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 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

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 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.

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?