floor prepartion advice

[Burnz0]

On the advice of the kind gentleman in the builders merchants I put down 9mm ply over the floorboards in my bathroom in prepartion for tiling. I've since learnt that 9mm is not thick enough and I should aim for 15mm minimum, ideally using backerboard instead. Having spent a bit on the ply already I'm wondering if there's any way of salvaging the situation? The options are - remove completely and redo in thicker ply or ply+backerboard, put another layer of ply on top - 6mm or 9mm, or some 6 or 9mm backerboard. I can't afford to lose too much height so the thinner the better and if possible my preference is to make use of what's been done so far rathing than starting again since these things take me ages and it'll feel like a wasted effort and money if I have to remove it all - and a load of unscrewing.
Can anyone advise the best course of action? If it makes any differnce - I did the water in the middle of the room test before the ply went down and it was fine so I'm quite confident the floors pretty sturdy. I may still pay someone to do the actual tiling so I don't want the subfloor being an excuse if things go wrong in the future

 

[Andy Allen]

if the floor is deflection free, then just overboard with 6mm cement boards glued and screwed..

 

[Time's Ran Out]

If you have zero deflection use 6mm hardie boards stuck with flexible adhesive and mechanical fixings. Cross bond the joints so there is no transfer of movement through the same place.

 

[Burnz0]

on closer inspection today ive realised the floor isnt quite as solid as i first thought and theres a small amount of give when moving around leading me to think i definitely should put something thicker down to be on the safe side. If i put 6mm over the top of the 9mm thats there already is that the same as a single piece of 15mm? i can see arguments for and against it being more or less solid. Or i could go 9mm on top again to really be sure - but with backerboard over the top of this im going to be raising the floor level a fair bit.
Any thoughts?

 

[Gazzer]

Just replace it with 18mm

 

[Paulyboy]

If your floor is deflecting, then it needs sorting. I would be inclined to follow the remedies suggested above, 12mm aquapanel or hardie backer cement boards, staggered joints, laid on flexi adhesive, and screwed at 150-200mm centres. Belt and braces maybe, but at least you know your floor is fit for tiles to be laid!

 

[DHTiling]

When you say movement..?.. what condition were the floorboards in to start with..?

 

[Burnz0]

sorry, movement is probably the wrong word. Basically when you walk around you can tell you're walking on a wooden floor (although i guess that may always be the case?). I did do the water in a mug (not glass if that makes a difference?) test before and after the 9mm went down and there was no spillage. The floorboards were pretty sound and well screwed down. Im not really sure how else to tell how solid it is?
Im sure it would be fine as is but think its probably worth making sure now while ive got the chance. Could i get away with putting more ply over what ive got there already - will that have the same effect as a thicker piece in the first place?

 

[Burnz0]

movement was probably the wrong word. I just noticed today when walking over it that you can tell it's a wooden suspended floor - whether or not that's always going to be the case? i did the water in a mug (not glass if it makes a difference) test before and after the 9mm ply and there was no spillage so im reasonably confident it's pretty sound but would prefer to make sure whilst i have the chance, and its cheaper to do so. Assuming it's not too bad could i put another layer of 6 or 9mm down on top of what's there already or does it need to be a single piece of 15mm or 18mm in the first place?
also, is there anything else i can check for to test how much deflection there is or is it just something that comes with experience?

 

[Paulyboy]

As its a bathroom, cement board is a better option (IMHO), drive a few more screws into the existing floor (be aware of pipe runs), then, as mentioned above, bed 9mm hardi backer or aqua panel (if FFL is an issue) onto single part flexi adhesive, and using screws for cementous boards, fix at 200mm centres....cant make it any clearer than that!!

 

[Burnz0]

Sorry, I couldn't work out if you meant take up the ply and then do it... Sounds like the way forward. I don't suppose anyone's local to Kent and fancies the work???

 

[Paulyboy]

Where are you in Kent?.........you can send me a PM if you would prefer....

 

[Burnz0]

I'm in Gillingham, in Medway

 

[DHTiling]

Where are you in Kent?.........you can send me a PM if you would prefer....

Why .? .. so you could poach the work ..

- - - Updated - - -

Just overboard with 6mm hardibacker and enjoy your taste of tiling..

 

[Burnz0]

huh?