Bathroom renovation on a timber-floor Wagga home is one of the most common renovation traps in older housing stock: the tiler and plumber arrive, the job looks fine for a year, then grout cracks, moisture finds the sub-floor, and the whole wet area has to come out again. The root cause is almost always a sloping floor that nobody addressed before the tiles went down. Book a foundation inspection before renovation quotes are requested, and you will know exactly what you are dealing with.
Quick answer (BLUF)
In most Wagga homes built before 1970, a sloping bathroom floor is a structural problem, not a tiling problem. One or more stumps have dropped, the joist frame has followed, and the floor pitches in a direction that has nothing to do with the waste outlet. Tiling over that slope without fixing the cause means water tracks the wrong way, grout fails under continued movement, and you pay for the bathroom twice. The correct sequence is: assess the sub-floor, restump or relevel what is causing the slope, then waterproof to the Australian Standard, then tile.
Why bathrooms expose floor slope worst of all
A 5 mm slope across a 3-metre hallway is barely perceptible underfoot. Across a 1.2-metre bathroom, that same rate of fall means one end of a bath sits noticeably higher, shower water runs toward the vanity instead of the waste, and grout joints open where the movement concentrates at one edge of each tile.
Bathrooms also concentrate water in a small area and depend on watertight grout and flexible sealant joints to keep moisture out of the sub-floor. Any pathway through those joints, whether from a tile that has lifted slightly, a grout crack, or a wall-to-floor junction that has opened as the frame moved, lets water into the joist cavity. In older post-war timber-floor homes in Wagga, those joists are often already softened from undetected historic leaks and inadequate sub-floor ventilation. A new bathroom renovation that does not address the floor structure first can turn a cosmetic problem into a structural one within a couple of seasons.
There is a second complication. Wet-area floors must have a deliberate fall to the waste outlet, typically between 1 in 60 and 1 in 80 for a domestic shower or bathroom. If the structural floor is already sloping in a different direction, a tiler cannot correct it using a standard tile bed without building up mortar unevenly. Thick mortar beds over a moving timber floor crack quickly, and once they crack the waterproofing above fails.
Fall to waste versus a house-wide slope
These two types of slope are often confused in conversations with tradies, and the confusion leads to wrong-sized quotes.
A fall to waste is a deliberate, designed slope toward a drain outlet. It is set by the tiler using tile bed mortar and screeds, and it is a tiling technique, not a structural one.
A house-wide slope is a structural matter. The joists and bearers have settled with the stumps beneath them, and one part of the floor is simply lower than another. No tile bed will fix this because the movement continues after the tiles are laid.
The critical question before any bathroom renovation in this housing type is whether the floor is still actively moving, or whether it has settled and is now stable. A floor that dropped noticeably in the last drought and has not moved since may be a different risk to one that dropped this past winter and is still changing. A builder or inspector who walks the floor and checks underneath can usually give a useful opinion on this within an hour.
Our guide to uneven and sloping floors explains the indicators that point to active versus settled movement, and what to look for when you check.
Restumping and relevelling before waterproofing
For the majority of Wagga timber-floor homes where a bathroom slopes because of stump movement, the fix starts below the floor. Restumping and reblocking replaces or adjusts the stumps under the affected bay to bring bearers and joists back toward level. Where full stump replacement is not needed, house relevelling can adjust bearers with packing to correct localised settlement.
Once the floor frame is level and confirmed stable over a short monitoring period, waterproofing can proceed. Standards Australia AS 3740 governs waterproofing of domestic wet areas in Australia and requires that the membrane be applied to a suitable substrate. A substrate that is not structurally stable is not suitable. Applying a compliant membrane to an actively moving floor produces a failed waterproofing job regardless of how well the membrane is installed.
Builders who regularly work in older Wagga homes know to ask about the floor history before they scope a bathroom renovation. A quote from a tiler or builder that makes no mention of sub-floor condition is leaving the structural question unanswered.
Look at signs your house needs restumping before your inspection so you can ask informed questions about the specific bay under your bathroom.
Sequence: assess, restump, level, waterproof, tile
The correct trade sequence for a bathroom renovation in a Wagga timber-floor home is predictable once you know it:
| Stage | Responsible trade | What happens |
|---|---|---|
| 1. Sub-floor assessment | Licensed builder or inspector | Confirm stump condition, measure slope, assess active vs stable movement |
| 2. Restump or relevel | Restumper or builder | Lift floor to level; replace or adjust stumps as needed |
| 3. Confirm level and stability | Builder or inspector | Re-check floor across the bathroom bay |
| 4. Demolish old wet area | Builder or tiler | Strip tiles, membrane, any damaged substrate |
| 5. Substrate and waterproofing | Licensed waterproofer | Apply membrane to stable substrate to AS 3740 |
| 6. Tile and grout | Tiler | Set correct fall to waste, tile, grout |
| 7. Flexible sealant joints | Tiler or builder | Wall-to-floor and internal corners sealed with flexible sealant |
Trying to collapse stages 2 and 5, or skipping stage 1 entirely, is where the expensive mistakes happen.
For the broader picture on what older Wagga homes need before renovation, see our guide to renovating or extending an older Wagga home.
Cost of doing it in the wrong order
The table below gives an indicative comparison only. Actual costs depend on the home, the extent of stump work, and what is found once the old tiles are out.
| Scenario | Indicative outcome |
|---|---|
| Correct sequence: assess, restump, waterproof, tile | Single mobilisation for each trade; no re-do |
| Tiles laid over unsupported sloping floor, grout fails at 12 to 24 months | Full tile strip-out, restump, re-waterproof, re-tile: effectively double the bathroom cost |
| Water tracking through failed grout into joist cavity for 12-plus months | Joist or bearer replacement added to re-do cost |
The sub-floor assessment and the call on restumping sits in the low hundreds of dollars for most single-bathroom jobs. It is the cheapest item in a bathroom renovation budget and the one most likely to prevent a costly repeat.
Knowing how long restumping takes in Wagga helps you sequence trade bookings so you are not waiting weeks between stages.
Coordinating trades: plumber, tiler, restumper
Bathroom renovations in older homes reliably involve three or four trades who do not naturally coordinate. Each quotes their own scope, assumes the prior stage is done correctly, and arrives when called. The homeowner becomes the de-facto project manager.
A few principles that prevent the common collisions:
The restumper needs unobstructed sub-floor access before demolition begins. Do not strip the old bathroom first and then book the sub-floor inspection; that is backwards. Get the assessment, confirm what is needed below, then demo.
The plumber’s rough-in location, particularly the new waste outlet, should be agreed before the tiler takes any floor measurements. Moving a waste after waterproofing has been applied adds cost.
The tiler should not begin until the waterproofer’s cure period has elapsed, which is typically at least 24 hours for most membrane systems, but the waterproofer’s data sheet governs.
If the bathroom renovation is part of a larger project, a foundation inspection before planning finalises will tell you whether the bathroom slope is an isolated stump issue or part of a wider foundation movement pattern that affects how the whole project should be sequenced.
FAQs
Can the tiler just use extra mortar to correct the slope?
On a stable floor, an experienced tiler can build up mortar to set the correct fall to waste. The risk is that on a moving timber floor, thick mortar beds crack under differential movement between joists. If the floor is still settling, the mortar follows. A licensed builder should confirm stability before you rely on mortar correction alone.
How do I know if the slope is a stump issue or just poor original tiling?
If the slope extends consistently beyond the bathroom into an adjacent room or hallway, the cause is structural, not tiling. A spirit level on the hallway floor beside the bathroom will confirm. A builder or inspector under the floor can usually see the stump condition directly.
Does the plumber need to come back after relevelling?
Usually yes, at least to check the waste outlet height relative to the new finished-floor level. Build a return plumber visit into the quote from the outset, rather than discovering it on the day.
Is a waterproofing compliance certificate required in NSW?
Licensed waterproofers typically provide a certificate of compliance for wet-area work. Whether a Building Inspector sign-off is required depends on whether the renovation triggers a Construction Certificate or Complying Development Certificate. Confirm with your builder and local council before work begins.