An Overlay Is Not Simply a Waterproofing System
A cement-sheet overlay can be installed in an attempt to stop water ingress, but if the sheets are poorly fixed, the junctions are unsealed and no continuous waterproofing membrane has been installed, it will not form a reliable waterproofing system.
Instead, it can conceal the defects that allow water to pass behind the new surface and remain trapped inside the wall cavity.
That is exactly what demolition revealed in this shower.
The shower had already been overlaid
At first glance, the shower appeared tired but serviceable. The visible problems included deteriorating joints, failed sealant and movement around the shower base.
However, this was not simply an old tiled shower requiring maintenance.
A previous installation had placed cement sheet over the existing standard plasterboard in an attempt to prevent water ingress, then applied the finished surface over that new layer.
The work had not been completed correctly.
Adding cement sheet does not automatically make a shower waterproof. It must form part of a correctly designed wet-area system, with suitable fixing, sealed joints, treated penetrations and a continuous waterproofing membrane.
None of those elements can be replaced by the wall finish itself.
The base junction showed signs of failure
The lower wall and shower-base junctions had open gaps, deteriorated sealant and poorly finished internal corners.
These were not isolated cosmetic defects. They were openings in an installation that did not have a waterproofing membrane behind it.
Once water passed through the failed joints, there was no secondary waterproof barrier protecting the wall lining or cavity.
The internal corner showed similar signs of poor finishing and movement.
Without a properly treated corner and continuous membrane, water could pass behind the surface and enter the wall assembly.
Cement sheet had been installed over standard plasterboard
Demolition exposed the previous wall build-up.
Rather than removing the unsuitable existing lining and rebuilding the shower wall correctly, cement sheet had been overlaid onto standard plasterboard as an attempted barrier against water ingress.
The overlay had also been poorly fixed. A sheet used in a shower must be securely installed onto a suitable structure, with the correct fastener spacing, stable junctions and properly treated joints.
Where sheets are inadequately supported or fixed, movement can develop between the layers. That movement places stress on the finished surface, corners and sealant joints.
Once those joints begin to separate, water gains access behind the overlay.
The original standard plasterboard remained behind the cement sheet, creating an unsuitable layered wall build-up for the shower.
There was no waterproofing membrane
The most critical discovery was the absence of a visible waterproofing membrane behind the shower finish.
Cement sheet is moisture resistant, but it is not a complete waterproofing system by itself. Water can still reach its edges, joints, penetrations and the materials behind it.
A shower requires a continuous waterproof barrier connecting the walls, internal corners, plumbing penetrations and shower-base junctions.
In this installation, that barrier was missing.
The overlay had not been properly sealed
The sheet edges, internal corners and base junctions had not been integrated into a sealed system.
There was no effective membrane protecting the changes of plane. The junction between the wall lining and shower base relied heavily on surface sealant, which had deteriorated and separated.
Sealant is an important finishing component, but it should not be the only defence against water entering a shower wall.
When the sealant failed, water was able to travel behind the cement-sheet overlay and become trapped against the original plasterboard and surrounding cavity.
Moisture was concealed between the layers
Overlaying one sheet material onto another created a concealed space where moisture could remain.
Demolition revealed moisture staining, mould growth and deterioration around the lower wall area. The plasterboard and surrounding materials had been exposed to prolonged damp conditions, while the finished shower surface concealed the extent of the problem.
This is one of the major risks of an incorrectly installed overlay: the shower may continue operating while water accumulates behind the visible finish.
By the time the symptoms become obvious, the problem may extend beyond the sealant or surface material.
Further deterioration was visible around the lower wall and base junction.
Why the shower needed to be stripped
The defects were part of the shower’s construction, so they could not be corrected while leaving the overlay in place.
The shower needed to be stripped back to expose the framing and plumbing. This allowed the failed materials to be removed and the area to be rebuilt as one complete system.
Rebuilding from the structure forward
The remediation included:
removal of the existing screen, base and defective wall overlay
removal of the affected plasterboard and unsuitable wall materials
inspection and preparation of the framing
plumbing alterations and a new waste connection
installation of a new shower base
installation of suitable new wall lining
reinforcement of internal corners, sheet joints and penetrations
installation of a continuous waterproofing membrane
waterproofing extended beyond the shower-base edges
installation of Sahara Gold wet-wall panels
installation of a new chrome shower screen
installation of new chrome tapware and shower fittings
New base and plumbing
A new shower base and waste connection were installed while the wall cavity remained accessible.
Completing the plumbing at this stage allowed the connections to be properly positioned and checked before the new wall lining enclosed the cavity.
The waste connection and associated plumbing were completed before the wall was closed.
New wall lining and waterproofing
New wall lining provided a stable substrate for the rebuilt shower.
The sheet junctions, internal corner, base perimeter and mixer penetration were reinforced before the waterproofing membrane was completed. The membrane extended beyond the outside edges of the shower base instead of stopping directly at the enclosure line.
Only the mixer spindle penetrated the finished waterproofed surface. The associated pipework remained concealed inside the wall cavity.
The waterproofing membrane was then applied across the walls, corners, base junction and treated penetrations.
The completed shower
Sahara Gold wet-wall panels were installed over the prepared and waterproofed walls.
The project was completed with a new white base, chrome shower screen, chrome tapware and a new shower system.
The finished shower is visually cleaner and easier to maintain, but its real value is in the work that can no longer be seen: suitable wall lining, secure construction, treated junctions and a continuous waterproofing membrane.
The new screen, tapware and shower fittings completed the rebuilt enclosure.
What this project demonstrates
Installing cement sheet over an existing wall in an attempt to stop water ingress does not, by itself, create a suitable shower enclosure.
An overlay must not be confused with waterproofing, particularly when it has not been correctly fixed, sealed or integrated with a continuous membrane.
Before an existing shower is covered, the installer must consider:
whether the original substrate is suitable
how the new sheets will be mechanically fixed
whether the structure is stable
how sheet joints and corners will be treated
how the base and walls will be connected
how plumbing penetrations will be sealed
where the continuous waterproofing membrane will be applied
If those details are missing, the new finish may simply conceal the old problem—and create additional layers that must eventually be removed.
Project Details
Project type: Wet Zone remediation
Primary defects: Cement sheet over plasterboard, inadequate sheet fixing, unsealed junctions and no visible waterproofing membrane
Work completed: New base, plumbing, wall lining, waterproofing, wet-wall panels, screen and tapware
Panel finish: Sahara Gold
Duration: 3 days
Project cost: Under $6,500
If your shower has been overlaid in an attempt to stop water ingress and you are uncertain about what was installed behind the finish, Aureumus can assess the construction and explain whether the existing system is suitable or requires remediation.
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