# Forum Home Renovation Bathrooms  Ceramic Tile Underlay for Bathroom

## Gooner

I am about to install some of the JH Ceramic Tile Underlay on my bathroom foor. 
I understand that I need to have flashing on the wall/floor intersections and that I need to apply waterproofing membrane on the entire floor and at least 30cm up the wall in the non-shower areas before tiling. 
My question is, I will obviously have to lay down more than one sheet of the underlay. What do I do at the joins (on the floor)? I have not seen any instructions as to what is recommended where the underlay sheets meet.  
Do I silicone up the joins and then apply the waterproofing?  
Can I apply a wet area join compound (usually used on plasterboard) before applying the waterproofing?  
Or can I simply only apply the water proofing membrane, making sure I saturate the joins to ensure they are properly waterproofed? 
Thanks in advance...

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## Gooner

No takers on this one? 
How about this question... Should I place/cement the shower base on the tile underlay, or should I cut out the underlay to go around the showerbase and hence cement the base to the timber floor? 
I would think to cement it to the underlay, but when I pulled the previous shower base out, I noticed they cut the underlay so that the base sat directly on the timber.

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## Dirty Doogie

The jions between the underlay sheets are filled with polyurethane sealant then covered by a bond breaker tape and a bandage in the waterproofing membrane.  The shower base can go down over the underlay , perferabley after waterproofing.   
You may need to note that some shower bases need a square cutout in the flooring to accomodate the outlet block. This means you might need to cut through the underlay before installing the base.

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## Pulpo

I'm now in the same boat. 
No guide addresses the joins between the tile underlay sheets. 
Wall and floor use some fibre glass sheets with water proof membrane but the the tile underlay joins? 
I guess that nothing is needed? 
I assume its ok to place the membrane over the tile underlay? 
It will be a bugger if not, expensive exercise to rectify if not. 
Cheers 
Pulpo

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## arms

you should put a layer of the waterproofing membrane over the joins then wait the prescribed time as directed then put the full coat over the floor as required ,this will give you 2 seals over the joins

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## Pulpo

Thanks 
I was told lay some gyprock mesh tape over the joins before waterproofing. 
Pulpo

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## SilentButDeadly

In our shower area I've used Bostik Seal N Flex 1 for the joins between the sheets of both Villaboard and the tile underlay on the floor.  The Villboard wall joins have been overlaid with standard jointing compound.  The whole lot has then been covered with Bostik Ultraseal to create the water proof membrane... http://www.bostik.com.au/pdf/datashe...l_n_flex_1.pdf http://www.bostik.com.au/pdf/datashe..._ultraseal.pdf

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## zacnelson

I would recommend polyurethane sealant between the sheets of underlay. Depending on which waterproofing membrane you purchase, you may not need to use the fibreglass paper. I used Davco K10 which didn't require anything but just painting 2 coats of the membrane (but still with the sealant along the joins).  
For joins in the villaboard lining the walls, I would recommend jointing them (just roughly because it will be tiled over) with base coat like normal plaster walls, however do not use top coat firstly because it's not going to be seen and secondly because the tile adhesive will not work properly over top coat.

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## New_Renov8or

Can you please tell me what you use to hold down the cement sheeting to the existing floor? Is it glued, screwed or just free floating?  Thanks.

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## Pulpo

I used stud adhesive, either James hardie or Gyprock. 
It was glue to structafloor [sort of particle board]. 
However I have my reservations as to how well it bonded. 
I also nailed to the flooring as per instructions. 
Buy the tile underlay with the line marking for nailing. 
Good luck 
pulpo

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## zacnelson

Liquid Nails and then hand-nailed clouts at each nailing point marked on the underlay (about every 100mm)

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## New_Renov8or

Thanks for the info.  I will definitely use the glue/nail combination to lay my cement sheeting. 
One more question.....doest the fibre cement sheeting require priming prior to gluing the tiles on?

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## Pulpo

I'm not a fan of liquid nails, fulaprene 303 seems better. 
Not that I would use it for this application although you could, just expensive. 
To the question priming before tiling yes but it depends on the tile adhesive. 
After the underlay I would coat with primer like bondcrete or asa multiprime. 
Does it need to have a water proof membrane? 
This goes down next. 
Then a screed if needing a fall. 
Then prime again. 
Then tile. 
Then another job done. 
Good luck  
Pulpo.

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## arms

you should put a layer of the waterproofing membrane over the joins then wait the prescribed time as directed then put the full coat over the floor as required ,this will give you 2 seals over the joins
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## Bloss

The manufacturer says to use stud adhesive for their underlay - I have for years and it works well:  http://www.jameshardie.com.au/Produc...llationManual/ 
The instructions on waterproofing the joins are given by the manufacturers of the various waterproofing systems - and it is wise to use the method described by the brand you buy as the compounds used vary and are not always compatible with each other. 
So if you use Davco see:  http://www.davco.com.au/davco/au/ima...eet%20v1.2.pdf 
For Wet-Seal see:  http://www.wet-seal.com.au/CouncilInfo.asp 
For Masterseal  http://www.basf-cc.com.au/en/product...s/default.aspx

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## Daren

Is it ok to use just the normal tile underlay for a bathroom?
I assume the waterproofing will take care of everything. 
or is there a special wet area underlay that MUST be used?

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## bcaso

Hi everyone,  I am in the middle of tile underlaying 3 bathrooms,  have done 2 so far (hard work). 
Have glued and nailed one room to florboards and the other room to yellow tounge. with Sikaflex to all joins and gaps for a seemless finish.  Now ready for bostik ultraseal. 
I have a question though.  Should the plasteres have applied tape and stopped the villaboard in the shower,  that way I can just apply the waterproofing over the top so it is even for tiles, or should I use Sikaflex for the join ? 
in the corners there is angle behind but a gap between the sheets in some places.  I would have liked to applied sekaflex behind the sheets where the angle was but didn't get there in time. 
Should I  use sikaflex pro int the gap or should the plaster stop the corner and I then apply waterproof membrane? 
Thanks

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## Gooner

I'm not a pro, but everything I have read says to silicone up the corner gap. Thats what I doing. I do not think it makes sense to "plaster" up the corner as it will be prone to cracking. 
As for the joins between the boards on the wall, I am opting on using tape with a wet area base coat. The water proofing should take care of the rest. 
Once again.. I'm not a pro.. just going by what I have read/researched.

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## bcaso

is wet area base coat just as brittle as plaster?

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## Gooner

Brittle, yes. But assumming your sheet joins are supported from behind along a stud or noggins (as it should be) it should not be a problem.

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## bcaso

My villaboard sheet join (rebate) is horizontal without  any noginns behind  the join, between the  450mm studs.  I may have stuffed up there but I am told by my plasterer this is normal and once tiled will be fine.
Still want to hear from someone in the know, wether wet area plaster and tape is best for this join.  TA

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## Gooner

Have you read the villaboard installation guide on the JH web site? 
Quote...  _"Although not mandatory, when noggings are used it is good practice to install the nogging row in-line to enable fixing of abutting sheets."_  So you have no real problem there.   In the section on joints, they recommend " HardiStop base coat" with paper tape for tiled applications.  I also recommend the wet area construction guide on the same Jame Hardie site.

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