Large cracks appeared during RSJs installation

Hi all,

Hoping for some advice on some concerningly large cracks that have appeared during our extension build.

They appeared during the couple of days that the acrows were in place to support the back wall of the house and another smaller structural wall that's required a short steel. The cracks don't appear to have got any worse in the 5 days since the RSJs were fixed in position.

I imagine some hairline cracks are normal as the house settles but these seem pretty significant to me. They're up to 3mm in the worst areas and in some places the plaster's shifted very slightly so the wall's no longer flush.

The first two images are either side of the same wall. This wall sits above the small steel that is bolted perpendicular to the large steel across the back of the house.

The next 2 images are of the wall that sits above what was previously the external wall ie: where the large steel is positioned.
Our builder has said they're not to be concerned about and that they can just be filled by plasterers, but I'd really appreciate a second opinion. Is this just aesthetic or is there a need to understand if there's been any structural damage?

Thank you,
Jack

 

Ouch! Did you take any photos of the steel going in and the supports used out of interest?

Builder will always try and fob you off in my experience

 

Here's a couple of photos of when the steels were in position but still supported by acrows until padstones were added/had cured.

 

Probably due to insufficient or widely-spaced props.
Some one-time cracking is often caused, though these look unduly prominent and widespread.
Infuriating, but usually not a structural issue.

The time to worry is if cracks appear below the level of the beams.

 

Thanks Tony. So do you reckon it would be a case of just being made good rather than a structural engineer having a look? Appreciate it's difficult to answer that just from a few photos.

 

The props do seem too few and too far apart, but also (more so) those strong boys are too far out and anyway should not be used on just one side of a double skin or cavity wall, and will tend to bend downwards.

Also, this happens if the wall is jacked up too high by the props, rather than just supported, and it then cracks when it comes back down to its original position.

The cracking is indicative of a poor quality/inexperienced install, and should not have happened.

But yes ask your engineer to confirm that the beam is adequate, especially for initial deflection. It's got a point load there from that other beam, and there is a chance that whilst it may be adequate long-term, the initial loading may have deflected it too much. This would be likely if the cracking is internal only on a cavity wall.

My money (any your refund) should be on the builders though.

 

I have doubts about how the inner skin was propped. Can't really see anything supporting it?

 

If the 3 props/strong boys were all that was supporting the wall during demolition of the opening and subsequent beam install I'm amazed you got away with just cracks....

I did a very similar job recently with a 4500mm opening. I used 6 props each side and brick brace with scaffold beam to external skin. Slight movement / cracks sometimes happens if the original structure is poor build quality. I would break some of the plaster from around the cracks and check the internal brickwork isn't cracked, any signs of cracking externally ?

 

This. ^^ The strong boys only appear to be on the outer skin, but of course it is the inner skin with most of the building loads because that's what the joists and wall plates are supported by...

 

Yeah the clues are in the pics.

I can't see any attempt at supporting ceiling joists or inner skin.

Usually it's necessary to cut out the ceiling plasterboard to gain access for support.

To support the joists it's good practice to use beefy length of timber section and prop it up with some across.

 

Thanks everyone for the feedback. Sounds like it wasn't done particularly well and there are some concerns.

Do you reckon I should ask builder to get a structural engineer to look at it (although I'm sure they'll say no) or would it be worth getting building control to look at the cracks next time they're about?

 

Everything I've read has said acros should be no more than 1m apart and you've only got 3 on a near 6m opening, and only on the one side!

I'd be asking the builder to replaster/redecorate that bedroom at their cost as a minimum.

Not sure what an SE could say that hasn't been stated already. Assuming an SE spec'd the beam, it should be fine for the job... the problem here was caused by the sketchy installation.

I've been stressing about the quality of the piers I've been building to hold up my steels, but looking at the job they've done on yours to hold up that massive beam, I think I've been worrying about nothing.

 

You've got a whole panel of brick wall that has dropped and is now loose.

It needs a proper repair, nor just plastering and not just looking at and being told "It's fine, the beam is OK"

And you need an independent professional to determine the extent of the repair and not leave it up to the builder to do whatever he wants.

And first and foremost you need to stop work, or stop any further payments until the repair and the full costs have been agreed.

 

I like the 3 inch thick perps on the one course of that block wall

 

I did notice that as well but didn’t want to kick them when they were already down