A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?

Wrote in message:
A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?


Whats the floor construction?

Can you get under it? Cellar, void, whatever?

--
Jimk


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On 31/01/2020 11:16, Jimk wrote:
Wrote in message:
A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?


Whats the floor construction?
Concrete, with insulation and DPM.
The wall is on the original footings.

Can you get under it? Cellar, void, whatever?

On 31/01/2020 12:39, wrote:
On 31/01/2020 11:16, Jimk wrote:
Wrote in message:
A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?


Whats the floor construction?
Concrete, with insulation and DPM.
The wall is on the original footings.

Can you get under it? Cellar, void, whatever?


Brick, presumably? Not too thick? Not cavity?

I think I would be inclined to be drilling and injecting silicone to
provide a full thickness barrier.

There is a risk of moisture rising higher if you seal off a lower band,
depending on local hydrogeology.

What I do (random stone rubble filled walls at the bottom of a wet hill)
is have the whole (limestone) wall exposed, with ventilated tongue and
groove wainscotting up to about a metre. This lets the wall dry out and
although I still get traces of salts above it, they are easily brushed
off every year or so. Prior to that, classic damp proof treatment
(electro osmotic with impervious plaster) resulted in the whole wall
getting saturated up to at least 1.5 metres.

Ah, that old sponge effect. Yuck.

Brian

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"newshound" wrote in message
o.uk...
On 31/01/2020 12:39, wrote:
On 31/01/2020 11:16, Jimk wrote:
Wrote in message:
A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?


Whats the floor construction?
Concrete, with insulation and DPM.
The wall is on the original footings.

Can you get under it? Cellar, void, whatever?


Brick, presumably? Not too thick? Not cavity?

I think I would be inclined to be drilling and injecting silicone to
provide a full thickness barrier.

There is a risk of moisture rising higher if you seal off a lower band,
depending on local hydrogeology.

What I do (random stone rubble filled walls at the bottom of a wet hill)
is have the whole (limestone) wall exposed, with ventilated tongue and
groove wainscotting up to about a metre. This lets the wall dry out and
although I still get traces of salts above it, they are easily brushed off
every year or so. Prior to that, classic damp proof treatment (electro
osmotic with impervious plaster) resulted in the whole wall getting
saturated up to at least 1.5 metres.

On Friday, 31 January 2020 11:08:51 UTC, wrote:

A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?

Rising damp does exist but is rare. It is very unlikely that this is what's going on. DPCs are therefore not often useful. You propose DPC failure - how exactly does a hard material such as slate entombed in lime or cement fail?

Bottom of interior wall damp is usually from condensation. A wet slab from a plumbing leak can also cause it.

Coating with impermeables normally results in the coated area not drying out, and the matter therefore worsening. I'd look at the slab if practical, and look to see if ambient RH in the area can be reduced. Other options are to scrape & paint the area with lime, which permits it to dry better than emulsion, and use of a dehumidifier. The last 2 are often sufficient to keep things in check.


NT

On 31/01/2020 16:34, wrote:
On Friday, 31 January 2020 11:08:51 UTC, wrote:

A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?

Rising damp does exist but is rare.

True, but if you have it it can be dramatic

It is very unlikely that this is what's going on. DPCs are therefore not often useful. You propose DPC failure - how exactly does a hard material such as slate entombed in lime or cement fail?

by cracking

Bottom of interior wall damp is usually from condensation. A wet slab from a plumbing leak can also cause it.

I'd say sometimes rather than usually. And you need plumbing there for
plumbing to leak


Coating with impermeables normally results in the coated area not drying out, and the matter therefore worsening. I'd look at the slab if practical, and look to see if ambient RH in the area can be reduced. Other options are to scrape & paint the area with lime, which permits it to dry better than emulsion, and use of a dehumidifier. The last 2 are often sufficient to keep things in check.

Completely with you on not trying to hide with impermeables (but OK to
create new "DPC" with silicone, if you have suitable materials and
construction. You can pour in an awful lot of fluid into a stone wall).


NT

On 01/02/2020 10:51, newshound wrote:
On 31/01/2020 16:34, wrote:
On Friday, 31 January 2020 11:08:51 UTC, Â* wrote:

A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?

Rising damp does exist but is rare.

True, but if you have it it can be dramatic

It is very unlikely that this is what's going on. DPCs are therefore
not often useful. You propose DPC failure - how exactly does a hard
material such as slate entombed in lime or cement fail?

by cracking

Bottom of interior wall damp is usually from condensation. A wet slab
from a plumbing leak can also cause it.

I'd say sometimes rather than usually. And you need plumbing there for
plumbing to leak


Coating with impermeables normally results in the coated area not
drying out, and the matter therefore worsening. I'd look at the slab
if practical, and look to see if ambient RH in the area can be
reduced. Other options are to scrape & paint the area with lime, which
permits it to dry better than emulsion, and use of a dehumidifier. The
last 2 are often sufficient to keep things in check.

Completely with you on not trying to hide with impermeables (but OK to
create new "DPC" with silicone, if you have suitable materials and
construction. You can pour in an awful lot of fluid into a stone wall).


NT



The 1976-built house that I bought in 1991 had had a leaking 28 mm
connection to the baxi bermuda back boiler since new, judging by the
stalagmites (-tites) of crud down the side of the heat exchanger.

Surveyor apologetic but said he couldn't get the access panel off
because of furniture, but added that he had noted unusually high damp
readings on his meter which was unexpected in this type of modern house.
He assumed it had been the result of 'cleaning'.

Luckily BG fixed it with a new heat exchanger as part of 3* service
at no cost to me (which they wouldn't do now).

The water had seeped into the slab and wicked all along the felt-
lagged CH copper pipes in the slab and where they crossed over the
3/4 inch iron gas feed to the kitchen, the latter has almost
corroded through.

I only discovered this in 2004 when I dug out the screed and put
down 70mm celotex between battens on a 2nd dpc, plus hardwood floor.

On Saturday, 1 February 2020 10:51:07 UTC, newshound wrote:
On 31/01/2020 16:34, tabbypurr wrote:
On Friday, 31 January 2020 11:08:51 UTC, wrote:

A cavity wall has a "tide mark" about 200mm above the floor. The wall
was originally an external wall but, as a result of building an
extension, is now an internal wall. The wall has a 1930s DPC and the
floors have modern DPMs.
I assume that the old DPC has failed so am wondering what the best
options are. At the moment I'm thinking of knocking-off the plaster to
about 300mm, coating the wall with something and then
rendering/plastering with an additive.
The question is what to put on the wall: liquid DPM? bitumen? cement
board (hardiebacker)? foil-backed plasterboard?
What does the team think?

Rising damp does exist but is rare.

True,

that's what matters

but if you have it it can be dramatic

any type of damp can

It is very unlikely that this is what's going on. DPCs are therefore not often useful. You propose DPC failure - how exactly does a hard material such as slate entombed in lime or cement fail?

by cracking

A crack means 99.99% complete prevention of what is a rare condition. Not worth spending time on.


Bottom of interior wall damp is usually from condensation. A wet slab from a plumbing leak can also cause it.

I'd say sometimes rather than usually. And you need plumbing there for
plumbing to leak

No you don't, a leak into a concrete slab can run a long way within the slab.


Coating with impermeables normally results in the coated area not drying out, and the matter therefore worsening. I'd look at the slab if practical, and look to see if ambient RH in the area can be reduced. Other options are to scrape & paint the area with lime, which permits it to dry better than emulsion, and use of a dehumidifier. The last 2 are often sufficient to keep things in check.

Completely with you on not trying to hide with impermeables (but OK to
create new "DPC" with silicone, if you have suitable materials and
construction. You can pour in an awful lot of fluid into a stone wall).

It's also ok to walk down the road throwing your money & time away. But I would not personally recommend it.


NT

Rising damp does exist but is rare.

True,

that's what matters

but if you have it it can be dramatic

any type of damp can

It is very unlikely that this is what's going on. DPCs are therefore not often useful. You propose DPC failure - how exactly does a hard material such as slate entombed in lime or cement fail?

by cracking

A crack means 99.99% complete prevention of what is a rare condition. Not worth spending time on.

Well I have seen damp regions inside a Victorian property with slate DPC
where there wasn't any obvious external problem.


Bottom of interior wall damp is usually from condensation. A wet slab from a plumbing leak can also cause it.

I'd say sometimes rather than usually. And you need plumbing there for
plumbing to leak

No you don't, a leak into a concrete slab can run a long way within the slab.

Yes, if you have a slab


Coating with impermeables normally results in the coated area not drying out, and the matter therefore worsening. I'd look at the slab if practical, and look to see if ambient RH in the area can be reduced. Other options are to scrape & paint the area with lime, which permits it to dry better than emulsion, and use of a dehumidifier. The last 2 are often sufficient to keep things in check.

Completely with you on not trying to hide with impermeables (but OK to
create new "DPC" with silicone, if you have suitable materials and
construction. You can pour in an awful lot of fluid into a stone wall).

It's also ok to walk down the road throwing your money & time away. But I would not personally recommend it.


Well the previous owner of my house cost me quite a lot of money by
putting up studding over a wall with rising damp, stapling polythene
over the whole area, and then plasterboarding inside. It didn't take
many years for dry rot to take out the staircase, the window frames, and
parts of the floor above. This is the one I cured by exposing *all* the
stone inside, and adding ventilated wainscotting. If I had wanted it
plastered, the only solution IMHO would have been silicone injection. I
didn't do it because of the cost and the risk of gaps.

On Saturday, 1 February 2020 22:53:12 UTC, newshound wrote:

Rising damp does exist but is rare.

True,

that's what matters

but if you have it it can be dramatic

any type of damp can

It is very unlikely that this is what's going on. DPCs are therefore not often useful. You propose DPC failure - how exactly does a hard material such as slate entombed in lime or cement fail?

by cracking

A crack means 99.99% complete prevention of what is a rare condition. Not worth spending time on.

Well I have seen damp regions inside a Victorian property with slate DPC
where there wasn't any obvious external problem.

Not unusual. Seldom does it have anything to do with rising damp, though it's often misdiagnosed as that.


Bottom of interior wall damp is usually from condensation. A wet slab from a plumbing leak can also cause it.

I'd say sometimes rather than usually. And you need plumbing there for
plumbing to leak

No you don't, a leak into a concrete slab can run a long way within the slab.

Yes, if you have a slab


Coating with impermeables normally results in the coated area not drying out, and the matter therefore worsening. I'd look at the slab if practical, and look to see if ambient RH in the area can be reduced. Other options are to scrape & paint the area with lime, which permits it to dry better than emulsion, and use of a dehumidifier. The last 2 are often sufficient to keep things in check.

Completely with you on not trying to hide with impermeables (but OK to
create new "DPC" with silicone, if you have suitable materials and
construction. You can pour in an awful lot of fluid into a stone wall)..

It's also ok to walk down the road throwing your money & time away. But I would not personally recommend it.


Well the previous owner of my house cost me quite a lot of money by
putting up studding over a wall with rising damp, stapling polythene
over the whole area, and then plasterboarding inside. It didn't take
many years for dry rot to take out the staircase, the window frames, and
parts of the floor above. This is the one I cured by exposing *all* the
stone inside, and adding ventilated wainscotting. If I had wanted it
plastered, the only solution IMHO would have been silicone injection. I
didn't do it because of the cost and the risk of gaps.

As has been repeatedly established elsewhere, rising damp is rare & a highly unlikely diagnosis. The common causes of damp problems in Victorian walls are blocking ventilation & evaporation, faulty rainwater goods, condensation and plumbing leaks. Silicone injection does not address those - but it does make poeple money.


NT

experts on damp are
Peter Ward
https://www.youtube.com/channel/UC55...-SAT3wgwUFtruw

also checkout Charlie at
https://www.youtube.com/watch?v=TIDb-pdOnXM

and hundreds of youtube videos selling injection solutions
which only work in 1% of cases

[g]