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MARVIN M 07-07-2009 03:06 PM

washroom reno questions
hey guys,

heres some info on the reno im doing..

10ft x 7ft washroom 1954 2 story house canada

ive gutted the room down to the studs and joist.. fernaco'd cast iron to pvc 3in for toilet 1 1/2 for tub/sink drains.. cleaned up plumbing with pex.. got rid of knob and tube rewired electrical for gfci, fan and lite.. ran 14/2 to panel with 15 amp breaker for heated floors.. sistered and braced my 2x8's 16o.c. joist.. glued and screwed 3/4 plywood.. insulated and vapour barrier walls.. just boarded up walls with the blue board and in the middle of tape and mud..

questions i have is when i finish with the walls after prime/painting and start building my box for my drop in tub.. will it be a problem to put cement board on top of the painted walls and deck for the tub/shower area???.. afterwards modified thinset, kerdi then unmod with 6x6 porcelain tiles.. or can i go straight to kerdi then tile without the cement board??

for my floors i will be laying a 6in kerdi strip along the corners of the wall and floor.. heated mats on top of the plywood with modified thinset.. ditra with unmod.. then 13x13 porcelain with unmod again.. but before i lay the ditra and scratch it wont that damage my mat?? is the 6in kerdi a waste of time??

i think those are my main questions for now.. so any help would be gratefull


Blondesense 07-08-2009 11:53 AM


Originally Posted by MARVIN M (Post 298573)
will it be a problem to put cement board on top of the painted walls and deck for the tub/shower area???

Perhaps you can give a bit more detail here. You mention a drop in tub. Is the shower going to be above the tub, or will the shower be totally separate unit?

Is blue board the same as what is called green board here in the U.S.? I've been reading these forums because I'm planning or re-doing my shower soon. I'm not an expert by any means but I understood green board is OK for the wall above a tub, if it is a tub only, but is no longer installed in wet areas, like a shower or tub deck at all.

Maybe I'm just misunderstanding your plan.


MARVIN M 07-09-2009 02:52 PM

yes the shower head is directly over the drop in tub..

i think they discoutinued green board and replaced it here with the blue board.. not really sure though..

i have the blueboard around the walls for the shower/drop in tub, but i plan on covering it with cement board then water proofing it with the kerdi.. then my tiles.. the box will be built with 2x4's with ledger and 1/2 in plywood afterwards cement board for the 32 x60 tub..

i can show pictures.. but i dont know how to upload them..

Bud Cline 07-09-2009 03:15 PM

In my experience greenboard has always been made of a moisture resistant formula and suitable for walls in areas of high humidity. Greenboard has been outlawed for use in wet areas such as showers.

Blue-board on the other hand is intended for a substrate for a plaster application with a moisture resistant paper cladding.

At any rate KERDI is warranted over all of it. I wouldn't do it personally but the KERDI-maker says I can.:)

Bud Cline 07-09-2009 03:17 PM


...the box will be built with 2x4's with ledger and 1/2 in plywood afterwards cement board...
And after that a waterproof membrane I hope.:yes:

MARVIN M 07-09-2009 03:48 PM

whoops.. forsure ill apply the kerdi over the box..

i went on site.. and it says i can go over primed painted walls.. i dont know if it would be a good move not to put the cement board up and then the kerdi

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