Tiling over tiles, how can I tell if it's a sound surface?

[Jayneo]

Hello hive mind!  I thought I would try tiling my kitchen floor but I have a concern…

 

The reason we are retiling is because I tried to spruce up the old ones with tile paint (reputable brand that seemed to offer a robust system), but the paint started peeling up very quickly in areas, particularly near the external door and washing machine (see photo).  I tried again, diligently degreasing and keying up everywhere and being overly cautious with drying times, and the same happened.  So I removed the flaky parts and we’ve just lived with it for over a year.  Now we’ve got hold of some nice new encaustic tiles that were on sale, and about to get stuck in installing them.

 

We were thinking of just tiling straight over the old ones, as the nice new kitchen cabinets (installed 2 years ago) stand on top of the current tiles, we thought it would just be simpler to tile up to the legs (the kick board would hide this anyway), and that the current tiles would give a nice level base.

 

However it’s started playing on my mind as to why the paint didn’t stick to the tiles…might it be a problem with damp?  Perhaps moisture within the substrate?  If the tile primer didn’t stick then why would the slurry bonding coat?

 

I have a feeling you’ll say pull up the tiles…

 

I think it’ll be concrete below, but to be honest I have no idea what horrors may be waiting under there.  When we had damp treated in the walls and then a new kitchen installed, we found out this extended part of the house (over 50YO, with no paperwork), is one brick between us and the neighbour (the electrician accidentally drilled a hole into the neighbours kitchen yikes!) so who knows what else may be discovered!

 

Any advice would be gratefully received.  Thanks in advance!

[bassanclan]

Put down lino or lvt

[Jayneo]

Thanks for the response!  Do you mean as a sort of membrane between the original tile and the new encaustic tile?

[jayc89]

May go into a bit of detail about the damp that was cured in the wall, same room/location? The only way to effectively treat damp is finding the source and fixing that, any damp prevention on the house itself will just move the problem elsewhere. You're typically looking for broken gutters/drain pipes etc. but depending on location and structure it could be driving rain, impermeable materials used (on older brickwork) etc. 

[saveasteading]

You could smack out the tiles in the dubious areas and see what's underneath. Bitumen paint that and replace with any old tile. Then overtile. Tile adhesive seems to stick to anything. Bug you score / abrade thd surface to break the glaze.

 

If there is a damp issue then the old tiles might come off reasonably easily, and that would be the better job.

 

[Jayneo]

Thank you Jayc89 and Saveasteading, I shall try pulling up what is in this area and investigate further.  It may be that there is some way moisture is getting in as you suggest, we did have the gutters replaced where it was needed but come to think about it, it was the same rogues who claimed they were going to fix our roof and then left more broken tiles than were there to begin with!  It's very high up so not obvious from below.  I like the sound of your solution Saveasteading!