The most expensive bathroom mistakes are invisible on handover day: no waterproofing under the shower, falls formed in the tile adhesive, drains not joined to the membrane, old pipes left in place behind new tiles and electrics placed without regard to the zones around the shower. Choosing finishes before fixing the layout and relying on silicone instead of a membrane complete the list. Each is avoidable with the right sequence.
Mistake 1: why is skipping waterproofing so common?
Because it cannot be seen, and because tiles look waterproof. In reality grout and joints let water through over time. Without a membrane underneath, that water soaks into the screed and walls. In an apartment, the first sign is often a stain on the neighbour’s ceiling. The fix is to take the shower back to the base and rebuild it with a membrane, which costs more than doing it right the first time. See the waterproofing guide.
Mistake 2: tiling over old tiles
It saves strip-out time and creates several problems. The walls get thicker, the floor rises and the door no longer closes, the old pipes stay hidden in place, and any loose tile underneath eventually loosens the new one on top. It also makes a future renovation harder, because there are now two layers to remove.
Mistake 3: poor falls in the shower
Water must run consistently to the drain. When the fall is made by varying the thickness of tile adhesive, it is uneven: water sits in hollows, finds its way under the screen or pools against the wall. Falls belong in the screed under the membrane, checked before waterproofing.
Mistake 4: leaving old pipes behind new tiles
A bathroom renovation is the one moment when the pipes are accessible. Leaving old galvanised or corroded pipes in place to save time means a later leak will require breaking new tiles. In a full renovation, the pipes inside the bathroom should be renewed.
Mistake 5: electrics in the wrong place
Sockets beside the shower, lights that are not suitable for the zone above the bath, a towel rail wired without protection. Spain’s low-voltage regulation sets zones around baths and showers that restrict what can go where. Ignoring them is unsafe. In our renovations the electrical work is done by authorised partner installers who apply these rules.
Mistake 6: choosing tiles before the layout
Owners often arrive with tiles already bought. Then the layout reveals that the shower must sit where a large tile cuts awkwardly, or that a flush floor needs a smaller format to follow the falls. Fix the layout, the drain and the niches first, then choose the finish to suit them. The layout guide explains the order.
Mistake 8: forgetting about ventilation
A new bathroom without an extractor, or with a fan that is too weak or wired so that nobody turns it on, will develop condensation, mould on the silicone and stained ceilings. This is especially common in inside bathrooms of apartments where the only ventilation is an old grille into a shaft. Planning an extractor and its switch costs little during a renovation and a great deal afterwards. See damp and mould in bathrooms.
Mistake 9: not planning the order of the trades
When owners hire a plumber, an electrician and a tiler separately, the trades arrive in whatever order their diaries allow. The tiler starts before the concealed valve is set; the electrician cuts a chase through fresh render; the plumber drills through a finished wall to fix a pipe he missed. Each problem is small, but together they turn a tidy job into a patched one. A single contractor is responsible for that sequence, which is the main thing you are paying for.
The same applies to decisions. A shower screen chosen after tiling may not fit the drain position; a mirror cabinet chosen after the electrics may not match the cable position. Every decision has a moment, and missing it means rework.
Mistake 10: not seeing the layers before they are covered
Many owners see the bathroom only when it is finished. By then the membrane, the pipe joints and the falls are hidden. Asking to see the work before tiling starts is the simplest protection against most of the mistakes above. We keep the waterproofing and pipework open until they have been checked, and you are welcome to inspect them at that stage.
Mistake 7: relying on silicone
Silicone is a movement joint, not a waterproofing. When it is used to fill gaps that should never have existed, it hides the fault for a while and then fails. Black, lifting silicone shortly after a renovation is often a sign that something underneath is wrong.
Avoiding all of these is what a properly sequenced bathroom renovation is for. If tiling is your concern, see bathroom tiling.
Bauman Raymond Attila · Reforma Baños Málaga · Avenida Antonio Belón 3, Marbella. Last reviewed: 05/11/2026.
