Mending cracking floor tile grouting

JohnB47

Any advice on this? We had an idiot fit our bathroom a few years ago and he used the blob system when laying the large floor tiles over electric under floor heating (UHF).
This has resulted in the grouting cracking here and there and cold spots.
In one part, at a corner, the grouting has completely disappeared leaving a small hole and I can see the UHF matting through the hole.
So, how to fix?
My first idea is to buy tile grouting power, mix it fairly sloppy and use a squeezable bottle, fitted with a small pipe, to squeeze grout in through the hole and hope that it spreads around to fill up the void.
I could instead do the same using tile adhesive powder. Edit: or maybe self levelling stuff?
Is one likely to be better than the other? Should I use a grout or adhesive specially made for UHF (if it exists and if it can be made up sloppy)?
Any other thoughts?

andyhop

Very short term fix

The UFH wire should be fully encapsulated, without adhesive or screws around it it will eventually burn out 

JohnB47

andyhop said:

Very short term fix

The UFH wire should be fully encapsulated, without adhesive or screws around it it will eventually burn out 

Surely not. Also, screws?

Boohoo

JohnB47 said:

andyhop said:

Very short term fix

The UFH wire should be fully encapsulated, without adhesive or screws around it it will eventually burn out 

Surely not. Also, screws?

Maybe andy meant to put in the word screed instead of screws?

andyhop

Meant to say SCREED!

Mickey666

JohnB47 said:

andyhop said:

Very short term fix

The UFH wire should be fully encapsulated, without adhesive or screws around it it will eventually burn out 

Surely not. Also, screws?

Yes, because the system relies on the wires being able to easily lose heat to the floor through the screed/grout.  Any air gaps will effectively insulate the wires (air is a good insulator) and so they will overheat with the risk of burning out.

Unfortunately, you were right about the fitter being an idiot.

JohnB47

Thanks everyone. Any comments on my ideas for a fix, however temporary?

Mickey666

Your idea of using a sloppy grouting mix and forcing it into the gaps sounds ok under the circumstances, given the alternative of lifting the tiles (which may not even be possible with breakages) but it will be impossible to know if you've fully filled all the voids under the tiles.  Indeed, depending on how the 'dot-and-dabs' have been laid out, it's possible there will be voids that cannot be reached by the grout lines.  The problem is that you'll never know for sure.   Even so, it doesn't seem like there's much to lose by trying - worst case is that it won't do much good but at least you won't do any harm.  If nothing else, at least the grouting will look ok, then it'll be fingers crossed that the UFH doesn't fail.

JohnB47

Mickey666 said:

Your idea of using a sloppy grouting mix and forcing it into the gaps sounds ok under the circumstances, given the alternative of lifting the tiles (which may not even be possible with breakages) but it will be impossible to know if you've fully filled all the voids under the tiles.  Indeed, depending on how the 'dot-and-dabs' have been laid out, it's possible there will be voids that cannot be reached by the grout lines.  The problem is that you'll never know for sure.   Even so, it doesn't seem like there's much to lose by trying - worst case is that it won't do much good but at least you won't do any harm.  If nothing else, at least the grouting will look ok, then it'll be fingers crossed that the UFH doesn't fail.

Thanks. Any thoughts on best material to use - grout, adhesive or leveller? What not to use? 

Mickey666

Not really, I've never done anything like this before.

It doesn't sound like you need adhesive as such and I'm not sure it would respond very well to a very sloppy mix anyway. 

Leveller is designed to flow freely so might be a good bet for really spreading well under the tile gaps, but probably not good as a grout, so might be best to leave enough space to grout over when it has set.

A really sloppy grout might work, but again I've never tried such a thing.

Good luck with whatever you choose!