cracking tiles along expantion gap ?

[2020Tiling]

tiles have cracked along the expantion gap of a floor a tiled a years ago, floor is chipboard over layed with 9mm ply ( i know i used ply but rest of tiles are solid and its taken a lot of effo rt getting the cracked ones up) primmed rear and edges and staggerd boards with expantion gap . floor had 0 deflection. any ideas ? addy was ultra spf, trowel was solid bed. only thing i can think of is the expantion gap was full of spf instead of Silicon< would this be a factor ? ive took some pics for you to look at . thanks.

 

[Del W]

Looks like your expansion gap is too big,leaving a void under the addy,gap should be 2mm,plus BS is min.15mm ply for overlay.

 

[2020Tiling]

hi thanks for the repy ,the expantion gap is 2mm in other places on the floor and tiles have still cracked m8 so i dont think thats the problem

 

[2020Tiling]

also the photo with with the void had spf in it utill i scrapped it out and hooverd it out to be replaced with Silicon. wondering if a 2 part will help

 

[Del W]

Must be movement then. 2 part will be more flexible

 

[Andy Allen]

who put the chip board down. is it on joist, or is it a floating floor?

 

[2020Tiling]

on joists mate . i had to change a couple of tiles on the same floor a while back, tiles where cracked due to a stress fracture as the lad that layed the ply butted a couple of boards up, so i thought i was going to have the same problem when lifting the tiles i thought ply would be butted up also.

 

[Andy Allen]

dose sound like a deflection issue, 9mm ply is to thin as already said bs is min 15mm..

 

[DHTiling]

Stress cracks and lack of adhesive coverage is what hits me first.

You say some boards were already butted together on a previous repair.

Then lateral stress will always be present and depending on chipboard thickness coupled with thin ply then you also have defection.

So IMO , incorrect preparation of the substrate and incorrect fixing method.

 

[2020Tiling]

Fair comment dave i didnt prep floor tho, and used solid bed and back skimed, see on one of the pics the tile is fully covered and crack runs through solid bed addy on ply.so solidly fixed. totaly agree with 9mm ply being to thin, but alot of tilers i no have used it for years without any problems. fair to say i wont be using it again ... its a big learning curve which i never want to repeat . just finished redoing tiles, i put more screws in floor re cut out expantion joints that where less than 2mm ,filled with Silicon scrim taped them back buttered and fixed the tiles using webber 2 part . thanks for your input fellas , onwards and upwards