Blown render = likely cause of damp?
 

At the risk of entering the 'most obvious question of the year'
competition within the final 10 days I have a question regarding the
likely cause of damp and, more importantly, the best way to 'cure'
it...

My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?) rear wall that is
rendered and has a Tyrolean top coat.

We have recently noticed signs of damp inside a dining room cupboard,
mounted on the rear wall, and initially put this down to the low
temperature inside the cupboard (~12-14C) due to the rear wall
position. However, it then dawned on me that temperature alone is
presumably not sufficient to cause damp, water is required for this,
and so given that the kitchen/dining room is well ventilated (okay, the
cupboard isn't) and there are no signs of damp anywhere else in the
room/house then it must be coming in from outside.

Looking at the back wall there are no obvious signs of a way in for the
water, no cracks and no dodgy gutters/downpipes. However, knocking on
the render around the area of the cupboard sounds hollow.

Thus, my competition entry question is: Does that fact that the render
has blown mean this is likely to be the cause of water ingress and,
ultimately, the cause of the damp? If so, how does this happen?
Presumably there may well be hairline cracks that I can't see and the
blown render traps a layer of water against the bricks which eventually
seeps through to the inside?

If my assumptions are correct, what is the best remedial action, both
short and long term (i.e. before/after Christmas!)? Replacement will
presumably be the long term fix - it's a small enough area that I'm
more than happy to do it myself - but what with? Would it be worthwhile
removing the blown render in the short term, or will the bare bricks
then suffer just as badly? Should the bricks, before rendering, be
'treated' with anything? Does the render on these old houses serve to
'waterproof' the wall, or is it largely decorative?

Grateful for any advice...

Mathew

Blown render = likely cause of damp?
 

Mathew Newton wrote:
At the risk of entering the 'most obvious question of the year'
competition within the final 10 days I have a question regarding the
likely cause of damp and, more importantly, the best way to 'cure'
it...

My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?) rear wall that is
rendered and has a Tyrolean top coat.

We have recently noticed signs of damp inside a dining room cupboard,
mounted on the rear wall, and initially put this down to the low
temperature inside the cupboard (~12-14C) due to the rear wall
position. However, it then dawned on me that temperature alone is
presumably not sufficient to cause damp, water is required for this,
and so given that the kitchen/dining room is well ventilated (okay, the
cupboard isn't) and there are no signs of damp anywhere else in the
room/house then it must be coming in from outside.

Looking at the back wall there are no obvious signs of a way in for the
water, no cracks and no dodgy gutters/downpipes. However, knocking on
the render around the area of the cupboard sounds hollow.

Thus, my competition entry question is: Does that fact that the render
has blown mean this is likely to be the cause of water ingress and,
ultimately, the cause of the damp? If so, how does this happen?
Presumably there may well be hairline cracks that I can't see and the
blown render traps a layer of water against the bricks which eventually
seeps through to the inside?

If my assumptions are correct, what is the best remedial action, both
short and long term (i.e. before/after Christmas!)? Replacement will
presumably be the long term fix - it's a small enough area that I'm
more than happy to do it myself - but what with? Would it be worthwhile
removing the blown render in the short term, or will the bare bricks
then suffer just as badly? Should the bricks, before rendering, be
'treated' with anything? Does the render on these old houses serve to
'waterproof' the wall, or is it largely decorative?

Depends where you are. Up here on a hilltop in Scotland, there's
absolutely no doubt!

May I add a related question?

Rusting and swelling of old iron downpipe fixing spikes is a known cause
of cracked render, and our house is a perfect example. But when removing
these spikes, they tend to snap off in the bottoms of the holes. Is it
OK to fill over the deeply buried bits... or is that storing up trouble
for later?

In other words, does it need a simple filling or the full root canal?



--
Ian White

Blown render = likely cause of damp?
 

Mathew Newton wrote:
At the risk of entering the 'most obvious question of the year'
competition within the final 10 days I have a question regarding the
likely cause of damp and, more importantly, the best way to 'cure'
it...

My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?) rear wall that is
rendered and has a Tyrolean top coat.

We have recently noticed signs of damp inside a dining room cupboard,
mounted on the rear wall, and initially put this down to the low
temperature inside the cupboard (~12-14C) due to the rear wall
position. However, it then dawned on me that temperature alone is
presumably not sufficient to cause damp, water is required for this,
and so given that the kitchen/dining room is well ventilated (okay, the
cupboard isn't) and there are no signs of damp anywhere else in the
room/house then it must be coming in from outside.

Looking at the back wall there are no obvious signs of a way in for the
water, no cracks and no dodgy gutters/downpipes. However, knocking on
the render around the area of the cupboard sounds hollow.

Thus, my competition entry question is: Does that fact that the render
has blown mean this is likely to be the cause of water ingress and,
ultimately, the cause of the damp? If so, how does this happen?
Presumably there may well be hairline cracks that I can't see and the
blown render traps a layer of water against the bricks which eventually
seeps through to the inside?

If my assumptions are correct, what is the best remedial action, both
short and long term (i.e. before/after Christmas!)? Replacement will
presumably be the long term fix - it's a small enough area that I'm
more than happy to do it myself - but what with? Would it be worthwhile
removing the blown render in the short term, or will the bare bricks
then suffer just as badly? Should the bricks, before rendering, be
'treated' with anything? Does the render on these old houses serve to
'waterproof' the wall, or is it largely decorative?

Grateful for any advice...

Mathew


IME, if the render sounds hollow, it will leak, whether you can see
cracks or not.
Given that it's presumably already painted, my short term solution would
be to paint it again using a pliolite solvent based paint. Go to a
proper trade paint outlet like Johnstones or Leyland. You can use it at
sub zero temperatures, so no need to wait for fine weather. Standard
masonry paint has virtually no water resistance.
If yours is anything like my 1900 terrace, the render was probably never
bonded properly to the wall in the first place. It looks like they
slapped on the full thickness in one go. If you repair it, use the
scratch coat method.
Stand by for finger-wagging from the purists.

Blown render = likely cause of damp?
 

Ian White wrote:
Mathew Newton wrote:

At the risk of entering the 'most obvious question of the year'
competition within the final 10 days I have a question regarding the
likely cause of damp and, more importantly, the best way to 'cure'
it...

My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?) rear wall that is
rendered and has a Tyrolean top coat.

We have recently noticed signs of damp inside a dining room cupboard,
mounted on the rear wall, and initially put this down to the low
temperature inside the cupboard (~12-14C) due to the rear wall
position. However, it then dawned on me that temperature alone is
presumably not sufficient to cause damp, water is required for this,
and so given that the kitchen/dining room is well ventilated (okay, the
cupboard isn't) and there are no signs of damp anywhere else in the
room/house then it must be coming in from outside.

Looking at the back wall there are no obvious signs of a way in for the
water, no cracks and no dodgy gutters/downpipes. However, knocking on
the render around the area of the cupboard sounds hollow.

Thus, my competition entry question is: Does that fact that the render
has blown mean this is likely to be the cause of water ingress and,
ultimately, the cause of the damp? If so, how does this happen?
Presumably there may well be hairline cracks that I can't see and the
blown render traps a layer of water against the bricks which eventually
seeps through to the inside?

If my assumptions are correct, what is the best remedial action, both
short and long term (i.e. before/after Christmas!)? Replacement will
presumably be the long term fix - it's a small enough area that I'm
more than happy to do it myself - but what with? Would it be worthwhile
removing the blown render in the short term, or will the bare bricks
then suffer just as badly? Should the bricks, before rendering, be
'treated' with anything? Does the render on these old houses serve to
'waterproof' the wall, or is it largely decorative?


Depends where you are. Up here on a hilltop in Scotland, there's
absolutely no doubt!

May I add a related question?

Rusting and swelling of old iron downpipe fixing spikes is a known cause
of cracked render, and our house is a perfect example. But when removing
these spikes, they tend to snap off in the bottoms of the holes. Is it
OK to fill over the deeply buried bits... or is that storing up trouble
for later?

In other words, does it need a simple filling or the full root canal?




Water borne rust particles will permeate water based coatings, but not
oil based. I don't know that they do any real harm though.

Blown render = likely cause of damp?
 

In article .com,
"Mathew Newton" writes:

Grateful for any advice...

Stick a large sheet of aluminium foil on the inside of the
wall with thick tape all the way around the edge, and then
move everything (cupboard, contents, etc) back into place
as it is now. After a week or two, inspect it.
There will be moisture on one side of it...
If it's on the room side, it's condensation.
If it's on the wall side, it's penetrating damp.

I would expect condensation in the situation you decribed.
What is the construction of the cupboard (fixed/movable,
rear panel or open to the wall), and what's stored in it?

--
Andrew Gabriel

Blown render = likely cause of damp?
 

Ian White wrote:
Rusting and swelling of old iron downpipe fixing spikes is a known cause
of cracked render, and our house is a perfect example. But when removing
these spikes, they tend to snap off in the bottoms of the holes. Is it
OK to fill over the deeply buried bits... or is that storing up trouble
for later?

Theoretically, as the holdfast (or whatever) rusts, it will increase
in size with an enormous force being created (to about 10 times as
big as it was, IIRC). IRL I shouldn't think it will create a great
problem, and you can always get them out anyway.

Blown render = likely cause of damp?
 

Mathew Newton wrote:
My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?) rear wall that is
rendered and has a Tyrolean top coat.
[ snip ]
Thus, my competition entry question is: Does that fact that the render
has blown mean this is likely to be the cause of water ingress and,
ultimately, the cause of the damp?

Possibly.


If so, how does this happen?

Water runs down between the render and the brickwork (various flora
and fauna can exacerbate problems, e.g. ants behind render). The
water can't evaporate because of the render and coating(s), so
migrates through the wall.


If my assumptions are correct, what is the best remedial action, both
short and long term (i.e. before/after Christmas!)?

Improve ventilation, possibly use a fan.


Replacement will
presumably be the long term fix - it's a small enough area that I'm
more than happy to do it myself - but what with?

1:1:6.


Would it be worthwhile
removing the blown render in the short term,

Not in th short term, as the wall will be wet if the damp is due
to blown render. It might help dry it out over time.


or will the bare bricks then suffer just as badly?

The bricks should be fine - these sort of houses (I've had one)
are often rendered to "cure damp problems", which are often due
to poor pointing or some other trivial cause. Sometimes the
house will have been painted before it is rendered, which makes
the problem much worse.


Should the bricks, before rendering, be
'treated' with anything?

No, unless they've been painted.


Does the render on these old houses serve to
'waterproof' the wall, or is it largely decorative?

It does help waterproof the walls, and it can help them dry out
after rain. Sometimes paint is applied which can be a problem
(depending on the type of paint).

N.B. if you're patching, tyrolean can be difficult to blend in,
it can be useful to mask off, and stipple with a stiff bristle
brush (broom head) to help lose the joint. Tyrolean is also a
hard cement facing, which itself often detaches from the
underlying render (if the render is hard, too, this can cause
other problems).

Blown render = likely cause of damp?
 

Stuart Noble wrote:

IME, if the render sounds hollow, it will leak, whether you can see
cracks or not.

I think there's probably a bit of 'chicken and egg' here, in that if
water does get in, it can freeze and expand, forcing the render away
from the brickwork.

When I moved into my current house about 10 years ago, I found a quite
bad damp patch on an outside wall: investigations outside found an area
of blown render about 2' square, with a crack down the middle. I didn't
have time to do anything permanent to it just then, as the to-do list
was far too long having just moved in, so I just bodged it by filling
the crack with Tetrion exterior filler, and slapping a coat of masonry
paint over the area - thinking I'd probably do the job properly the
following summer.

Well, the wall inside dried out quite quickly, and the round tuit still
hasn't come home to roost! - the render is still blown, but it is
cosmetically fine and all still waterproof. One day...

David

Blown render = likely cause of damp?
 

Andrew Gabriel wrote:
In article .com,
"Mathew Newton" writes:

Grateful for any advice...

Stick a large sheet of aluminium foil on the inside of the
wall with thick tape all the way around the edge, and then
move everything (cupboard, contents, etc) back into place
as it is now. After a week or two, inspect it.
There will be moisture on one side of it...
If it's on the room side, it's condensation.
If it's on the wall side, it's penetrating damp.

I would expect condensation in the situation you decribed.
What is the construction of the cupboard (fixed/movable,
rear panel or open to the wall), and what's stored in it?

I'll give that a go - it has got to be prudent to not jump to
conclusions based on potential coincidences (i.e. the blown render).
Also, it'll give me a week delay on the tuit list... ;-)

As for the cupboard, it is a waste height built-in cupboard (in the
alcove adjacent to the chimney), with MDF doors, a wooden top/shelf and
no back or sides. The damp is only present on the side (exterior)
wall). As for the contents, just a blender!

The ventilation in the kitchen/dining room is pretty good - we always
use the (powerful) extractor hood when cooking etc, and there are two
vented chimneys providing background ventilation.

Will wait and see the results of the foil test before taking further
action - if it turns out to be the render I'll follow the advice given
(thanks all for the suggestions there).

Cheers,

Mathew

Blown render = likely cause of damp?
 

Chris Bacon wrote:
Ian White wrote:
Rusting and swelling of old iron downpipe fixing spikes is a known
cause of cracked render, and our house is a perfect example. But when
removing these spikes, they tend to snap off in the bottoms of the
holes. Is it OK to fill over the deeply buried bits... or is that
storing up trouble for later?

Theoretically, as the holdfast (or whatever) rusts, it will increase
in size with an enormous force being created (to about 10 times as
big as it was, IIRC). IRL I shouldn't think it will create a great
problem, and you can always get them out anyway.

This is not theoretical. In Real Life the swelling *does* create a
problem: long cracks in the render, where water can be driven in.

Obviously most of this happens close to the surface - but the water,
rust and swelling penetrate down the whole length of the spike, locking
it solidly into the wall. As soon as you try to pull these rusted spikes
out, they snap, leaving a rusty end embedded in the wall. They won't
come out without drilling away a substantial amount of wall around them.

My question was whether the broken-off ends can be covered over when the
render is patched, or whether they really do have to be dug out to
prevent a recurrence later on.


--
Ian White

Blown render = likely cause of damp?
 

Ian White wrote:
My question was whether the broken-off ends can be covered over when the
render is patched, or whether they really do have to be dug out to
prevent a recurrence later on.

It depends on whether there's going to be a problem later on.

Blown render = likely cause of damp?
 

Mathew Newton wrote:
At the risk of entering the 'most obvious question of the year'
competition within the final 10 days I have a question regarding the
likely cause of damp and, more importantly, the best way to 'cure'
it...

My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?)

yes, often

rear wall that is
rendered and has a Tyrolean top coat.

ugh.

We have recently noticed signs of damp inside a dining room cupboard,
mounted on the rear wall, and initially put this down to the low
temperature inside the cupboard (~12-14C) due to the rear wall
position. However, it then dawned on me that temperature alone is
presumably not sufficient to cause damp, water is required for this,
and so given that the kitchen/dining room is well ventilated (okay, the
cupboard isn't) and there are no signs of damp anywhere else in the
room/house then it must be coming in from outside.

Looking at the back wall there are no obvious signs of a way in for the
water, no cracks and no dodgy gutters/downpipes. However, knocking on
the render around the area of the cupboard sounds hollow.

Thus, my competition entry question is: Does that fact that the render
has blown mean this is likely to be the cause of water ingress

probably, though it could be condensation.


and,
ultimately, the cause of the damp?

Cement render is one of the main causes of damp on old properties. Its
a real poor choice, but unfortunately is still being widely applied.
Awaerness takes time to travel it seems.


If so, how does this happen?
Presumably there may well be hairline cracks that I can't see and the
blown render traps a layer of water against the bricks which eventually
seeps through to the inside?

yup, thats one part of it. The other is that old walls use soft porous
bricks, and the bricks stay dry by evporation of whatever damp gets
into them. Cement render stops this evaporation dead, thus eventaully
causing a wet wall.


If my assumptions are correct, what is the best remedial action, both
short and long term (i.e. before/after Christmas!)?

Remove any blown render. Do not try to pull off fixed render, as it
would break the bricks, which would then deteriorate badly over the
years. Patch with lime mortar. Lime mortar does not contain any cement.
This will enable the wall to continue to evaporate dry, while keeping
most of the rain off the bricks. If you want to paint it, use a lime
based paint, these are porous unlike modern paints.


Replacement will
presumably be the long term fix - it's a small enough area that I'm
more than happy to do it myself - but what with?

3:1 sand: lime putty. You can buy lime putty but I prefer to make it.
Mix fresh bagged lime with water, store it airtight for 3 weeks before
use. Lime mortar is on the dry stiff side, dont be tempted to make it
thinner/wetter.

However this is the wrong time of year to do this. For now, just remove
blown render. When risk of frost is passed, re-render. Bare bricks will
dry out even in cold weather. Drying takes weeks to months.


Would it be worthwhile
removing the blown render in the short term, or will the bare bricks
then suffer just as badly?

Bare bricks will do much better than rendered bricks, because they can
dry out.


Should the bricks, before rendering, be
'treated' with anything?

definitely not, another popular mistake.


Does the render on these old houses serve to
'waterproof' the wall,

yes, and thats precisely the problem. The net flow of water on thesse
walls is from the inside out, not vice versa.


or is it largely decorative?

Cement render is applied for a few reasons, but on old properties it is
simply an inappropriate treatment.

If you want a fuller explanation:
http://www.periodproperty.co.uk/cgi-...ing/forum2.pl?


NT

Blown render = likely cause of damp?
 

Mathew Newton wrote:
My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?)

Sorry, missed that bit.

If it's 1905, it ain't Victorian, it's Edwardian.

Some of these old buildings did have "cavities", but very, very
few. Some examples date back to the late C.19th., but normally
"cavity walls" were not built at all, any "cavities" being only
by there accident of construction - "rat trap" construction as
used to cheapen construction (bricks laid on edge) is a good
example. If you've walls made of bricks laid with some going
right through the wall, others being laid along it (sorry for
the ultra-simplistic description!) then it is not a cavity wall,
although there may well be hollows in it due to incomplete
filling with mortar. Proper cavity walls only really became
generally used later.

Blown render = likely cause of damp?
 

Blown render = likely cause of damp?
 

Stuart Noble wrote:
wrote:
The net flow of water on thesse
walls is from the inside out, not vice versa.

Am I alone in thinking this is utter nonsense?

No Stuart, there are plenty of people like you, who havent got the
brain to actually find out how it works, and assume the simplistic
storise you've been brought up on must be correct.

NT

Blown render = likely cause of damp?
 

Chris Bacon wrote:
Mathew Newton wrote:
My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?)

Sorry, missed that bit.

If it's 1905, it ain't Victorian, it's Edwardian.

Some of these old buildings did have "cavities", but very, very
few. Some examples date back to the late C.19th., but normally
"cavity walls" were not built at all, any "cavities" being only
by there accident of construction - "rat trap" construction as
used to cheapen construction (bricks laid on edge) is a good
example. If you've walls made of bricks laid with some going
right through the wall, others being laid along it (sorry for
the ultra-simplistic description!) then it is not a cavity wall,
although there may well be hollows in it due to incomplete
filling with mortar. Proper cavity walls only really became
generally used later.

Cavity walls were in the minority in Victorian times, but they were a
standard form of wall construction. They were used primarily in high
wind or wet climates, eg coastal regions. The advantage recognised was
that penetration of water into the outer leaf did not make the inner
leaf wet, and the outer leaf would dry out again before the inner
became damp. Only in the 1930s was the insulation benefit widely
appreciated, and only then did cavities become the norm.

Victorian cavity walls were not the uniform cavity walls we're used to
today. Vic houses typically used a variety of brick bonds. Half inch
cavities were common, often tied, often not. 4" bridged cavity ratbond
walls were also used, though not very common. And of course there is
also the random cavity stone wall, which dates back a very long way.


NT

Blown render = likely cause of damp?
 

Blown render = likely cause of damp?
 

Blown render = likely cause of damp?
 

The message
from contains these words:

My parent's house was built with cavity walls in 1902. It and most others in
that area were the same. Certainly a lot of the later Victorian ones had
cavity walls.

My first house (in Stafford) was built some time between the wars and
had solid walls and no foundations.

--
Roger Chapman

Blown render = likely cause of damp?
 

Stuart Noble wrote:
wrote:
Stuart Noble wrote:
wrote:

The net flow of water on thesse
walls is from the inside out, not vice versa.

Am I alone in thinking this is utter nonsense?


No Stuart, there are plenty of people like you, who havent got the
brain to actually find out how it works, and assume the simplistic
storise you've been brought up on must be correct.

NT


I've had plenty of opportunity to observe damp over the years, having
had it to varying degrees in every house I've ever lived in, and many
that I've worked on.

I wonder why.

In most cases I have cured or greatly improved the
situation with modern materials without any of the dire consequences you
go on about.
I repeat that, almost without exception, damp inside coincides with rain
outside. It rains, the wall gets wet, and the water soaks through the
wall. End of story.

you just confirmed what I said.

Go stir your lime putty.

:)


NT

Blown render = likely cause of damp?
 

Chris Bacon wrote:
wrote:
Chris Bacon wrote:
Mathew Newton wrote:

My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?)

Sorry, missed that bit.

If it's 1905, it ain't Victorian, it's Edwardian.

Some of these old buildings did have "cavities", but very, very
few. Some examples date back to the late C.19th., but normally
"cavity walls" were not built at all, any "cavities" being only
by there accident of construction - "rat trap" construction as
used to cheapen construction (bricks laid on edge) is a good
example. If you've walls made of bricks laid with some going
right through the wall, others being laid along it (sorry for
the ultra-simplistic description!) then it is not a cavity wall,
although there may well be hollows in it due to incomplete
filling with mortar. Proper cavity walls only really became
generally used later.


Cavity walls were in the minority in Victorian times, but they were a
standard form of wall construction.

Absolute, utter, complete, rubbish.

tell those that own such places.


NT