Difference between primer mortar kc and fine plaster kc?

[onatakosha]

I have flexed the walls in the basement due to old moisture and bad paint. There is plaster left, they are not flexed down to the stone (in a few places). Now I want to re-plaster them but I'm not sure about the different mortars. I would think it is KC plaster on the walls, the house is from '51 and the plaster is not completely white like lime but gray enough to not be cement. At the building stores (here in my area) there is only C mortar or lime mortar or KC base mortar. Can't you use base mortar? Won't the surface be good enough? I can use lime mortar but it seems expensive, it's a few m2 and the consumption is 20 kg per m2 at 10 mm, or can I use it and make a thinner layer?

 

[Plupp 405730]

I have flexed the walls in the basement due to old moisture and bad paint. There is plaster left; they are not flexed down to the stone (in some spots). Now I want to replaster them but can't make sense of the different mortars. I would assume it is KC plaster on the walls, the house is from '51 and the plaster is not completely white like lime but gray enough to not be cement. At the building supply stores (here in my town) there is only C mortar, lime mortar, or base KC mortar. Can't you use base mortar? Won't the surface be good enough? I could use lime mortar but it seems expensive, it's a few square meters and the consumption is 20 kg per m2 at 10 mm, or can I use it and make a thinner layer?

Internally, plaster mortar-C might be good, or perhaps plaster mortar-B if the old one is hard.

 

[onatakosha]

Inside, it might be good with plaster mix C, maybe plaster mix B if the old is hard..

But you can't use c mix on old kc mix, can you? The c mix is harder and won't stick. That's what I've understood. I'm really just wondering if you can use base coat as plaster or if it creates an ugly surface that needs to be plastered over? And if the lime mortar can be plastered thinner than 10 mm if I were to choose that?

 

[Plupp 405730]

What do you mean by old KC mortar?

A common C mortar is a KC mortar..

https://www.se.weber/fasad-puts-och...stem/murbruk/weberbase-224-puts-och-murbruk-c

Most base rendering mortars are A mortar, the harder the C is, thus unsuitable for coating interior surfaces..

 

[onatakosha]

What do you mean by old KC mortar?

A regular C mortar is a KC mortar...

[link]

Most base mortars are A mortar, the harder is C, thus unsuitable for plastering indoor surfaces.

KC is lime and cement, C is cement. Unless I'm completely off track, which is possible.

 

[onatakosha]

KC is lime and cement, C is cement. If I'm not entirely off track, which is possible.

I mean the old render that is original and partially still remains

 

[Plupp 405730]

KC is lime and cement, C is cement. Unless I'm completely mistaken, which is possible.

No, that's not correct. B and C mortar are all KC mortars with different proportions of lime and cement mixtures for different strength classes.

Here comes a simple description according to Byggmax:

https://www.byggmax.se/putsa-på-murblock

 

[onatakosha]

No, that's not correct. A, B, and C mortar are all KC mortar with different proportions of lime and cement mixtures for different strength classes.

But then what is KC plaster? Now I'm even more confused haha. I've been told not to use C mortar because it's too hard, but to use KC mortar/plaster (I can't tell the difference between plaster and mortar either), and KC exists as a product, so what's the difference between C and KC if C also contains lime? Is it different amounts of lime/cement in them?

 

[Plupp 405730]

But what is KC mortar then? Now I'm getting even more confused haha. I've been told that I shouldn't use C mortar because it's too hard and that I should use KC mortar/plaster (I don't know the difference between plaster and mortar either) and KC exists as a product, so what is the difference between C and KC if C also contains lime? Is there a different amount of lime/cement in them?

Read the description from byggmax above B and C mortar are KC mortar hence your explanation from the beginning becomes a bit confusing, you need to reset yourself so that you learn the different classes...

 

[onatakosha]

Read the Buildingmax description above B and C mortar is KC mortar, hence your explanation from the beginning is a bit confusing, you need to reset yourself so you learn the different classes.

Yes, I have probably misunderstood or been misinformed but then ordinary c-mortar should work on a basement from the 50s where the original plaster is most likely some sort of lime/cement plaster?

 

[Plupp 405730]

Yes, I might have misunderstood or been misinformed but then ordinary c-bruk should work on a basement from the 50s where the original plaster is most likely some kind of lime/cement plaster?

Most likely, it's a lime plaster with a little cement in it..
It's common to skip lime plasters nowadays because they become too expensive, and they shed a lot (very porous), which you don’t want in an indoor environment unless you have to and there are preservation requirements on the building..
So indoors, absolutely plaster C is preferable..

 

[onatakosha]

Most likely it is a lime plaster with a bit of cement in it.
It is common to skip lime plasters nowadays because they become too expensive and they shed a lot (very porous), which you don't want in an indoor environment unless you have preservation requirements for the building.
So indoors, render mortar C is definitely preferable.

Yes, the room is going to be used, so I would rather avoid lime plaster if it makes the walls porous and sheds. Is there a risk that there will be more cement in the new mortar if I use C-mortar from Byggmax so that it doesn't adhere well enough to the old mortar? I'm not really sure how sensitive this is, you shouldn't have the hardest plaster on the outside as I understand it. I want to get it right from the start if possible Thanks for all the clarifications!

 

[Plupp 405730]

Yes, the room will be used so I'd rather avoid lime plaster if it makes the walls porous and flaky. Is there a risk that the new mortar will have more cement if I take C-mortar from byggmax, so that it doesn’t adhere well enough to the old mortar? I'm not quite sure how sensitive that is, I understand you shouldn't have the hardest plaster on the outside. I want to get it right from the start if possible Thanks for all the clarifications!

No, it’s not a problem as long as you remove all loose plaster and pre-wet the wall before applying..
Then it should be post-wet as well so it doesn’t crack unnecessarily..
A low-pressure spray is preferable for the pre and post-wetting..
The following brands are good, Weber, Finja, and Combimix, I would buy one of these😊