Complete failure of adhesive to bond - grateful for advice

[Doing My Best]

Newbie member here. I've checked the threads and I can't see the answer to this one elsewhere. Thanks in advance for any replies.

I've given myself a problem, and I'd like advice on what to do next.

Situation: DIY install of 100mm square, 9mm thick low grade tumbled trav on shower floor. Pre-formed level-access shower base is in place, and hardie backer walls + shower base all primed, taped and tanked. Electric UFH cables installed correctly.

My rookie error: I put tile adhesive (Larsen flexible standard set, S1) down on the floor to fill the gaps between the heating cables as a kind of leveller, and let it go off. Few days later I laid the trav tiles, buttering the back of each before laying, ie fresh tile adhesive going down on old stuff.

While grouting, a couple of tiles just failed, and came up. Total failure to bond at the interface between old and new tile adhesive. I see now I should have a) not used adhesive in this way in the first place, or b) sealed the dry adhesive bed first with something suitable (SBR bond etc), before laying tiles.:mad2:


Advice wanted on painful question: (Given than shower floor is half-grouted) - do I assume that the rest of them will, in time, fall off, and therefore bite the bullet and rip them all up now and replace…… (god, really don’t want to), or do I kid myself that this was a couple of rogue tiles and the rest are fine, so press ahead….

Very grateful for any views.

 

[Stef]

It's not a fixing method I would use.
You have to key the adhesive into the substrate or you will end up with what you are experiencing.
Hard call but I would try & salvage what I could at this stage.

 

[Doing My Best]

Thanks Stef

I think I'll seal the substrate properly, bed new tiles in, grout and hope for the best...

 

[Spud]

how did you mix the first batch of adhesive , if its ws too runny you may have had a layer of laitence on the surface which is extremely weak the new adhesive would pull this from the surface causing a failure

 

[Doing My Best]

how did you mix the first batch of adhesive , if its ws too runny you may have had a layer of laitence on the surface which is extremely weak the new adhesive would pull this from the surface causing a failure

Garythetiler, many thanks for your suggestion, and helping me try to diagnose this problem.

The first batch of adhesive was mixed about right, so I don't think the problem could have been a weakened surface layer. My best guess is that the dry adhesive substrate has quite a suck, so pulled moisture out of the fresh adhesive as it went down, plus maybe I didn't bed the tiles down firmly enough. I've since (non-destructively!) tested all the neighbouring tiles to the ones that failed, and they seem OK. I've therefore sealed the surface of the old adhesive substrate with SBR bond, bunged down new tiles, and so far so good.

 

[jollyroger]

Very interesting...I use a lot of 6mm Hardi backer on timber floors and tape the joints with flexible addy and let it set before tiling the floor. Should I be priming this layer before tiling ?

 

[nybor62]

i would have covered the whole floor with a slc , before tiling , it would protect the ufh cables and give a great surface ti tile onto .

 

[High Peak Tiling]

Very interesting...I use a lot of 6mm Hardi backer on timber floors and tape the joints with flexible addy and let it set before tiling the floor. Should I be priming this layer before tiling ?

I don't quite know what you mean by taping the joints with spf... but when I board a floor I tape the joints and they get filled naturally with adhesive during tile installation. I also prime the surface of the boards before tiling

 

[White Room]

I've never primed Hardie boards...

 

[Perry]

I've never primed Hardie boards...

I haven't ether Mark. But I don't use them.:8:

 

[jollyroger]

I don't quite know what you mean by taping the joints with spf... but when I board a floor I tape the joints and they get filled naturally with adhesive during tile installation. I also prime the surface of the boards before tiling

What I mean is, I put the tape on the joints, go over it with SPF, and let it set before tiling. The reason for this is I don't want my trowel pulling the tape back off when I tile the floor.

 

[Rookery]

I've never primed Hardie boards...

Me neither but I do give them a wipe over with a damp sponge to remove dust before tiling.

 

[Jelthetiler]

Good advice. Prime the life out of the original flooring, lay UFH, cover with SLC, prime again and then tile. Rather be OTT than picking up/digging up tiles.
I wouldn't switch the UFH on until 1-3 weeks after finishing the floor. I only used Warm Up wire and that's what they state for guarantee reasons.