Help tile grout/floor [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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06-17-2010, 07:38 AM
A handyman just installed a porcelain tile bathroom floor 9x10 over 1/4" wonderboard and the grout is cracking already. How do we repair this? Do we have to remove the tiles and wonderboard and start all over? someone suggested epoxy grout, but I heard it doesn't look nice. I'm so heartbroken because the bathroom looked great and I'm worried the whole floor will start to crack.

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06-17-2010, 07:44 AM
Cracking grout is usually the result of improper subflooring. First thing, using the 'Deflecto' tool in the bar above, put in your numbers and see if the floor joists are strong enough for tile.

Did he put thinset down UNDER the wonderboard? Did he tape the seams? Did he use thinset or mastic? How wide are the grout lines? Do you know if he used sanded or unsanded grout? Is the subfloor plywood, or planks?

Unsanded grout in greater than 1/8" grout joints will crack. Other reasons for cracking are usually bad preparation or inadequate subflooring.

06-17-2010, 07:48 AM
Welcome, Ellen. :)

Give us a bit more specific time frame than "already," please.

And we'll need lots more information to help you evaluate your problem. Some pichers would also be helpful. We like pichers. :)

What is the joist structure under the floor. You can fill in the information asked for in the Deflecto in the dark blue bar near the top of the page.

What subflooring have you over the joist structure?

Was the Wonderboard installed per manufacturer's instructions, including thinset mortar under the boards and mortar and tape at all the joints?

What size tiles were installed?

What size grout joint is between the tiles?

What type grout was used? Brand name and number would be good.

We'll wait here. :)

06-18-2010, 07:07 PM
Sorry. I don't have the info yet. I'll ask my husband on Monday and get back to you. In the meantime, the tiles have only been down 2 weeks. Don't know anything about joists, etc. But is wonderboard okay to use on a floor? Now I'm even questioning that choice.

Brian in San Diego
06-18-2010, 07:17 PM

Wonderboard or any other CBU is specified for use on wood subfloors. However, there are certain installation instructions that often get overlooked or ignored the most egregious being setting the CBU in a bed of thinset prior to screwing it to the subfloor. Speaking of fastening it, some like to use less fasteners than the manufacturer recommends as well.