Friday, January 22, 2016

What's the crack? The importance of correct diagnosis of cracking in buildings

Due to the many different factors that can contribute to cracking, this is one of the most easily mis-diagnosed defects that can occur in buildings.

When cracking is identified in a building the usual reaction is one of alarm and sometimes panic. Over the years as a Building Surveyor I have learned to be very cautious in diagnosing the cause of cracking, because it is necessary to fully understand the underlying factors that are causing it to ensure that an accurate and appropriate solution is recommended.

Cracking in a building can occur for a variety of reasons and sometimes there maybe a combination of factors that contribute to the problem.  For example drains could be damaged allowing surface or foul water to permeate into the sub-soil below a foundation.  Over time the soil will start to erode and the rate of erosion will depend on the type of soil (e.g granular soil will be more vulnerable than other types of soil), climatic condition, location etc. It is clear that the drainage will need to be rectified to ensure that the surface or foul water, finds its way through the drainage system correctly. However, what has caused the problem to the drains? Are there tree roots in the drains? Are there other trees in close proximity? Has the ground under the drains been affected in some way (i.e nearby excavations)? Is there a damaged rainwater down pipe or guttering in close proximity to the drains that are allowing large volumes of water into the sub-soil, particularly for shallow drainage? etc.etc. 

Source: own
It is therefore fundamentally important that anyone who undertakes inspections or gives advice in respect of cracking in buildings should not make rash judgements and should gather all of the evidence before arriving at a possible cause. In order to aid the inspector, which can be a Building Surveyor or Structural Engineer, it might be necessary to recommend other investigations such as geo-technical surveys to establish ground type, composition, contaminants etc., trial holes to establish foundation depths, CCTV inspection of the drainage system and possibly an arboricultural survey to give advice on any trees that may be an influencing factor. It may also be necessary to undertake monitoring of the crack to establish whether movement is still occurring. For cracking of a less significant nature these types of investigations might not be necessary at all. The choice of which investigations are needed will be decided once the inspector has made an initial assessment of the cracking.

Not all cracking in buildings is serious, which is why it is so fundamentally important to diagnose the cause correctly.  In some situations remedial measures may be as simply as rake out and re-point mortar joints, or possibly a technique called 'stitch repairing', which is basically raking out horizontal bed joints every five or six courses either side of a crack and installing steel bars which are set in epoxy resin (see video below). After the resin has cured the bed joints are simply re-pointed. At the other end of the scale however remedial measures  could be much more substantial and include underpinning or possibly even partial or even full demolition and re-build.  Therefore it is clear that the costs of dealing with cracking in buildings is extremely wide ranging, and mis-diagnosis could result in either undertaking repairs that may not have been necessary (which can be very expensive), or not dealing with the problem appropriately, with the cracking re-occurring.

I sometimes have a rye smile when I watch property programmes such as Homes under the Hammer. It is interesting to hear the presenters talk about defects that 'they have discovered' when they visit the various properties, particularly cracking.  You can bet that they will say, 'that could be serious and needs checking out', they obviously do not have a clue what the cause of the problem actually is. What is even funnier is when they ask the purchaser if they were aware of the cracking when they had bid for the property and they will always say 'yes, but we had it checked out and it is nothing serious!'. In all of the many episodes of that programme that I have seen over the years I have never heard any purchaser be perfectly honest and admit that the cracking was serious and had cost them a fortune! I suppose it is because they do not want to admit too being a complete fool on national television!

The subject of cracking in buildings is extremely wide ranging and it is not the purpose of this article to try to consider every aspect, in fact there are numerous books and other publications that cover the topic extensively.  What is important however is that when cracking occurs that the reasons for it are fully investigated and understood so that appropriate remedial works can be carried out.  Due to the many different factors that can contribute to cracking in buildings, this is one of the most easily mis-diagnosed defects that can occur.  It would therefore seem sensible to seek the advice of a professional at the earliest opportunity. Although this advice may have a cost attached, it could prevent a much higher cost in the future.

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  1. Interesting article Gary which brings to my mind a point worth considering... Underpinning has an incredibly high failure rate and needs very careful justification. In my experience it is very rarely required and where movement is progressive and ongoing it can often be arrested by addressing the fundamental problem with local ground conditions rather than focussing on alleged foundation defects.

    Joe Malone

  2. Joe is correct, the problem is rarely failure of the foundations but much more likely, failure of the ground UNDER the foundations and simply putting new and bigger foundations under the existing ones won't necessarily address the problem of failures in the sub-soil beneath. If wash-out of granular soil is occurring, then if nothing is done to arrest the water movement, then the new, beefed up foundations will simply slide out from under just like the original ones did. Hence the importance of exploring the situation and thinking very carefully what the mechanism of failure really is before doing anything. Simply saying cracking = underpinning could just make the problem no better but far more expensive.

    Michael Ney

  3. Good info, thanks. Still need to talk about ways of monitoring the cracks. Proper monitoring helps determine the causes of the cracks.

  4. Underpinning certainly requires careful justification because it is very costly and disruptive, but to state that it is rarely required is not correct. Furthermore failure of the ground UNDER the foundations has the knock on effect of failure of the foundation and consequent cracking of the superstructure. The purpose of underpinning is commonly to extend foundations to a level below which factors such as tree roots and desiccation of shrinkable clay can affect the building, hence the importance of site investigations including bore holes and tree root analysis. An underpinning design prepared by an ASUC registered Contractor, based on a detailed site investigation report and backed up by an ASUC guarantee should not cause concern about future failure.

    Richard M