Gypsum vs cement plaster

[Tomtomtom]

I'm a DIY noob but I've noticed something which is that gypsum plaster on west-facing interior walls in older Cape Town houses does not work.

I have a wall that had holes popping open and was looking disgusting but once I got to work stripping it I realised it had been partly redone in the past. Half of it was finished in sand and cement, and that part was rock solid (even the paint was okay), vs the gypsum which was just peeling off like sheets of cardboard. The wall obviously gets a bit damp in winter, but that had only been a problem for the gypsum.

So why is gypsum/Cretestone so popular? Is there any reason why I wouldn't want to refinish this wall in sand and cement? Is there anything better than either of those for a damp wall?

I know ideally the outside needs waterproofing but that's never going to be 100% for various reasons so I am at peace with the fact I will be repainting more frequently. I just don't want to be re-plastering as well.

 

[WAslayer]

It's popular because you can get an extremely smooth finish..

Redo the section with standard plaster and you can add some waterproofing additives to help with the damp issues..

 

[tetrasect]

I'm a DIY noob but I've noticed something which is that gypsum plaster on west-facing walls in older Cape Town houses does not work.

I have a wall that had holes popping open and was looking disgusting but once I got to work stripping it I realised it had been partly redone in the past. Half of it was finished in sand and cement, and that part was rock solid (even the paint was okay), vs the gypsum which was just peeling off like sheets of cardboard. The wall obviously gets a bit damp in winter, but that had only been a problem for the gypsum.

So why is gypsum/Cretestone so popular? Is there any reason why I wouldn't want to refinish this wall in sand and cement? Is there anything better than either of those for a damp wall?

I know ideally the outside needs waterproofing but that's never going to be 100% for various reasons so I am at peace with the fact I will be repainting more frequently. I just don't want to be re-plastering as well.

Are you talking about outside walls?

Gypsum is only for indoors.

 

[Tomtomtom]

Are you talking about outside walls?

Gypsum is only for indoors.

No I should have been clear, these are internal walls. But in older houses in the southern suburbs they might as well be outdoors for the amount of damp that migrates through.

 

[Tomtomtom]

It's popular because you can get an extremely smooth finish..

I was wondering about that, but honestly before I started stripping it I didn't realise it was two different materials on this wall. So whoever did the cement work got it to as fine a finish as the gypsum, or at least once paint was applied, it was imperceptible. Maybe it's a skill thing too?

 

[tetrasect]

Half of it was finished in sand and cement, and that part was rock solid (even the paint was okay), vs the gypsum which was just peeling off like sheets of cardboard.

One should apply a bonding agent before applying the gypsum. Perhaps this step was not done?

 

[WAslayer]

I was wondering about that, but honestly before I started stripping it I didn't realise it was two different materials on this wall. So whoever did the cement work got it to as fine a finish as the gypsum, or at least once paint was applied, it was imperceptible. Maybe it's a skill thing too?

Definitely skill thing, because if the gypsum was applied correctly or at least surface prep was done properly, it shouldn't have come off..

 

[Tomtomtom]

One should apply a bonding agent before applying the gypsum. Perhaps this step was not done?

Pretty sure something was missing in the prep, for sure. It was basically completely delaminated.

But nothing was going to stop it getting damp and breaking apart because from what I have read (and on this thread) gypsum plaster is incompatible with water. So it seems like a bad idea to use it on any wall subject to damp. Which is any wall on the west side of an older house in Cape Town.

I'm definitely going to go with sand + cement to replace it.