# Forum Home Renovation Tiling  Tiling over masonite

## JontyG

Hi All, 
I am soon going to be laying ceramic floor tiles in our kitchen (~12sqm). The area currently has 4mm masonite over pine floorboards (used to have lino over the masonite). 
Would it be advisable to remove the masonite before laying the CTU, or could I lay the CTU over the masonite? 
The masonite is VERY securly nailed and glued down, and is a nightmare to lift - I've lifted some small areas with a sharpened spade (quite effective) for installing new cabinets. 
Also, I don't want the total height of the newly tiled floor to exceed 23 - 25mm, which is going to be the height of the abutting T & G floor (4mm ply + 19mm T & G). Is this going to be possible if I leave the 4mm masonite in place? 
I'm hoping the layers will pan out something like this:
Masonite - 4mm
CTU - 6mm
adhesive - 6mm 
tile - upto 9mm 
Does this seem feasable? 
Thanks in advance for any advice, 
Jonty
PS: Does anyone have any recommendations for good tile suppliers in Melbourne? Thanks!

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## mic-d

It's OK to lay the ctu over masonite.  It might be an idea to seek installation recommendations from the ctu supplier, but for hardies ctu the recommendation is to glue it down with acrylic stud adhesive as well as nail it when you have particle board or ply underlay.  I use a 3mm notch trowel and apply it over the entire back of the sheet. 
Chhers
Michael

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## JontyG

> It's OK to lay the ctu over masonite. It might be an idea to seek installation recommendations from the ctu supplier, but for hardies ctu the recommendation is to glue it down with acrylic stud adhesive as well as nail it when you have particle board or ply underlay. I use a 3mm notch trowel and apply it over the entire back of the sheet. 
> Chhers
> Michael

  Thanks Michael.  
Excuse my ignorance  :Blush7: , but does using a 3mm notch trowl mean tht the glue will add a 3mm layer to the overall height of the floor? 
thanks,
Jonty

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## addo

No, that's the width of the square shaped "peaks and troughs" on the trowel edge.  It should squish down to a mil or less when the job's done correctly.   
Cheers, Adam.

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## mic-d

> No, that's the width of the square shaped "peaks and troughs" on the trowel edge.  It should squish down to a mil or less when the job's done correctly.   
> Cheers, Adam.

  yeah that's right, and you hold it at 45º. 
cheers
Michael

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## scottyb

Similarly, your tile adhesive bed will be a lot less than 6mm once the tiles are down - more like 2mm.  I understand why you're not wanting to lift the masonite, those vinyl layers go ape with staple gun when installing masonite.

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## bob w

If it is masonite underlay it will be 5.5mm thick and the manufacturers instructions are strict when it comes to fixing, so yes there will be "lots" of staples or ring shanked nails. These sheets are only 1220x915mm by the way.
If your sheets are larger than this it will be standard or maybe tempered masonite and could well give heaps of heartache if you put additional layers over it. What may happen is by adding ceramic tiles and its underlay you form an impervious barrier that will cause the moisture that rises from the sub-floor to build up under this barrier and that is just where the masonite is. You will therefore have a "drummy floor" due to the masonite buckling. I know its a major job but I would be lifting the masonite and starting from floor level.
You stated it was glued down, this is also contrary to all fixing instructions that I know of and again would make me cautious. :Frown:

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## JontyG

> If it is masonite underlay it will be 5.5mm thick and the manufacturers instructions are strict when it comes to fixing, so yes there will be "lots" of staples or ring shanked nails. These sheets are only 1220x915mm by the way.
> If your sheets are larger than this it will be standard or maybe tempered masonite and could well give heaps of heartache if you put additional layers over it. What may happen is by adding ceramic tiles and its underlay you form an impervious barrier that will cause the moisture that rises from the sub-floor to build up under this barrier and that is just where the masonite is. You will therefore have a "drummy floor" due to the masonite buckling. I know its a major job but I would be lifting the masonite and starting from floor level.
> You stated it was glued down, this is also contrary to all fixing instructions that I know of and again would make me cautious.

  Hmm, thanks for that. 
I have looked at the sheet again. Seems it is more like 6mm. I am struggling to find a full size sheet, but the measurement you give seems to be about right (1220 x 915). The sheets are fixed with ring shanked nails...and circular patches of glue. 
If I remove the masonite, I still have the issue of trying to get the newly tiled floor to the same floor height as the abutting T & G floor. Any suggestions on the best way to have the tiled floor sitting 23mm high? Is the CTU available in different thicknesses? I've only seen it in 6mm. 
Also, is it going to be necesary to remove the remnants of glue and masonite that are left behind after removing the sheets of masonite (the attached pic illustrates what is left behind when i remove the masonite). These are raised up to about 2mm?  
Cheers,
Jonty

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## bob w

I can't see any reason why you would have to remove the residue of glue or board as the ctu should bridge the lumps so long as they are not right on a joint where they may lift one side more than the other and form a lip. 
As for a thicker ctu I can't answer that question but a quick look at the hardies or other manufacturers site should make all clear. If they don't make a thicker board you may have to settle for one of the compressed sheets which come in varying thicknesses and should do the job.
Good luck. :2thumbsup:  :2thumbsup:

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## Dirty Doogie

Jonty  I would suggest selecting your tiles before calculating how to bring the levels up. Floor tiles range in thickness from 6mm  up to 20 mm. I would go so far as to actually buy your tiles - I got caught a short while ago - different batches in the same tile range are different thicknesses .

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## JontyG

> Jonty I would suggest selecting your tiles before calculating how to bring the levels up. Floor tiles range in thickness from 6mm up to 20 mm. I would go so far as to actually buy your tiles - I got caught a short while ago - different batches in the same tile range are different thicknesses .

  Good tip, thanks  :2thumbsup:

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