I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

Question: should the PVA be allowed to fully dry or should
the mortar be spread on top while the PVA is still moist?
Or should I do two coats and allow the first to fully dry
then apply mortar while the second one is still tacky?

What way would give the best adhesion between clay and
cement mortar?

--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.

David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

Question: should the PVA be allowed to fully dry or should
the mortar be spread on top while the PVA is still moist?
Or should I do two coats and allow the first to fully dry
then apply mortar while the second one is still tacky?

Technically I don't think it makes any difference. It doesn't act as an
adhesive, but prevents water from the mortar being sucked into the
original surface before it's had a chance to cure. IME it's better to
thin it heavily, say 10:1, and apply lots of it.

What way would give the best adhesion between clay and
cement mortar?


Mortar will stick to anything (try getting it off a steel shovel!)
providing it doesn't lose its water prematurely, hence the pva seal.

Stuart Noble says...
David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

Question: should the PVA be allowed to fully dry or should
the mortar be spread on top while the PVA is still moist?
Or should I do two coats and allow the first to fully dry
then apply mortar while the second one is still tacky?

Technically I don't think it makes any difference. It doesn't act as an
adhesive, but prevents water from the mortar being sucked into the
original surface before it's had a chance to cure. IME it's better to
thin it heavily, say 10:1, and apply lots of it.

OK, that is what I'll do then.


What way would give the best adhesion between clay and
cement mortar?


Mortar will stick to anything (try getting it off a steel shovel!)
providing it doesn't lose its water prematurely, hence the pva seal.


I take your point, when you think about it you just
wouldn't think it possible for mortar to stick so well to a
smooth metal surface. I always take care to wash every bit
off my tools - as a kid I was given the task of trying to
clean a shovel a few days after it had been used to mix
concrete. The shovel was a write off.
--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.

David in Normandy wrote:
Stuart Noble says...
David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

Question: should the PVA be allowed to fully dry or should
the mortar be spread on top while the PVA is still moist?
Or should I do two coats and allow the first to fully dry
then apply mortar while the second one is still tacky?
Technically I don't think it makes any difference. It doesn't act as an
adhesive, but prevents water from the mortar being sucked into the
original surface before it's had a chance to cure. IME it's better to
thin it heavily, say 10:1, and apply lots of it.

OK, that is what I'll do then.

What way would give the best adhesion between clay and
cement mortar?

Mortar will stick to anything (try getting it off a steel shovel!)
providing it doesn't lose its water prematurely, hence the pva seal.


I take your point, when you think about it you just
wouldn't think it possible for mortar to stick so well to a
smooth metal surface. I always take care to wash every bit
off my tools - as a kid I was given the task of trying to
clean a shovel a few days after it had been used to mix
concrete. The shovel was a write off.

By the same principle paint sticks really well to glass. You often see
blobs of Victorian paint on windows that have survived intact when the
woodwork is shot to pieces.

On 19 Mar, 14:12, David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

Question: should the PVA be allowed to fully dry or should
the mortar be spread on top while the PVA is still moist?
Or should I do two coats and allow the first to fully dry
then apply mortar while the second one is still tacky?

What way would give the best adhesion between clay and
cement mortar?

--
David in Normandy. * *
*To e-mail you must include the password FROG on the
*subject line, or it will be automatically deleted.

Dear David
Unless it is a modern PVA (?Group/Type 4) Forget it and use an SBR
This does not re-emulsify and does act as an adhesive - blankets and
brownstuff comes to mind
mix the SBR in the bedding mortar as well as putting it on the
recipient wall

I have done this many times with mortar and concrete and it always has
worked a treat

It IS pricy tho

Chris

wrote:
On 19 Mar, 14:12, David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

Question: should the PVA be allowed to fully dry or should
the mortar be spread on top while the PVA is still moist?
Or should I do two coats and allow the first to fully dry
then apply mortar while the second one is still tacky?

What way would give the best adhesion between clay and
cement mortar?

--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.

Dear David
Unless it is a modern PVA (?Group/Type 4) Forget it and use an SBR
This does not re-emulsify and does act as an adhesive - blankets and
brownstuff comes to mind
mix the SBR in the bedding mortar as well as putting it on the
recipient wall

I have done this many times with mortar and concrete and it always has
worked a treat

It IS pricy tho

Chris

I'd say SBR was overkill for the job in hand.

Stuart Noble says...
wrote:
On 19 Mar, 14:12, David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

Question: should the PVA be allowed to fully dry or should
the mortar be spread on top while the PVA is still moist?
Or should I do two coats and allow the first to fully dry
then apply mortar while the second one is still tacky?

What way would give the best adhesion between clay and
cement mortar?

--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.

Dear David
Unless it is a modern PVA (?Group/Type 4) Forget it and use an SBR
This does not re-emulsify and does act as an adhesive - blankets and
brownstuff comes to mind
mix the SBR in the bedding mortar as well as putting it on the
recipient wall

I have done this many times with mortar and concrete and it always has
worked a treat

It IS pricy tho

Chris

I'd say SBR was overkill for the job in hand.


The single row of blocks isn't for a "structural" purpose.
They are just to sit on top of the existing wall. The
reason being the new ceiling I'm fitting will actually be
about 10cm higher than the height of the existing walls due
to having to take the new level from the top of big fat oak
beams. So to fill the "gap" and make the structure weather
proof I'm adding the layer of blocks.

It's all a bit complicated to try to explain, there is
nothing "standard" about the house by today's standards,
though it was probably run of the mill standard two or
three hundred years ago when it was built using whatever
rocks were available in surrounding fields, nearby clay and
trees hewn to make beams and joists of all shapes and
sizes.
--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.

David in Normandy wrote:
Stuart Noble says...
wrote:
On 19 Mar, 14:12, David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

Question: should the PVA be allowed to fully dry or should
the mortar be spread on top while the PVA is still moist?
Or should I do two coats and allow the first to fully dry
then apply mortar while the second one is still tacky?

What way would give the best adhesion between clay and
cement mortar?

--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.
Dear David
Unless it is a modern PVA (?Group/Type 4) Forget it and use an SBR
This does not re-emulsify and does act as an adhesive - blankets and
brownstuff comes to mind
mix the SBR in the bedding mortar as well as putting it on the
recipient wall

I have done this many times with mortar and concrete and it always has
worked a treat

It IS pricy tho

Chris
I'd say SBR was overkill for the job in hand.


The single row of blocks isn't for a "structural" purpose.
They are just to sit on top of the existing wall. The
reason being the new ceiling I'm fitting will actually be
about 10cm higher than the height of the existing walls due
to having to take the new level from the top of big fat oak
beams. So to fill the "gap" and make the structure weather
proof I'm adding the layer of blocks.

It's all a bit complicated to try to explain, there is
nothing "standard" about the house by today's standards,
though it was probably run of the mill standard two or
three hundred years ago when it was built using whatever
rocks were available in surrounding fields, nearby clay and
trees hewn to make beams and joists of all shapes and
sizes.

Sounds like fun.
IMO there is no benefit in using SBR for basic stuff like this. It's
normally used for screeding damp floors and tanking cellars etc.

On Thu, 20 Mar 2008 17:11:57 GMT, Stuart Noble
wrote:

David in Normandy wrote:
Stuart Noble says...
wrote:
On 19 Mar, 14:12, David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

I'm wondering why you want to do this at all. The best bond with the
top of the old wall will be achieved if you dampen it down and then
extend it using exactly the same material as was used before

That way there wont be any differential cracking, the materials will
be cheap / free, the skill set is fairly basic and you will enjoy
doing it (think sand and water play at nursery school). The downside
is that it will be messier to do and will take longer to dry which
might be important if it is structural and you are on a tight
timetable

Many would say that I have a bee in my bonnet about traditional
materials, but I think they tend to work better as additions to an old
house as they keep it as a unified system which always used to work
and still does. New materials are great on newbuild (which has deep
foundations, is of rigid build, made of impermeable layers etc).
Mixing the two systems should be done cautiously * and not at all if
it is not necessary imo

* Exceptions exist. I am a fan of silicon frame sealant - they would
have used it if they had it

Anna
--

~ ~ Anna Kettle, Suffolk, England
|""""| ~ Lime plaster repair and conservation
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk

Anna Kettle wrote:
On Thu, 20 Mar 2008 17:11:57 GMT, Stuart Noble
wrote:

David in Normandy wrote:
Stuart Noble says...
wrote:
On 19 Mar, 14:12, David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

I'm wondering why you want to do this at all. The best bond with the
top of the old wall will be achieved if you dampen it down and then
extend it using exactly the same material as was used before

That way there wont be any differential cracking, the materials will
be cheap / free, the skill set is fairly basic and you will enjoy
doing it (think sand and water play at nursery school). The downside
is that it will be messier to do and will take longer to dry which
might be important if it is structural and you are on a tight
timetable

Many would say that I have a bee in my bonnet about traditional
materials, but I think they tend to work better as additions to an old
house as they keep it as a unified system which always used to work
and still does. New materials are great on newbuild (which has deep
foundations, is of rigid build, made of impermeable layers etc).
Mixing the two systems should be done cautiously * and not at all if
it is not necessary imo

* Exceptions exist. I am a fan of silicon frame sealant - they would
have used it if they had it

Anna

They would have used concrete blocks as well I expect.

Anna Kettle says...
On Thu, 20 Mar 2008 17:11:57 GMT, Stuart Noble
wrote:

David in Normandy wrote:
Stuart Noble says...
wrote:
On 19 Mar, 14:12, David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.

I'm wondering why you want to do this at all. The best bond with the
top of the old wall will be achieved if you dampen it down and then
extend it using exactly the same material as was used before

That way there wont be any differential cracking, the materials will
be cheap / free, the skill set is fairly basic and you will enjoy
doing it (think sand and water play at nursery school). The downside
is that it will be messier to do and will take longer to dry which
might be important if it is structural and you are on a tight
timetable

Many would say that I have a bee in my bonnet about traditional
materials, but I think they tend to work better as additions to an old
house as they keep it as a unified system which always used to work
and still does. New materials are great on newbuild (which has deep
foundations, is of rigid build, made of impermeable layers etc).
Mixing the two systems should be done cautiously * and not at all if
it is not necessary imo

* Exceptions exist. I am a fan of silicon frame sealant - they would
have used it if they had it

Anna


There are a number of issues here. It would be "nice" from
a romantic point of view to do everything using original
materials and methods. And as you say there are also
conflicts in the way old and new materials work which can
cause problems when they are mixed and matched together in
the wrong way.

If the house was of historic significance then that too
would be a good reason to use traditional methods and
materials. However, the house is just one of tens of
thousands of similar properties all over France.

There are constraints of time, money and accessibility of
old materials. While superficially clay may sound free, in
practice it means finding a source and digging it up, which
would need to be agreed to by the land owner, possibly also
involving payment. There are similar issues with the old
timber shingle ceilings which have rotted. I could get a
timber yard to cut oak shingles for me, but again the cost
starts to mount up. There is also the issue of what to put
over them, traditionally this was clay mixed with straw.
Making this sort of floor would be good from an aesthetic
point of view, but utterly impractical as an upper floor,
not least because of the colossal weight of the clay and
the deterioration of the beams over the years. Modern
floors are much lighter and put less stress on ancient
wormy beams.

In practice I'm doing a balancing act between keeping
original features and appearance and using new materials
where the alternative is impractical or too costly. There
are also issues of insulation to consider. The old
materials had very poor heat insulating qualities which
meant the typical French family spent most of their time
huddled in one room around an open fire and had an outdoor
toilet. Modern lifestyles mean more rooms are in use and
need to be kept warm. This means it is necessary to use
modern insulation materials.

The concrete blocks I am using are in a position where they
will be completely invisible, part of the hidden structure
of the building, so there is no compelling cosmetic reason
to use clay here.

I am very keen on using lime mortar for the pointing. To
use cement mortars here would be both cosmetically wrong
and also structurally wrong as it can lead to
disintegration of the stone as cement mortar cannot breath
and allow moisture to evaporate, leading to freeze damage
of the surrounding stone.

As I say, it is a balancing act. I think I've got it about
right for the nature of the property.
--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.

David in Normandy wrote:
Anna Kettle says...
On Thu, 20 Mar 2008 17:11:57 GMT, Stuart Noble
wrote:

David in Normandy wrote:
Stuart Noble says...
wrote:
On 19 Mar, 14:12, David in Normandy wrote:
I'm putting a single layer of concrete blocks on top of our
house walls. The walls are made of irregular sized stones
with an ancient mortar made of clay and straw. It is quite
an uneven and dusty surface so I plan to brush off the
loose debris then give it a good wetting with dilute PVA.
I'm wondering why you want to do this at all. The best bond with the
top of the old wall will be achieved if you dampen it down and then
extend it using exactly the same material as was used before

That way there wont be any differential cracking, the materials will
be cheap / free, the skill set is fairly basic and you will enjoy
doing it (think sand and water play at nursery school). The downside
is that it will be messier to do and will take longer to dry which
might be important if it is structural and you are on a tight
timetable

Many would say that I have a bee in my bonnet about traditional
materials, but I think they tend to work better as additions to an old
house as they keep it as a unified system which always used to work
and still does. New materials are great on newbuild (which has deep
foundations, is of rigid build, made of impermeable layers etc).
Mixing the two systems should be done cautiously * and not at all if
it is not necessary imo

* Exceptions exist. I am a fan of silicon frame sealant - they would
have used it if they had it

Anna


There are a number of issues here. It would be "nice" from
a romantic point of view to do everything using original
materials and methods. And as you say there are also
conflicts in the way old and new materials work which can
cause problems when they are mixed and matched together in
the wrong way.

If the house was of historic significance then that too
would be a good reason to use traditional methods and
materials. However, the house is just one of tens of
thousands of similar properties all over France.

There are constraints of time, money and accessibility of
old materials. While superficially clay may sound free, in
practice it means finding a source and digging it up, which
would need to be agreed to by the land owner, possibly also
involving payment. There are similar issues with the old
timber shingle ceilings which have rotted. I could get a
timber yard to cut oak shingles for me, but again the cost
starts to mount up. There is also the issue of what to put
over them, traditionally this was clay mixed with straw.
Making this sort of floor would be good from an aesthetic
point of view, but utterly impractical as an upper floor,
not least because of the colossal weight of the clay and
the deterioration of the beams over the years. Modern
floors are much lighter and put less stress on ancient
wormy beams.

In practice I'm doing a balancing act between keeping
original features and appearance and using new materials
where the alternative is impractical or too costly. There
are also issues of insulation to consider. The old
materials had very poor heat insulating qualities which
meant the typical French family spent most of their time
huddled in one room around an open fire and had an outdoor
toilet. Modern lifestyles mean more rooms are in use and
need to be kept warm. This means it is necessary to use
modern insulation materials.

The concrete blocks I am using are in a position where they
will be completely invisible, part of the hidden structure
of the building, so there is no compelling cosmetic reason
to use clay here.

I am very keen on using lime mortar for the pointing. To
use cement mortars here would be both cosmetically wrong
and also structurally wrong as it can lead to
disintegration of the stone as cement mortar cannot breath
and allow moisture to evaporate, leading to freeze damage
of the surrounding stone.

As I say, it is a balancing act. I think I've got it about
right for the nature of the property.

I imagine your approach is rescuing a lot of buildings that would
otherwise remain derelict. In some ways the balancing act is more
creative than slavishly restoring things and pretending we live in the
Middle Ages.

Stuart Noble says...
I imagine your approach is rescuing a lot of buildings that would
otherwise remain derelict. In some ways the balancing act is more
creative than slavishly restoring things and pretending we live in the
Middle Ages.


Definitely. There are hundreds (thousands?) of old French
properties that are falling into dereliction. I pass
several on the drive into the nearby town. Some are beyond
renovation and literally have no roof, the walls are
crumbling and are heading to being a pile of rubble. This
happens fairly quickly when the roof has gone. The elements
wash out the ancient clay mortar.

Most French prefer to live in towns in new properties and
think the hoards of Brits are mad who move over here and
spend our own money restoring their heritage!
--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.