Hi all

Got a couple of bathroom floors to tile on monday i'm laying down 12mm WBP ply onto old floorboards just wanted to check 5mm expansion around room 2mm between boards...prime underside of ply with SBR and what about screwing 300mm centres but through the board into the joists or only into the floorboards? what type of screws? thanks.

into floorboard only mate or your luck will run out one day and you'll hit a pipe. I use turbo screws

I was blamed once by customer for putting screw into pipe under ply which i layed in bathroom prior to tiles,plumber told her i done it 2 days after i finished,oh and that i had turned her hot water off in attic !! (some hope! )
Anyway a lot of damage done but i had 12mm ply onto 18mm floor boards and deliberately used 25mm screws to avoid such probs,i proved my innocence easily enough,plumber was one bad ass mother**** !

If the floorboards are sucured to the joists then you can fix to them, if not then imo you need to fix floorboards first then secure ply to boards after sealing as you have said, i go the extra mile and use screwfix stainless steel screws, probably overkill but dont want the screws to corrode and creat a bouncy floor do we.
Being a plumber i screw into joists knowing where all the pipes and cables are (marking out on the ply areas to avoid etc. But like the others have said if you cant see under every board to check you will be unlucky one day.
Gary

, jmc;.vcx;m,v]cijmf,.;cpodiujdm clxdosiuhb

Originally Posted by doug boardley

, jmc;.vcx;m,v]cijmf,.;cpodiujdm clxdosiuhb

Clear as mud Doug.

all sounds right to me pal, would use 25mm screws, and stagger the joints of the ply boards,

If theres flex in the floorboards you have to scew them down. I think if it can be screwed down then screw it. yes if its chip board flooring its hard to locate the joists. i think they use ring nails a lot of the times. I rather have a few screws in myself. go as close as you can to the nail and screw in should be ok. Failing that let the customer do it if you can. Personly i never use ply I always recommend no more ply.

hello mate you will be better off useing Backerboard instead of ply and fix every 150mm

Originally Posted by Gazebo

Clear as mud Doug.

no idea what that's all about! wasn't me!

Originally Posted by doug boardley

, jmc;.vcx;m,v]cijmf,.;cpodiujdm clxdosiuhb

Well it wasnt me, must be the phantom keyboard mice.

whenever I ply a floor I preffer to ply every 100mm or 150mm max.

Even if you use screws that are less than the depth to both ply and floor boards (e.g. 18mm floor and 12mm ply = 30mm and only use 25mm screw) you can still hit plumbing as remember the screw needs to countersink into the subfloor so, it can at times be possible to hit a pipe if you countersink too far. (some times floor boards are checked out on the underside to accomadate for pipes therefore making the board thinner)