Concrete Slab - Collapsed wall help

[carlosdeanos]

Hey, building a single storey extension. 3.3m x 8m. Trench fill foundation, then I built up to damp with 2 course of blocks. Outer is medium concrete blocks, inner is quinn lites.

 

So I had all my oversite prepped and the ready-mix turned up. I needed a bit more than average after I made a mistake on existing floor levels. So I needed 150mm slab. I put some A142 mesh in to reinforce it. So, going well, tamped all the away across and about a foot from the end the inner leaf of the outer wall (8m) detaches, pushes out and is resting on the outer wall. The whole course is completely together and its come away at each corner.

 

To cut it short I let it dry a bit and dug half a foot of the slab away from the wall. I took it out and rebuilt it, just the top course. Its now drying and I will have to fill the slab in myself.

 

Any idea why this happened? I did not have any cavity fill concrete in place as I was advised I did not need it. I have since mixed up a no fines mix and dropped it in the cavity and angled it to the outer wall. I do have a bit more to do on that but the majority is now supported. I am hoping this was the big mistake.

 

I am not a builder. Now I'm really worried my walls will just fall down!

 

 

[Temp]

Photos?

 

So the inner leaf didnt bond to the foundations? Were they very wet when the first course was laid? 

 

[PeterW]

What mix were the bottom courses laid in, and when were they done..?

[Declan52]

Did you have dpc or membrane under the block???

[carlosdeanos]

@Temp the lower course held to foundation, the second course came away.  It wasn’t wet, had a bit of rain on them within a day of laying. Added pics below.

 

@PeterW I have been laying 1:4 sand/cement mortar. To be honest maybe a bit stronger as I started very slow so was hand mixing. Onto the big mixer now. These went in a couple weeks ago.

 

@Declan52 I haven’t put a dpc in yet. That was meant to start tomorrow!

 

 

 

Edited July 1, 2020 by carlosdeanos

[carlosdeanos]

[Russell griffiths]

Reason it happened.

Blocks too dry, mortar to dry, insufficient bond between the two, too much concrete,  

don’t dwell on it too much, learn and move on. 

Here’s a wild idea. 

Smash off the top course of bricks that have collapsed. 

Extend dpm into cavity. 

Fill cavity with concrete level with what you have. 

Build inner leaf from that adding a tray dpc to end on top of block shown. 

 

You dont need an open cavity below dpc, you could fill it, well you started to ??, sorry couldn’t resist it. 

 

Obviously without seeing levels of ffl this could all be nonsense. 

 

 

Otherwise i think you need to get the kango out. 

 

 

 

Edited July 2, 2020 by Russell griffiths

[Miek]

Did you compact the ground before concreting? Over enthusiastic whacking can create a lot of outward pressure on the internal leaf, depending on soil type. Possibly the internal ground pressure pushed the wall out or cracked the block bond, and the oversite was the final bit of pressure and pushed the wall over. 

 

Just a thought.

 

Weak mix cavity fill below DPM is typical and it is done in order to resist the soil pressure on the cavity. 

 

Mike

 

 

[carlosdeanos]

@Russell griffiths thanks, so I probably need too look at my mortar mixing. Agreed it’s one of your reasons. Was hoping to see no major problems brought up on here. As you said I will learn and move on. I will get that cavity fill in today.

 

@Miek I did give it a good go on whacker! Got a few cracks in the concrete slab now but it was hot and windy yesterday. I will fill the cavity today. Cheers

[Russell griffiths]

You need to get your floor level worked out and damp course levels to make sure it all works. 

And look at weep holes if you now have a full cavity. 

 

Check it it all out before you go further.