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radnrs 09-14-2008 09:00 AM

Shower floor grout cracking
Six months after installing a tile floor in our shower the grout began to crack. We removed the grout and let it dry for a month because water had gotten under the tiles then we re-grouted the floor with sanded grout (the first time we used unsanded) and used a different sealer recommended by the tile store. It has been 2 weeks since we started using the shower and the grout is cracking again. This is occurring mostly in one area of the shower. Any suggestions?

DangerMouse 09-14-2008 09:26 AM

perhaps the water underneath the tiles has weakened them to the point they shift? what is underneath the tiles? how did you mount them? you may have to pull them and redo the job. i'll no doubt get poopooed on this, but in one case, i used black waterproof caulking to 'grout' them and it's still leak free years later. (she wanted it that way, so who was i to argue?) but hey, it worked....


Bud Cline 09-14-2008 09:30 AM

Tile is not waterproof.
Grout is not waterproof.
Tile and grout together are not waterproof.

So...water under the tile is natural. Doesn't matter which grout is used, makes no difference.

I suspect you have one of two possibilities taking place - maybe both. In either event, the shower is improperly constructed and you need to call the installer.:)

radnrs 09-14-2008 10:08 AM

We installed the floor ourselves. Although we have done other tile projects, floors and shower walls, we had never installed a shower floor so we went with a custom tile ready shower base from "Tile-Basin". It is an upstairs shower so the floor under the base is wood. We installed the base as recommended with thin set under the base and ensured that it was solidly embedded in the mortar. We used tile mastic on top of the shower base and installed the tiles. The grout did not just crack it broke up and came out of the joints. I understand that some water gets under the tiles, but we unfortunately didn't notice the cracks right away and the tiles actually lifted up some in the area this happened. It's a small shower 4' x 2.5' and this is happening on the end where the shower head is. I'm thinking maybe we are having movement of the floor, why else would the grout have started cracking this soon after it was redone.

JazMan 09-14-2008 10:21 AM

MASTIC? You used mastic? Why on earth did you do that? :no:

Start by removing all the tiles and mmmmastic. Get the base clean like when it was new. Start over.


radnrs 09-14-2008 11:03 AM

My husbands idea. I'm a direction freak and the directions with the base said thin set. What should we have used.

radnrs 09-14-2008 11:17 AM

I found the container from tile adhesive. It was AcrylPro ceramic tile adhesive. My husband called it mastic. Sorry but I don't know if they are one in the same.

Termite 09-14-2008 11:26 AM

You should have used thinset. I presume that the product you mentioned is a mastic, although their website doesn't specifically call it that. It certainly isn't thinset.

You do need to tear up the entire floor and start over. Use bagged thinset mortar this time, not the pre-mixed stuff.

Also, I'm assuming (and hoping) that your shower floor substrate included some sort of drain membrane or pan to collect water that will inevitably penetrate the tile and direct it to the drain???

No amount of sealant will keep water from getting past your tile and grout. You just have to plan on it and use materials that won't degrade.

poppameth 09-14-2008 11:27 AM

Mastic is an acrylic tile adhesive. Same thing. Mastic is absolutely not to be used in high moisture areas.

JazMan 09-14-2008 11:49 AM

AcryPro is mastic, and not a very good one either. It's fine for a kitchen backsplash or other vertical dry areas. You shouldn't use any mastic for showers, even walls. Floors are absolutely out of the question. Says so on the container too.


Bud Cline 09-14-2008 12:33 PM

THAT "Tile Basin" product is "one poorly designed product" in my appraisal. So-be-it, it's done now.

The mastic was the big mistake. The instructions say "use thinset" and you didn't do it.

The next problem is the flimsy basin itself. The instructions say to install it in thinset but the unit may have a little warp in it based on what the one in the website photo looks like. The basin pictured in their website photos looks sort of cheesy. They show it being driven over by a car. Unless you plan on driving your car into your shower that's a stupid way to try to sell a shower receptor. Thinset won't take out the "quality control warp" that I suspect your unit has and thinset won't support the resulting voids that may occur under the unit. Movement in the substrate means loose and cracking grout and tile. Period.

Take out all of the tile and remove all of the AcrylPro. Check the basin for flexing. If there is even the slightest flex (and I'm betting there is) then remove the basin. It should be thrown away at that point and another method adopted. If you try to reuse the basin IT MUST BE FIRMLY INSTALLED WITH NO FLEXING.:yes: The tile is then installed with thinset according to the instructions that come with the unit.

radnrs 09-14-2008 08:49 PM

Thanks for your help. I guess we will be starting over with the floor.

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