Tiling on window sill beside a shower

Can you post a picture as I'm struggling to envisage how they tiled over an existing timber window sill (sill is typically external and window board internal but that's more semantics). Did they cut off the overhang prior to tiling to leave it square with the wall?

A window board where there was no bath/shower previously will have a flat level surface but that could have still pre-sloped with adhesive as it only needs a few degrees to enable water run off. It's not the worst surface to tile on provided it's solid wood and not mdf and well sealed/tanked. However it would have made more sense and easier overall to remove prior given everything else was replaced and use cement board or a tile backer board as you mention.

It sounds like the main issue is the lack of slope and water pooling so that would need to be redone. How big is the window opening and does one tile cover the window board section or are there multiple grout line along it. Standard grout is not waterproof so with water pooling you're relying on the tanking underneath to hold indefinitely which is a tough ask on a flat level surface with no run off.

The cracked grout sounds like it's along where the vertical and horizontal tiles meet. You'll always have movement along internal/external joins which is why they should be siliconed rather than grouted.

To confirm I'm not a tiler so only have limited experience when I had to re-tile my bathroom after the previous owners had a "professional" in only a year prior on a fresh install. Everything had to be gutted back to the external walls and studs due to water damage leading from that tile job.

I have a window within my shower area and opted for a single piece of 20mm quartz stone as the window board and then tiled around that. Didn't fancy grout lines on a horizontal surface even though I have it sloped and used epoxy grout throughout. You have a lot of grout lines in that window are so it's very vulnerable even if it was properly sloped.

It's a tough call but on a fresh job like that after paying hard earned money I'd have the tilers back to re-do. The cracked grout under the window is even more of a concern given it's a flat section of wall rather than the join as I suspected. That could be related to the window board left in situe if it wasn't solid to begin with.

Window board aside, that's a poor effort. The tiles aren't aligned well on the wall, in the window they are up and down and grout lines are very noticably different.

that's a really poor job. Struggling to believes its new work and not 10 years old.

The grout is a bas choice and poorly done. It's letting water through. Tanking on the window board is not enough. The whole thing needs to be tanking. Even if tanked well, the window creates a point of failure.

I think this will be to be at least partially redone.

I don't believe an experienced tiler did that job. I've done a couple of small DIY jobs and they've been better than that. No way would I use small tiles around the window either with water resistant grout. You need as few points of failure at the window as possible. I personally went with large format tiles 60cm long on my window surround and used epoxy grout.

Your cut stone idea could be very expensive, and trying to match it in with the tiles may not be easy. Also it may always look like a patch up job. But not half bad as PVC fascia which someone else suggested. Fully tiled bathroom is always the best looking job. I have explained what the most likely problem is further up. When you talk about a contractor is he a builder or why didnt he do the work if a tiling contractor ? who has the 20 years experience you mention ?.