Vertical crack in extension through padstone under new steel

[lookseehear]

Hi all, pretty crappy discovery this week of a very small crack running directly through a concrete padstone under a new steel beam picking up the one side of our new extension, running through mortar joints and blocks down to the slab (or as far as I can see). It's a concrete block sized padstone built into the inner skin of the wall built from dense concrete blocks. There's no crack evident on the outer skin and the foundation is probably 800mm thick there due to having to excavate all the soggy clay, so I don't think there's any issue with the foundation at this point. See link below for a video - apologies if it doesn't show it very well.

 

 

The roof has been built to SE spec, and has been designed to potentially hold a 2.5t hot-tub on top. The bizarre thing is there's barely any load on there at the moment - just the steel beams themselves plus joists and plywood.

 

Any ideas why this could have happened and likely remedial works required? I'm hopeful it will be just supporting the beam and chopping out and replacing the padstone.

 

[bmj1]

Steel should be centered on the padstone. I wonder if that could be the issue ?

Edited April 17 by bmj1

[Temp]

Is that wall very long? I think walls over 11m(?) are meant to have an expansion gap in them.

 

[MikeGrahamT21]

8 hours ago, Temp said:

Is that wall very long? I think walls over 11m(?) are meant to have an expansion gap in them.

 

Every 6m from memory, and yeah could be a cause, I’ve seen walls without expansion gaps literally rip themselves apart 

[lookseehear]

The wall is about 8m with no expansion joint, so could be that maybe, but seems a bit odd that the crack goes directly through the padstone rather than around it or elsewhere. SE said to check foundation (couldn't see any issues) and replace the padstone but nothing else required if it's just a hairline crack and doesn't get any wider.

 

We've decided to cast in a padstone instead and have put in some reinforcement too for good measure. The new padstone is also more evenly spaced under the steel so fingers crossed there's no more movement.

[JohnMo]

Does your foundations change at that point from new to old? It could be a little differential srinkage.

[Mr Punter]

Some closeups would be useful.  I can see a tiny hairline crack in the padstone and the first mortar bed but not much else.  It looks like this is a junction with another wall so you may have a few more perps than otherwise.  From what I can see, nothing to see.  Unless the padstone is taking an unusual load or on on the existing / new junction, I would leave it as is.

[torre]

Close ups at both ends would really help. Pausing the video it looked like the steel doesn't/didn't even bear entirely on the padstone. Can't tell if it's not quite level or just packed with something but if there's more load on the outside edge of the steel maybe that caused the crack? The other end of the steel looks to sit right at the opposite edge of its padstone too.

[William Leveret Hare]

Hummm, have you sorted it out yet? First thought, that lintel should not be hanging off the end of the pad stone. It is intended to spread the load, this one does not. My first port of call would be to install the pad stone correctly and repoint below for a couple for the cracked mortar joint and keep an eye on it. I'm guessing the blocks are medium density not aircrete? If medium density then the crack running through theses blocks almost vertically would be a further concern. Usually the mortar for the blocks would be softer so that the mortar fails before the block, but here the crack is happy to run right through the block. I would get my structural engineer to look at this to be happy.

[lookseehear]

On 18/04/2025 at 12:55, JohnMo said:

Does your foundations change at that point from new to old? It could be a little differential srinkage.

 

Nope, foundations were poured continuously for the whole length of this wall and the outer skin is unaffected which would indicate the foundations are probably fine.

 

On 18/04/2025 at 15:49, torre said:

Close ups at both ends would really help. Pausing the video it looked like the steel doesn't/didn't even bear entirely on the padstone. Can't tell if it's not quite level or just packed with something but if there's more load on the outside edge of the steel maybe that caused the crack? The other end of the steel looks to sit right at the opposite edge of its padstone too.

 

I think you're right - I'm not convinced the bearing is even on the padstone.

 

On 22/05/2025 at 22:16, William Leveret Hare said:

Hummm, have you sorted it out yet? First thought, that lintel should not be hanging off the end of the pad stone. It is intended to spread the load, this one does not. My first port of call would be to install the pad stone correctly and repoint below for a couple for the cracked mortar joint and keep an eye on it. I'm guessing the blocks are medium density not aircrete? If medium density then the crack running through theses blocks almost vertically would be a further concern. Usually the mortar for the blocks would be softer so that the mortar fails before the block, but here the crack is happy to run right through the block. I would get my structural engineer to look at this to be happy.

 

We've sorted this out now - we chopped out the padstone plus one more block and poured in place a new reinforced padstone. The SE was happy with this solution. They are dense blocks which obviously does make it a bit more concerning, but the way I look at it it's now no different than having a little expansion joint.