The mistakes that cost the most
Almost every expensive bathroom problem was a decision made in a place nobody looks. Here is where they happen.
A bathroom that fails rarely fails because of bad luck. It fails because of a choice made at a stage you were never going to see, on a day you were not there.
Here are the ones that come up most.
Tiling over the old tiles
It saves a day of labour and a skip. It also means the new work is bonded to whatever the old adhesive is still holding onto, and it costs you floor-to-ceiling height every time. We have opened up rooms with six layers stacked on each other. Every layer took space nobody got back.
Skipping the primer
Primer is cheap, fast and completely invisible. Nothing that comes after it bonds properly without it. It is the single easiest thing to leave out of a job and the single hardest thing to detect afterwards, until adhesion starts to fail.
Treating the tile as the waterproofing
Tiles are not waterproof. Grout is not waterproof. The waterproof layer underneath them is what stops water reaching your floor, and the corners and junctions are where it always fails. That is why they get taped rather than just coated.
If a written quote does not mention a waterproofing system and sealing tape, it is worth asking why not.
Estimating the falls instead of measuring them
A fall that is roughly right drains, mostly. What it leaves is standing water in one corner, and standing water finds every weakness in the work around it. Throw a bucket of water on a finished shower floor. If it does not run to the waste, the falls are wrong.
Compressing the drying time
Drying times are not an opinion, they are printed on the tub. This is the stage that gets compressed when somebody has promised a week, and it is the one stage that cannot be. A waterproof layer tiled over before it has cured never fully forms.
Two to three weeks is not slowness. It is chemistry.
Taking the full payment up front
A handover is only worth something if there is money still outstanding. That is the entire mechanism. A firm that wants the full amount before the last day has removed every reason to come back and fix what you find.
What you can check yourself
None of this needs a tradesman. Discoloured grout that stays discoloured after cleaning means moisture is sitting in it. Sealant lifting means water is running behind it. Tap a tile with a coin: if it sounds hollow, there is air where adhesive should be. A grout line should be the same depth everywhere, and where it thins, it is nearly gone.
None of those are proof on their own. All of them are worth a question.