Reinforcement of walls for basement stairs

[andreashe]

Hi everyone,

I'm planning to build walls for a basement staircase. I envision it shaped like a U, with walls 1.7m high and 150mm thick. Attached is a small sketch of how it should look, along with some questions I've noted.

Regarding the formwork, lying 70 and standing 95-rule or are coarser dimensions needed? What is the spacing for the horizontal and vertical ones?

Has anyone tackled this or is skilled with concrete and can give me some advice?

Thanks in advance.

 

[Installation]

You should create a hanging mold so you cast the floor and walls in one piece. Bend the B-bars at the bottom plate's underside that go to the inside of the wall. Consider the cover layer. 50 mm against the ground in the floor and wall. 12-bar is sufficient. Cc 150.

Usually, you use horizontal and vertical 45*95 with board mold.
Don't forget the braces.

 

[andreashe]

You should make a hanging form so you cast the floor and walls in one piece. You need to bend B-rebar at the bottom plate's lower edge going to the inside of the wall. Remember the cover layer. 50 mm towards the ground in floor and wall. 12-rebar is sufficient. Cc 150.

Normally you use horizontal and vertical 45*95 with board form.
Don't forget the braces.

Okay, but with the hanging form, how does it work with the concrete that's in the wall? It doesn't get pushed down into the slab so it overflows there?

A bit unsure how to explain.

 

[Installation]

Okay, but with the hanging form, what happens to the concrete in the wall? Doesn't it get pressed down into the slab so it overflows there?

A bit unsure of how to explain.

Of course, it can if there's too much flow in the mix. But you start by casting the slab.
At the bottom of the form, you have a horizontal 45*95 at the upper edge of the joist. Pour there to the underside of the stud. Wait for 20 minutes, then fill the walls a little at a time. Don't vibrate like crazy but take it easy, and it will be fine. I've cast many hanging forms in my time, and it works perfectly well.

 

[Davion]

I recast the walls in a room in my basement. The completely worn-out lightweight concrete blocks had taken a beating due to the idiotic construction in the 70s and an undrained foundation that previously constituted the walls. It was impossible to repair without going broke, so I built a casting mold out of OSB boards.

Joints were sealed with scrap planks I had from both facade and corners. I made an enormous amount of supports and braces from additional scraps and anchored them.

The thickness extended about 5 cm outward + inward toward the undamaged lightweight concrete, which varied between 2 to 12 cm more, so the total thickness of the material varied approximately between 7-17 cm. I reinforced it with thick reinforcement mesh I bought at Byggmax, I don't remember the thickness, but are they maybe 3 mm?

It went fine, except for one place where there was extremely little old wall left (i.e., deep), it bulged out a bit. This was quickly resolved. It affected the final result, but in my case, it was okay because I plastered a bit afterward and wanted to achieve the look you find in church walls or in the old apartments in Gothenburg where it is "rough-plastered and white-painted." It wouldn't have happened if I hadn't been optimistic with the sealing and can easily be prevented by adding another layer of OSB so the frame was twice as thick.

The end result was good after all. I knocked at regular intervals like a total idiot to ensure it was really packed downwards and got rid of the bubbles.

It might be unorthodox to use OSB, but as I said, I wanted the texture and unevenness + the size of the boards was perfect when laid down.

 

[bossespecial]

Why not use masonry instead? 200mm leca blocks with reinforcement steel in every other course. If you use the staircase as a counterforce, you could probably get away with reinforcement steel in every 3rd course.
Is there a specific reason why the footing protrudes so much? A few inches should be enough?

 

[andreashe]

Of course it can if you have too much flow in the pjucket. But you start by casting the slab.
At the bottom of the form you have a lying 45*95 at the top of the joist. Cast to the bottom edge of the stud. Wait for 20 minutes then fill the walls a little at a time. Don't vibrate like crazy but take it easy and it will work. I've cast many forms in my day and it works perfectly fine.

I was thinking of taking a concrete truck that pours everything, shouldn't be a problem then?

I imagine you don't want it standing too long and ticking...

 

[andreashe]

Why not build with masonry instead? 200mm Leca blocks with reinforcing steel in every other course. If you use the staircase as a counter-support, you could probably reduce to reinforcing steel in every 3rd course.
Is there a specific reason why the foundation protrudes so much? A few centimeters should be sufficient?

There is a car parking along the long wall, so it must withstand some ground pressure. 2/3 of the wall's height is a rule of thumb when it comes to retaining walls. Building with geo grid might be an idea to withstand the ground pressure.

 

[bossespecial]

There is a parking lot along the long wall, so it must withstand some ground pressure. 2/3 of the wall's height is a rule of thumb when it comes to retaining walls. Building with geo grid might be an idea to withstand the ground pressure.

Then reinforced concrete might be good instead of masonry. Since you have the short sides and the slab holding against the longer wall, the footing doesn't need to be so big. The rule of thumb you mention applies more to the type L-support.