Lesser Of Two Evils [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-20-2010, 05:34 AM
Like to hear some opinions on which way to go. I'm going to do 300 sq ft of 13 x 13 tile in Kitchen/Entry/Powderoom. I have 2 x 8 joists with 5/8 OSB. Already checked the Deflecto meter and I'm good to go. I have to keep any additional underlayment and tile combo to an additional 1 & 1/4 inch. I am going to use 1/4 CBU under the tile. Here are my 2 choices as far as I can see.

1. Use 1/2 plywood, 1/4 inch CBU without thinset underneath, then tile and thinset . That combo equals 1 & 1/4 inch.

2. Use 3/8 plywood, 1/4 inch CBU with thinset underneath, then tile and thinset. That also equals 1 & 1/4 inch.

I know Ditra is held in high regard here but I have decided against because it is three times the cost of CBU and I don't see anyway to put a grid of layout lines on it.

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02-20-2010, 05:48 AM
Hi Brad.:)

Somewhere in your equation, you need to factor in the cost of a potentially failed tile installation.:shades:

The no-thinset-under-the-CBU option is right out. Skipping the thinset under the CBU is a common reason for failure.

Option 2 might work. 3/8" of the right grade of plywood is minimally acceptable.

Ditra is still your best option to save height.

Why is the height restriction so critical?

02-20-2010, 06:36 AM
True Ditra costs more but from my perspective it is way easier to handle and a time-saver on the install.

You can snap chalk lines on Ditra just fine. Hit them with a bit of hairspray after snapping so they don't disappear on you.

If you stick with the CBU then don't skip the thinset underneath, absolutely critical to bed the CBU in thinset. Also proper fastening and using alkali resistant fiberglass tapes on all seams.

02-20-2010, 11:06 AM
Thanks for the replies guys. The height restriction is due to clearance with an exterior door. I know the clearance could be modified but it would be a PITA and unnesessary if additional height is kept to 1& 1/4.
I've never used Ditra but thought because of the corrugated nature of the product that layout lines would be difficult to put down on it.
If I were to use Ditra do you recommend putting it down immediately prior to installing tile or is it stable enough to put up with minor traffic ( a few people walking on it for a day or so) prior to putting down the tile?

02-20-2010, 11:37 AM
Hi Brad,

I usually lay the Ditra and fill the wafer holes the 1st day,then tile the next day.You'll have an easier time seeing your chalk lines in that scenario.

02-20-2010, 12:04 PM
Don't know so I'm asking, doesn't that create what would be considered a cold bond between the thinset used to fill the holes and the thinset used to bond the tile to the Ditra?

02-20-2010, 12:32 PM
Thinset mortar is designed to be used over dried/cured concrete and "mud" and other such cementitious surfaces, Brad. It's not a problem.

And Herr Schluter approves it with his Ditra membrane.

My opinion; worth price charged.