Preparing subfloor for ceramic tile

syogod · 06-19-2011, 01:06 PM

I just had a quick question about preparing my subfloor for ceramic tile.

After lots of research, I got my floor joists where they need to be, structurally.

My current subfloor is 7/8" thick planks. My current plan is to put down 1/2" plywood over that to get a flatter surface, then, 1/4" hardibacker over that. Will this be sufficient? Or overkill?

JazMan · 06-19-2011, 10:18 PM

That's not overkill, it's what I'd recommend. Be sure to use the right plywood and install it correctly. Don't forget the thin set under the Hardie too.

Jaz

syogod · 06-20-2011, 05:27 PM

Great! that's exactly what I was hoping I'd hear.

One question though, what is considered the right plywood? And how should it be installed correctly? Just screw it into the floor joists every 12" or so?

Bud Cline · 06-20-2011, 05:38 PM

Use "underlayment quality exterior-grade" plywood.
DO NOT screw it into the floor joists. Attach it only to the subfloor material deliberately missing the floor joists.

JazMan · 06-20-2011, 05:43 PM

Quote:

One question though, what is considered the right plywood? And how should it be installed correctly? Just screw it into the floor joists every 12" or so?

Absolutely..........not!

The right plywood should be labeled as underlayment grade having the plies glued together with a waterproof glue. Do not use cheap sheathing grade such as CDX. The sheets are oriented with the face grain running across the joists as always, and fastened only to the subfloor, not the joists too. Leave about 1/8" between sheets and 1/4" around the perimeter.

Follow the thin set manufacturer's instructions about whether to fill the 1/8" gaps between sheets or not. Leave the perimeter gaps open.

Then install the backer board per directions. Then the fun part.... the tiles.

Jaz

syogod · 06-20-2011, 08:57 PM

Good thing I asked! Thanks guys.

This leads me to two more questions though.

1) Lowe's seems to only have 1/4" underlayment grade, can I just double it up? Or should I go looking elsewhere for 1/2"?

2) More for my curiosity than anything, what's the reason for not screwing into the joists? Does it have something to do with expansion/contraction and warping (just my guess)?

Bud Cline · 06-20-2011, 09:51 PM

Quote:

1) Lowe's seems to only have 1/4" underlayment grade, can I just double it up? Or should I go looking elsewhere for 1/2"?

They have it. Do not use 1/4". Quarter inch underlayment is strictly forbidden for use under a tile installation. Look for "BC Exposure 1".
There is more than one way to label the underlayment grade products but I'm positive they have it.

Don't expect those characters working there to understand, they usually don't.

Quote:

2) More for my curiosity than anything, what's the reason for not screwing into the joists? Does it have something to do with expansion/contraction and warping (just my guess)?

Good guess. It has to do with allowing a little separation between the tile installation and the structure. I know I know, it is arguable but that's the standard.

syogod · 06-22-2011, 01:55 PM

I found BC Exterior on the website, assuming I can't find Exposure 1, I'm assuming this is fine?

Should I be using screws or nails for attaching to the subfloor? Also, what about glue?

Bud Cline · 06-22-2011, 01:58 PM

Quote:

I found BC Exterior on the website, assuming I can't find Exposure 1, I'm assuming this is fine?

That will work.

Quote:

Should I be using screws or nails for attaching to the subfloor?

I prefer screws.

Quote:

Also, what about glue?

No glue.

06-19-2011, 01:06 PM	#1
syogod Member Join Date: Feb 2010 Location: southern Indiana Posts: 44	Preparing subfloor for ceramic tile I just had a quick question about preparing my subfloor for ceramic tile. After lots of research, I got my floor joists where they need to be, structurally. My current subfloor is 7/8" thick planks. My current plan is to put down 1/2" plywood over that to get a flatter surface, then, 1/4" hardibacker over that. Will this be sufficient? Or overkill?

06-19-2011, 10:18 PM	#2
JazMan Tileguy Join Date: Feb 2007 Location: Troy, Michigan Posts: 3,287	Preparing subfloor for ceramic tile That's not overkill, it's what I'd recommend. Be sure to use the right plywood and install it correctly. Don't forget the thin set under the Hardie too. Jaz __________________ Tile 4 You LLC Troy, MI KERDI Shower Specialist ... DITRA Installs ... Product-Method suitability consultation. I have NEVER made a mistake, I thought I did once...........but I was wrong! - PRODUCTS ADVERTISED WITHIN MY POST ARE NOT ENDORSED BY ME!

06-20-2011, 05:27 PM	#3
syogod Member Join Date: Feb 2010 Location: southern Indiana Posts: 44	Preparing subfloor for ceramic tile Great! that's exactly what I was hoping I'd hear. One question though, what is considered the right plywood? And how should it be installed correctly? Just screw it into the floor joists every 12" or so?

06-20-2011, 05:38 PM	#4
Bud Cline Tileguy Join Date: Mar 2006 Posts: 9,104	Preparing subfloor for ceramic tile Use "underlayment quality exterior-grade" plywood. DO NOT screw it into the floor joists. Attach it only to the subfloor material deliberately missing the floor joists.

06-20-2011, 08:57 PM	#6
syogod Member Join Date: Feb 2010 Location: southern Indiana Posts: 44	Preparing subfloor for ceramic tile Good thing I asked! Thanks guys. This leads me to two more questions though. 1) Lowe's seems to only have 1/4" underlayment grade, can I just double it up? Or should I go looking elsewhere for 1/2"? 2) More for my curiosity than anything, what's the reason for not screwing into the joists? Does it have something to do with expansion/contraction and warping (just my guess)?

Preparing subfloor for ceramic tile