Pre-mixed bagged plaster advice.

nobananas

New Member
Hi all. Didn't know whether to post this here or in the DIY section. Very new to lime plastering so be kind ! A little background to what I'm doing first. We have a fairly old Georgian property (semi derelict !) and currently I am renovating two attic rooms. The intention is simply to get them clean and tidy to use as storage. We had to have the building re-roofed a short while ago which included having new dorma windows fitted. The walls are part brick and part lathe where the sloped roof joins the walls.
I am keen on keeping as much of the original plasterwork as possible and dispite the roofing company telling me I would have to pull down all the sagging ceilings I have managed to lift and reattach them, there's cracks everywhere but that's part of the charm ! Unfortunately the gable end walls have a wrought iron tie bars running through them which are plastered over and due to corrosion has blown all the plaster so I decided to board the gable ends with wood wool board, I have also used wood wool to board the inside of the dormas and as in-fills over the oak wall plate between the wall and sloped ceiling. I decided for ease of use to buy in bagged pre-mixed glass fibre haired coarse mix to use as a base coat and bagged fine-stuff as a finishing coat.
Now this is where we get to the novice inexperienced part ! Now obviously, no amount of reading books, internet research is ever going to be substitute for years of training and experience but I initially knocked up the haired coarse mix in a standard cement mixer before doing the final mix in the attic with a paddle mixer. It worked ok, I got it on the walls etc and it has stayed put. The finishing coat however has been an issue. I knocked it up basically the same way but the results I got were that the water added to the mix just seemed to 'drop out' rather than mix in resulting in an experience akin to plastering with wet sand and a couple of weeks later I basically removed it like dry sand ! I was concerned that perhaps it had 'gone off' before use as it has been stored (in sealed bags) for a while but I contacted the manufacturer who said it should store indefinately and was likely a result of knocking it up in a regular cement mixer.
So, what is the best way to knock up relatively dry pre-mixed plaster before use ?
My apologies for the rather long first post !
 

Tinytom

Well-Known Member
Hi all. Didn't know whether to post this here or in the DIY section. Very new to lime plastering so be kind ! A little background to what I'm doing first. We have a fairly old Georgian property (semi derelict !) and currently I am renovating two attic rooms. The intention is simply to get them clean and tidy to use as storage. We had to have the building re-roofed a short while ago which included having new dorma windows fitted. The walls are part brick and part lathe where the sloped roof joins the walls.
I am keen on keeping as much of the original plasterwork as possible and dispite the roofing company telling me I would have to pull down all the sagging ceilings I have managed to lift and reattach them, there's cracks everywhere but that's part of the charm ! Unfortunately the gable end walls have a wrought iron tie bars running through them which are plastered over and due to corrosion has blown all the plaster so I decided to board the gable ends with wood wool board, I have also used wood wool to board the inside of the dormas and as in-fills over the oak wall plate between the wall and sloped ceiling. I decided for ease of use to buy in bagged pre-mixed glass fibre haired coarse mix to use as a base coat and bagged fine-stuff as a finishing coat.
Now this is where we get to the novice inexperienced part ! Now obviously, no amount of reading books, internet research is ever going to be substitute for years of training and experience but I initially knocked up the haired coarse mix in a standard cement mixer before doing the final mix in the attic with a paddle mixer. It worked ok, I got it on the walls etc and it has stayed put. The finishing coat however has been an issue. I knocked it up basically the same way but the results I got were that the water added to the mix just seemed to 'drop out' rather than mix in resulting in an experience akin to plastering with wet sand and a couple of weeks later I basically removed it like dry sand ! I was concerned that perhaps it had 'gone off' before use as it has been stored (in sealed bags) for a while but I contacted the manufacturer who said it should store indefinately and was likely a result of knocking it up in a regular cement mixer.
So, what is the best way to knock up relatively dry pre-mixed plaster before use ?
My apologies for the rather long first post !
If the manufacturer is telling you how not to mix their product then surely they are also telling you how to mix their product
 

nobananas

New Member
If the manufacturer is telling you how not to mix their product then surely they are also telling you how to mix their product
They were not terribly helpful although they did say I should try mixing with a paddle mixer not a cement mixer. I used a cement mixer after viewing a Ty Mawr video on their website that was mixing a similar product and it worked fine for the base coat and I assumed it would be ok for the top coat but I guess not !
 
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