Quick answers
After rain, water sits on my balcony, mostly by the door. What's wrong?
Usually the falls: the floor doesn't slope towards the drain, or it has hollows. If the drain is clear, the slope only changes if the layer under the tiles is redone.
A balcony floor isn't completely flat. It slopes gently towards the drain or the gutter, and always away from the door. That slope comes from the layer under the tiles, laid when the floor is built. If that layer was laid unevenly, or has sunk in a spot, water stays there or runs the wrong way.
Check the simplest thing first: if the drain is blocked with leaves and soil, the water has nowhere to go, however good the slope is. If the drain is clear and water still sits, the problem is in the floor itself.
On this balcony, dirt and black marks from standing water had built up in the corners and along the door sill, and the grout had turned black. Marks like these show where water sits. There it has more time to find a crack or an open joint and get through to the ceiling below or under the door.
Small hollows can be filled locally before a new coating goes on. But if the whole floor leans towards the door, a coating on top follows the same surface and doesn't change the slope. Then the tiles usually have to come up, a new layer with proper falls and waterproofing goes down, and the floor is laid again. What exactly is needed can only be judged on site.
Jobs that show it
Balcony Tiles Sealed with a White Coating
Stained tiles with blackened grout were cleaned and covered with a white waterproof coating, without lifting them, that also runs up the skirting.
See the job step by step
Terrace Stripped of Old Tiles and Given a New Cement-Based Layer
The broken tiles came up, the joints were cleaned out and sealed, and the terrace and the narrow balcony beside it got a new cement-based coating.
See the job step by step