Smooth door opening in concrete block

[bighenk]

Hello! I have recently opened up the old garage opening a bit so that I can put a door on the "new" garage. But I would need advice on what material I can now use to make the sides smooth and straight.

I prefer not to use plaster as, from my own experience, it crumbles and comes off the surface over time. I need to build a thicker edge on the right side to make it straight, so I thought of using planks on both sides of the walls to scrape off the material I decide to use.

Is it possible to mix fine concrete a bit thicker and "plaster" it up? Or what better suggestions might you have? I would need to smooth out the "ceiling" too. So I need something that stays put upside down 😅

 

[Plupp 405730]

Fine and coarse concrete have almost no adhesion properties as they are intended for casting, so you either have to shape and cast, or you have to use concrete repair mortar that works like plaster when it comes to adhesion.

This mortar is what we use, and it also works on ceilings.

https://cdnmedia.mapei.com/docs/lib...80c4b9382c8304d44604c84.pdf?sfvrsn=1a4508d4_0

 

[bighenk]

Looked like a perfect product. But will this become as hard as concrete in principle and not crumble away over time like plaster? Can it be left untreated behind the doorframe then?

 

[Plupp 405730]

Looked like a perfect product. But does this become as hard as concrete in principle and doesn't crumble away over time like plaster? Can it be left untreated behind the door casing then?

Yes, but if you need to apply a bit more at a door, I recommend you secure a plaster mesh first, because the vibrations from slamming a door can cause most materials to crack.