Which mortar in the pictures?

[Erik Waenerlund]

I am going to clean up an old chimney where the render/mortar has come off after years of moisture and other factors. I've read that you need to use the same mortar as before, otherwise it might crack, contract differently, etc. What do we think the type of mortar used is?

 

[Svanteman]

Hard to say, I think the lower part looks like something cement-based. When do we think the plaster is from? That might give a clue. But you can do a test: Lime mortar dissolves in vinegar, and if there is still a piece left in the vinegar after a day or 2, then it is at least mixed with cement. K/C mortar or harder.

 

[Stefan1972]

If it's lime mortar, you can crumble it in your hands.........cement becomes rock-hard. A stone in a chimney with lime mortar can be loosened by scraping out the mortar with a chisel. It's that soft. You can't do that with cement mortar.

 

[Erik Waenerlund]

It's really hard. Seems to be the same mortar that was used for bricklaying. The house is from 1966.

 

[Lerstenstegel]

You don't have to use the same bruk but a weaker one.
It looks like a b-bruk or maybe a so you can plaster with c-bruk and be calm.
But I would still have primed it with b-bruk or rödgrund before applying the plaster.

 

[Erik Waenerlund]

You don't have to use the same mortar but a weaker one.
It looks like a b-mortar or maybe a so you can plaster with c-mortar and be calm.
But I would still prime it with b-mortar or rödgrund before applying the plaster.

Probably go with b-mortar. What is rödgrund?

 

[Erik Waenerlund]

Ended up using C material in the end. It turned out okay. Different colors though. The new one leans more towards beige-brown.