Running casting plaster in situ

Jordan lawrence

New Member
Hello people,

I’m an ex plaster and I re doing the front room of my house I thought it would be a good to over board the ceiling as lath are cracking and run a fresh mould over the original solid cove however I have really struggled getting a decent finish in my first run because the casting plaster keeps going off in about 3 minutes could someone point me in the right direction as I need to get bigger areas run and I know that it will look terrible….. I could do with a bout 15 minutes delay on the cure/set period
 

MakeItSmooth

Well-Known Member
Hello people,

I’m an ex plaster and I re doing the front room of my house I thought it would be a good to over board the ceiling as lath are cracking and run a fresh mould over the original solid cove however I have really struggled getting a decent finish in my first run because the casting plaster keeps going off in about 3 minutes could someone point me in the right direction as I need to get bigger areas run and I know that it will look terrible….. I could do with a bout 15 minutes delay on the cure/set period

Are you certain you need to re-do the existing moulding?

Would it be viable for you to apply a stop bead or shadow gap bead around the perimeter of the room, up against the existing moulding, and then plaster the ceiling up to it. There are a few TPF members who do it that way, and it looks neat enough to avoid modifying the moulding.

Not everyone's cup of tea, but some like it.

See this thread:

www.plasterersforum.com/threads/some-days.81799/
 
Last edited:

BryanJ

Well-Known Member
Fine Caster Plaster should be 20 minutes if in date and stored correctly.
If its going off in 3 minutes then check the date.
Have you cored out the background with a muffle, and left about 5mm for the finishing coat?
If you are running in-situ the mix should be 50% plaster to 50% lime putty.
There are some useful video's on You Tube.
 

Nath80

Well-Known Member
Are you certain you need to re-do the existing moulding?

Would it be viable for you to apply a stop bead or shadow gap bead around the perimeter of the room, up against the existing moulding, and then plaster the ceiling up to it. There are a few TPF members who do it that way, and it looks neat enough to avoid modifying the moulding.

Not everyone's cup of tea, but some like it.

See this thread:

www.plasterersforum.com/threads/some-days.81799/
Bless you, always knew you loved the quality of my work :coffe:
 

Nath80

Well-Known Member

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Jordan lawrence

New Member
Unfortunately I have s studded the joining wall to sound proof next doors dogs lol so completely lost the previous solid cove moulding.
I purchased fine casting plaster from industrial plaster supplies website the bag has a date of 16/05/21 I assume this is the manufacture date as it is absent of a use by date.
what are you’re thoughts of using British gypsum for my final pass ?
 

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Jordan lawrence

New Member
That’s
Fine Caster Plaster should be 20 minutes if in date and stored correctly.
If its going off in 3 minutes then check the date.
Have you cored out the background with a muffle, and left about 5mm for the finishing coat?
If you are running in-situ the mix should be 50% plaster to 50% lime putty.
There are some useful video's on You Tube.
probably where I have gone wrong then I have used casting plaster straight from the bag not like putty added I best head to the merchant in the morning
 

BryanJ

Well-Known Member
Unfortunately I have s studded the joining wall to sound proof next doors dogs lol so completely lost the previous solid cove moulding.
I purchased fine casting plaster from industrial plaster supplies website the bag has a date of 16/05/21 I assume this is the manufacture date as it is absent of a use by date.
what are you’re thoughts of using British gypsum for my final pass ?
Do you mean Multi finish for the final pass?
Multi may look like fine plaster but it is more course and final finish would not be as smooth.
I have never used Multi for finishing moulding work but would give you more time.
For the final pass, mix it like very wet and use a brush to paint and splash on, don't forget safety glasses.
Another option would be to run the mould on a bench and then fit.
 

BryanJ

Well-Known Member
That’s

probably where I have gone wrong then I have used casting plaster straight from the bag not like putty added I best head to the merchant in the morning
You can use hydrated lime add water mix to lump free creamy texture. Leave in bucket over night cover with plastic bag, knock back up before use.
Put small some lime putty on spot, form hole/circle in middle add clean water, sprinkle fine casting plaster into water and fully mix with lime putty.
Only mix the amount you can use. Don't go lower than 50/50.
Look on Youtube there are some good videos
 

Jordan lawrence

New Member
You can use hydrated lime add water mix to lump free creamy texture. Leave in bucket over night cover with plastic bag, knock back up before use.
Put small some lime putty on spot, form hole/circle in middle add clean water, sprinkle fine casting plaster into water and fully mix with lime putty.
Only mix the amount you can use. Don't go lower than 50/50.
Look on Youtube there are some good videos
Thank Bryan J for the pointers I have finally got hold of some Lime yesterday and have made some new zinc plates for my final pass hopefully it goes ok I’m just worried about the suction rates as it’s been a Herod few days since I started it however I will post how it goes I think I will be running it on Sunday…wish me luck I should have stuck to the float&set only
 

Beerboy

New Member
Hello people,

I’m an ex plaster and I re doing the front room of my house I thought it would be a good to over board the ceiling as lath are cracking and run a fresh mould over the original solid cove however I have really struggled getting a decent finish in my first run because the casting plaster keeps going off in about 3 minutes could someone point me in the right direction as I need to get bigger areas run and I know that it will look terrible….. I could do with a bout 15 minutes delay on the cure/set period
Add a retarder to the water. Borax as I remember. But then I used to use glue size which was water, bone glue with a bit of lime in it and boiled up. I'm going back fifty years. I'm sure there are modern retarders now.
 

The Hobo

Well-Known Member
Add a retarder to the water. Borax as I remember. But then I used to use glue size which was water, bone glue with a bit of lime in it and boiled up. I'm going back fifty years. I'm sure there are modern retarders now.
trisodium citrate is the gear
 

graham hurt

New Member
Hello people,

I’m an ex plaster and I re doing the front room of my house I thought it would be a good to over board the ceiling as lath are cracking and run a fresh mould over the original solid cove however I have really struggled getting a decent finish in my first run because the casting plaster keeps going off in about 3 minutes could someone point me in the right direction as I need to get bigger areas run and I know that it will look terrible….. I could do with a bout 15 minutes delay on the cure/set period
Control the background suction and add some lime putty to the casting plaster and run the finish over a muffle. That will help.
 
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