What is the best treatment for "salt damp" caused by hygroscopic salts on a
chimney breast?

First, hack out the affected area of plaster and a good margin around it,
and check the water isn't coming in through the bricks. I'm only talking
about the case when water isn't still coming in.

But then?

Is it better to use a bond coat of SBR and then a cement render, perhaps
itself with a splash of SBR in it, and then plaster or emulsion on top? I
thought SBR wasn't breathable.

Or is it better to use a special "renovating plaster" that is sold
precisely as breathable?

I don't quite get whether you want breathability or the opposite.

Advice would be welcomed.

Thanks in advance!

Harry

The Peeler wrote in
eb.com:

On Mon, 30 Jan 2017 21:07:21 -0000 (UTC), Harold Davis wrote:

What is the best treatment for "salt damp" caused by hygroscopic
salts on a chimney breast?

First, hack out the affected area of plaster and a good margin around
it, and check the water isn't coming in through the bricks. I'm only
talking about the case when water isn't still coming in.

But then?

You need to find the cause for the moisture that produces the "salt
damp" before renovating. Maybe YOUR chimney needs a little roof over
it to keep out the rain? If the chimney is dead (with no air
circulation) it could be caused by condensation.

Is it better to use a bond coat of SBR and then a cement render,
perhaps itself with a splash of SBR in it, and then plaster or
emulsion on top? I thought SBR wasn't breathable.

Or is it better to use a special "renovating plaster" that is sold
precisely as breathable?

I don't quite get whether you want breathability or the opposite.

Advice would be welcomed.

Normal advice would be, if the moisture comes from the outside, the
inside has to breathe (and not get insulated). If the damp is from the
inside (like in a kitchen) the inside can be insulated against the
moisture going into the wall.

Many thanks for this.

There's no obvious water coming in through the roof. The chimney has been
blocked up and unused for maybe 15 years, but the one next to it and
sharing a stack with it is used. The stains are in the kitchen, so there
is a lot of moisture inside the room. I haven't noticed the stains get
smaller when the day outside is dry, but maybe that effect is less likely
to happen in a kitchen.

It is possible that the wet is rain getting in through the chimney pot.
It has got a cowl but the winds can be strong. I am not sure how it would
then get through the chimney wall but doubtless there are some
unevennesses.

I will hack back to the brickwork and report back

When you say condensation, where would the condensing moisture come from?
Inside the kitchen or down the chimney?

Thanks again!

Harry

In article ,
Harold Davis writes:
The Peeler wrote in
eb.com:

On Mon, 30 Jan 2017 21:07:21 -0000 (UTC), Harold Davis wrote:

What is the best treatment for "salt damp" caused by hygroscopic
salts on a chimney breast?

First, hack out the affected area of plaster and a good margin around
it, and check the water isn't coming in through the bricks. I'm only
talking about the case when water isn't still coming in.

But then?

You need to find the cause for the moisture that produces the "salt
damp" before renovating. Maybe YOUR chimney needs a little roof over
it to keep out the rain? If the chimney is dead (with no air
circulation) it could be caused by condensation.

Is it better to use a bond coat of SBR and then a cement render,
perhaps itself with a splash of SBR in it, and then plaster or
emulsion on top? I thought SBR wasn't breathable.

Or is it better to use a special "renovating plaster" that is sold
precisely as breathable?

I don't quite get whether you want breathability or the opposite.

Advice would be welcomed.

Normal advice would be, if the moisture comes from the outside, the
inside has to breathe (and not get insulated). If the damp is from the
inside (like in a kitchen) the inside can be insulated against the
moisture going into the wall.

Many thanks for this.

There's no obvious water coming in through the roof. The chimney has been
blocked up and unused for maybe 15 years,

Bing! there's your problem. Chimney must be vented top and bottom.
If it's not, it will slowly fill with condensation - 15 years is
quite typical period for it to end up soaking wet inside. When you
get to look in the flue, you will probabaly find it's so wet water
is visibly running down the inside.

You need to get it vented properly, and then leave it to dry out
before assessing what decorative repairs are required.
This will take a long time - a minimum of a week per inch thickness
of the walls, so allow 3 months unless it's very thick brickwork,
in which case it will take longer.

If the chimney is on an outside wall, the lower vent can be to the
outside, to avoid drawing air from the room. Another option is from
the subfloor. Failing these, you'll need to have it vented from the
room.

but the one next to it and
sharing a stack with it is used. The stains are in the kitchen, so there
is a lot of moisture inside the room. I haven't noticed the stains get
smaller when the day outside is dry, but maybe that effect is less likely
to happen in a kitchen.

It is possible that the wet is rain getting in through the chimney pot.
It has got a cowl but the winds can be strong. I am not sure how it would
then get through the chimney wall but doubtless there are some
unevennesses.

Rain going into an open pot will not be a problem providing the
flue is properly vented. (It's better to provide a vented cap if
you can, but that's rather more to reduce the frost damage in
exposed stack brickwork.) However, capping the top off without
venting it is worse than leaving it open.

I will hack back to the brickwork and report back

When you say condensation, where would the condensing moisture come from?
Inside the kitchen or down the chimney?

Several sources. From air in the flue if the ventilation is poor.
Moisture which comes through the brickwork. Rain entering the pot.
Generally, there are several ways in, but ventilation is the only
way out.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

"Harold Davis" wrote in message
...
What is the best treatment for "salt damp" caused by hygroscopic salts on
a
chimney breast?

First, hack out the affected area of plaster and a good margin around it,
and check the water isn't coming in through the bricks. I'm only talking
about the case when water isn't still coming in.

But then?

Is it better to use a bond coat of SBR and then a cement render, perhaps
itself with a splash of SBR in it, and then plaster or emulsion on top? I
thought SBR wasn't breathable.

Or is it better to use a special "renovating plaster" that is sold
precisely as breathable?

I don't quite get whether you want breathability or the opposite.

Advice would be welcomed.

Thanks in advance!

Harry

hard to get rid of efflorescence if not impossible.....

On 31/01/17 05:47, Jim GM4DHJ ... wrote:
"Harold Davis" wrote in message
...
What is the best treatment for "salt damp" caused by hygroscopic salts on
a
chimney breast?

First, hack out the affected area of plaster and a good margin around it,
and check the water isn't coming in through the bricks. I'm only talking
about the case when water isn't still coming in.

But then?

Is it better to use a bond coat of SBR and then a cement render, perhaps
itself with a splash of SBR in it, and then plaster or emulsion on top? I
thought SBR wasn't breathable.

Or is it better to use a special "renovating plaster" that is sold
precisely as breathable?

I don't quite get whether you want breathability or the opposite.

Advice would be welcomed.

Thanks in advance!

Harry

hard to get rid of efflorescence if not impossible.....


easy.

Just remove water.


--
"Women actually are capable of being far more than the feminists will
let them."

On 1/31/2017 12:26 AM, Andrew Gabriel wrote:
In article ,
Harold Davis writes:
The Peeler wrote in
eb.com:

On Mon, 30 Jan 2017 21:07:21 -0000 (UTC), Harold Davis wrote:

What is the best treatment for "salt damp" caused by hygroscopic
salts on a chimney breast?

First, hack out the affected area of plaster and a good margin around
it, and check the water isn't coming in through the bricks. I'm only
talking about the case when water isn't still coming in.

But then?

You need to find the cause for the moisture that produces the "salt
damp" before renovating. Maybe YOUR chimney needs a little roof over
it to keep out the rain? If the chimney is dead (with no air
circulation) it could be caused by condensation.

Is it better to use a bond coat of SBR and then a cement render,
perhaps itself with a splash of SBR in it, and then plaster or
emulsion on top? I thought SBR wasn't breathable.

Or is it better to use a special "renovating plaster" that is sold
precisely as breathable?

I don't quite get whether you want breathability or the opposite.

Advice would be welcomed.

Normal advice would be, if the moisture comes from the outside, the
inside has to breathe (and not get insulated). If the damp is from the
inside (like in a kitchen) the inside can be insulated against the
moisture going into the wall.

Many thanks for this.

There's no obvious water coming in through the roof. The chimney has been
blocked up and unused for maybe 15 years,

Bing! there's your problem. Chimney must be vented top and bottom.
If it's not, it will slowly fill with condensation - 15 years is
quite typical period for it to end up soaking wet inside. When you
get to look in the flue, you will probabaly find it's so wet water
is visibly running down the inside.

You need to get it vented properly, and then leave it to dry out
before assessing what decorative repairs are required.
This will take a long time - a minimum of a week per inch thickness
of the walls, so allow 3 months unless it's very thick brickwork,
in which case it will take longer.

If the chimney is on an outside wall, the lower vent can be to the
outside, to avoid drawing air from the room. Another option is from
the subfloor. Failing these, you'll need to have it vented from the
room.

but the one next to it and
sharing a stack with it is used. The stains are in the kitchen, so there
is a lot of moisture inside the room. I haven't noticed the stains get
smaller when the day outside is dry, but maybe that effect is less likely
to happen in a kitchen.

It is possible that the wet is rain getting in through the chimney pot.
It has got a cowl but the winds can be strong. I am not sure how it would
then get through the chimney wall but doubtless there are some
unevennesses.

Rain going into an open pot will not be a problem providing the
flue is properly vented. (It's better to provide a vented cap if
you can, but that's rather more to reduce the frost damage in
exposed stack brickwork.) However, capping the top off without
venting it is worse than leaving it open.

I will hack back to the brickwork and report back

When you say condensation, where would the condensing moisture come from?
Inside the kitchen or down the chimney?

Several sources. From air in the flue if the ventilation is poor.
Moisture which comes through the brickwork. Rain entering the pot.
Generally, there are several ways in, but ventilation is the only
way out.


+1

On 31/01/2017 00:26, Andrew Gabriel wrote:
Bing! there's your problem. Chimney must be vented top and bottom.
If it's not, it will slowly fill with condensation - 15 years is
quite typical period for it to end up soaking wet inside. When you
get to look in the flue, you will probabaly find it's so wet water
is visibly running down the inside.

Our flue in the kitchen is like that.

It's got a cap at the top with breathing space, and a vent at the bottom.

I suspect what happens is warm moist air from the kitchen goes up into
the cold flue and condenses out (the bottom of the flue is at ceiling
level). I can't really see that the ventilation is helping at all...

Trying to decide what to do long term. We need a cooker hood (the PO
seems to have lost it - apparently there was one 15 years ago) and it
seems to me that if we vented that into a pipe running the entire height
of the chimney then the chimney would be warm, and probably dry out.

And there would be lots of condensation in the pipe

Andy