Hi all,

Having tiled my floors in my flat over old tile I've now just got the kitchen to finish off. This, unlike the rest of the flat has already had a layer of tiles (laid 25yrs ago by PO) over the original tiles. So I'm just removing the top tiles to retile over the bottom tile and found the thinset bed is 12mm (1/2"). Is this too much for 30x30 tiles? I've been tiling 45x45 with 6-8mm (1/4") using a 1/2"x1/2" trowel so am I not using enough?

Also I notice that whilst the thinset on these 25 year old tiles became detached from the substrate with one hit of the hammer and a screwdriver, because the thinset is so thick it essentially came detached for a whole m2 and stayed together as it's own floor and was very very difficult to break the tiles apart (I only want to do it bit by bit so don't want to remove the lot)...so maybe that's why they used so much thinset so as to essentially create their own floor of such mass/strength that the strength of bond of this to the tiles underneath was irrelevant?

Any thoughts on this and should I keep on with how I've been doing it or aspire to increase the amount of thinset I'm using? I know tilign over tiles is not ideal but I don't have skills/time for removal and the kitchen tiles previously tiled over the tile have lasted 25 years in a heavy used kitchen without any problem.

TIA for any responses

Thinset is an american term. It's tile adhesive. and no it's not too much. I'd probably use a 15mm notched trowel assuming everything is level.

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i dont understand your post and photo. are the red tiles the kitchen floor and is that top tilethe finished floor level?
can you do a photo of the 25mm you are trying to make up?

thinset is not just a adhesive.its the modern go-to cementitious adhesive sometimes called thinset mortar.it comes in powder in bags.and is used in all external or wet area work.
defnitly the adhesive for kitchen floors

mastic adhesive is not cementitious andlike pva glue it can dissolves in water so is only safe to use in dry areas.

just saying but
yeah the name thinsetcomes from america but some uk mfr's and tilesuppliers are now using the name

Sorry I didn't explain it that well, firstly the tile adhesive (thinset was in the American videos I watched and as I'm in Spain I don't use the English name much); it's powdered addy with polymer resins suitable for tilign over tiles, flexible and suitable for wet areas.

I've done the whole floor of flat using it in 45x45 standard ceramic tiles (new photo) tiling over level and fixed original tiles (except loose ones which I removed and put mortar in the gap). Used a 12mm trowel for all this as that's what the instructions on addy said and so I have a 6-8mm adhesive bed. Now just the kitchen, the only room already with new red tiles tiled over tile as in photo. Now even I won't have 3 layers of tile down so I removed them and despite being down 25yrs one smash of a hammer on a screwdriver and a huge amount of the tile adhesive bed and tiles detached from floor but was still difficult to get them up as the adhesive bed was so strong and was 12-14mm thick which is twice as much as mine despite teh tiles being smaller (30x30). Photo shows both adhesive bed still down and on tile I ripped up)

So question is for 45x45 tiles is the 6-8mm I did good or is this 12-14mm better (and I assume that would need a 25mm trowel?). As I know tilign over tiles is never a great bond, maybe the extra thick addy creates such a mass that the tiles don't move as has happened with the kitchen the PO did. I know that's not how it's meant to work but if they stay down, they stay down! To finish the kitchen I can't really add height as I don't want a step but I'm trying to learn as much as I can from this project and any mistakes I make as I have other flats to do in future and also I just really enjoy understanding/learnign how things work so appreciate your comments.