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New Bathroom Grout Cracking

7 replies [Last post]
Joined: Aug 30 2003

Three months ago we had new tile installed around the tub/shower in our bathroom. The grout is cracking in two places.

The tile was installed using greenboard. I have since learned that greenboard is not the best backing for longterm support of the tile - if the greenboard gets wet.

My question: Is cracking normal? Will the cracks now allow water to seep in behind and damage the greenboard?

Thank you,

R. Brisco

1959 A. Quincy Jones atrium model in The Highlands, San Mateo

Joined: Aug 12 2004

Yes and no, cracking is normal.

Yes, as all will crack in time.

No, as in too soon. Shows movement.

It's all to do with the foundation or backing. The more stable it is, the longer it will go before cracking, but it will crack over time.

The best backing is mortor/cement on chicken wire over the greenboard/cement board that is nailed to the studs. Then either mastic or mortor to hold the ceramic tiles.

Then just cement board.

Then just greenboard.

It all has to do with the amount of movement the foundation surface has.

Nothing to be done about it now, other than to tear it out and redo.

Joined: Jan 29 2004


You didn't indicate WHERE the grout was cracking. For instance, is this on the boundary between the top of the tub and the bottom of the tile? Some tile installers grout this joint to get the job done more quickly, but this union of two dissimilar surfaces is better caulked as the two materials do not move as one.

Agreed that greenboard is a poor backing material for tile. As I understand it, ALL tile installations are porous, so water WILL make contact with the backing material, cracks or no cracks. I'm not an expert, but my understanding is that the criticality of this issue depends on the frequency of use. Is this a frequently used tub/shower? If not, you could probably let it slide.


Joined: Aug 30 2003

Robert and Ben, thanks for your comments. Most of the cracking is not at the tub/tile interface, though in one spot at the front right top corner of the tub, on the face (the face of this alcove tub/shower is tiled) there is a small crack. There is cracking at the top left corner of the enclosure that runs down about 15 inches, and there is a smaller crack at the top right corner of the enclosure.

The tile is 12" slate squares and is less than 3 months old. This is our guest bathroom and will get very little use once we remodel our master bath next year (we hope). We do not have any kids and refrain from violent movements in the shower, so impact damage can be ruled out as a cause. We only have two bathrooms in our 1959 Eichler.

I do not think this cracking occurred because of foundation settling as Ben suggested. The house is 45 years old. The foundation could not possible have shifted significantly in the past 3 months, particular since there have been no major earthquakes.

I would say the grout cracking has occurred because of poor quality work. And I am going to complain to the installer, whose name I will not reveal on this board but anyone who wants to contact me directly at form3ATtothewebDOTcom will get that information.


1959 A. Quincy Jones atrium model in The Highlands, San Mateo

Joined: Aug 30 2003

Robert wrote: "ALL tile installations are porous". I think it is more complex than that. Yes, water is the ultimate solvent and can penetrate anything in time. However, if tile and grout are PROPERLY sealed and maintained, and there is no grout cracking, water will not penetrate to the backing board. At least not in the liftspan of several generations of humans.

Water does get behind tile if there are cracks in the tile or grout, or those using the shower/tub splash water up and it goes down the wall and seeps behind the tile (if it is not sealed well) or if the plumbing fixtures are not properly sealed.


1959 A. Quincy Jones atrium model in The Highlands, San Mateo

Joined: Aug 12 2004

"Foundation"...anything that is the basis to build from, even side walls.

Not just settling of dirt, but slamming of doors, wind on the side of the house, etc all moves walls ever so slightly.

A "wall" with cement board, then a layer of cement/mortor laid onto chicken wire is the best and most expensive. Plus it reduces the interior dimension by a couple of inches.

This won't crack for a long, long time and is what I'd have used for tile of that size. Plus I'd not use mastic, but mortor behind that sized tile, as their weight gurrantee's that it will crack if the "foundation" isn't up to the task.

The cement board will be the interface between that mortor/chickenwire and the studs. Any movement of the studs (there always will be some...slamming doors, wind on the side of the house, etc) will not easily be transfered to the tiles. This usually will have the first crack propagate from a corner or edge, not from the middle...if done right.

Yes, everything has porousity, but the above construction will have it staturate a "bit" and then no more. Mastic, if not enough and not pushed down into to mooosh out the air, will have voids. Then the grouting only hides. You can tell if the tiles are set well or not, as the grouting will crumble/crack/etc when the tiles move from steping/touching/vibration/etc.

Sorry to hear of you plight. Not much can be done other than to patch with a more pliable material (you can tell the transition between them) or redo it all.

I never use grouting around a tub, as it will crack quickly from the weight of the tub moving ever so slightly down/up. Best to use a silicone or RTV of some sort that is pliable. There should be a half inch raiser of the tub behind the tiles, but some times they wick moisture and rot out the greenboard over time. Again, why best to use cement board and/or chickenwire/cement.

Joined: Jan 4 2004

I would really question the experience of any person installing tile in a wet location without a moisture barrier and contrete/mortar substrate (it is illegal, for starters).
That is really asking for trouble. If you think about how many locations in which there are joints (which are potential for leaks) and the fact that I can't even count how much rotten green sheetrock we've removed over the years, you won't be enjoying this bathroom for years to come.
The grout cracking is likely caused by:
1. Improper curing
2. Lack of additive in the grout
3. The fact that you have a joint along the tub base, which is a cold joint, which is not sufficient backing to support grout, and/or
4. The drywall may have shifted down due to the additional weight of having large slate tile glued on with tile mastick
5. The installer smoked way too much dope before coming to work those days

These reasons are indicitive of your "tile setter" either: using shortcuts to save money, or being inexperienced. If he did not use tile mastick to glue the tile to the drywall, then I'd venture to guess that it is inexperience causing your trouble, which might be more hopeful in your recovery of your loss (rather than willful intent; I'm pretty sure that it was not accidental that he forgot to put in mud or concrete backer board).
This guy is in a lot of trouble now. I almost feel sorry for him, (but not really).
If you want me to come by and look at it, I'll be in the SM Highlands for the rest of the winter working on various projects. Good Luck.


Joined: Mar 22 2003

Hi Barry:

I suggest that you post your inquiry over at the Tile Advice Forum at - The pros over there are terrific in providing this kind of advice and feedback and the more specific you can be about the problem, the more useful their advice will be.


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