Horsham Ceramic Tilers

Yes you can layover the original tiled floor without the extra matting, however, the height of your surface will increase, meaning at the door into your kitchen will now be alot higher, so won't be a good finish to the next room. the other thing to note would be that your underfloor heating won't work very well temp' wise, as you've raised the thickness. i completely understand your situation. to note, laying on top of other tiles on a high footfall area, your risking tiles cracking. bottom line, the old tiled floor + the heating cables would need to be replaced with new. not what you want to hear i guess, however, you 'maybe' able to save the matting underneath the heating cables. bear in mind, if tiles do start to crack, then replacing can get expensive to do. so at the of the day, its wiser to rip up the old, and replace all with new. good luck with your decision.

I'm assuming you mean the grout. it sounds to me that you only need to re-grout it. if it's in a wet area, shower area, you should re-grout it asap. or yes it will damage the wall. if the grout has gone blackish, then the damage has already been done, which will mean re-tiling that area.

If you have damp grout on the floor tiles, you'll need to remove that tile and some others around it. sounds to me that water from somewhere is getting to that low point in your floor. but before removing, have a quick look at the bottom of you basin, w/c and bath pipes, as there maybe a small leak happening.

In construction you have what's called 1st fix and 2nd fix. this means installing your bath/shower/basin/wc 1st, plumb it all in 1st. in your case and in every case, a shower mixer should be plumbed in 1st, an also the shower tray installed 1st. then and only then start to tile. tip: the first row of tiles on the shower tray, should be cut tiles, so then when i comes to the sling of the tray, you get a much better seal, protecting from any water leaks down the side of the shower tray. as for your boiler, it's hard to advise without seeing the placement of it. what you need to bear in mind is, when the boiler is installed, can you still tile around it? most times though, at least have the pipework done 1st. eg, 1st fix. get the pipes in the right place first, if the pipes are coming out of the wall. if your pipes aren't coming out of the wall, then simply tile before installing the boiler.

Your tiler should never end up with a tile of 2inchs. this is because the job as not been set out / laid out properly. (though it can happen in some rare cases, so i won't be to critical as i can't see the layout of all the tiles) i could be wrong, but at a guess, as you mentioned a window, he may of had a good finish on your window sill, placed one tile there, and was then left with approx 2inchs at the back (that can happen alot), towards the window. however, i have to wonder why a tile of any type can't be cut at 2inchs, as it's very do-able, very. there's no tile that i know of that can't be cut 2inchs in width. (my strongest guess would be, he's using the wrong cutting tool to cut that 2inch tile) bottom line, a 2inch grout line is an absolute no no. 2inch = 50mm. most grouts are designed/made to do lines of up to 20/25mm max / less than 1nch. read the guidelines on packet of grout.