# Forum Home Renovation Waterproofing  Bathroom floor 101

## paddyjoy

Doing some planning for my first level bathroom and would appreciate it if someone could give me a 101 on bathroom floors. 
What does a typical bathroom floor consist of? FC sheeting, screed,  waterproofing, adhesive and tiles? 
If all the other rooms on the level have yellow tongue and t+g flooring would I continue the yellow tongue under the bathroom or would it be best to omit the yellow tongue to reduce the finished floor level of the bathroom? 
Thanks

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## Overkill

I'm no expert, but I just had to do the same thing as you. 19mm FC sheet is the best flooring to use; yellow-tongue is used where builders want to save money but its decidedly inferior to FC in a bathroom. Do you know what the existing floor is, or is this a new bathroom? The FC is the same thickness as your other flooring, but after you add screed and tiles. the floor level at the door will likely be 20 to 30mm higher. I thought that would be a huge issue but in practise, I have never tripped on it. If you are starting from scratch, you could cut into the floor joists by 15 to 20 mm to get the finish floor height closer to the rest of your floors, but I'm no longer sure its worth the effort.

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## Gaza

19mm James Hardie sycon you will love it so much lighter than Cfc  
Normal have set down with joists too so that when screed finish floor level is flush with rest of house, ie normal joists 240mm use 200 mm in bathroom but you may have trouble as for memory your joists are long lengths where we normal use joists that run shortest distance   
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## phild01

> Doing some planning for my first level bathroom and would appreciate it if someone could give me a 101 on bathroom floors. 
> What does a typical bathroom floor consist of? FC sheeting, screed,  waterproofing, adhesive and tiles? 
> If all the other rooms on the level have yellow tongue and t+g flooring would I continue the yellow tongue under the bathroom or would it be best to omit the yellow tongue to reduce the finished floor level of the bathroom? 
> Thanks

  Not making much sense about your existing flooring as you say yellow tongue and t&g.  Does this mean t&g over yt as you are talking about rebating with a reduced floor height.  What you say isn't making sense to me when you mention omitting the yt to do this.  Anyway, don't use yellow tongue in a bathroom.  There was another coloured tongue for bathrooms but I forget what it it is and may no longer be made.  However, just use Scyon secura as already mentioned.  It's a bit lighter than compressed cement, but far easier to work and more manageable.

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## paddyjoy

Thanks everyone, sycon followed by screed seems like the go then. 
Yes my joists are long and need to be continuous over the red supports so cutting into them probably isn't going to be an option unfortunately. Not a big deal I'll just have to live with the step up and hopefully the design authority will accept it! How thick is the screed usually 10mm?

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## paddyjoy

If I have my drain 1m in from the bathroom door and a fall of 1:100, tile thickness of 10mm + 3mm adhesive, screed thickness of 19mm reducing down to 9mm it seems like best case the step up will be 13mm.   
Is there a way I could ditch the 19mm sycon and use 6mm fc sheeting supported by installing blocking or something similar between the joists?   
The step up isn't a big deal but it is bugging me a bit and I know there will be a request to make everything flush ;-)

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## phild01

> Is there a way I could ditch the 19mm sycon and use 6mm fc sheeting supported by installing blocking or something similar between the joists?  
> The step up isn't a big deal but it is bugging me a bit and I know there will be a request to make everything flush ;-)

  Flush is best, but a simple NO to 6mm, can't be done.  The screed offers very little additional strength.  You might be able to get a couple mm back by using 15mm compressed cement sheet.  Maybe your joists can be removed and replaced with a higher grade F27. 
Just checked your drawing.  Step up can be reduced by moving floor waste closer to door.  9mm too thin for screed, although placing a gal reinforcing micro type mesh would help with a thin screed.  I did this when I first did my bathroom and it is still perfect after more than 20 years on a water rated particle board floor.  I suggest scyon and bondcrete a thinner screed (with flexual additive) to it, but waterproof over the screed, not under.            
o

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## phild01

its late, sorry.  you have 19mm yt with 22mm t&g at a guess.  seems floor waste is not far from door.  Even with thicker Scyon, carefuk screeding, your tile level would be barely above your existing floor level and maybe 15mm cc sheet is a better choice.  As I see it 15mm will leave around 25mm for screed and tiles.

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## Oldsaltoz

You could us a self levelling compound with a little clay free (washed) sand added, it can be only a few mm thick without risk of cracking. 
Good luck.   :Smilie:

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## paddyjoy

> its late, sorry.  you have 19mm yt with 22mm t&amp;g at a guess.  seems floor waste is not far from door.  Even with thicker Scyon, carefuk screeding, your tile level would be barely above your existing floor level and maybe 15mm cc sheet is a better choice.  As I see it 15mm will leave around 25mm for screed and tiles.

  Thanks yes that's right I would have about 25mm, if it's only a few mm above the timber floor level then I think it would be barely noticeable. 
Would it be an option to install the fc sheet slopped and ditch the screed? 
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## paddyjoy

> You could us a self levelling compound with a little clay free (washed) sand added, it can be only a few mm thick without risk of cracking. 
> Good luck.

  Thanks does the self levelling compound go down instead of the screed?

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## Overkill

> Thanks everyone, sycon followed by screed seems like the go then. 
> Yes my joists are long and need to be continuous over the red supports so cutting into them probably isn't going to be an option unfortunately. Not a big deal I'll just have to live with the step up and hopefully the design authority will accept it! How thick is the screed usually 10mm?

  You could probably still notch the joists and bolt on secondary joists to make up the strength; it might be as easy as using structural ply.

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## paddyjoy

> You could probably still notch the joists and bolt on secondary joists to make up the strength; it might be as easy as using structural ply.

  Thanks I'm just concerned because the bathroom walls will be holding up the roof so I don't want to do anything that will reduce the capacity of the floor, but if the strength could be made up add you suggested then it could be an option.

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## shauck

You really want to double up the joists under the bathtub anyway. It's going to weigh a lot when full of water and one or two of you soaking.

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## paddyjoy

> You really want to double up the joists under the bathtub anyway. It's going to weigh a lot when full of water and one or two of you soaking.

  Thanks I have one double joist specified under the bath, hopefully the one is enough.

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