Why did my tiles and grout get loose?

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Hello,

A few years ago I re-tiled our family bathroom, laying the tiles onto backer boards (see pic below). Unfortunately after a while the (flexible) grout started splitting, with a probable root cause of the tiles becoming loose. This may in turn be due to flexibility in the floorboards below.

I'm now in the process of starting over again, at lease for part of the room, and would like some advice please on how to do a better jop this time. For starters, I noticed that while the adhesive was doing a great job of sticking to the backer boards, there is hardly any on the back of the tiles themselves.

Any help appreciated.

IMG_7085.JPG
 
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I would be inclined to say it's the adhesive.
Did you use a ready mixed by any chance?
Are tiles ceramic or porcelain?
 
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The correct way to avoid future problems starts with a solid, flattish and deflection free subfloor. When you remove everything check that there is no bounce in the floor or else you will be back in the same position at some point. Strengthen floor with noggings if there is movement. Overboard with either construction board (min 10mm) or cement backerboard (min 6mm) and run these perpendicular to your subfloor, staggering the joints. Follow the instructions for whichever board you choose. I can see in your picture that you've got a backerboard joint almost on top of your subfloor joint which may have added to your problems. Also it looks like you didn't strengthen the backer board joints after laying. Construction boards and Hardibacker needs alkali resistant mesh tape over the joints followed by a thin layer of cement based tile adhesive to cover it. No More Ply uses their Mega Adhesive to bond it to the subfloor and also to join the boards together. Prime boards using acrylic tilers primer and use a flexible cement based tile adhesive. C1 is strong, C2 is really strong, S1 is flexible, S2 is really flexible, so if you want a strong, flexible adhesive look for a C2,S2. It sounds like you didn't get a good bond to your tiles last time. Any number of reasons can be the cause such as if your adhesive is mixed too dry, backs of the tiles dusty, porcelain tiles, wrong size trowel. For tiles 300mm and above I'd use a 12mm square notch or a 20mm u notch trowel and back skim your tiles before laying. Make sure you allow at least 5mm around the edges of the room for movement which isnt filled with adhesive or grout. Have a min 3mm grout joint and use a flexible grout. Silicone floor to wall joints. Good luck this time.
 
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I would be inclined to say it's the adhesive.
Did you use a ready mixed by any chance?
Are tiles ceramic or porcelain?

Not ready mixed if I recall, and porcelain tiles.

Thanks for the advice JaimieH, I'll think it over.
 
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Was it a specific adhesive for porcelain?
I found out years ago that porcelain tiles need a specific adhesive which dries by chemical reaction.
Had to redo that job all over and the tiles came off like yours.
 
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Dont ever use ready mixed adhesive for floor tiles. Cement based powder adhesives are what you want to use. Porcelain tiles are sometimes more difficult to achieve a bond with so make sure you use a deep enough notched trowel to get good coverage and always back skim every tile before laying.
 
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