Joining new to old plaster
 

Hi,

I have to plaster a bare patch on a brick wall. What is the best way
for joining the new plaster to old one?

Should I have a sharpish vertical cut of the old plaster towards the
bricks (it is quite crumbly and easy to remove with a scraper)

or

should I let it be feathered as it has come off (remove lose bits)?

I am going to use undercoat and finishing plaster.

TIA
Charles

Joining new to old plaster
 

On 27 July, 22:20, Charles C
wrote:
Hi,

I have to plaster a bare patch on a brick wall. What is the best way
for joining the new plaster to old one?

Should I have a sharpish vertical cut of the old plaster towards the
bricks (it is quite crumbly and easy to remove with a scraper)

or

should I let it be feathered as it has come off (remove lose bits)?


IMHO just tease off anything obviously loose and donlt worry about
straight edges - they would tend to be more noticeable when patched.

Cheers
Jim K

Joining new to old plaster
 

In article ,
Jim K writes:
On 27 July, 22:20, Charles C
wrote:
Hi,

I have to plaster a bare patch on a brick wall. What is the best way
for joining the new plaster to old one?

Should I have a sharpish vertical cut of the old plaster towards the
bricks (it is quite crumbly and easy to remove with a scraper)

or

should I let it be feathered as it has come off (remove lose bits)?

You can't really feather plaster.

IMHO just tease off anything obviously loose and donlt worry about
straight edges - they would tend to be more noticeable when patched.

Spot on - the eye is extremely good at identifying straight line
imperfections. A random jagged edge should be a less noticable
imperfection.

PVA (dilute) the bricks and the broken plaster edges first.
You want to use a scratch (under) coat to about 2mm behind the
finished surface, and then finish coat to bring it level.
Apply finish coat whilst scratch coat is still wet, and ideally
before scratch coat completely sets.

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

Joining new to old plaster
 

Andrew Gabriel said the following on 27/07/2010 23:00:
In article ,
Jim K writes:
On 27 July, 22:20, Charles C
wrote:
Hi,

I have to plaster a bare patch on a brick wall. What is the best way
for joining the new plaster to old one?

Should I have a sharpish vertical cut of the old plaster towards the
bricks (it is quite crumbly and easy to remove with a scraper)

or

should I let it be feathered as it has come off (remove lose bits)?

You can't really feather plaster.

IMHO just tease off anything obviously loose and donlt worry about
straight edges - they would tend to be more noticeable when patched.

Spot on - the eye is extremely good at identifying straight line
imperfections. A random jagged edge should be a less noticable
imperfection.

Yes I will do that ... I might have to randomise it a bit more.


PVA (dilute) the bricks and the broken plaster edges first.

what dilution roughly?

You want to use a scratch (under) coat to about 2mm behind the
finished surface, and then finish coat to bring it level.
Apply finish coat whilst scratch coat is still wet, and ideally
before scratch coat completely sets.

Thank you for the last bit. I would not have done that :-(

C.

Joining new to old plaster
 

In article ,
Charles C writes:
Andrew Gabriel said the following on 27/07/2010 23:00:
In article ,
Jim K writes:
On 27 July, 22:20, Charles C
wrote:
Hi,

I have to plaster a bare patch on a brick wall. What is the best way
for joining the new plaster to old one?

Should I have a sharpish vertical cut of the old plaster towards the
bricks (it is quite crumbly and easy to remove with a scraper)

or

should I let it be feathered as it has come off (remove lose bits)?

You can't really feather plaster.

IMHO just tease off anything obviously loose and donlt worry about
straight edges - they would tend to be more noticeable when patched.

Spot on - the eye is extremely good at identifying straight line
imperfections. A random jagged edge should be a less noticable
imperfection.

Yes I will do that ... I might have to randomise it a bit more.


PVA (dilute) the bricks and the broken plaster edges first.

what dilution roughly?

Not very critical, 4 water to 1 PVA should be fine.
Add the water to the PVA slowly initially whilst mixing,
as a dollop of PVA in water doesn't mix easily.
You can buy it pre-diluted in 5l containers.

You want to use a scratch (under) coat to about 2mm behind the
finished surface, and then finish coat to bring it level.
Apply finish coat whilst scratch coat is still wet, and ideally
before scratch coat completely sets.

Thank you for the last bit. I would not have done that :-(

Bonding coat is probably the easiest scratch coat plaster to
use, as it contains glue too, so it sticks easily to almost
anything (including your plastering tools if you don't wash
it off well).

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