that the interior has a higher vapour content.

Lordy. We take in the outdoor air and add more vapour from breathing, cooking and washing. Do you think that dries the air?

In walls without a VB, you also have higher water vapour content on
one side than the other, so the vapour slowly migrates through the
walls from inside to outside.

Its basic physics.

Fortunately the average housewife knows perfectly well how to keep a
house dry and healthy without your in-depth knowledge of physics.

Whether a home stays dry is more to do with its design & construction. Only a minority of buildings require significant care over interior activities.

You continue to adopt this high handed and patronising attitude to
anyone that disagrees with you, which I don't find at all constructive

Well, you demonstrate a determined failure to grasp the basics, you can't be bothered to read up on the subject, yet you insist your confusion is right. Lets just agree to disagree, its easier.


NT

Lordy. We take in the outdoor air and add more vapour from breathing,
cooking and washing. Do you think that dries the air?

You are forgetting that outdoor air is normally cooler than indoor. When
it enters the house, it is heated and, what was a high RH outside,
quickly becomes a low RH inside. Buildings with modern standards of
heating and insulation will invariably be too dry in winter. Ask anyone
who owns a piano. The RH in my house is between 40% and 60%. Lower than
that you get static problems, and higher than that you can get thrush
and similar ailments.

Whether a home stays dry is more to do with its design &
construction. Only a minority of buildings require significant care
over interior activities.

On that we agree! The only insurmountable problems I have encountered
were in a 60s concrete north facing flat that was in constant shade and
should not have been built in the first place. Low RH is a major problem
in offices, despite the occupants breathing in and out all day. It's
only a slightly lesser problem in modern houses where kitchens and
bathrooms raise moisture levels, and it probably isn't a problem at all
if you live in a listed building on Dartmoor.

You continue to adopt this high handed and patronising attitude to
anyone that disagrees with you, which I don't find at all
constructive

Well, you demonstrate a determined failure to grasp the basics, you
can't be bothered to read up on the subject, yet you insist your
confusion is right. Lets just agree to disagree, its easier.

The lack of comments from anyone else suggests that is probably a good
idea. Actually it's QI that there is no interest from a group that will
argue the toss about virtually anything :-)

On Tuesday, November 6, 2012 10:33:38 AM UTC, stuart noble wrote:

Lordy. We take in the outdoor air and add more vapour from breathing,
cooking and washing. Do you think that dries the air?

You are forgetting that outdoor air is normally cooler than indoor.

Of course i'm not forgetting it, its totally obvious. You only show your position to be foolish by such suggestions.

When
it enters the house, it is heated and, what was a high RH outside,
quickly becomes a low RH inside.

Correct. Then you add the usual indoor vapour sources, and the result can only possibly be more water vapour in the air than outdoors (unless you're using ac).

Buildings with modern standards of
heating and insulation will invariably be too dry in winter.

Some are, some aren't

Ask anyone
who owns a piano. The RH in my house is between 40% and 60%. Lower than
that you get static problems, and higher than that you can get thrush
and similar ailments.

Whether a home stays dry is more to do with its design &
construction. Only a minority of buildings require significant care
over interior activities.

On that we agree! The only insurmountable problems I have encountered
were in a 60s concrete north facing flat that was in constant shade and
should not have been built in the first place. Low RH is a major problem
in offices, despite the occupants breathing in and out all day.

Yes, when a/c is used. It extracts water vapour.

NT


It's
only a slightly lesser problem in modern houses where kitchens and
bathrooms raise moisture levels, and it probably isn't a problem at all
if you live in a listed building on Dartmoor.

You continue to adopt this high handed and patronising attitude to
anyone that disagrees with you, which I don't find at all
constructive

Well, you demonstrate a determined failure to grasp the basics, you
can't be bothered to read up on the subject, yet you insist your
confusion is right. Lets just agree to disagree, its easier.

The lack of comments from anyone else suggests that is probably a good
idea. Actually it's QI that there is no interest from a group that will
argue the toss about virtually anything :-)