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ponch37300 11-10-2008 09:45 PM

ceramic over basement concrete
I would like to put ceramic tile in my basement. I have done some ceramic before but never directly on concrete. What is different in the process of laying ceramic over concrete instead of backer board? What prep do i need to do to the concrete, check for moisture, leveling, etc? I've done alot of reading but still have these questions. Does the floor have to be perfectly level or can it be a little off? Are minor cracks ok or are they going to cause problems down the road? Do i just use regular thinset? Thanks for heading me in the right way with any help!

ponch37300 11-13-2008 05:08 PM

I've done alot of reading on laying tile on concrete but still have a few questions. Like how to test for moisture if i need to, what to do about hairline cracks, if i need to use a self leveler, what kind of thinset to use? Thanks for any help with this, just don't want to lay the ceramic tiles down and have problems with them down the road. Thanks

JazMan 11-13-2008 09:03 PM

Hi Ponch,

The floor need to be flat, clean and dry. A level floor is not necessary and may not be possible. But, the floor needs to be flat, otherwise you'll have trouble unless the tiles are fairly small in size.

Cracks in the concrete must be addressed. There are many choices. There are liquid membranes, (like Redguard and several made by Laticrete and many other brands), you can also use one of the many crack-isolation thin set mortars. If there are any cold joints or control joists, you have to continue the expansion joints into the tile work. Also install expansion joints around the perimeter and in the field depending on the size and layout.

We would need more details and maybe a layout to consult further. What specific type of tile and size? Ceramic, porcelain?


ponch37300 11-13-2008 09:58 PM

thanks for the repley jazman. I'm thinking a 12" ceramic tile. You said i will need an expansion joints around the perimeter, what do you use there? Can it just be a 1/4" gap around the perimeter covered with base trim? You also said i will need to continue any control joints that are in the concrete with expansion joints in the tile. Does the tile expansion joint need to be directly above the concrete control joints? Some of the control joints are cut diagonally and probably wouldn't look the best cut into the tiles. Do you use a modified thinset or regular thinset? Thanks again for any help with this project.

JazMan 11-13-2008 10:33 PM

You have to leave at least 1/4" around the walls and also at any solid object including door jambs. Leave open or you can caulk in a color to match the grout. Large rooms also require joints in the field and doorways depending on the layout. Expansion joints must continue into the tile work directly over them. That is one reason they are often omitted and floors fail. I have yet to see expansion or control joints in concrete that are perfectly straight or square. It's a problem and most homeowners reject their use as recommended. Oh well.....

Check out The Noble Company's site and look for Nobleseal CIS. This product allows you to skip the industry standard and will bridge joints so that you continue the pattern without adding joints in the tile work.


ponch37300 11-14-2008 12:42 PM

Thanks again for your help jazman. hopefully it'll work out.

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