Gap appearing between floor and wall tiles

There can be several reasons for the movement between the floor tiles and wall tiles which is causing a gap to appear. It could be that there is movement in the floor joists which is transferring up and causing the gap to appear. It could also the that there were loose floorboards and therefore the plywood subfloor they installed will also be loose, due to the expansion and contraction in the timber it is causing the movement to move up into the tiles and loosen them up, thus creating a gap. These two explanations can only be verified by lifting up the floor. However, there is a very likely cause to the gap and it is the fact that they did not use an uncoupling membrane, such as ditra matt on top of the plywood subfloor. This is will 100% cause the tiles to loosen over time. An uncoupling membrane system provides an intermediate substrate between the tile covering and load bearing substrate. They can be used over a variety of substrates, which include timber. It is highly recommend to install an uncoupling membrane when tilling over a timber subfloor to guarantee a professional job.

Hi theres a few possible problems there first one that springs too mind that the orginal floors boards underneath the tiles are not secured on a joist so when walking theres movement between the wall and floor. The other possible problem the plywood or cement board underneath the tiles hasent enough fixings usaully wee screw every 100x100 sqaure so there is no movement underneath and theres a secure fixing between timber floor and plywood floor. And if the shower tray is moving theres not bein bedded down properly with cement and it riding on the floor boards. A have seen this first hand when people bed the shower tray down with silicone which is not the correct way. Hope this helps with the problem.

It's difficult to say for certain without seeing the bathroom and inspecting the tiles and floor, but based on the information provided, there are a few possibilities for what could be causing the gap between the floor and wall tiles: Subfloor movement: It's possible that the plywood subfloor is not securely fastened to the original floorboards or that the original floorboards are not stable. If the subfloor is not properly anchored to the floorboards, it could shift or move slightly over time, causing the tiles to shift and creating a gap. Inadequate waterproofing: If the tradespeople who installed the bathroom did not properly waterproof the area around the external wall, water could be seeping through and causing the subfloor to expand and contract, which could create gaps between the tiles. Poor installation: It's possible that the tiles were not properly installed on the subfloor, which could cause them to shift and create gaps. Structural issues: There could be underlying structural issues with the house that are causing the subfloor to shift or the tiles to separate. To determine the root cause of the gap, it may be necessary to bring in a professional to inspect the bathroom and identify any underlying issues

For a gap to appear where the floor meets the wall I suspect there is movement in the sub floor, ie joists. If the tiles are still fixed firmly to the ply then there is no need for membranes. Membranes won't fix joist movement. With the information you have provided, old house, gable end, 9 months after installation. It sounds like the original floor had movement in. You could rectify this from the ceiling below if you didn't want to rip out the tiled floor