# Forum Home Renovation Structural Renovation  crack in double brick wall

## redred

Hi!
There is a crack in my double brick house which is around 55 years old. This is a two storey house with concrete ceiling and the crack is in the ground floor. The soil is clay and I recently put concrete all around the house on the outside. Since then the crack has significantly increased. It is 14 mm wide at one point. The crack is visible inside and outside the house.
Can anyone pls tell me how to fill and fix the gap?
Thanks 
red

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## TermiMonster

It may be a water problem...look for any particularly thirsty trees near that area of the house.  Most gums will send roots out to quite long distances in dry weather, which can cause drastic problems.
Are there any trees close to that area?
TM

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## Bloss

That sort of crack is indicative a failure in the foundations - no doubt through movement of highly reactive clay soils (as they get wet & dry out) and insufficiently sized & reinforced footings (there has been much greater awareness of the issues involved in building on reactive soils and new design criteria have been adopted to cover it in the last 20-25 years or so). 
Filling the gap is one thing - but will be waste of time unless you find out what is the cause. The increase since you put concrete around the perimeter is likely due to drying out of the sub-soil under the foundation. If there is just this one crack I would be digging down on the outside of the wall to get a look at the foundation. 
Almost guaranteed that the footing will also have crack going all the way through too although if yu are lucky you might find that there is a void or wash away of some sort the has allowed the footing to drop and crack (in which case you can simply fill it with concrete). Likely long term answer is under-pinnning - which needs engineering advice and professional work. 
After 55 years it is unlikely to get too much worse and unless it starts moving sideways or coming away at the roof the problem is more likely aesthetic than structural so you could just patch it using a flexible filler and then paint. The fault line will always be visible, but not so clearly.

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## GraemeCook

I bought a house with a similar problem in the early eighties for a bargain price.   In this instance the local council had realigned the road and left an exposed clay bank along the road side of the footpath, less than 10 metres from the front of the double brick house.   The exposed bank caused the underlaying clay to dry out and contract and the subsoil moved and the three large cracks appeared in one brick wall (cracks about 20mm wide) and which followed a zigzag through the mortar - no bricks were broken.  There were also cracks in the internal solid plaster walls, the floor had moved away from the wall and the skirting had moved.    I reasoned that if the price was low enough then I could make a profit on the deal. 
Initially I planned on simply rendering the walls and filling the cracks, but a council planner referred me to an hydraulic engineer .   He inspected the sight, used a hand auger to take out a number of plugs, measured the moisture at different depths and also in a neighbours place, and advised us to drill 2.5 metre vertical holes and install agricultural pipe (with holey walls)  and to put in three moisture meters buried beside the foundations at a depth of 600mm.   We then hosed water into the vertical pipes to re-hydraulise clay.   The engineer took measurements and monitored the process.   Over a period of 6-8 months the cracks slowly closed from 20mm to about 5mm and then stabilised at that.  A year later we had the house rendered and we patched the internal plaster and repainted inside.    
We had to monitor the clay moisture level weekly;  hose water into the vertical pipes if the meter needle was below the mark the engineer made; do nothing if the needle was above the mark.   We have been told that a later owner automated this watering process. 
Over twenty years later there are no visible cracks in the rendered walls of this house. 
It was a nice little earner. 
Cheers 
Graeme

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## djboonie

Was very interested to read this thread. 
I own(or the bank does anyway) a Art Deco home built in 1928 and have cracks in nearly every wall.  The render underneath the paintwork is in places cracking and crumbling. 
By the sound of things getting the stumps redone is the first thing I need to do however I was very interested to read about the hydraulic engineer and his solution. 
Graeme was this engineer Melbourne based?  I wouldn't mind talking to him as your solution sounds like a very sensible way of dealing with dried out foundations.

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## djboonie

Was very interested to read this thread. 
I own(or the bank does anyway) a Art Deco home built in 1928 and have cracks in nearly every wall.  The render underneath the paintwork is in places cracking and crumbling. 
By the sound of things getting the stumps redone is the first thing I need to do however I was very interested to read about the hydraulic engineer and his solution. 
Graeme was this engineer Melbourne based?  I wouldn't mind talking to him as your solution sounds like a very sensible way of dealing with dried out foundations.

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## autogenous

Does it have limestone footings? 
Do you have any failed soak wells or downpipes in the vicinity of the wall failure?
Stick some masking tape over the crack to see if it moves any more? 
You may have to underpin the failed footing with some concrete pad footings then pack with fibre cement sheeting and non-shrinking grout between the underside of the footing and the top of the new one. 
DO you have a photo of the footing on the outside?

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## djboonie

I will take some pics over the weekend and re-post.   :Wink:

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## GraemeCook

> Does it have limestone footings? 
> Do you have any failed soak wells or downpipes in the vicinity of the wall failure?

  
Hi Chris 
This is also a good point.   Movement can be caused by excessive drying causing the soil to shrink or excessive moisture causing it to soften.   You must identify the cause before you start effective remedial action. 
Cheers 
Graeme

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## dan26789

hello, i was wondering how did these walls crack? and whats the solution to fix the cracks?[IMG]file:///C:/Documents%20and%20Settings/DAN/Desktop/B-tec%20Assignment%20due%2019th/07092009%28007%29.jpg[/IMG]

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## rrobor

Yes I agree with an above poster. I would suspect you are in Melbourne and in the clay belt. What you have done is shield your house from moisture so the foundations are drying out.  It is essential in that type of soil to be able to hydrate your foundation. My neighbour had a similar issue and had to cut a slot out of his concrete to install a weeper pipe to rehydrate. Tree roots near the edge of the concrete will add to the problem. Filling the crack is the least of your problems.

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## Brian Watts

Hello Red, 
From your 2nd photo it seems that the crack is wider at the top than the bottom.  Is that true ?  If so, it means that the foundation soil (clay) has dried out more away from the crack than at the crack.  Or the clay has been allowed to moisten and swell at the crack.  Either way, the footing would be convex upwards at the crack. 
To reduce the size of the crack, it would be necessary to artificially moisten the clay soils away from the crack so that the footing can be made less convex.  The method of sinking vertical pipes into the ground and watering the pipes would be a valid way of rectifying or reducing the crack and maintaining a stable moisture content through future climatic cycles of wetting and drying. 
If you have concreted around the house (pathways I presume) you might have made this stabilisation method a bit more difficult. 
Brian

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