Hello everyone,

I've tiled a bathroom floor, in a large format porcelain tile, however im having problems with the grout cracking over time. (job done about a year ago) the joints are 2mm wide, and the grout used is bal super flex. (yes i know it should only be used on joints at least 3mm wide)

The floor has had 9mm ply put on it, primed, and had a coat of latex put over a heat mat.

do mapei have a decent flexible grout, that would be more suitable?

hi jon,i would be more concerned why the grout was cracking....you may be right it may be as they say it should be 3mm minimum however 9mm ply isnt thick enough and that may be your root cause

try bal non flexi grout and mix it with gt1 admix tghis is the strongest solution i can come up with hope it works let us know

I think it might be substrate prep that is the problem here.. if you have deflection issue then the grout will crack, no matter who's brand you use.

I must admit im nervous of the job, when i had a look today about 6 tiles had the grout cracking around it. But not in the high traffic areas which was surprising to me. I also noticed large amounts of cracking over the skirting boards, and she said they've had a lot of building work done to the house, which maybe the cause. But i dont want replace the cracked grout with the same stuff if its only going to happen again. I do have some gt1 in the van, just dont like using the stuff!

So you didn't tile it originally.?

As said there could other issues causing the grout to crack.

Yes i tiled it last year, the couple were doing the house up at the time, new kitchen etc.....

Im normally very good when it comes to customer care, and i don't mind re-grouting the floor (10m2) as the grout i used, technically was the wrong stuff. But i would rather find the solution to the problem rather than keep going back again and again

I agree, about finding why it has happened..

Sounds like really weak subfloor you had to start with, where it's cracking rake out joints and fill them with sbr bonding agent, let it dry for a day, then grout it with flexy grout, if that will not help, then you best bet is to lift 1 tile and see the problem yourself
good luck

cheers for that info, can you tell us a little more about this sbr bonding agent?? exactly how do i use it?

I'm going back there Friday morning to repair the grout.

You say the grout is cracking, are there any tiles loose? They normally go hand in hand. I'm not convinced a re-grout will solve the problem if there are, as mentioned above, underlying problems with the substrate.

There were NO loose tiles, when i checked on Monday to my surprise!

However i did change 1 tile about 4 weeks after doing the job, it was the very first tile as you walked in the bathroom, the grout had cracked around it like the rest, but i just put it down as 1 of those things, heavy traffic or not stuck down properly. I remember having a right job beating the old adhesive out, because of the UFH. But when i looked on Monday it was fine. i will take a few pictures on Friday and post them up, so you can see for yourself.

To have a 2mm joint on a timber floor with UFH has, IMO, been part of the cause of the cracking. BS states a minimum of 3mm for floors anyway and when you add a flexible substrate with UFH I personally would have gone no less than 4mm. But, as it is already down I don't think you have many options in your remedial actions. BAL standard grout with GT1 admix or Ardex stuff with their admix may well be the only way to go. I do feel though that the problem will re-occur because of the substrate and the joint width.

as above 9mm ply is the issue here if its re grouted im sure it will fail again

Well i've just returned, and had a tile up, the latex has pulled away from the ply. I don't think i have ever seen that happen before, the latex is well with-in normal thickness 5-10mm, but it has cracked and lifted. it appears to be half the floor that is effected. I have asked the customer if they have had any works done to the house, which they assure me they haven't. I no they have had a set of french doors fitted to the rear, so i thought maybe the building company used stilts to support ceiling which may have pulled the floor out of shape. either way, the only for this to be fixed is to have the loose tiles removed and re-layed. Is it possible to hack away the loose latex around the UFH (about 3m2) and put another coat of latex down?

As I'm still unsure wot has caused the latex to lift, I'm worried that I'll do all this work, and it will happen again?
I want to put this right, but at the moment it has cost me a days wages so far, and i don't want to continue the works for free, if its not my responsibly.