When a drain fails, most people picture the pipe. It is a reasonable picture and it is usually the cheapest part of the job. The pipe is a length of material and a couple of fittings.
What actually decides the bill is getting to it. On the ridgelines here that means Hawkesbury Sandstone, which across large parts of the metro area sits within a metre or two of natural ground level. It is hard rock, quarried by hand for a century to build colonial Sydney, with compressive strength measured up to around seventy megapascals. Cutting a trench through it is slow, loud and expensive, and none of that has anything to do with the pipe at the bottom.
On this ground, excavation is usually the largest number in a drain repair quote, because rock frequently appears within excavation depth. That makes the first question not "what is wrong with the pipe" but "can this be repaired without opening the ground". Where a line is cracked rather than collapsed, relining answers that, and it is worth more here than anywhere west of the harbour.
- Get the line inspected on camera before anyone quotes excavation
- Ask specifically whether it can be relined
- Ask what the quote assumes about rock, and what happens if it is wrong
- Compare a reline quote against a dig quote on the same footage
- Reinstating a driveway or paving is part of the dig cost, not an extra
On this page
1. Why this ground is the opposite of the western suburbs
Out west the problem is reactive clay: ground that swells and shrinks with the seasons, moving what is buried in it and opening pipe joints over the years. The ground is the cause of the damage, and getting to the damage is comparatively easy.
Here it is reversed. The ridgeline sandstone barely moves at all, which is genuinely good news for the drainage in it. But when a pipe does fail, for any of the ordinary reasons pipes fail, reaching it means cutting rock.
That single fact reorganises the economics of every drain repair on this ground. The material cost of a repair is roughly what it is anywhere. The access cost is not remotely comparable.
The formation carries shale lenses, thin bands under a metre thick, which is why depth to rock can differ sharply between adjoining properties. It is a reason to establish what is actually under yours rather than assuming the street is uniform.
2. What a dig actually involves when there is rock
A trench through soil is a straightforward machine job. A trench through sandstone is a different exercise, and the things that make it expensive are mostly not the digging itself.
- Equipment changes. Breaking rock needs different machinery from moving soil, and getting that machinery onto a property is its own problem.
- It is slow. Progress through rock is measured differently, and a job quoted in a day can become a job measured in days.
- It is loud. Which matters on a residential street and matters considerably more if the property is in a strata scheme.
- Reinstatement. What was on top of the trench, whether that is a driveway, paving, a path or a garden, has to be put back.
- Uncertainty. The depth at which rock appears is not always known until somebody is digging, which is why an honest quote will say what it has assumed.
That last point is the one worth pressing a quoting plumber on. Ask what the price assumes about rock, and what happens to the number if the assumption turns out to be wrong. A straight answer to that is a good sign.
3. What relining does, and when it is the right answer
Relining repairs a damaged pipe by forming a new pipe inside the existing one. The liner goes in through an existing access point, is cured in place, and becomes a continuous new wall along the damaged section. The ground above stays exactly where it is.
On an open block west of here, that is a convenience worth weighing against a dig. On sandstone it frequently changes the entire scale of the job, because the thing it eliminates is precisely the thing that costs the most.
It is not universal. A line that has collapsed rather than cracked may not accept a liner, a badly displaced joint may need a point repair first, and some layouts are harder to line than others. Those are questions for a camera, not for a preference.
4. Get the footage before anybody quotes
A quote for excavation given without a camera inspection is a quote written from an assumption. It might be right. There is no way for you to know, and no way for the person writing it to know either.
A camera answers the things that decide the job: where the fault is, how long it is, what kind of failure it is, and whether the line is a candidate for relining. All four of those change the price, and three of them change the method.
Ask for the footage itself rather than a description of it. It is your property and it is your evidence, and it lets you put two quotes side by side on the same facts instead of comparing two opinions.
Told you need the yard dug up?
Ask for the camera footage first. We will inspect the line and tell you honestly whether it can be lined.
5. The questions worth asking every quote
- Have you put a camera down it, and can I have the footage?
- Can this section be relined, and if not, exactly why not?
- What does your excavation price assume about depth to rock?
- What happens to the price if you hit rock shallower than assumed?
- Does the quote include reinstating the surface, and to what standard?
- How long will the property be without drainage?
These are not aggressive questions and a good plumber will answer all six without hesitating. The pattern of the answers tells you more than the total at the bottom does.
6. If you are planning work rather than repairing damage
The same arithmetic applies to a renovation, a pool, a granny flat or anything else that needs new drainage. On this ground the drainage route is a cost driver rather than a detail, and it is much cheaper to design around than to discover.
Establish where the existing lines run before the plans are finalised. Where a new fixture can connect into an existing route, the job stays reasonable. Where it needs a new run through rock, that should be a known number early rather than a surprise at excavation stage.
It is also worth knowing what is under your particular block rather than what is under the street. The shale lenses in this formation mean neighbouring properties genuinely differ, and the assumption that yours is like theirs has cost people real money.
- Hawkesbury Sandstone often sits within a metre or two of the surface on these ridgelines.
- That makes excavation, not the pipe, the largest number in most drain repair quotes here.
- Relining repairs a cracked line from the inside and leaves the ground untouched.
- It is not universal: a collapsed line may not take a liner, and a camera decides that.
- Shale lenses mean depth to rock differs between neighbours. Do not assume the street is uniform.
- Get the camera footage before comparing quotes, so both are priced from the same facts.
Digging on sandstone FAQs
Is relining always cheaper than digging?
Not always, and anyone who says it is is overselling. What is fair to say is that on ground where excavation means cutting rock and reinstating a surface, the comparison tilts much further toward relining than it does on an open block with soft ground.
How do I know if my line can be relined?
A camera inspection. It shows the type of failure, the length of the damaged section and the layout, which together decide whether a liner will work. It is not something anybody can tell you from the surface.
How deep is rock on my property?
We cannot tell you that, and neither can anyone who has not looked. This formation carries shale lenses under a metre thick, which is exactly why one property strikes rock shallow and the one next door does not.
Does hard ground mean my pipes are safer?
In one specific sense, yes. Ground that does not move seasonally is not working your pipe joints loose the way reactive clay does out west. Pipes here still fail for other reasons: age, roots, damage from other work, and the ordinary life of the material.
Will relining reduce the size of the pipe?
A liner takes up some wall thickness, so the internal diameter reduces slightly. In a properly sized domestic drain that is not usually a practical problem, and the smooth new wall often flows better than the damaged pipe it replaced.
Can you reline a stormwater line too?
Often, yes, and the same logic applies: on this ground the value is in not opening the surface. Whether a particular line is suitable is a question for the camera rather than a general rule.