Help - How to test I'm getting the right adhesion

[D215YQ]

Hi all,

I just found that unlike before my primer started peeling off the tiles below when doing the final wipe preparing to tile...so I decided to test a piece laid 48hours ago which came up undamaged with a screwdriver (well it chipped a bit but didn't need much force). Now I probably didn't do it as well as some as it's an edging piece but, although a bit has peeled the primer off (the green) the rest has failed in the thinset itself and more worryingly some of it has not stuck to the tile at all, which I'm surprised because I've been back buttering and troweling these tiles (dampening them first): I thought the fault would be in the primer not the adhesion to the tile...

Tiles are ceramic 45x45, 1/2" notch trowel floor/tile in lines
Base is an old (non glossy) tile, cleaned thoroughly before priming.

I am a little worried as not only have I done the whole room but I've also finished two other rooms 2 months ago and been using them since without any problems. I also used the same method (though on most walls using mortar substrate) for my bathroom tiles 6 months ago and they're still hanging on the wall without problems despite the uneven walls/humidity.

Is it a case of 48h not being enough for the thinset to completely cure and if left another week it would not have pried off so easily...?

Thanks in advance for your advice.

[wine~o]

What adhesive have you used... please tell me it's not ready mixed.

[D215YQ]

Im in spain so you might not know the brand...its axton c1te flexible for attaching ceramic to all surfaces. Its not ready mix and thinking about it i might be doing it a bit wet as thats what i did when attaching to the porous mortar before. That said all ridges held and it still stuck to trowel etc. As thats an edge piece the coverage is bad - been checking every 6th as i go and no ridge lines.

Going forward im going to change primer and mix thicker...unless i should change thinset...With the ones so far i suppose i just leave them and hope? If after 2 months foot traffic and dragging a heavy sofa across them does that mean they should be ok even if not done perfectly.

Appreciate your advice.

[wine~o]

If it's a bagged addy and a reputable make (You are right I don't know the brand) then either you are mixing it too thin or the primer is incompatible with the previously tiled surface, maybe remove the existing, thoroughly abrade the existing tiles and straight over with addy (no primer)

[OchAye]

If I may demonstrate how clueless I am with tiling. Is it not the case that tiles give or take 45x45cm and larger require an adhesive that dries by chemical reaction as opposed to an adhesive that dries by evaporation (drying by evaporation will be difficult tilling over tiles). Not that I can suggest any adhesive...
Wine~o if my post is misleading feel free to slap it down please.

PS. As an afterthought, do all powder adhesives meant to dry by chemical reaction?

[wine~o]

If I may demonstrate how clueless I am with tiling. Is it not the case that tiles give or take 45x45cm and larger require an adhesive that dries by chemical reaction Yes

PS. As an afterthought, do all powder adhesives meant to dry by chemical reaction?

Certainly all the powdered (cementitious) addys available in the UK are...

Tubbed (ready mixed) adhesives are always "air dryers" otherwise they would set in the tub...

[OchAye]

Thank you Wine~o. I thought I was just about on the right track kind of thing. Over to the OP

[D215YQ]

The old tiles cant be sanded (too much noise for neighbours) but theyre old and lost their shine and absorb water so maybe just score them and theyre ok as you say..i think i may have been using a primer to reduce porosity which am i right in thinking is the wrong way? The overspill is sticking hard on non primed bits and the stuff between the graut lines too is set hard (forgot to clear those out, can you tell im new to this?).

Ive checked with the store, its compatible with all ceramic used same make with same tiles (but 33*55) when i did the whole bathroom walls with as my first job are still standing despite huge lippage and unevenness where i did my own mudding (so almost certainly air gaps).. i covered tiles too on one wall using this primer and theyre also still there. Just amazed it hasnt bonded to the tile...

Its funny as the last 10sqm ive finally managed to get very even and 0 lippage so was happy until this and now im listening for noises when i walk anywhere!

So if i did go too runny will it suddenly all fail or is it more just it will always be weaker and if it survives 2months should survive many more? And what is too weak? If theyre laid flat have some adhesion and are grauted properly might that be ok? Sorry for the endless questions...its just worrying me a bit as spent a lot of time on getting this far and 50sq m more to go...but all part of the fun i suppose...

[wine~o]

Score them with whatever tools you have to hand to break the ceramic surface, adhesion will be better. Too much water in the adhesive will weaken the bond.

[D215YQ]

Score them with whatever tools you have to hand to break the ceramic surface, adhesion will be better. Too much water in the adhesive will weaken the bond.

Thanks, I think I'm beginning to understand this a little bit better....so the weak thinset means there will be some bond, and it won't get weaker with time, it will just never be as strong as it could have been?

To finish room (just edge pieces to do) I roughed up tiles (though they are pretty rough to touch anyway - like they could hurt your finger if you rubbed it across them hard) and bought some peanut butter (not eaten the stuff in 15 years so forgot it's consistency) and realised my thinset before wasn't as thick as that. It wasn't exactly soup and held the ridges but was a lot looser than peanut butter. Lesson learnt and new tiles done much thicker and after 72h dragged a 75kg wardrobe and 50kg bed across the whole floor and no tiles are loose and no graut is cracked. So should I just stop worrying as I won't be dragging any more heavy furniture and the cement should get stronger still in the next month? Or will the weaker thinset still likely fail after a year of foot traffic so I should dig up those that were put on with the weaker stuff?

Sorry for the "how long's a piece of string?" question but it seems a bit drastic ripping them all up. It's not like I can't do the odd one or two that may fail in the fuure anyway as and when that happens as I have the tools and (hopefully) better know-how :)

Appreciate your advice as always, a great help/reassurance

[wine~o]

Basically, you've got a weak bond that won't weaken over time. Sounds like you will only disturb them by scraping lifting them.

Stop worrying for now would be my advice.

[D215YQ]

Well finished another 20sq m with thicker thinset and no primer and chipping away the excess thinset after 2 days is much harder than the weaker stuff after 2 weeks so I suppose that's a good thing. One thing I notice though with the weaker stuff is whenever I pulled up a tile to check as i laid them (not an edge piece where there's no room to wiggle it down so these seem to be worse) there was pretty much always 100% coverage. Now with the thicker stuff typically the middle seems to have the odd ridge and I'd say I'm getting about 75-90% coverage, never 100%. The floor isn't perfectly flat so I use the ridges as a guide and sometimes put a bit more here or less there and also when back buttering I do the same which might explain it, and I suppose the weaker stuff just spread out easier.

So given I can't level the floor is it better with the thicker stronger thinset at 75-90% coverage than thinner stuff at 100%? Got the final 30 sq m left so trying to perfect for these. Got to say the last bits I've done are almost perfectly level and no cracked graut/tile/looseness after over 2 weeks of use so if no future problems I'll be very happy.

[wine~o]

if you are losing 20% of the area/addy try a slightly bigger notch.

Provided your 80 odd percent is evenly spread though with small voids you should be OK.