Hello,
The pebbledash above my bay window (30s semi) had cracked extensively,
revealing a galvanised mesh that was now beyond rust.

So, I have knocked all the exterior render off the bay and now have
stainless steel expamet mesh ready to start the repair.

I understand that I should use stainless nails and tie wire with s/s
mesh, not galvanised.

That I should overlap sections of mesh by four inches.
That the mesh is backed by 1/4" thick wooden battens to allow the
render to penetrate the mesh and hang on.

That these battens are also to hold the bituminised felt sheet* behind
the mesh in place against the wooden studding behind it (I guess I
could use 1200 ga polythene sheet too).

*Thinking of 'undertile felt' from B&Q - similar thickness to the
original, though the B&Q stuff is lightly sanded.

Things I am less certain about - my house is from 1938 and has lime
plaster inside and lime mortar between the bricks, it's quite white in
appearance and the mesh had this in it too - but there appear to be
three coats of render, the inner one fairly white, the next a little
darker, the third with all the pebbles stuck in it. I am thing the
base coat is not pure lime mortar though? More likely 1:1:5
lime:cement:sharp sand? What about coarse sand - is that better?

I believe the layers should get weaker as you go out, so the next
layer might be 1:1:6?

Not sure about the pebbledash layer - needs to be able to take pebbles
though having tried this once they just seem to bounce off ;0)

Also not sure about 'bonding' to the mesh and/or the brickwork at the
edges with pva or 'sbr' slurry?

Is the initial 'pricking' coat to the mesh done in a special way or is
it just a thin coat to get the 'tongues' of render stuck through the
back?

Also not sure about putting waterproofer in the render - after all,
lime mortar is breathable, so is cement/lime mortar to a certain
extent. I don't want to trap water where a lime render could have
'breathed' it out so to speak.

Any comments/advice/tips??

Andy

Andrew Phillips wrote:
Hello,
The pebbledash above my bay window (30s semi) had cracked extensively,
revealing a galvanised mesh that was now beyond rust.

So, I have knocked all the exterior render off the bay and now have
stainless steel expamet mesh ready to start the repair.


If it's a square bay, I'd strongly advise you to clad it in upvc rather than
rendering, if it's rounded, IE curved, then render is the way forward.

I understand that I should use stainless nails and tie wire with s/s
mesh, not galvanised.

yes

That I should overlap sections of mesh by four inches.
That the mesh is backed by 1/4" thick wooden battens to allow the
render to penetrate the mesh and hang on.


You've lost me already, 1/4 of an inch batens? - these are lath, like what's
used indoors - they won't last long outdooors, nor would I fancy trying to
affix them to mesh.

That these battens are also to hold the bituminised felt sheet* behind
the mesh in place against the wooden studding behind it (I guess I
could use 1200 ga polythene sheet too).

Breathable membrane is what you require

*Thinking of 'undertile felt' from B&Q - similar thickness to the
original, though the B&Q stuff is lightly sanded.

Things I am less certain about - my house is from 1938 and has lime
plaster inside and lime mortar between the bricks, it's quite white in
appearance and the mesh had this in it too - but there appear to be
three coats of render, the inner one fairly white, the next a little
darker, the third with all the pebbles stuck in it. I am thing the
base coat is not pure lime mortar though? More likely 1:1:5
lime:cement:sharp sand? What about coarse sand - is that better?

Red building sand, like what's used for mortar is what everyone renders with

I believe the layers should get weaker as you go out, so the next
layer might be 1:1:6?

I'd be temted to use 3:1 sand cement on first coat, then 4:1 for top coat
and pebbledashing.
You don't need three coats.

Not sure about the pebbledash layer - needs to be able to take pebbles
though having tried this once they just seem to bounce off ;0)

They stick better when wet.


Also not sure about 'bonding' to the mesh and/or the brickwork at the
edges with pva or 'sbr' slurry?

not required on the mesh at all, but yes everywhere else

Is the initial 'pricking' coat to the mesh done in a special way or is
it just a thin coat to get the 'tongues' of render stuck through the
back?

Just applied as normal, although it will need to be a fairly stiff mix, too
wet and it will just sag through the mesh

Also not sure about putting waterproofer in the render - after all,
lime mortar is breathable, so is cement/lime mortar to a certain
extent. I don't want to trap water where a lime render could have
'breathed' it out so to speak.

Any comments/advice/tips??

You can put W/P in the top coat but not the first
(the 2nd coat won't stick to it when it's dry.)

Also, forget about the lime

(30s semi)

If it's a square bay, I'd strongly advise you to clad it in upvc rather than
rendering,

Also if you'd like it to look fecking ugly afterwards and entirely
inappropriate for a '30s house.

You can round the UPVC "Shameless accident compensation cheque" effect
off nicely by finding a '30s semi with a semicircular arch porch, then
fitting a tiny UPVC door into the middle of it. Fill the gap with
more UPVC - you can get this in raised & fielded panels for a classy
effect.

On Monday, 13 August 2012 23:51:07 UTC+1, Phil L wrote:
Andrew Phillips wrote:

Hello,

The pebbledash above my bay window (30s semi) had cracked extensively,

revealing a galvanised mesh that was now beyond rust.



So, I have knocked all the exterior render off the bay and now have

stainless steel expamet mesh ready to start the repair.





If it's a square bay, I'd strongly advise you to clad it in upvc rather than

rendering, if it's rounded, IE curved, then render is the way forward.

Sadly, I can't stand the sight of uPVC. Instant character bypass for a house
;0) In any case, it's a single return bay and cladding that would look odd. If I were to go that way I'd do it in slate shingles, but I'd probably need planning permission to change the look of the house at the front like that plus it'd still look odd as a single return bay done in slate.



I understand that I should use stainless nails and tie wire with s/s

mesh, not galvanised.



yes

Tick.



That I should overlap sections of mesh by four inches.

That the mesh is backed by 1/4" thick wooden battens to allow the

render to penetrate the mesh and hang on.





You've lost me already, 1/4 of an inch batens? - these are lath, like what's

used indoors - they won't last long outdooors, nor would I fancy trying to

affix them to mesh.

The laths are as good as they day they were nailed in position 75 years ago - seriously, if I don't damage them taking them off, I'll use them again. They go behind the mesh - they (a) give a 1/4" gap for 'pricking out' of the mortar to occur through the mesh before the felt starts and (b) hold the bituminous felt dpm to the wooden studs behind.



That these battens are also to hold the bituminised felt sheet* behind

the mesh in place against the wooden studding behind it (I guess I

could use 1200 ga polythene sheet too).



Breathable membrane is what you require

Surely breathable membrane is not of much use if pressed hard up against the render coming through the mesh - it also looks too flimsy to have something touching it - since there is no airflow in the stud what is the point of breathable membrane? I would in effect be rendering onto breathable membrane, as the render will reach back through the mesh to it. If warm humid air could enter the stud from inside somehow then it might condense on the back of the cold render, but it can't so I don't see why brethable is necessary. The bituminous felt isn't breathable and the studwork behind is 100% sound.



*Thinking of 'undertile felt' from B&Q - similar thickness to the

original, though the B&Q stuff is lightly sanded.



Things I am less certain about - my house is from 1938 and has lime

plaster inside and lime mortar between the bricks, it's quite white in

appearance and the mesh had this in it too - but there appear to be

three coats of render, the inner one fairly white, the next a little

darker, the third with all the pebbles stuck in it. I am thing the

base coat is not pure lime mortar though? More likely 1:1:5

lime:cement:sharp sand? What about coarse sand - is that better?



Red building sand, like what's used for mortar is what everyone renders with



I believe the layers should get weaker as you go out, so the next

layer might be 1:1:6?



I'd be temted to use 3:1 sand cement on first coat, then 4:1 for top coat

and pebbledashing.

You don't need three coats.



Not sure about the pebbledash layer - needs to be able to take pebbles

though having tried this once they just seem to bounce off ;0)



They stick better when wet.

Good idea





Also not sure about 'bonding' to the mesh and/or the brickwork at the

edges with pva or 'sbr' slurry?



not required on the mesh at all, but yes everywhere else

Excellent



Is the initial 'pricking' coat to the mesh done in a special way or is

it just a thin coat to get the 'tongues' of render stuck through the

back?



Just applied as normal, although it will need to be a fairly stiff mix, too

wet and it will just sag through the mesh

Stiff mix, check.



Also not sure about putting waterproofer in the render - after all,

lime mortar is breathable, so is cement/lime mortar to a certain

extent. I don't want to trap water where a lime render could have

'breathed' it out so to speak.



Any comments/advice/tips??



You can put W/P in the top coat but not the first

(the 2nd coat won't stick to it when it's dry.)

Good point - needs suction I suppose as well as scratches.


Also, forget about the lime

You want me to mix a lime rendered house with a cement render? As I understand it, cement is very hard and can crack with older houses, plus if any moisture gets in through a crack it can't get out again - except inside. My brother had this problem with his house which had been inappropriately cement-rendered.

Thing is, the original house render is fine after 75 years so I'm loathe to change it or mix and match - the only thing that failed was the galvanised mesh...



On Monday, 13 August 2012 23:51:07 UTC+1, Phil L wrote:
Andrew Phillips wrote:

Hello,

The pebbledash above my bay window (30s semi) had cracked extensively,

revealing a galvanised mesh that was now beyond rust.



So, I have knocked all the exterior render off the bay and now have

stainless steel expamet mesh ready to start the repair.





If it's a square bay, I'd strongly advise you to clad it in upvc rather than

rendering, if it's rounded, IE curved, then render is the way forward.



I understand that I should use stainless nails and tie wire with s/s

mesh, not galvanised.



yes



That I should overlap sections of mesh by four inches.

That the mesh is backed by 1/4" thick wooden battens to allow the

render to penetrate the mesh and hang on.





You've lost me already, 1/4 of an inch batens? - these are lath, like what's

used indoors - they won't last long outdooors, nor would I fancy trying to

affix them to mesh.



That these battens are also to hold the bituminised felt sheet* behind

the mesh in place against the wooden studding behind it (I guess I

could use 1200 ga polythene sheet too).



Breathable membrane is what you require



*Thinking of 'undertile felt' from B&Q - similar thickness to the

original, though the B&Q stuff is lightly sanded.



Things I am less certain about - my house is from 1938 and has lime

plaster inside and lime mortar between the bricks, it's quite white in

appearance and the mesh had this in it too - but there appear to be

three coats of render, the inner one fairly white, the next a little

darker, the third with all the pebbles stuck in it. I am thing the

base coat is not pure lime mortar though? More likely 1:1:5

lime:cement:sharp sand? What about coarse sand - is that better?



Red building sand, like what's used for mortar is what everyone renders with



I believe the layers should get weaker as you go out, so the next

layer might be 1:1:6?



I'd be temted to use 3:1 sand cement on first coat, then 4:1 for top coat

and pebbledashing.

You don't need three coats.



Not sure about the pebbledash layer - needs to be able to take pebbles

though having tried this once they just seem to bounce off ;0)



They stick better when wet.





Also not sure about 'bonding' to the mesh and/or the brickwork at the

edges with pva or 'sbr' slurry?



not required on the mesh at all, but yes everywhere else



Is the initial 'pricking' coat to the mesh done in a special way or is

it just a thin coat to get the 'tongues' of render stuck through the

back?



Just applied as normal, although it will need to be a fairly stiff mix, too

wet and it will just sag through the mesh



Also not sure about putting waterproofer in the render - after all,

lime mortar is breathable, so is cement/lime mortar to a certain

extent. I don't want to trap water where a lime render could have

'breathed' it out so to speak.



Any comments/advice/tips??



You can put W/P in the top coat but not the first

(the 2nd coat won't stick to it when it's dry.)



Also, forget about the lime

On Tuesday, 14 August 2012 00:21:05 UTC+1, (unknown) wrote:
On Monday, 13 August 2012 23:51:07 UTC+1, Phil L wrote:

Andrew Phillips wrote:

Regarding the studding behind the render etc - if it is ventilated I haven't seen how yet, but I only took a quick peek behind the bituminous felt dpm sheet. Since it is not ventilated from inside or outside, the only way it could be is via cavity wall air but again I'll have to have another look. The felt dpm by the way had a horizontal overlap join in it near the top - so does actually pass air, though as I say the air has nowhere to go as far as I've yet seen.



Hello,



The pebbledash above my bay window (30s semi) had cracked extensively,



revealing a galvanised mesh that was now beyond rust.







So, I have knocked all the exterior render off the bay and now have



stainless steel expamet mesh ready to start the repair.











If it's a square bay, I'd strongly advise you to clad it in upvc rather than



rendering, if it's rounded, IE curved, then render is the way forward.



Sadly, I can't stand the sight of uPVC. Instant character bypass for a house

;0) In any case, it's a single return bay and cladding that would look odd. If I were to go that way I'd do it in slate shingles, but I'd probably need planning permission to change the look of the house at the front like that plus it'd still look odd as a single return bay done in slate.







I understand that I should use stainless nails and tie wire with s/s



mesh, not galvanised.







yes



Tick.







That I should overlap sections of mesh by four inches.



That the mesh is backed by 1/4" thick wooden battens to allow the



render to penetrate the mesh and hang on.











You've lost me already, 1/4 of an inch batens? - these are lath, like what's



used indoors - they won't last long outdooors, nor would I fancy trying to



affix them to mesh.



The laths are as good as they day they were nailed in position 75 years ago - seriously, if I don't damage them taking them off, I'll use them again.. They go behind the mesh - they (a) give a 1/4" gap for 'pricking out' of the mortar to occur through the mesh before the felt starts and (b) hold the bituminous felt dpm to the wooden studs behind.







That these battens are also to hold the bituminised felt sheet* behind



the mesh in place against the wooden studding behind it (I guess I



could use 1200 ga polythene sheet too).







Breathable membrane is what you require



Surely breathable membrane is not of much use if pressed hard up against the render coming through the mesh - it also looks too flimsy to have something touching it - since there is no airflow in the stud what is the point of breathable membrane? I would in effect be rendering onto breathable membrane, as the render will reach back through the mesh to it. If warm humid air could enter the stud from inside somehow then it might condense on the back of the cold render, but it can't so I don't see why brethable is necessary. The bituminous felt isn't breathable and the studwork behind is 100% sound.







*Thinking of 'undertile felt' from B&Q - similar thickness to the



original, though the B&Q stuff is lightly sanded.







Things I am less certain about - my house is from 1938 and has lime



plaster inside and lime mortar between the bricks, it's quite white in



appearance and the mesh had this in it too - but there appear to be



three coats of render, the inner one fairly white, the next a little



darker, the third with all the pebbles stuck in it. I am thing the



base coat is not pure lime mortar though? More likely 1:1:5



lime:cement:sharp sand? What about coarse sand - is that better?







Red building sand, like what's used for mortar is what everyone renders with







I believe the layers should get weaker as you go out, so the next



layer might be 1:1:6?







I'd be temted to use 3:1 sand cement on first coat, then 4:1 for top coat



and pebbledashing.



You don't need three coats.







Not sure about the pebbledash layer - needs to be able to take pebbles



though having tried this once they just seem to bounce off ;0)







They stick better when wet.



Good idea











Also not sure about 'bonding' to the mesh and/or the brickwork at the



edges with pva or 'sbr' slurry?







not required on the mesh at all, but yes everywhere else



Excellent







Is the initial 'pricking' coat to the mesh done in a special way or is



it just a thin coat to get the 'tongues' of render stuck through the



back?







Just applied as normal, although it will need to be a fairly stiff mix, too



wet and it will just sag through the mesh



Stiff mix, check.







Also not sure about putting waterproofer in the render - after all,



lime mortar is breathable, so is cement/lime mortar to a certain



extent. I don't want to trap water where a lime render could have



'breathed' it out so to speak.







Any comments/advice/tips??







You can put W/P in the top coat but not the first



(the 2nd coat won't stick to it when it's dry.)



Good point - needs suction I suppose as well as scratches.





Also, forget about the lime



You want me to mix a lime rendered house with a cement render? As I understand it, cement is very hard and can crack with older houses, plus if any moisture gets in through a crack it can't get out again - except inside. My brother had this problem with his house which had been inappropriately cement-rendered.



Thing is, the original house render is fine after 75 years so I'm loathe to change it or mix and match - the only thing that failed was the galvanised mesh...







On Monday, 13 August 2012 23:51:07 UTC+1, Phil L wrote:

Andrew Phillips wrote:



Hello,



The pebbledash above my bay window (30s semi) had cracked extensively,



revealing a galvanised mesh that was now beyond rust.







So, I have knocked all the exterior render off the bay and now have



stainless steel expamet mesh ready to start the repair.











If it's a square bay, I'd strongly advise you to clad it in upvc rather than



rendering, if it's rounded, IE curved, then render is the way forward.







I understand that I should use stainless nails and tie wire with s/s



mesh, not galvanised.







yes







That I should overlap sections of mesh by four inches.



That the mesh is backed by 1/4" thick wooden battens to allow the



render to penetrate the mesh and hang on.











You've lost me already, 1/4 of an inch batens? - these are lath, like what's



used indoors - they won't last long outdooors, nor would I fancy trying to



affix them to mesh.







That these battens are also to hold the bituminised felt sheet* behind



the mesh in place against the wooden studding behind it (I guess I



could use 1200 ga polythene sheet too).







Breathable membrane is what you require







*Thinking of 'undertile felt' from B&Q - similar thickness to the



original, though the B&Q stuff is lightly sanded.







Things I am less certain about - my house is from 1938 and has lime



plaster inside and lime mortar between the bricks, it's quite white in



appearance and the mesh had this in it too - but there appear to be



three coats of render, the inner one fairly white, the next a little



darker, the third with all the pebbles stuck in it. I am thing the



base coat is not pure lime mortar though? More likely 1:1:5



lime:cement:sharp sand? What about coarse sand - is that better?







Red building sand, like what's used for mortar is what everyone renders with







I believe the layers should get weaker as you go out, so the next



layer might be 1:1:6?







I'd be temted to use 3:1 sand cement on first coat, then 4:1 for top coat



and pebbledashing.



You don't need three coats.







Not sure about the pebbledash layer - needs to be able to take pebbles



though having tried this once they just seem to bounce off ;0)







They stick better when wet.











Also not sure about 'bonding' to the mesh and/or the brickwork at the



edges with pva or 'sbr' slurry?







not required on the mesh at all, but yes everywhere else







Is the initial 'pricking' coat to the mesh done in a special way or is



it just a thin coat to get the 'tongues' of render stuck through the



back?







Just applied as normal, although it will need to be a fairly stiff mix, too



wet and it will just sag through the mesh







Also not sure about putting waterproofer in the render - after all,



lime mortar is breathable, so is cement/lime mortar to a certain



extent. I don't want to trap water where a lime render could have



'breathed' it out so to speak.







Any comments/advice/tips??







You can put W/P in the top coat but not the first



(the 2nd coat won't stick to it when it's dry.)







Also, forget about the lime

On 13/08/2012 23:34, Andrew Phillips wrote:

Hello,
The pebbledash above my bay window (30s semi) had cracked extensively,
revealing a galvanised mesh that was now beyond rust.

So, I have knocked all the exterior render off the bay and now have
stainless steel expamet mesh ready to start the repair.

I understand that I should use stainless nails and tie wire with s/s
mesh, not galvanised.

That I should overlap sections of mesh by four inches.
That the mesh is backed by 1/4" thick wooden battens to allow the
render to penetrate the mesh and hang on.

I am guessing you are describing similar to what I did he

http://www.internode.co.uk/loft/rendering.htm

That these battens are also to hold the bituminised felt sheet* behind
the mesh in place against the wooden studding behind it (I guess I
could use 1200 ga polythene sheet too).

Or building paper is a another common backing...

*Thinking of 'undertile felt' from B&Q - similar thickness to the
original, though the B&Q stuff is lightly sanded.

Yup, something with some Hessian reinforcement is easier to fix.

Things I am less certain about - my house is from 1938 and has lime
plaster inside and lime mortar between the bricks, it's quite white in
appearance and the mesh had this in it too - but there appear to be
three coats of render, the inner one fairly white, the next a little
darker, the third with all the pebbles stuck in it. I am thing the
base coat is not pure lime mortar though? More likely 1:1:5
lime:cement:sharp sand? What about coarse sand - is that better?

If you use cement in it, then its not really lime render. The lime in
these situations acts as a plasticiser, but does not bestow the
traditional attributes of "proper" lime mortar.

I believe the layers should get weaker as you go out, so the next
layer might be 1:1:6?

Not sure its that critical. You don't want the render stronger than the
substrate though.

Not sure about the pebbledash layer - needs to be able to take pebbles
though having tried this once they just seem to bounce off ;0)

Never tried it, so can't comment... there are some videos on youtube
though.

Also not sure about 'bonding' to the mesh and/or the brickwork at the
edges with pva or 'sbr' slurry?

Use corner beads at the corners (fixed first), and a render stop at any
edges. Keeps it all tidy an in place.

Is the initial 'pricking' coat to the mesh done in a special way or is
it just a thin coat to get the 'tongues' of render stuck through the
back?

I just apply normal thickness backing coat, which pretty much hides the
mesh. Scratch it up, and then stick the finish coat on that.

Also not sure about putting waterproofer in the render - after all,
lime mortar is breathable, so is cement/lime mortar to a certain
extent. I don't want to trap water where a lime render could have
'breathed' it out so to speak.

Don't think I would. Impermeable coatings can cause as many problems as
they solve.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Tuesday, August 14, 2012 1:14:55 AM UTC+1, John Rumm wrote:
On 13/08/2012 23:34, Andrew Phillips wrote:



Hello,

The pebbledash above my bay window (30s semi) had cracked extensively,

revealing a galvanised mesh that was now beyond rust.



So, I have knocked all the exterior render off the bay and now have

stainless steel expamet mesh ready to start the repair.



I understand that I should use stainless nails and tie wire with s/s

mesh, not galvanised.



That I should overlap sections of mesh by four inches.

That the mesh is backed by 1/4" thick wooden battens to allow the

render to penetrate the mesh and hang on.



I am guessing you are describing similar to what I did he

Hello John,

Yes, That's exactly what I'm doing!



http://www.internode.co.uk/loft/rendering.htm



That these battens are also to hold the bituminised felt sheet* behind

the mesh in place against the wooden studding behind it (I guess I

could use 1200 ga polythene sheet too).



Or building paper is a another common backing...

I've heard of it, will look it up - sounds...fragile.



*Thinking of 'undertile felt' from B&Q - similar thickness to the

original, though the B&Q stuff is lightly sanded.



Yup, something with some Hessian reinforcement is easier to fix.

Mine is held onto the studding by laths and clout nails and onto the brickwork at the edges by clout nails into wooden rawlplugs and with penny sized copper washers.



Things I am less certain about - my house is from 1938 and has lime

plaster inside and lime mortar between the bricks, it's quite white in

appearance and the mesh had this in it too - but there appear to be

three coats of render, the inner one fairly white, the next a little

darker, the third with all the pebbles stuck in it. I am thing the

base coat is not pure lime mortar though? More likely 1:1:5

lime:cement:sharp sand? What about coarse sand - is that better?



If you use cement in it, then its not really lime render. The lime in

these situations acts as a plasticiser, but does not bestow the

traditional attributes of "proper" lime mortar.

I understand that, although I do believe it is somewhat breathable compared to solely cement mortar - the cement fills up the inter-grain spaces pretty much completely I believe.

My problem is that I can't tell if the original builder used lime mortar or cement/lime mortar. The sand where I am is silver and when you add lime it's snowy white. That's the colour the base coat is, snowy white. The next coat is a shade darker, but that could just be a weaker mix so more sane. I guess it's hard to tell what mortar is made of...



I believe the layers should get weaker as you go out, so the next

layer might be 1:1:6?



Not sure its that critical. You don't want the render stronger than the

substrate though.

The substrate is mesh and those common bricks that are too ugly to use without a coating.



Not sure about the pebbledash layer - needs to be able to take pebbles

though having tried this once they just seem to bounce off ;0)



Never tried it, so can't comment... there are some videos on youtube

though.



Also not sure about 'bonding' to the mesh and/or the brickwork at the

edges with pva or 'sbr' slurry?



Use corner beads at the corners (fixed first), and a render stop at any

edges. Keeps it all tidy an in place.

The render stop at the bottom - the bell-casting - must have been a piece of wood, removed after the render set. The render also sits partly on a beam above the window below. The beam has the outside edge sloping so as to offer the render some support where it touches it. There is a little rot in the centre where the render sat on it but the beam is otherwise sound. I will cut the rot out and splice in a small facing strip profiled to blend in, with nails and Cascamite boat glue, plus treat the wood.

There is no corner bead that I could see - the mesh just went around the corner. There are extra laths in the corner to support the mesh at it turns 90 degrees.



Is the initial 'pricking' coat to the mesh done in a special way or is

it just a thin coat to get the 'tongues' of render stuck through the

back?



I just apply normal thickness backing coat, which pretty much hides the

mesh. Scratch it up, and then stick the finish coat on that.



Also not sure about putting waterproofer in the render - after all,

lime mortar is breathable, so is cement/lime mortar to a certain

extent. I don't want to trap water where a lime render could have

'breathed' it out so to speak.



Don't think I would. Impermeable coatings can cause as many problems as

they solve.

Yes, I have seen this with my own eyes in other places. It is a concern, this render mix/waterproofer business, as the success of this type of construction might depend on the use of breathable lime - I don't know enough about it either way to make my mind up. Like I said, everything in the house contains lime, the brickwork mortar, the render, the interior lime plaster. The only unknown is if it's got any cement in it at all...





--

Cheers,



John.



/================================================== ===============\

| Internode Ltd - http://www.internode.co.uk |

|-----------------------------------------------------------------|

| John Rumm - john(at)internode(dot)co(dot)uk |

\================================================= ================/

On 14/08/2012 02:00, wrote:
On Tuesday, August 14, 2012 1:14:55 AM UTC+1, John Rumm wrote:

I am guessing you are describing similar to what I did he

Hello John,

Yes, That's exactly what I'm doing!

http://www.internode.co.uk/loft/rendering.htm

Or building paper is a another common backing...

I've heard of it, will look it up - sounds...fragile.

Ultimately the strength comes from the rendered metal lath - all you
really need is something to stop it falling through as you render.

*Thinking of 'undertile felt' from B&Q - similar thickness to
the

original, though the B&Q stuff is lightly sanded.



Yup, something with some Hessian reinforcement is easier to fix.

Mine is held onto the studding by laths and clout nails and onto the
brickwork at the edges by clout nails into wooden rawlplugs and with
penny sized copper washers.

That ought to do it. Sticking in normal wire nails half way and
clenching them over was another common way (gives a length of grip along
the nail rather than just the head)


If you use cement in it, then its not really lime render. The lime
in
these situations acts as a plasticiser, but does not bestow the
traditional attributes of "proper" lime mortar.

I understand that, although I do believe it is somewhat breathable
compared to solely cement mortar - the cement fills up the
inter-grain spaces pretty much completely I believe.

My problem is that I can't tell if the original builder used lime
mortar or cement/lime mortar. The sand where I am is silver and when
you add lime it's snowy white. That's the colour the base coat is,
snowy white. The next coat is a shade darker, but that could just be
a weaker mix so more sane. I guess it's hard to tell what mortar is
made of...

Since you are replacing it all, you don't necessarily have to use the same.
Use corner beads at the corners (fixed first), and a render stop at
any

edges. Keeps it all tidy an in place.

The render stop at the bottom - the bell-casting - must have been a
piece of wood, removed after the render set. The render also sits

Yup, quite common. Also common to staple a bit of sash cord along the
wood before putting in place. That then casts a "drip" into the bottom
of the render so the water falls away from the wall rather than run down
it.

partly on a beam above the window below. The beam has the outside
edge sloping so as to offer the render some support where it touches
it. There is a little rot in the centre where the render sat on it
but the beam is otherwise sound. I will cut the rot out and splice in
a small facing strip profiled to blend in, with nails and Cascamite
boat glue, plus treat the wood.

There is no corner bead that I could see - the mesh just went around
the corner. There are extra laths in the corner to support the mesh
at it turns 90 degrees.

Nothing to stop you adding them though - its easier to render up to beads.


Don't think I would. Impermeable coatings can cause as many
problems as

they solve.

Yes, I have seen this with my own eyes in other places. It is a
concern, this render mix/waterproofer business, as the success of
this type of construction might depend on the use of breathable lime
- I don't know enough about it either way to make my mind up. Like I
said, everything in the house contains lime, the brickwork mortar,
the render, the interior lime plaster. The only unknown is if it's
got any cement in it at all...

I suppose if you add an impermeable coat, you can always add trickle
ventilation somewhere if you need it.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
John Rumm writes:
On 14/08/2012 02:00, wrote:
On Tuesday, August 14, 2012 1:14:55 AM UTC+1, John Rumm wrote:

I am guessing you are describing similar to what I did he

Hello John,

Yes, That's exactly what I'm doing!

http://www.internode.co.uk/loft/rendering.htm

Or building paper is a another common backing...

I've heard of it, will look it up - sounds...fragile.

Ultimately the strength comes from the rendered metal lath - all you
really need is something to stop it falling through as you render.

I've only rendered onto expanded stainless steel lath once.
The problem I had was forcing the render through the lath at all.
It tends to just push the lath against the wall behind, but not
go through and stick to the wall itself, and springs away when
you stop applying the pressure. I was only doing a very small area,
but I was very close to taking the lath off, rendering a very thin
layer direct to the wall, and then putting the lath back in the top
of that layer before continuing.

BTW, handling a sheet of expanded stainless steel lath is not very
dissimilar from handling a coil of razor wire - very difficult to
avoid cutting yourself to shreds. I might even suggest wearing
goggles.

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

On 14/08/2012 15:18, Andrew Gabriel wrote:
In article ,
John Rumm writes:
On 14/08/2012 02:00, wrote:
On Tuesday, August 14, 2012 1:14:55 AM UTC+1, John Rumm wrote:

I am guessing you are describing similar to what I did he

Hello John,

Yes, That's exactly what I'm doing!

http://www.internode.co.uk/loft/rendering.htm

Or building paper is a another common backing...

I've heard of it, will look it up - sounds...fragile.

Ultimately the strength comes from the rendered metal lath - all you

Sorry - meant to say the lath and the render there!

really need is something to stop it falling through as you render.

I've only rendered onto expanded stainless steel lath once.
The problem I had was forcing the render through the lath at all.
It tends to just push the lath against the wall behind, but not
go through and stick to the wall itself, and springs away when
you stop applying the pressure. I was only doing a very small area,
but I was very close to taking the lath off, rendering a very thin
layer direct to the wall, and then putting the lath back in the top
of that layer before continuing.

Might have needed a wetter mix... generally I have found that it flows
through easy enough. You get better integration of the lath if there is
a bit of space behind it every now and then.

BTW, handling a sheet of expanded stainless steel lath is not very
dissimilar from handling a coil of razor wire - very difficult to
avoid cutting yourself to shreds. I might even suggest wearing
goggles.

I used the galvanised stuff last time. Slightly less nasty, but still
quite hazardous. Stiff gloves and a small disc in an 115mm AG to cut.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Andrew Gabriel wrote:
In article ,
John Rumm writes:
On 14/08/2012 02:00, wrote:
On Tuesday, August 14, 2012 1:14:55 AM UTC+1, John Rumm wrote:
I am guessing you are describing similar to what I did he
Hello John,

Yes, That's exactly what I'm doing!
http://www.internode.co.uk/loft/rendering.htm
Or building paper is a another common backing...
I've heard of it, will look it up - sounds...fragile.
Ultimately the strength comes from the rendered metal lath - all you
really need is something to stop it falling through as you render.

I've only rendered onto expanded stainless steel lath once.
The problem I had was forcing the render through the lath at all.
It tends to just push the lath against the wall behind, but not
go through and stick to the wall itself, and springs away when
you stop applying the pressure. I was only doing a very small area,
but I was very close to taking the lath off, rendering a very thin
layer direct to the wall, and then putting the lath back in the top
of that layer before continuing.


When the guys did here, (wood frame) they ply-ed the whole exterior,
shoved a semi-permeable membrane over that and then nailed *vertical
battens* to that and the metal lath over that, with a drip bead at the
bottom.
That meant the render keyed very well and there was an air gap between
the render and the wood, which allows it to dry out if there is any
penetration, and also allows the walls to breath a little.



BTW, handling a sheet of expanded stainless steel lath is not very
dissimilar from handling a coil of razor wire - very difficult to
avoid cutting yourself to shreds. I might even suggest wearing
goggles.


Good idea. Gloves certainly.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Tuesday, 14 August 2012 01:14:55 UTC+1, John Rumm wrote:
Things I am less certain about - my house is from 1938 and has lime
plaster inside and lime mortar between the bricks,
I am thinking the
base coat is not pure lime mortar though? More likely 1:1:5
lime:cement:sharp sand? What about coarse sand - is that better?

If you use cement in it, then its not really lime render. The lime in
these situations acts as a plasticiser, but does not bestow the
traditional attributes of "proper" lime mortar.

nods I'd go for a hydraulic lime render. Hydraulic lime comes in bags like cement, and sets like cement - but the result isn't as stiff, and is breathable.



I believe the layers should get weaker as you go out, so the next

layer might be 1:1:6?



Not sure its that critical. You don't want the render stronger than the

substrate though.



Not sure about the pebbledash layer - needs to be able to take pebbles

though having tried this once they just seem to bounce off ;0)



Never tried it, so can't comment... there are some videos on youtube

though.



Also not sure about 'bonding' to the mesh and/or the brickwork at the

edges with pva or 'sbr' slurry?



Use corner beads at the corners (fixed first), and a render stop at any

edges. Keeps it all tidy an in place.



Is the initial 'pricking' coat to the mesh done in a special way or is

it just a thin coat to get the 'tongues' of render stuck through the

back?



I just apply normal thickness backing coat, which pretty much hides the

mesh. Scratch it up, and then stick the finish coat on that.



Also not sure about putting waterproofer in the render - after all,

lime mortar is breathable, so is cement/lime mortar to a certain

extent. I don't want to trap water where a lime render could have

'breathed' it out so to speak.



Don't think I would. Impermeable coatings can cause as many problems as

they solve.





--

Cheers,



John.



/================================================== ===============\

| Internode Ltd - http://www.internode.co.uk |

|-----------------------------------------------------------------|

| John Rumm - john(at)internode(dot)co(dot)uk |

\================================================= ================/

On Aug 13, 11:34*pm, Andrew Phillips wrote:
Hello,
The pebbledash above my bay window (30s semi) had cracked extensively,
revealing a galvanised mesh that was now beyond rust.

So, I have knocked all the exterior render off the bay and now have
stainless steel expamet mesh ready to start the repair.

I understand that I should use stainless nails and tie wire with s/s
mesh, not galvanised.

That I should overlap sections of mesh by four inches.
That the mesh is backed by 1/4" thick wooden battens to allow the
render to penetrate the mesh and hang on.

That these battens are also to hold the bituminised felt sheet* behind
the mesh in place against the wooden studding behind it (I guess I
could use 1200 ga polythene sheet too).

*Thinking of 'undertile felt' from B&Q - similar thickness to the
original, though the B&Q stuff is lightly sanded.

Things I am less certain about - my house is from 1938 and has lime
plaster inside and lime mortar between the bricks, it's quite white in
appearance and the mesh had this in it too - but there appear to be
three coats of render, the inner one fairly white, the next a little
darker, the third with all the pebbles stuck in it. I am thing the
base coat is not pure lime mortar though? More likely 1:1:5
lime:cement:sharp sand? What about coarse sand - is that better?

I believe the layers should get weaker as you go out, so the next
layer might be 1:1:6?

Not sure about the pebbledash layer - needs to be able to take pebbles
though having tried this once they just seem to bounce off ;0)

Also not sure about 'bonding' to the mesh and/or the brickwork at the
edges with pva or 'sbr' slurry?

Is the initial 'pricking' coat to the mesh done in a special way or is
it just a thin coat to get the 'tongues' of render stuck through the
back?

Also not sure about putting waterproofer in the render - after all,
lime mortar is breathable, so is cement/lime mortar to a certain
extent. I don't want to trap water where a lime render could have
'breathed' it out so to speak.

Any comments/advice/tips??

Andy

Metalwork to enable easy clean edges makes work quicker, but it also
builds in a failure point, since its galv, and its perfect
straightness doesn't always suit old houses. I'd be inclined to leave
it out and form your edges by hand.

I would defintely not use plain cement render for the base layer when
you can use an insulating render such as papercrete, or standard
render with expanded stone included.

Vapour barrier should go on the warm side of any insulation, otherwise
condensation and rot is likely.

Pure white render is pretty well bound to be lime. Lime mortar is
normally 3:1 to 2.5:1, and isnt generally varied the way cement mixes
are. Lime is much softer, takes ages to set, and needs to be trowelled
during setting as it cracks. Unlike cement, trowelling when it part
set doesn't harm it.

Finally mixing a very little plastic fibre into the 1st coat can
reduce the risk of cracking to a degree. You can buy it at daft
prices, or just cut synthetic carpet and rag into diagonal strips and
feed it through a shredder.


NT

On Monday, August 13, 2012 at 11:34:13 PM UTC+1, Andrew Phillips wrote:
Hello,
The pebbledash above my bay window (30s semi) had cracked extensively,
revealing a galvanised mesh that was now beyond rust.

So, I have knocked all the exterior render off the bay and now have
stainless steel expamet mesh ready to start the repair.

I understand that I should use stainless nails and tie wire with s/s
mesh, not galvanised.

That I should overlap sections of mesh by four inches.
That the mesh is backed by 1/4" thick wooden battens to allow the
render to penetrate the mesh and hang on.

That these battens are also to hold the bituminised felt sheet* behind
the mesh in place against the wooden studding behind it (I guess I
could use 1200 ga polythene sheet too).

*Thinking of 'undertile felt' from B&Q - similar thickness to the
original, though the B&Q stuff is lightly sanded.

Things I am less certain about - my house is from 1938 and has lime
plaster inside and lime mortar between the bricks, it's quite white in
appearance and the mesh had this in it too - but there appear to be
three coats of render, the inner one fairly white, the next a little
darker, the third with all the pebbles stuck in it. I am thing the
base coat is not pure lime mortar though? More likely 1:1:5
lime:cement:sharp sand? What about coarse sand - is that better?

I believe the layers should get weaker as you go out, so the next
layer might be 1:1:6?

Not sure about the pebbledash layer - needs to be able to take pebbles
though having tried this once they just seem to bounce off ;0)

Also not sure about 'bonding' to the mesh and/or the brickwork at the
edges with pva or 'sbr' slurry?

Is the initial 'pricking' coat to the mesh done in a special way or is
it just a thin coat to get the 'tongues' of render stuck through the
back?

Also not sure about putting waterproofer in the render - after all,
lime mortar is breathable, so is cement/lime mortar to a certain
extent. I don't want to trap water where a lime render could have
'breathed' it out so to speak.

Any comments/advice/tips??

Andy

Need some info on rendering a round bay window.All the rendering had blown and cracked just on the round bay,so i removed all the loose,then found a like a corrugated plastic sheet with bitumen on it,and felt behind it.Their isnt many supports ie timber behind the sheet,so could this be reason why it had blown ?If i added more timber supports and made it more secure,would this cure it ?

In article ,
writes:
Need some info on rendering a round bay window.All the rendering had blown and cracked just on the round bay,so i removed all the loose,then found a like a corrugated plastic sheet with bitumen on it,and felt behind it.Their isnt many supports ie timber behind the sheet,so could this be reason why it had blown ?If i added more timber supports and made it more secure,would this cure it ?

It doesn't sound like a product suitable for rendering on.
Is this on the inside or the outside?

If you are pulling it off anyway, now is the time to make sure
it's well insulated behind it.

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