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GeauxCajuns82 11-18-2010 11:58 AM

Adhesive for large ceramic tile over concerete slab
I'm about to install 16" x 16" ceramic tile on my kitchen floor and need a recommendation for the adhesive. I've done a little research that suggests using a medium base mortar for floor tiles larger than 12" x 12" because it can be applied thicker to account for any imperfections in the sub-floor. My slab certainly isn't perfect so this seems like the logical choice. Unfortunately this isn't a stock item at either of the two big box stores in my area. All they have are "fortified thinset mortars" with various grades ranging from $13 to $30 for a 50 lb bag. Will these work for my application or do I need to visit an actual flooring store to obtain medium base mortar?

Also, what is the difference between the various adhesives offered for tile?

JazMan 11-18-2010 04:36 PM


Take a long straight edge 8-10' or chalk line to measure how much out of plane the floor is. It still needs to be very flat esp. with large tiles like that. The standard for concrete floors is within 1/4" in 10 ft. and 1/16" in 12" of the required plane. It used to be 1/8" in 10', but the cement workers had a hard time meeting that. With large, smooth or shiny tiles, you really need the old standard if at all possible. You may need to do some extra prep work.

The big box stores probably have medium bed thin set mortar, they just don't know it. The orange place has Marble & Granite as an example of a medium bed mortar. It would be smart to visit a real tile store regardless.

How's the condition of the floor? Any cracks? What's the plan for that?


GeauxCajuns82 11-18-2010 05:13 PM

I did a little research and the local big blue store carries Mapei Ultracontact mortar which is suitable for the larger tiles (according to Mapei's website at least). I'm assuming that's a medium base mortar from the description.

As for my floor, the area is 30' x 14' and has a small crack right through the center of the room. I've got plenty Aquadefense (waterproof membrane) left over from when I did the counter top tiles and I will spread it on each side of the crack. House was built in 78' and the crack has been there since I bought it 5 years ago. I haven't checked the floor with a straight edge for any imperfections but I'll do that tonight. If it doesn't conform to the standard what should I do? Use leveling compound?

Thanks for the help.

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