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How to patch spalling brickwork?



 
 
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  #1  
Old June 19th 08, 08:00 PM posted to uk.d-i-y
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Posts: 2,362
Default How to patch spalling brickwork?

I've got a large North-facing house wall of soft Norfolk red bricks -
and a large number have spalled.

It's really an impractically large number to cut out and replace.

I've been trying to patch over them with lime mortar (lime putty,
sharp sand and red brick dust).

Mix is good consistency & sticky - but it still isn't bonding very
well to the bricks (which have been gone over roughly with a wire
brush, brushed down and then wetted).

So I'm thinking - maybe wet down with 10% pva solution?

Other suggestions?
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  #2  
Old June 19th 08, 08:12 PM posted to uk.d-i-y
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Posts: 379
Default How to patch spalling brickwork?


wrote in message
...
I've got a large North-facing house wall of soft Norfolk red bricks -
and a large number have spalled.

It's really an impractically large number to cut out and replace.

I've been trying to patch over them with lime mortar (lime putty,
sharp sand and red brick dust).

Mix is good consistency & sticky - but it still isn't bonding very
well to the bricks (which have been gone over roughly with a wire
brush, brushed down and then wetted).

So I'm thinking - maybe wet down with 10% pva solution?

Other suggestions?


Use this in the cement mix,as you have done wet the brick first.
http://tinyurl.com/6o3w92


  #3  
Old June 20th 08, 05:30 AM posted to uk.d-i-y
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Posts: 121
Default How to patch spalling brickwork?

On Thu, 19 Jun 2008 19:12:58 GMT, "George"
wrote:


wrote in message
...
I've got a large North-facing house wall of soft Norfolk red bricks -
and a large number have spalled.

It's really an impractically large number to cut out and replace.

I've been trying to patch over them with lime mortar (lime putty,
sharp sand and red brick dust).

Mix is good consistency & sticky - but it still isn't bonding very
well to the bricks (which have been gone over roughly with a wire
brush, brushed down and then wetted).

So I'm thinking - maybe wet down with 10% pva solution?

Other suggestions?


Use this in the cement mix,as you have done wet the brick first.
http://tinyurl.com/6o3w92


You dont need to add plasticiser to lime putty, it _is_ a plasticiser

I suspect that your layer of mortar a bit thin. 6-10mm works best

Consolidate the mortar once it has picked up a bit (ie some of the
water has migrated into the brickwork leaving air voids)

Try painting the brick with limewash before plastering. It will soak
into the brick a bit so when the lime sets there will be a chemical
bond between the brick and the lime mortar

Try drilling a few holes in the brick to give added mechanical key.
Hoover out the holes, wet them, limewash them, then plaster

But whatever you do it is still patching and you will never get a good
colourmatch. Cutting out and replacing the bricks will look better :-)

I wouldnt add PVA, it impairs the breathability and so will tend to
make the spalling worse in the future

Anna
--

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

  #4  
Old June 20th 08, 06:10 AM posted to uk.d-i-y
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Posts: 121
Default How to patch spalling brickwork?

On Fri, 20 Jun 2008 04:30:16 GMT, (Anna Kettle) wrote:

and really do wet the wall down well, several times. An exposed wall
in midsummer gets very dry. Protect the setting mortar from the sun.
You may need to spray it down once or twice as it sets

Anna

On Thu, 19 Jun 2008 19:12:58 GMT, "George"
wrote:


wrote in message
...
I've got a large North-facing house wall of soft Norfolk red bricks -
and a large number have spalled.

It's really an impractically large number to cut out and replace.

I've been trying to patch over them with lime mortar (lime putty,
sharp sand and red brick dust).

Mix is good consistency & sticky - but it still isn't bonding very
well to the bricks (which have been gone over roughly with a wire
brush, brushed down and then wetted).

So I'm thinking - maybe wet down with 10% pva solution?

Other suggestions?


Use this in the cement mix,as you have done wet the brick first.
http://tinyurl.com/6o3w92

You dont need to add plasticiser to lime putty, it _is_ a plasticiser

I suspect that your layer of mortar a bit thin. 6-10mm works best

Consolidate the mortar once it has picked up a bit (ie some of the
water has migrated into the brickwork leaving air voids)

Try painting the brick with limewash before plastering. It will soak
into the brick a bit so when the lime sets there will be a chemical
bond between the brick and the lime mortar

Try drilling a few holes in the brick to give added mechanical key.
Hoover out the holes, wet them, limewash them, then plaster

But whatever you do it is still patching and you will never get a good
colourmatch. Cutting out and replacing the bricks will look better :-)

I wouldnt add PVA, it impairs the breathability and so will tend to
make the spalling worse in the future

Anna
--

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


--

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

  #5  
Old June 20th 08, 07:55 AM posted to uk.d-i-y
external usenet poster
 
Posts: 307
Default How to patch spalling brickwork?

On 19 Jun, 20:00, " wrote:
I've got a large North-facing house wall of soft Norfolk red bricks -
and a large number have spalled.

It's really an impractically large number to cut out and replace.

I've been trying to patch over them with lime mortar (lime putty,
sharp sand and red brick dust).

Mix is good consistency & sticky - but it still isn't bonding very
well to the bricks (which have been gone over roughly with a wire
brush, brushed down and then wetted).

So I'm thinking - maybe wet down with 10% pva solution?

Other suggestions?


Dear Dom
Without question the best repair will be the lime - which is in effect
a lime render shaped to look like bricks. However, if you wish to
reconsitute the bricks then one way of doing this that I have done
sucessfully with a 20 year (so far) no-problem success rate is to:
key the brick and remove all friable material (you don't want
expanding salts contaminating the substrate
if it needs it screw in some stainless steel eml with stainless screws
apply SBR and put in a light coloured sand /brick dust/ cement mortar
(you will have to get lots of damaged old bricks)with sbr in the mix
and when set but not hard cut out the pointing area later to be
pointed
once set point in gaps

Chris
  #6  
Old June 20th 08, 07:58 AM posted to uk.d-i-y
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Posts: 2,362
Default How to patch spalling brickwork?

Thanks for those tips Anna - I think we're going to have a change of
tactics today - I'm going to concentrate solely on prepping the
spalled bricks and limewashing the damaged area.

Coverage was generally 15-25mm (i.e.fairly deep spalling) and North
facing so not getting the sun - but it's 100's of bricks. Having the
whole face lime-rendered might be necessary at some point.

Overnight the patches have taken a good set (the ones rubbed down with
a wire brush late last night have taken the most natural, blended-in
appearance, ones brushed down earlier - less so) - but probably only
50-60% have a good bond.

I think the change of tactics today will reduce any tendency to "get
the mortar on" without sufficiently thorough prep.
  #7  
Old June 20th 08, 10:10 PM posted to uk.d-i-y
external usenet poster
 
Posts: 9,056
Default How to patch spalling brickwork?

Anna Kettle wrote:
On Thu, 19 Jun 2008 19:12:58 GMT, "George"
wrote:

wrote in message
...
I've got a large North-facing house wall of soft Norfolk red bricks -
and a large number have spalled.

It's really an impractically large number to cut out and replace.

I've been trying to patch over them with lime mortar (lime putty,
sharp sand and red brick dust).

Mix is good consistency & sticky - but it still isn't bonding very
well to the bricks (which have been gone over roughly with a wire
brush, brushed down and then wetted).

So I'm thinking - maybe wet down with 10% pva solution?

Other suggestions?

Use this in the cement mix,as you have done wet the brick first.
http://tinyurl.com/6o3w92


You dont need to add plasticiser to lime putty, it _is_ a plasticiser

I suspect that your layer of mortar a bit thin. 6-10mm works best

Consolidate the mortar once it has picked up a bit (ie some of the
water has migrated into the brickwork leaving air voids)

Try painting the brick with limewash before plastering. It will soak
into the brick a bit so when the lime sets there will be a chemical
bond between the brick and the lime mortar

Try drilling a few holes in the brick to give added mechanical key.
Hoover out the holes, wet them, limewash them, then plaster

But whatever you do it is still patching and you will never get a good
colourmatch. Cutting out and replacing the bricks will look better :-)

I wouldnt add PVA, it impairs the breathability and so will tend to
make the spalling worse in the future


that depends on whether the PVA stops the water getting in,or getting out.

Below damp course, no. Above damp. well it may actually help
Anna



  #8  
Old June 21st 08, 11:23 AM posted to uk.d-i-y
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Posts: 8,237
Default How to patch spalling brickwork?

On Jun 20, 7:58*am, " wrote:

Thanks for those tips Anna - I think we're going to have a change of
tactics today - I'm going to concentrate solely on prepping the
spalled bricks and limewashing the damaged area.

Coverage was generally 15-25mm (i.e.fairly deep spalling) and North
facing so not getting the sun - but it's 100's of bricks. Having the
whole face lime-rendered might be necessary at some point.

Overnight the patches have taken a good set (the ones rubbed down with
a wire brush late last night have taken the most natural, blended-in
appearance, ones brushed down earlier - less so) - but probably only
50-60% have a good bond.

I think the change of tactics today will reduce any tendency to "get
the mortar on" without sufficiently thorough prep.


how are you defining a 'good bond'? One thing I've noticed is that if
the layer of material is strong enough in its own right then voids
under it cease to be an issue. Whether thats going to apply to an inch
of lime is another question.


NT
  #9  
Old June 21st 08, 03:45 PM posted to uk.d-i-y
external usenet poster
 
Posts: 2,362
Default How to patch spalling brickwork?


how are you defining a 'good bond'?


Good bond is when rubbed down very firmly with a wire brush 24hours
later there's no chance of dislodging the patch.

Update - we spent Friday solely on prepping the old spalled faces with
wire brushes (have now done about one-third of the wall). We also
pulled out all the less than satisfactory patches from Thursday. Most
of those still in place are brilliant, strong bond and good surface -
they look like pinky bricks mixed in with the reds.

The key factors seem to have been very through wire brushing of the
old faces and thorough wetting.

Our plan now is to complete the wire brushing of the damaged faces
(and reinspecting them until we're really confident we haven't got
sloppy anywhere), then limewash a few, then more thorough wetting,
patching - but with more experience of when to brush over (for the
surface texture) and when to wire brush (to clear off unwanted excess
mortar).

We've been using red brick dust to get the colour (and its pozzolanic
effect) - but the proportion has been 25% (i.e 1 part lime putty, 3
parts sharp sand, 1 part brick dust).

Can anyone tell me more about the possible effects of using such a
large proportion of brick dust?

Many thanks for all the helpful replies here.
  #10  
Old June 21st 08, 09:47 PM posted to uk.d-i-y
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Posts: 8,237
Default How to patch spalling brickwork?

On Jun 21, 3:45*pm, " wrote:

how are you defining a 'good bond'?


Good bond is when rubbed down very firmly with a wire brush 24hours
later there's no chance of dislodging the patch.


Well there's your problem. 24hrs is way too early to mess with lime,
its strength is close to zero after so little time.



We've been using red brick dust to get the colour (and its pozzolanic
effect) - but the proportion has been 25% (i.e 1 part lime putty, 3
parts sharp sand, 1 part brick dust).

Can anyone tell me more about the possible effects of using such a
large proportion of brick dust?


Its pozzolanic property means it sets quicker and harder, and
breathability is reduced a bit. Dont think it has any other effect.
Just give it much longer before hassling it.


NT
 




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