Knowledge about plaster

[Fastpedaller]

I've been doing some plastering of our Daughter's house. One thing that struck me....... All the plaster is just specified as 'gypsum'. I've used bonding plaster (very useful for deep areas eg if filling a chasing), multifinish (seems an odd name) and finishing plaster. The finishing plaster can only be used to about 2mm thick, the bonding plaster can go to 11mm thick - but they are both described as gypsum! Can anyone shed any light on what's different in the make-up between these two plasters?

 

[Cycleops]

From doing a bit many years ago I seem to remember the bonding plaster was rather coarser than the finishing plaster which was finer. That's all really.

 

[Kingfisher101]

No, But if you dont know the absolute basics then should you be doing the job at all?

 

[Drago]

I know zero about nothing and I'm a masterful DIY bodger. I've erected entire houses using silicone sealant and recycled self tapping screws of the wrong type.

 

[presta]

I've got some experience of getting plastered if that's any help.

 

[Cycleops]

I've got some experience of getting plastered if that's any help.

I think the OP was after someone who has experience of plastering while plastered.

 

[newts]

Bonding/hardwall plaster is an undercoat, an alternative to sand & cement undercoat. It is a thicker coat(s) to smooth the wall from a rough brick/stone substrate. Finish plaster is the top coat that is smooth & harder, finer particles. Multifinish is just a finish plaster that is suitable for most undercoats gypsum, plasterboard & sand/cement etc.

 

[Cycleops]

Spoken like a pro @newts .

 

[newts]

Spoken like a pro @newts .

Not a pro plasterer, but I've been working within the building industry for 40+ years😉

 

[Fastpedaller]

Bonding/hardwall plaster is an undercoat, an alternative to sand & cement undercoat. It is a thicker coat(s) to smooth the wall from a rough brick/stone substrate. Finish plaster is the top coat that is smooth & harder, finer particles. Multifinish is just a finish plaster that is suitable for most undercoats gypsum, plasterboard & sand/cement etc.

Thanks - I'd worked all that out, but it's still unclear what's in the different products which are all simple described as 'gypsum'. Particularly why for example one can be layered up to 11 thick without cracking and an other will crack if more than 2mm?

 

[Fastpedaller]

No, But if you dont know the absolute basics then should you be doing the job at all?

Does anyone 'know the basics' of the product ? I'm familiar with using them, as I'm sure many people are.

 

[newts]

Thanks - I'd worked all that out, but it's still unclear what's in the different products which are all simple described as 'gypsum'. Particularly why for example one can be layered up to 11 thick without cracking and an other will crack if more than 2mm?

Gypsum based undercoat dries quicker than cement based renders, allowing the finish plaster to be applied much sooner. Gypsum bonding/undercoat plaster will also contain a good % of larger particle size to allow for thicker coats without slumping or cracking. A bit like the difference between mortar & concrete.

 

[Cycleops]

You might all be interested to know that plaster is unavailable here apart from plasterboard and PoP. which is used for all decorative ceiling work with fibre. All wall rendering , in and out, is done with sand & cement.

 

[Fastpedaller]

Gypsum based undercoat dries quicker than cement based renders, allowing the finish plaster to be applied much sooner. Gypsum bonding/undercoat plaster will also contain a good % of larger particle size to allow for thicker coats without slumping or cracking. A bit like the difference between mortar & concrete.

Ah!, so are the ingredients the same for both bonding and finishing plaster, but larger particle size in the bonding is key to avoiding cracking and slumping?

 

[Kingfisher101]

Does anyone 'know the basics' of the product ? I'm familiar with using them, as I'm sure many people are.

Yes a lot of people know, hence you have had your question answered.