Floor/tile/stud wall issue

[23vc]

en suite floor, 6x2 c24 joists, 400mm centres, loads of noggins, rock solid each end into block work, span 2.8m.
18mm ply on top, screwed down with lots of 80mm screws, with noggins along all board edges.
Tiled on top with flex adhesive and grout.
Done this before and pretty confident it’s an acceptable setup. However...
2 tiles seem to have “popped” ie you can feel a crunch when you push your foot on them and the grout is starting to crack slightly. Rest of the room rock solid with no issues.
Only possible reason I can think of, is I built a stud wall running across the joists, in the room below, AFTER tiling the floor. I reckon when I did this, I smashed the top plate tight up to the joists as I wedged the uprights in, causing the joists to lift up slightly (near mid span) which has “popped” a couple of tiles at that spot.
Feasible? It’s that only thing I can think of other than a compete design fault, so am hoping it’s just that....any thought appreciated

 

[Ian H]

I think your right.

If your wall is very tight to the ceiling your tiled floor might have raised slightly in the middle so when you walk accross the room it goes Soft > Hard > Soft.

Best rip it out and start again

 

[acurachris]

Is the 18mm the only boards down or do you have another 18mm t&g below that? Where have the tiles popped, in the centre of the room?

When i've tiled an upstairs floor before, I lay plywood boards over the existing flooring then the tiles on that.

1. It helps sturdy the floor and restricts movement .
2. If you take your tiles up in the future, you can take up the plywood if needed and the original floor is still relatively untouched.

You're probably right though, it's likely when you did the stud wall. Scrape the adhesive out, re-lay the couple that are loose and see if it happens again. The stud wall might help now to restrict movement a little.

 

[23vc]

Best rip it out and start again

Ok, I’ll start by demolishing the extension and try and salvage as many materials as possible

 

[23vc]

Thanks guys I’m hoping it’s that too.
Chris, no floorboards, just the ply but it’s fully supported at all edges, and I reckon that should be ok from experience...

 

[^woody^]

Info here applies to tiled floors too. Same concept.

www.diynot.com/diy/threads/best-board-to-use-for-sub-floor.517461/

 

[23vc]

Info here applies to tiled floors too. Same concept.

www.diynot.com/diy/threads/best-board-to-use-for-sub-floor.517461/

So I should have cross bonded with something thin? Hmm, that’d be a bummer, I’m hoping it’s more my heavy handed stud walling. Don’t fancy ripping the whole floor out.

 

[acurachris]

Don’t fancy ripping the whole floor out.

I wouldn't bother ripping it up yet, see if it happens again first.

You might get two years out of it before the wife wants to change it anyway!

 

[^woody^]

It might be your initial diagnosis or a bit of both.

If its just two tiles, rake the joints, cut them and the bed out and rebed them. If a joist is there put a few more screws in. If the borad is not flat and cant be dealt with in the base adhesive, then plane or shave it.

Worry about the rest of the floor when (if) it becomes a problem.