Vertical cracks on external brick wall

[tony1851]

According to BS 5628 Part 3:2001 Appendix B4, Table B1, fired clay brick has a coefficient of thermal expansion of between 4 and 8 x 1/10^6 per deg C.
If we take atemperature range of, say, 15 deg C (ie 5 deg to 20 deg) 1 brick will expand at most by;

8 x 215 x 15/10^6 = 0 0258mm.

According to BS 1256 (Testing of clay bricks) the irreversible expansion of a London clay brick from 3 - 128 days is 0.03%. So a London brick will expand by;
215 x 0.03/100 = 0.0645mm.

Therefore the long-term expansion is more significant than the cyclical expansion due to temperature fluctuations.

 

[^woody^]

Its brickwork, not theoretical physics

 

[RonnyRaygun]

This is an east-facing wall with pilasters at about 13ft centres and no expansion joint. Crack caused by long-term irreversible expansion of brickwork, independent of the day-to-day variations caused by temperature changes.

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• tony1851
• 18 Apr 2013
• 1

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• tony1851
• 18 Apr 2013
• 1

I don't know the answer so I'm just going to ask more questions, as I'm always interesting in learning...
Tony, wouldn't the above crack have been caused by the expansion of the main bay brickwork pushing on the returned brickwork? I've seen that movement joists should be provided where returned are less than 665mm. I agree that in this case it's probably caused by expansion, but not sure it applies in the OPs case?

With regard to the irreversible expansion, presumably whether or not the leaf expands depends on the age of the bricks when the wall is built. If any initial, irreversible expansion has already taken place, then no more expansion (other than due to temperature effects) is possible?

Maybe we need to know the length of the wall panel. A long wall panel is more likely to crack due to movement than a short one. If the panel is sufficiently long could thermal effects have caused that crack?

Lots of questions, no answers, I know, but maybe the experts have the answers?

 

[theoldun]

Lots of questions, no answers, I know, but maybe the experts have the answers?

Shogun,
Google the two sites below and you will find all the answers, including Tony's crack.

www.hansonbrick.com/english/pdf/technotes/control_joint.pdf
www.gobrick.com/portals/25/docs/technical notes/tn18a.pdf
Regards oldun

 

[tony1851]

Ronny;

The building in the pics is (or was) a 3-storey commercial block just round the corner from me. Built mid-70s; the cracks didn't appear until a few (3, maybe 4 years) after it was built. This makes me think it was long-term expansion rather than just thermal movement.

I think the 'pilasters' were 13/14 ft centres, and they had very short returns, which is the classic case where the expansion causes rotation and fracturing of the brickwork. The long-term shrinkage of the concrete frame will not have helped matters.

I wouldn't deny that thermal movement can cause problems, and these are likely to be compounded by the ratchet-effect. There is also the long-term shrinkage of the mortar to consider, so all these forces acting simultaneously produce a complicated picture.

(The block was recently converted to flats, and the brick skin completely removed and re-built [with expansion joints this time!]).

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• tony1851
• 19 Apr 2013
• 1

 

[stuart45]

Tony, wouldn't the above crack have been caused by the expansion of the main bay brickwork pushing on the returned brickwork? I've seen that movement joists should be provided where returned are less than 665mm. I agree that in this case it's probably caused by expansion, but not sure it applies in the OPs case?


The OP's case is a straight wall, whereas Tony's is not.

With regard to the irreversible expansion, presumably whether or not the leaf expands depends on the age of the bricks when the wall is built. If any initial, irreversible expansion has already taken place, then no more expansion (other than due to temperature effects) is possible?

Thermal movement is different in that the cracking occurs when cooling, whereas moisture causes cracking by putting pressure on certain points.




Lots of questions, no answers, I know, but maybe the experts have the answers?

 

[tony1851]

Tony, wouldn't the above crack have been caused by the expansion of the main bay brickwork pushing on the returned brickwork? I've seen that movement joists should be provided where returned are less than 665mm. I agree that in this case it's probably caused by expansion, but not sure it applies in the OPs case?


The OP's case is a straight wall, whereas Tony's is not.

With regard to the irreversible expansion, presumably whether or not the leaf expands depends on the age of the bricks when the wall is built. If any initial, irreversible expansion has already taken place, then no more expansion (other than due to temperature effects) is possible?

Thermal movement is different in that the cracking occurs when cooling, whereas moisture causes cracking by putting pressure on certain points.




Lots of questions, no answers, I know, but maybe the experts have the answers?

And?

 

[^woody^]

So what are we now talking about here? The OP's problem or the random office block?

In the OP's case the panel has contracted, shrunk. This has caused the crack at the return where the corner has held fast and is a stress point. So the bricks snap close to that. The other stress point, below an opening has resulted in a crack there too

By the look of it, the bricks are a soft clay and the [very grey] mortar is too strong. That is the overriding cause.

Non of this 0.00002 mm per brick nonsense. That is a typical domestic elevation, the movement of large panels does not apply to this. Its a straightforward case of soft bricks and strong mortar. Expansion has not caused the crack, just contraction ... hence the gap

Don't look for scientific explanations where a simple one will do.

With the random office block that crack has a different cause - expansion of one panel has pushed the return, caused it to pivot and so cracked the pier on the return face. It is incorrect to describe this crack as being "caused by expansion" as the cause and effect are distinct, and in different parts of the structure. And that is not just semantics either

All of this movement is thermal movement - caused by heat in one way or another. It goes on daily

The only other time there could ever be a similar crack is in initial shrinkage - which would be once only as the wall dries out after construction

 

[RonnyRaygun]

Tony, wouldn't the above crack have been caused by the expansion of the main bay brickwork pushing on the returned brickwork? I've seen that movement joints should be provided where returns are less than 665mm. I agree that in this case it's probably caused by expansion, but not sure it applies in the OPs case?

The OP's case is a straight wall, whereas Tony's is not.

With regard to the irreversible expansion, presumably whether or not the leaf expands depends on the age of the bricks when the wall is built. If any initial, irreversible expansion has already taken place, then no more expansion (other than due to temperature effects) is possible?

Thermal movement is different in that the cracking occurs when cooling, whereas moisture causes cracking by putting pressure on certain points.

There you are Stuart/Tony...these responses are a pain in the arse to edit sometimes

That's mainly what I was getting at though Stuart

 

[tony1851]

blah, blah, blah...

yes yes yes i agree with evverything you say...

 

[johnss77]

Hi,

First of all, thank you very much for the interest and for the lively discussion! However, I must say that I am really confused now

It seems to me that ^woody^ is convinced it is not serious, but all the others seem to have some doubts. Would any other type of photo help? I can call the estate agent, book another viewing, and take more pictures.

If you were buying the house, what would you do? Would you worry and get a structural engineer? Or would you monitor the cracks after you bought it?

Many thanks,
John

 

[noseall]

I would say that Woodpulp has nailed it.

 

[tony1851]

Like most posters, my belief was that it is not serious; the debate (or was it discord!?) was more on the lines of what has caused the cracking.

 

[RonnyRaygun]

A crack that size wouldn't put me off buying a house in the slighest...

 

[johnss77]

Hi,

just to let you know that my offer on the house was accepted! Hopefully, I'll move in next month. Many thanks for all the advice, I appreciate it!

Now, the next step is to get rid of those cracks. Since it is not serious, I will attempt to fix the problem by myself. Woody suggested to fill the gap on the bricks with clear silicone. Any advice on which brand/product I should buy? What about repointing the mortar joints? I have never done that before; any advice about that?

Thanks,
John