Are these cracks in mortar a symptom of subsidence?

[puffinPoundtsock]

Hi everyone,

My 1930s detached house has stepped diagonal cracks in the front brickwork, difficult to see from the pictures but the cracks originate in the decorative brickwork above the porch and stagger up across the left had side of the front.

There doesn't seem to be a huge gap between, but can see the mortar has cracked. There are some cracks in the render in internal walls on that front left bedroom, mainly starting from the window and moving across the internal wall (have no pics of that at the moment, as I am at work).

I'm mainly worried about it being due to subsidence, the affected wall in the house is adjacent to a more recent extension (late 1980s), and can see no examples of any cracks in the newer part of the house, nor anywhere else in the old part of the house.

Some things to consider:
- Live next to a mildly busy main road (small town, but before the bypass was built maybe 40 years ago it would have been much busier)
- Clay soil area
- Have some issues with puddles forming on gravel driveway after wet weather
- No sign of any cracks lower than the ones shown

Any advice would be greatly appreciated.

Images:

https://imgur.com/a/RqNToy2

 

[Ivor Windybottom]

Doesn't look like anything to worry about from the photos. In fact it's very hard to see at all.

Subsidence | ABI

Subsidence is when the foundations of a property begin to sink into the ground below the building.

www.abi.org.uk

If it looked like this you'd definitely have a problem!...

 

[^woody^]

They are indicative of the type of cracking from foundation movement, especially if there are corresponding cracks internally.

They do look old though, so may not be an ongoing issue. If a new foundation trench was dug out adjacent to this wall, that could have caused movement.

 

[Ivor Windybottom]

Looks like at most a few mm of movement.

I've viewed houses where entire corners had dropped, you could stick your finger in the gaps that had opened up.

More likely it's just a bit of movement due to that archway sinking slightly. It all may have happened a fortnight after it was built, and not moved since.

It looks overdue for a repoint. I'd just get the wall repointed and not worry about it.

 

[puffinPoundtsock]

They are indicative of the type of cracking from foundation movement, especially if there are corresponding cracks internally.

They do look old though, so may not be an ongoing issue. If a new foundation trench was dug out adjacent to this wall, that could have caused movement.

Was hoping you would reply, I had seen plenty of your expertise on other threads I had searched prior to posting!

A new foundation trench definitely would have been dug out for the adjacent extension, presumably deeper than the original given the age of the house. Does the extension help at all in that scenario? As in, will it reduce the risk of the older part of the house potentially subsiding?

Also, what would you recommend as the next steps to take? I guess determining if it is still moving would be a good idea, would using a tell-tale/ruler on the internal wall be the best way to approach that?

 

[puffinPoundtsock]

Looks like at most a few mm of movement.

I've viewed houses where entire corners had dropped, you could stick your finger in the gaps that had opened up.

More likely it's just a bit of movement due to that archway sinking slightly. It all may have happened a fortnight after it was built, and not moved since.

It looks overdue for a repoint. I'd just get the wall repointed and not worry about it.

With the archway sinking slightly, would that cause cracks in the internal walls upstairs?

 

[^woody^]

Looks like at most a few mm of movement.

I've viewed houses where entire corners had dropped, you could stick your finger in the gaps that had opened up.

More likely it's just a bit of movement due to that archway sinking slightly. It all may have happened a fortnight after it was built, and not moved since.

It looks overdue for a repoint. I'd just get the wall repointed and not worry about it.

Its more than a few mm, and in several places and directions.

Why would that arch sink. And why would the arch crack where it has?

 

[^woody^]

From just three photos, the patterns and locations seem to suggest a down and outwards movement, so yes potentially if a trench was dug to the left on the images, the corner could have moved slightly causing those types of cracks and the crack in the arch.

There could be other reasons, and if this was investigated properly there would be other checks to confirm a most likely cause and whether remedial work is required. Normally, buildings won't move unless there is an ongoing cause of the movement. Excavation tends to be a once only event so cracks happen and then don't get any worse, whilst things like drain leaks and tree growth are ongoing events with ongoing cracking.

Ivor is the forum tell-tale meister IIRC. . I would not bother as a DIYer unless you know how to interpret normal and abnormal movement. If one is placed inside, it needs to go on the wall not the plaster. Outside, there are several locations that need monitoring.

The only definitive way to determine what's going on or gone on, would be to involve a Structural Engineer to report. However, that would potentially mean trial holes, drain survey and regular monitoring for a while. And the costs of that.
You could monitor it yourself by just observing the cracks and looking out for any widening or extending - ie fresh clean cracks instead of soot filled old ones.

For repairs, first the cause needs to be determined and if need be, dealt with. If further movement is not expected, then just repointing and replastering will do. If further movement is likely but limited, then reinforcing bars and repointing can be done. Only in extreme cases would foundation underpinning be required, and that will be for the engineer to determine after proper investigation.

 

[puffinPoundtsock]

From just three photos, the patterns and locations seem to suggest a down and outwards movement, so yes potentially if a trench was dug to the left on the images, the corner could have moved slightly causing those types of cracks and the crack in the arch.

There could be other reasons, and if this was investigated properly there would be other checks to confirm a most likely cause and whether remedial work is required. Normally, buildings won't move unless there is an ongoing cause of the movement. Excavation tends to be a once only event so cracks happen and then don't get any worse, whilst things like drain leaks and tree growth are ongoing events with ongoing cracking.

Ivor is the forum tell-tale meister IIRC. . I would not bother as a DIYer unless you know how to interpret normal and abnormal movement. If one is placed inside, it needs to go on the wall not the plaster. Outside, there are several locations that need monitoring.

The only definitive way to determine what's going on or gone on, would be to involve a Structural Engineer to report. However, that would potentially mean trial holes, drain survey and regular monitoring for a while. And the costs of that.
You could monitor it yourself by just observing the cracks and looking out for any widening or extending - ie fresh clean cracks instead of soot filled old ones.

For repairs, first the cause needs to be determined and if need be, dealt with. If further movement is not expected, then just repointing and replastering will do. If further movement is likely but limited, then reinforcing bars and repointing can be done. Only in extreme cases would foundation underpinning be required, and that will be for the engineer to determine after proper investigation.

Thanks for the detailed response.

Maybe a dumb question, but I would have expected cracks all the way down to the base of the building if it were subsiding, is that not the case?

 

[^woody^]

No. Part of a wall will stay together, and the crack appears along a weak point typically stepped through the mortar joints.

 

[puffinPoundtsock]

No. Part of a wall will stay together, and the crack appears along a weak point typically stepped through the mortar joints.

Understood, thank you.

So… on a scale of 1-10, how worried should I be?!

 

[^woody^]

Probably less than 5.

If you can get up and look at the external cracks see if they are dirty inside indicating age - pay attention to each end of the cracks to see if they are extending (cleaner inside). And internal cracking too - new or extending.

Then perhaps check them again mid summer after the ground has dried.

The arch crack should be a priority as that could progress and cause the brick to slip due to lack of compression. That will be difficult to point up and make it clean and matching unless the bloke doing it is good. Perhaps wedge it with slate first, but not so hard that it moves the brick, just gently so it's tight. Get that done as soon as you can, not for safety, but to save more work later.

 

[Notch7]

To strengthen mortar joints in brickwork, stainless steel helical bars are sometimes used

not sure if this may be a solution in this case, but I’ve done it on a listed building with cracks that are old

heres a typical kit

HELICAL FIXINGS CRACK STITCHING KIT - Brighton Tools

Crack Stitching Kits are available for next day delivery from Brighton Tools

www.brightontools.co.uk

 

[Ivor Windybottom]

Don't accuse me of having expertise! I'm just a DIY serial house renovator, definitely not pro in any way.

Sounds like you already know the culprit, the extension being dug allowed it to move sideways/down a bit. It's possible/likely that modern building regs required the new foundation to be deeper than the original, so there was a hole next to it for it to fall into for a time.

In which case it was just a one-off thing, as the hole was then stuffed full of concrete shortly after.

As stated above, the arch is dependent on compression for its strength. So would be a good precaution to fill that gap with something. Looking at the rest of the wall, a total repoint would be a good solution, this way it won't look repaired due to inevitable colour differences, plus it looks like it all needs it anyway so would be a big improvement and IMO unlikely to crack again.

While your carefully selected builder is doing the repointing, you could swap out the cracked bricks with old ones from elsewhere on the house, put the new ones in a less visible place where the donor bricks come from.

I'd re-route those tacked-on cables internally too, they're a pet hate of mine.