Cracked Grout

[sparky]

just tiled a mates kitchen floor used grey wide joint flexible grout with a 4mm spacer told him to leave it for 24 hrs before cleaning but he told me today that the floor s grout has fine cracks apearing already he also told me that he washed it aftrer 12 hrs could this be causing the cracks i also laid 9 mm ply on the advice of a joiner he knew that says my 12mm ply was a bit over the top and that 9mm would be fine i had my doubts and told my mate that it was his choice but i ve been told 12 mm very least so i think maybe the floor is moving causing this which one do you think it will be

 

[DHTiling]

what substrate did you ply over

 

[tony TLC]

depending on the sub floor you can get away with using 9mm ply and 2 part flexy but did you use flexy grout too?was there movement in the floor?and washing the floor after 12 hours should not have done any damage to the grout washing too quickly will weaken grout but 12 hours is plenty hope this helped

 

[Varley]

Also what type of tile was it?

 

[sparky]

plyed over tounge & groove the tile was porcelain

 

[GazLC81]

How far did you space your screws?

 

[lm tiles]

when you washed your floor was there too much water on your sponge leaving sall puddles in the grout lines

 

[DHTiling]

if the grout is cracking this quick it could be down to excessive movement in subfloor.
9mm ply is only ok on floors that are ridged, Or the grout was mixed to dry causing it break away from tiles edges.........