Basement wall, plaster thick layer on the inside

[spaxx]

Hello,

I have basement walls made of raw concrete. Two walls are extremely uneven and slant a lot as they were poorly cast from the start, however, the concrete is rock hard and in good condition.

I would like to make the walls straight and completely smooth. This means I would need to apply up to 5cm of plaster on an area of certainly 80m2.

- Can you plaster that thickly, or should I use something else?

- How should I do to make it straight, level, and similar? Is it to take it in stages with a plastering trowel and follow it?

 

[logic]

Have the same problem and the same thought!

 

[garvin]

Probably possible but will likely need to set a net. But the material supplier should have a grasp on it.

 

[justusandersson]

Such thick layers of plaster need to be reinforced. The working method is crucial. You may need to work with temporary guide strips. You might need to use filler material on certain parts.

The question is what a true vertical wall is worth in terms of time and money? It might be easier to build a new wall inside with 75 mm Leca blocks and plaster it.

 

[spaxx]

Such thick plaster layers need reinforcement. The working method is crucial. You need to work with temporary screed guides. You might be able to use filler material on certain parts.

The question is, what is a vertical wall worth in time and money? It is probably easier to build up a new wall inside with 75 mm leca blocks and plaster it.

Hello,

If you build a new 75mm wall on the inside, can you fill up with fine concrete or coarse concrete between these two walls to get a solid construction where you can attach heavy items?

Let's say you pour a few rounds, then fill up behind, pour a few rounds again, fill up behind.

Any disadvantage to doing it that way?

 

[justusandersson]

I think it will be difficult, time-consuming, and unnecessary. A 75 mm lecamur can withstand quite a bit, especially if you reinforce the layers.

 

[spaxx]

I think that will be difficult, time-consuming, and unnecessary. A 75 mm leca wall can withstand a lot, especially if you reinforce the courses.

My basement exterior walls are also completely uninsulated, 30 cm of pure coarse concrete. Bad

 

[justusandersson]

Then you could place custom-cut styrofoam between the concrete and the new leca wall. Even a little insulation has an effect in that situation.

 

[spaxx]

Then you could place cut-to-shape polystyrene between the concrete and new leca wall. Even a little insulation has an effect in that situation.

Yes, just to break the thermal bridge, right? It feels like it would make a big difference, pure concrete has a U-value of 1.5 - 1.8

If you insulate so little, perhaps it is even okay to "insulate" on the inside, right?

 

[justusandersson]

There is almost nothing that conducts cold as well as concrete. Preferably, one should insulate on the outside to prevent condensation in the wall. It's also fine on the inside with a material that withstands moisture, such as styrofoam.

 

[spaxx]

There is almost nothing that conducts cold as well as concrete. Ideally, you want to insulate on the outside to prevent condensation in the wall. It works well on the inside with a moisture-resistant material, for example, styrofoam.

Interesting this.

The house is from 1945, painted Falu red with white corners. I will probably insulate the facade and move out the windows.

This will then allow for insulating the basement wall on the outside. 10-15cm and 20cm below ground.

Does that seem good?

 

[justusandersson]

You probably have a plank frame, about 3 inches thick, which corresponds to 25 mm of mineral wool from an insulation perspective. External insulation improves the heat-retaining effect of the outer walls, which also saves energy. However, there is no reason to overdo the amount of insulation, max 100 mm. Moving out the windows is a given.

The very best option is to have the basement wall insulated all the way, but that is naturally associated with significantly more work.

 

[spaxx]

Thank you,

I have insulated the inside with 45+45 (wood fiber boards) and a vapor barrier between these boards.

Yes, 10cm on the outside will probably make a big difference.

The attic had 15cm of white slag, now there are instead 25cm of wood fiber boards.

Everything we do makes a big difference compared to before.

Yes, board frame with air gap on the inside.

Panel, tar paper, 3 inches, air gap, 1 inch, 45mm wood fiber, vapor barrier Isover Vario, 45mm wood fiber, 23mm tongue and groove, plasterboard.

 

[justusandersson]

It seems great, but the insulation is most effective on the outside because you have the heavy plank structure.

 

[spaxx]

Yes, there should be good inertia in this. Bunkrande or whatever it's called. Good leveling of temperature throughout the day.

It's fun to renovate with care for the old house.