Why does my shower grout crack?

[Spokes11]

I tiled my shower with 4 x 4 tiles, and used the proper non sanded grout. About a month or so later, I noticed thin cracking along some of the lines, more towards the bottom rear of the shower. Now I am noticing more cracking towards the front. Also, I used white grout, then applied tile sealant. For some reason some of the grout lines along the bottom of the wall and along the shelf (which are 4x4's as well) are now gray discolored. Why is the grout cracking and what can I do to prevent that from happening again?

Thanks.

[Mike2]

Weclome aboard Spokes My name's Mike, what should we call you?

The first thing we need to know is what tile spacing was used for your non-sanded grout and in particular, is it wider that 1/8" ? Additionally, are these cracks limited to the perimeter of the floor where is meets up with the wall or curb (those perimeter joints shoud be caulked)?

[Spokes11]

Hi Mike. I don't think the lines are greater than 1/8". I believe the tiles come with built in spacers, and that's what I used. I did use caulk appropriately along the tubline and corners, etc. And it is only cracking in some places. The majority of the grout lines are just fine.

Dorothy

[Dave Taylor]

What did you use to stick them tiles on with?
What are your shower walls built of and, perhaps, why did you tile this shower?
Was this a re-tile or a new shower?

Thanks :---)

[Mike2]

Hi Dorothy.

Spacing should be fine for non-sanded grout. More than likely you had too much water in the mix resulting perhaps in a combination of shrinkage cracks and a very weak grout joint.

Tell us a little about the floor, how it was build and what type of grout was used. It wasn't a pre-mixed "grout" in a bucket product was it?

[Spokes11]

Hi guys. This was a new shower. My first big home reno. I just bought this house and gutted the old moldy bathroom. I used durock, some sort of mastic for the tiles, and then grout that was not premixed. (mike, is premixed grout not good to use??) I think your comment about there being too much water in the mix sounds like a feasible explanation. However, I made sure to mix the grout well to a peanut butter consistency, and let it sit for 10-15 minutes before applying. Also, any idea why there are little sections where the lines of some of my grout lines look discolored and gray?

Thanks.

[Mike2]

Mastic used on a shower floor....dark grout line stains....cracking.....that pretty much all goes hand in hand Dorothy. See the problem with mastic is it can readily re-emulsify when wet as it will become on a shower floor. Coupled with the fact that it can take forever to dry down there. The stains could very well be mastic goo coming up through the grout. Tiles are not well bonded to the substrate resulting in movement and cracking grout. I'll end the saga there as the story doesn't get any better.

Sorry about all that Dorothy but there is no "easy fix".

[Spokes11]

Mike, thanks for breaking the news gently to me. (BTW, I really enjoy all these smiley characters.) Now, this is not a shower floor, but rather a tiled shower wall (perhaps I gave the wrong info). I have a bathtub with surrounding tiled walls. Is it still not a good idea to use mastic on the walls? Maybe I should have let the tiles dry longer than 1 day. It doesn't seem like the mastic is coming through, but I am certainly no expert. Perhaps I will grout over the cracked areas, or should I scrape out the old stuff before I do that?

Dorothy