Slab heave crack

How to Fix Slab Heave

Slab heave can be fixed. The cracks in your house that open and close can be stabilised. Cornell Engineers has the experience and knowledge to help you fix slab heave.

Do This First

If you are a homeowner and your house is starting to move and crack, do this first:

  • Read “What is Slab Heave” and watch our video on Slab Heave.
  • Start a Crack Diary.
  • Find water sources that are entering the ground around your house and eliminate them.
    • Fix leaking pipes.
    • Repair dripping taps.
    • Fix broken pipes under your house.
    • NEVER plant trees near your house.
    • Capture condensate from air-conditioners and hot water systems and divert it away from your house.

Do these things before you talk to your builder. Do them before you lodge a claim with your insurance company. Do them before you start paying for engineers and expensive chemicals. Do them before you fix ANY damage.

What’s Next

The problems associated with slab heave can often be overcome by one of these solutions:

  • Improve the tolerance of the building to uneven movement. This solution includes articulation gaps and joints and wall strengthening but is only appropriate if the slab doesn’t feel uneven.
  • Remove the cause of the uneven movement. Identify sources of soil moisture and eliminate them or isolate the building from them.
  • Isolate the building from uneven movement. This method includes jacking and underpinning so that the house is supported clear of the ground movement. Not all houses can be fixed this way.
  • Demolition and reconstruction of the house using one or more of the above techniques and/or a stiffer/stronger footing system.

Do it Right

I’m sad to say – unless slab heave damage is repaired correctly, it will come back again, and again, and again. Concrete slab repairs have to be done correctly.

Some builders think that houses with slab heave damage can’t be repaired. Houses with slab heave can be stabilised!

Cornell Engineers have engineered successful repair and rectification projects many times. Matt Cornell has never had to recommend demolition of a whole house because of slab heave.

Let me say that again: In twenty years of full-time practice as a structural engineer, Matt Cornell has never ordered the demolition of a house because of concrete slab heave.

Cornell Engineers can Fix Slab Heave

If your house has moved and cracked because of uneven soil moisture conditions, I can diagnose this problem and help you fix it. I can help you fix your concrete slab heave, reduce cracking and reduce ongoing movement.

In time you will be able to fix the cracks and enjoy your house.

37 thoughts on “How to Fix Slab Heave”

  1. Rochelle, do you have an engineer’s Construction Report that you signed, along with the building Contract as I did? These hold a lot of information useful to you. Under planning approval here in SA adjacent properties are not allowed to discharge stormwater onto neighbouring properties during construction or afterwards, I believe. I have had issues with my home since 2010 and still ongoing, although I have made some progress. I hope QBCC are able to assist and help you find solutions. Please look after your health at this stressful time.

  2. Rochelle, although council did not approve my dwelling as a private certifier was used, they were concerned enough to get involved and this prompted my builder to repair the skirting, 24 wall cracks and sticking doors which appeared within the first year of build and they also rebuilt my non-compliant en-suite shower. Have you approached your local council yet? I was also able to access relevant BCA ‘Building Code of Australia’ at the council’s office which shows the building standards (albeit minimum) and a great tool with which to get your head around re your builder’s compliancy (or lack of). In SA there is a five year statutory warranty – you should also check your building contract and engineer’s report if possible for any breach of contract from the builder. These are SA conditions – yours may be different but bound to carry more weight in looking after the consumer.

    1. Hi Maggie,
      Got hold of the structural engineers report late this afternoon after trench digging had begun on both sides of my home.

      Builders are not following the recommendations and not hearing my concerns. I have compiled a complaint file for our QBCC – 70 pages in total of information, contract, emails, photographs and have it ready to go.

      The engineers report states edge slab heave due to poor drainage in highly reactive clay soil, lack of drainage in adjacent properties. Recommending immediate drainage at 50mm over first meter from home and then continued fall. Non-replacement of current pebbles recommended.

      The builders have dug trenches and installed drains but are not following fall recommendations and are returning the pebbles.

      I’m at my end. This is my new home, 8 months old and a massive investment. Due to their poor design, poor drainage around waffle slab and smaller than industry standard drains on both my property and that of my adjacent neighbours my house is no longer straight or I believe sellable in this condition.

      I need help and hoping the QBCC can be of urgent assistance.

      Thanks for getting back to me.

  3. Hi Matt,

    Bought my new home already completed and settled in December 2015. Moved in on 17th December and started noticing cracks and sticking doors in January 2016.

    My home is 8 months old built on a waffle pod on reactive clay. House occupies most of our small 370m2 block. Numerous cracks in ceilings, cornices, walls, skirts lifted from floors, doors failing to open, Windows moving, fluorescing of bricks, moss growing up side of bricks, cracked mortar, cracked pathways and corners of garage.

    Structural engineer paid for by Villaworld. Refusing to let me see a copy. Insisting built to industry standard and council approved. Minor cracks replastered when I mentioned reporting to QBCC and now re-openining 3 weeks later. Terrible noises can be heard at night. Slab heave mentioned and poor drainage as issue by builder representative this week. Builder proposing to put drains around house and replace current pebbles over the top as their way of fixing the solution. Structural engineer recommended verbally that pebbles were not recommended at time be attended to view the home. When I questioned the builder this week he said it was only the Structural engineers opinion they would do what they thought was necessary and I would not be living in it if not approved by Council in the first place. Having difficulty liaising with builders and only have one number I can call at Head Office on Gold Coast.

    Submitted complaint against defective build to QBCC. Very concerned as home is only 8 months old that this is not a solution and being intentionally mislead by builder.

    Any advice – is it time to engage legal representation?

      1. Rochelle
        I am speaking from down in Victoria, Matt Cornell will be more familiar with the Queensland situation and QBCC.My next move would be getting a independent report done maybe Matt’s company and getting together all the information about your built you can, especially photos while waiting for QBCC.Floor levels done now will be of great importance and show the degree of movement and whether the movement is on going in the future

    1. Hi Rochelle
      Queensland has gone from severe drought to extreme wet these are slab heave conditions.
      I would engage your own geotech to supply you with a comprehensive report.Slab floor levels will indicate the movement of you slab and must be part of your commissioned report.
      Considering the short time frame after construction to the emergence of damage , poor site drainage during construction would be a concern.Photos of the site during construction would be of great value if you consider taking the matter further.If you can show the builder didn’t create proper drainage conditions and did not use temporary downpipes during construction then this may be cause for legal action against your builder.
      Gravels around your perimeter allow water in but stop evaporation and can great add to moisture levels.
      Did the builder put the gravels down or grade the ground away from the footings?

  4. Thanks for your good advice Jason. The paved pathway around the house has a good fall and a PVC barrier plus waterproofing compound has been applied to the slab perimeter. On the NE side where the slab heave began, a slotted ag pipe covered with bio cloth sleeve (encased with plenty of gravel) runs beneath the edge of the paving alongside a garden border that needs minimal watering.
    Despite these measures there is still spalling with efflorescence along the slab edge on this side. Professional advice has suggested moisture is coming from ‘somewhere’ and perhaps a spoon drain may help? I am not convinced this will be a solution if there is an underlying problem to resolve.

  5. Thank you Jason for your advice. Sadly a return verandah would be out of the question and the small front entrance porch is thankfully only a problem when rain and prevailing winds drive the moisture in (which is fairly infrequent). I have purchased the tiles in readiness for the contractor to lay, for when he is available. I do have a question though please; would it work if I removed paving from around the perimeter and replaced it with gravel, as a border against the remaining width of the paving? At the moment the paving is 1100 cm wide. I have to get my head around it looking odd perhaps, or it may just look planned?

    1. Maggie
      Replacing paving with gravel on a flat or reverse slope area is probably the worst thing you could do.The gravels allow moisture from rain in but restrict evaporation therefore increasing the overall moisture around the edge of your slab.I have seen clay beneath gravel landscaping become saturated.It’s the same principle behind mulching your garden
      it will definitely increase the moisture level.
      The only exception to this is if you have a plastic barrier below the gravel that slopes away from the house and is puncture proof.
      Builders plastic can be used but it must run the water away from the house preferably into a agi drain or storm water system.
      Covering the area with plastic will of course slow down drying of the wet clay.
      Grading the ground level away from the house is what is recommend at the start of construction but is rarely done.
      It is very difficult to do this post construction but if it is feasible
      to do this in your situation then I would consider that method.

  6. Jason – not sure if I can answer your question re shrink/swell test as my private contractor (using Atterberg limits) shows material test report as Liquid Limit – sample air dried and dry sieved 68% result. The E-D classification was confirmed by three separate engineers ranging from 70mm (builder) to 110/115mm by another builder and geotechnical engineer.
    The remedial work carried out has been slab edge waterproofing (which still needs monitoring as it is fretting) and waterproofing en suite shower. Garage rebate has also been waterproofed. Front porch still to be relaid due wrong alignment for drainage and the interior doors swing due heave.

    1. Maggie- Atterbergs can really be compared to other Atterberg tests and not put into a ground movement calculation but by the sounds of it you have enough consensus to say the site was misclassified anyway.
      The porch needs urgent re alignment as we may be heading into another wet period and any heave associated with incorrectly sloping paving may get worse.
      One of the best ways I have experienced to improve soil heave is have the perimeter around the house covered (pergola/varandah) but the soil below exposed.This protects against weather but allows evaporation to dry the soil.Of course this is not always practical but it may get you thinking along this line and coming up with ideas to improve your own specific situations.

  7. Jason, the slab was laid Dec 2009 – handover Jul 2010. Perimeter paved Aug 2010. It was perceived that surface water pooling at NE corner during construction (where heave is prominent) caused the heave but the builder said it was owner’s responsibility, re surface water, during construction. I still dispute this. The slab was designed for 70 Ys movement but my private bore log report showed 110 Ys. There is currently slab edge dampness despite remedial work in waterproofing same.

    1. Maggie Unfortunately 2009 was the worst year for slab heave as that was the height of the drought and was followed by two
      of the wettest years,the fall out we are still dealing with.
      You said your slab is a E-D which is designed to handle in excess of 75mm but you also said the slab is design for 70mm which is a H2. Was that E-D determined after your own investigation and was that done with a shrink swell test?.
      And what was the remediation work done ?

  8. Thank you Jason (and Matt) for your comments. 24 wall cracks were repaired by builder in July 2013 and have held thus far. I have to accept the slab heave and 127 delaminated interior tiles because I settled out of court with builder on other issues.

    I am hoping the slab continues to stabilize as the last levels survey suggested.

    1. Maggie
      There is some evidence that between 4-6 years after slab heave occurs the slab will begin to stabilise.This doesn’t mean returning
      to the original level but minimal seasonal movement.
      E-D is a very strong slab and will resist returning back to anywhere near it’s original level.
      If the source of excess water is removed then stabilisation could begin .Proper landscaping will help the soil moisture levels.Was your house built before 2010?

  9. Hi Maggie
    AS2870 states the design goal is no more than 30mm differential movement but this is a design aim not a requirement.
    Damage(cracks) that exceeds the standards expectation is a more compelling case against a builder but the legal argument is continuing.

  10. Hi Matt,
    Great website, appreciate the conversation.
    I’ve found I have a broad high spot emerging in a slab near a bathroom (brick veneer slab on ground, reactive soils), resulting various small cracks and a stuck internal door etc (estimate approx 35mm) – this high spot tapers down less severe across the whole house and sharply back down to the base of a load bearing wall across the room to the back (perhaps that wall / roof weight is holding it down more?). The high spot / cracks/ stuck door became most severe when it was a long dry spell in weather.

    There is no pressure water lines under the slab. Therefore, I intend to get the sewer line servicing this nearby bathroom pressure tested as it seems to be almost under the highest point. Otherwise, could it be general waterproofing failure in the tiled base of the shower (although I think this is less likely and would show other signs)? In the meantime I have stopped using this bathroom.

    I read your page about the ‘tea towel’ bowl experiment – based on this, would it be fair to say it may take a very long time to notice this swell dry out after the pipe is no longer used or repaired – perhaps weeks, months, or years? I’m hoping the door becomes ‘unstuck’ as my indicator that it is recovering, or might it never go back down?

    Should that reveal nothing, then I guess will have to look outside for sources of other moisture drawing in under the slab in that location (it is near a concave L shape corner), and will then also look to improve drainage and concrete a path around the house perimeter (although I am unsure about how to finish concrete against the ‘charged system’ of downpipes to seal it off but still allow for movement).


    1. Hi Nathan. It sounds like you have got some great ideas for solving your house movement problem. Great work. Yes, the timeframe for reversing soil moisture related movement is normally six to twelve months. A set of floor levels will help you monitor the movement as will crack width and sticking doors to a lesser extent. Fixing pipes is my favourite first step along with fixing site drainage. The effec of current and previously removed trees, consolidation of soft fill should be considered and ruled out if possible too. Finally you have the option of improving the building’s tolerance to movement by adding control joints in walls and ceilings. Best of luck solving you house movement issues. If none of your trials work out, at least you have ruled out some common problems before you engage a forensic engineer.
      Matt Cornell

    2. Hi Nathan

      You could engage a forensic plumber to either flood test the sewer pipe or perform a camera inspection to determine if the pipe is failing.If it is failing and is not dramatically broken then re lining is a good solution and can be done externally.
      As far as the slab returning to the original level this is unlikely
      as the reo in the slab may be bend.Recent experience with a similar situation involving a pipe broken under the slab in highly reactive clay has not returned after several years.
      The solution was to screed the floor not completely level but
      enough to reduce the uneven feeling when walking over the heave spot.
      This type of slab movement is unusual and involves a very localised lifting and often doesn’t involve the external load bearing wall heaving.
      If the source of water was external and making it’s way under the slab then in most cases the heave would be first noticeable at the perimeter wall with the slab at the wall being the highest point.This doesn’t sound like your situation.
      First identify the source of water ingress(possible pipe)
      Then screed level with the possibility of minor localised grinding of the slab first but you must be careful not to get to close to the slab mesh.

  11. Hi Matt,
    We recently built a new home and there are horizontal and diagonal cracks in nearly every room of our home mainly in the joints and around doors between 2-3mm in thickness with the longest one running about 1m. The builder’s structural engineer came and said it is because the concreter has laid a concrete perimeter around our home with no slope. The was laid about 4 months ago and is level or slopping towards trench drains which apparently do no have end caps. Can 4 months of lets say incorrectly laid concrete cause this many cracks. We are in Melbourne at although we have had rain these past few weeks it hasn’t been pouring down.
    I am not sure if the builder is trying to just put the blame on the concreter or would there be other underlying factors I should be looking at?

    1. Dear Jennifer
      Thanks for your question. Although I haven’t been involved in investigating cracks in such a young house, I would imagine that it is entirely possible that slab movement could occur that quickly. To protect your interests it might be time to engage an engineer to do some independent investigations including:
      – a soil test to confirm the original site classification.
      – an independent assessment of the original engineer’s design.
      – a review of the site inspections carried out during construction.
      – recording of floor levels and crack widths as a datum for future movement.
      – a review of the weather patterns in the four months before and after your slab was poured.
      – a look at historic aerial photos to see if your house is built over any natural features such as trees or creeks or dams.
      – a plumbing test to see if your pipes are leaking or have been affected.
      – measurements if the as- constructed slab beam depth and slab thickness
      These investigations are fairly normal work for an independent investigation into house movement. It sounds like an experienced forensic engineer might be your next step.
      Matt Cornell

      1. Thanks Matt. I have reviewed photos of our construction and have come across that our builder did not put any temporary downpipes down nor grade the slope of the perimeter of our slab as required in the engineering drawings as we are on ‘P’ class soil. Reading your advice about not to engage in lawyers and try to come to a resolution with the builders first, what can the builder really do to rectify this though? As wont the soil under our slab just keep moving for years to come?

    2. Hi Jennifer
      Definitely reverse or flat perimeter concrete can cause slab heave even with very little rainfall.The water saturates the clay
      directly near your footing and the path doesn’t allow it to evaporate so the moisture level rises and the clay swells.
      You may have a case against the concreter who constructed your pavement.
      You first need to determine the cause independently with a geotechnical engineer.
      What suburb are you in and how old is your house?

  12. Hi Matt,
    A few years ago we had a sink hole open up in our back yard (approx. 1m deep),
    After calling a plumber he told us it was a problem with the councils pipes behind our property. I notified the council and they rectified a number of problems in the park directly behind us. You can physically see ground shrinkage in the back yard caused by the problem.
    Since then we have developed cracks on our walls, ceiling and I’m concerned about the slab movement as our gutter run is now leaning the wrong way.
    I have a waffle Pod Slab and we were given a 20 year warranty on it (1 Year remaining).
    Can you suggest what I should do moving forward as in my eyes the problem either lays with our council or Metricon.
    Am I correct and what should I do moving forward?
    Any advice you could give would be greatly appreciated.


    1. Hi Scott
      It would be worth having an engineer inspect your property, take levels, record damage and prepare a report.
      There are a number of issues that can cause movement in a house. The report will help you identify and eliminate the issues that can be fixed. If the council pipe is one of them then I imagine you could use the report to start negotiations with council.
      Matt Cornell

  13. Hi Matt,

    Myself and my neighbour have homes built on a waffle slab. Slab construction in 2004. Nothing happened in my house for 6 years, although my neighbour had cracks and leaks. In the past 4 years my house has cracks in the centre wall between 2 buildings and the east facing wall which backs on to units with garden beds next to the dividing wall and slab.
    I recently took action in VCAT to avoid bring statute barred against the builder. The inspection I had done uncovered slab heaving although no crack is bigger than 3mm. Also uncovered were RLs which were some 900ml lower at the front of the house than the back. At mediation the builder blamed the engineer as he followed his advice. Also he agreed to install an agricultural drain down one side of the house and make good all the cracks.

    Should I have settled my action and be satisfied that after 11 years some wall (internal and external) cracks and ceiling cracks is all that is arisen? There is no problem with doors, windows etc.

    1. Hi Rodney
      It’s never very satisfying to see cracks in your house – but I think it’s worse when the cracks reappear straight after you have then repaired. After 11 years I’d expect your home would be due for some maintenance, repainting etc and this would be your opportunity to have any damage repaired and painted over. However if the house is still moving the cracks are likely to reappear.
      Therefore you are right to have movement that has occurred after 6 years of good performance investigated. Maybe something has changed in the ground moisture regime under your building? Normally solving this issue will get your house back to a good level of performance.
      You’ll already be aware that footing designs to current Australian standards are meant to offer a reasonably low risk of large cracks and a medium risk of hairline cracks. Whether you should be satisfied with these limits lies with personal perception of the cracks and where they appear. I’d focus on identifying and solving the issue that has caused your house to move after 6 years. Reverse that issue and get back to enjoying your house.
      Best of Luck
      Matt Cornell

  14. Thank you Matt. The deviation is now 65 mm with further movement expected on this E-D site. Latest engineer’s report states home is structurally sound although I worry about further heave movement as in 2013 it was 58 mm and at that stage deemed to have reached 80% of the design parameter.

  15. What is the maximum deviation of floor level tolerance to entire building footprint in SA please? My slab has heave of 58 mm and wondering whether SA has legislation similar to Vic and NSW tolerances where it is 20 mm.

Leave a Reply