dude, it would then be 6mm ply screwed at 100mm squared intervals on to 25mm ply... thats more than good enough. 9mm would raise the floor too much as there is already a bad step in to the room. if i cant get a perfect lift on the old floor and it is uneven, then i will have to consider lifting the 25mm ply as well and replacing with 18mm caber flooring glued and screwed with 9mm screwed on top of that.6mm ply?!
6mm on a perfectly flat solid newly constructed floor is fine.. agreed not good enough for anything else.... christ almighty.... clint eastwood once said.... opinions are like assholes.... everybody has one.6mm ply?!
i have only ever used plywood and never had any issues at all... easy to cut.. bastard to screw down, has to be primed, but does the job. I always thought backer was too expensive.
im being double macced
my only fail with ply was an 18mm bath panel which i forgot to prime... banana within 2 days. but there is my proof that 'live' material works.... ply works.... a bath panel if primed on both sides and then tiled can last for years and years standing vertical with little support....
Not at all mate, just trying to steer you in the right direction, you've asked for ideas and in doing so we're simply pointing out that quite probably the fundamental failure here is the ply.
marine ply is more expensive but good.... i take all your points on board (ply board ?) thanks guys.. i now work for a firm so if i can find an excuse to try out backer boards, i will... cheers.
Your only supposed to prime the back face and edges of ply with an SBR to prevent moisture ingress, that is of corse if you've used WPB or Marine grade ply
you need to prime the tiled surface also to let the cement based glue bond to the plasticised ply surface.
ho stef, the job is in Musselburgh edinburgh.... really appreciate the offer.. again I know what the failure is... its the horizontal movement between the 25mm ply boards expanding and contracting. lack of overboard. however if I decide to rip it all up , I am paying someone else to do the new job so you might want to quote 🙂 going to try to get client to put up with it for a year though until i can save some money..... pass me a gun with the safety off..... never ever being a builder again, im a meticulous bathroom fitter... dealing with subbies and lazy ones at that..... no thanks.
Hardie shouldn't be used on a concrete floor.
I think they allow(ed) it in Australia. UK James Hardie say NONO!
been thinking about this thread all day.... simply put... i have never seen a tile lift from a well installed, primed section of plywood with a decent adhesive and a well laid tile. as i said, the bastard is in the number of screws you need to go through to make the ply overboard totally inflexible... and in response to aussie tiler.... you are effectively creating a cross ply section with overboarding which makes it vastly stronger. like anything, if it is done well it will last.
If it's done well it will last but not using 6mm ply.
