Standard mm for bathroom floor board...

[Carpello]

Hi All,

Can anyone tell me the official thickness of board to be used in an upstatirs bathroom, prior to floor tiles going down.
I have a job that involves bringing existing tiles up (and possibly the board with it) and putting new ones down.
The existing floor has signs of cracked grout so was intending on potentially having to replace the board with Hardi backer.......but at what thickness? Im guessing 12mm would be the official standard??

Anyone done a similar job? and reccomend a tile board other than Hardi to use?

Cheers

[timeless john]

From what I understand the minimum plywood required for BS standards is 15mm wbp. If the floorboards at present are in sound and deflection free condition, I'd consider 9mm plywood with an overlay of 6mm Hardie tile backer boards, making sure you cross cover all the plywood joints.

[suave]

BS is 15mm wbp (minimum)

[grumpygrouter]

From a building point of view, I understand that the board thickness is dependent on the joist spacing - i.e 600mm joists will have 22mm boards and 400mm joists can have 18mm boards though I have to confess that this is only info I have "picked up" along the way from reading some construction specs.

As the other guys have said, for overboarding for tiling purposes then 15mm is the BS minimum thickness.

[Carpello]

Thank you for your replys......if i have to put board back down will ensure it equates to 15mm.....

Cheers !!

[Rich]

Min of 15mm BWP ply and then 6mm cement board, really not worth messing about with. Also might need to add some extra noggins before the ply goes down. Seal the underside and edges of the ply, leave a 2-3mm joint between the boards (that should be staggered) and screw down about every 200mm centers. The cement boards will need sticking down with either tile adhesive or glue, depending on the brand of boards, and then screwed down. Then you should be good to rock and roll

[Carpello]

Just had a chat with a rep from a tile shop and he says.......'no need to glue/adhesive Hardi Backer down, but 200-300mm centres a must'

It seems within this industry, from top to bottom, everyone has good advice which often conflicts with others good, advice.

Im certainly not looking to cut corners in anyway but is with 200mm centre screws into the Backer board is there any need for glue/adhesive??

[Rich]

Yes, trust me on this one, that guy is speaking out of his backside and clearly hasnt put as many floors right as I have. The expanding glue or the adhesive is not there to hold the boards down, it is there to fill any voids under the boards. You really will be asking for trouble not doing it properly.


Plywood floors...

This is a post that I put up a little while ago, might give a little more info.

[Rich]

When you say he is a rep, do you mean a Hardie rep or just some1 who works in a tile shop?

[Carpello]

I phoned a popular tile shop who stock Hardi, so im guessing he is not that experienced in actually using the materials he is selling.
And by 'voids in the board' do you mean between the backer board and ply below....?

[Rich]

Yeah, you dont want any voids between the cement boards and the ply below, these can cause the tiles to crack and lift.
Most staff (not all) get plenty of training in how to sell products but very few of them have ever used them. This isnt an opinion thing, this is the manufacturers installation instructions. Iv seen a lot of trades and customers lay these boards and just screw them down because they havnt looked into how to lay them and it usually ends in tears.

[Carpello]

Brilliant advice, thank you. Just need to gather as much info as possible as this will add time to the job which will need to be explained correctly to the customer. I would rather take a bit longer knowing i am in line with manufacturers installation instructions etc.
So, just re capping (excuse my ignorance!) if i lift the existing tiles and board with it this will more than likely leave me with exposed joists?? I then put down a marine plywood 15mm min thickness (screwed into joists) then tile adhesive with 6mm Backer board on top..........???

[Rich]

Bang on

[Carpello]

Nice one!! This may explain a few things......the house is 15yrs old, so fairly modern. The existing grout is starting to crack which is what set the alarm bells ringing when pricing up the job.
I have also heard of other people in the area with similar problems in upstairs bathrooms. Im now thinking when they built the house they prob just tiled directly onto plywood of some sort and now experiencing similar problems which your thread relates to.
That thread is spot on and will now give me confidence to explain to customers on why my quotes include extra time to prepare the floor and confidence when i walk away knowing i have done everything correctly.
Once again....that thread is quality.
Thanks for your time

[Rich]

Nice one!! This may explain a few things......the house is 15yrs old, so fairly modern. The existing grout is starting to crack which is what set the alarm bells ringing when pricing up the job.
I have also heard of other people in the area with similar problems in upstairs bathrooms. Im now thinking when they built the house they prob just tiled directly onto plywood of some sort and now experiencing similar problems which your thread relates to.
That thread is spot on and will now give me confidence to explain to customers on why my quotes include extra time to prepare the floor and confidence when i walk away knowing i have done everything correctly.
Once again....that thread is quality.
Thanks for your time

I will put money on it being chipboard, see it all the time. Builders dont like to pay for ply and just get the tiler to tile straight onto chipboard because its cheap and then the floor fails


Really glad that we have helped, thats what the site is for

[Phil Hobson]

I agree with Rich on this spot on advice. I recently ripped up 3 bathroom floors in the same house. The builder had told the customer he had installed a special backer-board, imported from the US. When I lifted the first tile ( using a scraper, and very little force) low and behold, what do I find? chipboard,

[Rich]

Makes my blood boil Phil, dont know how these people get away with it

[deanotile]

http://www.jameshardie.co.uk/pdf/ins...eBacker250.pdf * *

in my humble opinion it is better to have a belt and braces than have your pants puled down. *

[Rich]

http://www.jameshardie.co.uk/pdf/ins...eBacker250.pdf * *

in my humble opinion it is better to have a belt and braces than have your pants puled down. *

I like that.