How To Repair Sewer Pipes And Collapsed Drains Under Slabs

There are three main ways to address collapsed drain pipes under slabs. This article considers the advantages and disadvantages of each method to assist home owners make the best decision for their particular situation.

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Water, sewer and drainage pipes become brittle, degraded or corroded for a number of reasons including age, earth movements, cold weather, encroachment of vegetation (i.e. tree roots), and external pressure forces. If damaged pipes are located beneath an open grassy area on your property, they can usually be repaired quite easily by digging out the soil around them and replacing the broken section of pipe. But if the offending pipe is a sewer line, or if you need to repair or replace water or sewer pipes leaking under a concrete slab, things become considerably more challenging.

11 Signs of a collapsed drain pipe under a slab

There are a number of ways to tell whether you have a broken water pipe or collapsed drain pipe under your house slab, including:

  1. The sound of running water when taps are not being used
  2. Warm spots on the floor
  3. Patches of wet grass around exterior walls
  4. Wet or damp carpet
  5. Low water pressure
  6. Moisture on internal flooring
  7. Mildew or mould under carpets, rugs or at the base of drapes
  8. A musty odour
  9. Unexplained increases in your water bill
  10. Rising damp
  11. Slow draining shower, sinks or toilets.

Signs of structural damage from sewer or water leaks under slabs

Broken sewer pipes under slabs can be more difficult to spot but they can be just as damaging, particularly in areas with expansive soil. Expansive soils contain minerals that absorb water (such as clay soils), and they can increase the soil volume by up to ten per cent. This change in volume can exert enough force on a building or other structure to lift the foundations, which is why leaking sewer lines under slabs can be so serious.

According to in a typical year in the United States, expansive soils cause greater financial loss to property owners than earthquakes, floods, hurricanes, and tornadoes combined. The cost of repairs and mitigation of something like a sewer leak under a house slab particularly when it occurs in a home built on expansive soil, can be extremely high; sometimes exceeding the value of the home. In many cases homeowners report they had noticed there was a problem with their pipes, but that they didn’t realise the severity or that it was progressing, until it was too late.

If slab leaks have been present for some time – or your property sits on expansive soil – some of the more ominous signs to look for are:

  • cracks in walls leading upwards from the floor
  • cracks in tiles or concrete flooring
  • raised (dome-shaped) areas of flooring
  • warped or squeaking timber boards.

These signs indicate there may have been significant damage to a home’s foundations and you should seek advice from a professional builder or engineer before proceeding with repairs.

Cracks in expansive soil:Desiccation cracks in soil caused by drying. Photo, US Army Corps of Engineers

What steps to take before deciding on a pipe repair strategy

There are a number of ways to fix drains or repair sewer lines under slabs, the three most common of which are detailed in the following section. However you may firstly want to consider whether it is worth having a leak detection specialist find the leak in water pipes and provide you with CCTV footage prior to arranging for quotes. Professional detection specialists have accurate listening devices, CCTV cameras and other leak detection equipment to find leaking and can do various tests, including pressure tests. An accurate assessment of the water pipe to pinpoint the fault also means less ‘just in case’ pipe patching. For collapsed drainage and sewer pipes under slabs, a CCTV camera inspection will survey the pipes to determine the location of the damaged pipe.

Whilst some repairers state they will have to do their own inspection prior to quoting, this may also mean they will charge you for the service. If you have three or four people come to quote, that will push your expenses up unnecessarily, so having your own report and footage of the damage may help keep costs down. It also shows that you’ve done your homework.

When you ring to arrange a quote, ask whether it is a free service. If not, and they want to charge for an inspection, make it clear you have recent, professional footage of the damage, and that you want them to quote based on those images. In all likelihood if you accept their quote and engage them to do the work they will need to do their own CCTV inspection before commencing, at which point any adjustments can be made, but you should not have to pay four different people to inspect the pipes just to get quotes.

Remember, too, that the tradespeople providing you with quotes can be a great source of information in terms of why their particular approach would work well (or not) in your situation. Ask what advantages they have over the other methods, and what some of the drawbacks of the other repair options are. Use what they tell you to guide you in further internet research, and to prepare questions for the service providers still to come.

3 main methods of repairing broken pipes under house slabs

There are three main approaches to repairing leaking drains under house slabs. It is important to obtain quotes from at least one tradesperson from each area of specialisation.

The three alternative approaches are:

1. Relining the broken sewer, water or drainage pipes using advanced composite resins to create a new pipe inside the old one without digging

Today, a broken drain or sewer pipe under a house slab doesn’t have to mean a huge excavation job. Advances in composite resin technologies mean materials commonly used for aeroplane frames, top-line sports equipment and even dental applications can also be used to reline broken pipes, thereby significantly reducing the cost of fixing drains under slabs.

All types of water, drainage and sewer pipes can be relined using composite resin and synthetic fibre compounds which are combined and cured to create an incredibly strong, crack resistant new pipe inside the old, broken one. Reputable relining companies in Australia, such as Nuflow, guarantee such relines to extend the life of the pipe for up to 50 years and the process requires no digging or excavation of your home whatsoever.

Professional relining companies can pull liners into place using existing access points around the home and the liners are cured where they sit, inside the pipe. Many relines can even be done using resins which cure in the presence of water (or sewage and other liquids) meaning very quick and cost-effective repairs with no disruption to the home at all.

It is important to note, however, that only the relined sections of pipe are guaranteed. This means that depending on your circumstances and the identified cause of the break, it is often useful to obtain a quote to have all the pipes under your slab relined once they start failing, rather than just the one found to be leaking.

2. Replacing the broken pipes under your slab by excavating and laying new ones

This involves accurately locating the leak, excavating inside your house (or under it if the leak is just inside the perimeter) to reach it, replacing or repairing the troublesome pipe, reinstating the concrete foundations (if removed) and cleaning up the mess.

Repairing the damaged line itself is not that hard, but locating and gaining access to it is a different matter. Once you locate the general area of the leak, you (or a tradesperson) will have to use a concrete cutter and jackhammer to cut and chisel your way through the concrete. Concrete cutting creates a lot of dust, so furniture and valuables should be covered and doors sealed prior to commencing works. It is also quite dangerous, so this stage of the job should really be left to professionals.

Soil (often contaminated with waste) will have to be removed from around the pipe and stored somewhere or disposed of. The broken pipes will then need to be repaired or replaced and the soil, reinforced concrete slab and flooring reinstated. This obviously causes a lot of mess and disruption, and requires significant labour, which can push the overall bill up considerably.

The most common type of pipe used for pressurised water lines under house slabs is copper tubing, but as the copper ages it is prone to pitting, corrosion and thinning – all of which lead to leaks. To repair copper pipes, cut the damaged section of pipe with a hacksaw, reciprocating saw or tubing cutter and insert new tubing with couplings soldered into place.

If you have to replace a sewer line under a concrete slab you really should engage the services of a plumber because of health-related issues regarding exposure to human waste.

Apart from the obvious disadvantages of disruption, inconvenience, high labour/trades costs, and the mess and destruction of this method, there is also the concern over whether the structural integrity of the house will be compromised. For example, if the break runs the full length of a pipe or there are numerous breaks in different areas, you may have to basically split your slab, which means the house is no longer on one integrated foundation. A builder or engineer may be required to advise on whether cutting of your concrete slab will impair structural integrity.

Finally, there is concern that if this pipe has failed once, it may do so again. For example, if a PVC pipe has failed because of encroaching tree roots, and it is replaced with another section of PVC pipe, what is to stop those same tree roots from invading the new pipe? Or, if copper pipes have corroded due to age in one section of the under-slab pipe network, what guarantee is there that other sections won’t soon begin to fail too.

3. Re-routing/re-piping some or all of the home’s plumbing

Sometimes it is better to re-plumb the entire house rather than waste money repairing old plumbing. This is particularly recommended when a home is plumbed with old galvanised piping, or it has an aging pipe network that is likely to continue to fail. In most regions, a qualified plumber will be needed to shut off the old pipes correctly and to lay the new pipes. This will involve creating new junctions that direct the water or waste in or out via the walls of the house, rather than the floor. The pipes will then lead down into the soil and trenches will be dug around the perimeter of the home to house the new plumbing system.

The drawbacks of this approach include the very high cost, the impact it can have on existing garden beds, paths and driveways and the unsightliness of having exposed pipes protruding from your home’s exterior. Future plumbing issues, however, will be able to be fixed without the need to excavate your home.

Overall, having new drainage or sewer pipes laid outside the perimeter of the slab causes less disruption to the household than excavating your floors to replace broken ones, but the price is often quite prohibitive. You may be able to negotiate with your plumber to do some of the manual work to reduce the cost however this will usually result in only a small saving.

Get quotes for CIPP pipe relining

Having to fix a collapsed drain or repair a sewer line under your slab definitely sits at the bottom of most people’s bucket list of things to do, but it’s no longer the nightmare it once was. Thanks to technological advances such as CIPP relining, homeowners with leaking pipes under their slab have options for repair they didn’t have in the past, and working through the problem with experienced professionals can be incredibly painless and stress-free.

The trick, however, is to be well informed and to consult a range of experts who will take the time and have the knowledge and experience to be able to assess which repair strategy is right for your particular circumstances.

Just as you wouldn’t go to your local GP to perform open heart surgery, using a generalist plumber, rather than an experienced drainage or relining specialist for a situation such as a leaking sewer pipe under your home’s concrete slab foundation is fraught with potential danger.

Whilst there is no doubt they will most likely be able to get things working again, you may be left reeling from the lifestyle and financial costs of their out-dated repair strategy. There is also no guarantee the same thing won’t happen again in a few months’ time, leaving you wishing you’d gone straight to the specialist in the first place.

If you’d like a quote on CIPP pipe relining from your local Nuflow pipe repair specialist, visit our contact page.


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