Happens because there's deflection (movement) in the floor. Usually the best fix is to make sure in the first place that the floor is very solid. Sometimes that includes screwing it down, etc. to make it more firm.

Do a search online in some tile forums and you'll find plenty of info. (john bridge tile forums is a good one)

No way to tell but is the grout a sanded type or non-sanded (smooth) ? Non-sanded grout will work for narrow joint widths but if the depth is too deep, that's just as bad as having too wide a width.....there is no sand mixed in to hold the grout together. That's why I never use a non-sanded type grout on floor insatllations.... even marble.

It could very well be cracking from floor deflection or using too much water. Numerous reasons this can occur.

Hello,

I'm pretty sure it is a sanded type of grout. It isn't smooth and is rough to the touch.
Is it something to worry about? How is it "fixed"? Do they regrout those areas?

Thanks!

Elaine

Another great place to ask some experts is at GroutCleaning.com. It's a fairly new forum for professionals to discuss issues like this with homeowners. There's a few hundred tile professionals that joined up to volunteer to help!

Here is a link that might be useful: www.GroutCleaning.com

Need to check for movement. When walked on, can you see any movement in the crack (such as change in width)? If cracks return, he subfloor may have to be secured better.

They'll probably regrout, but that doesn't necessarily mean it's fixed. How are are the areas, anyway? If you're lucky, it could just be it was grouted improperly (like mix was too wet, or it wasn't allowed to "slake" (That basically means mix grout, then let it rest for like 5 minutes, then remix and grout.

Also, knock with your knuckle on the tile in those spots. If it's hollow in spots underneath (different sound), that can cause it to move. If that's the case, then those tiles may need to be pulled up and reset.

I will chime in on this one! We have the same problem on a floor done 2 years ago. lots of cracks in the grout, and the floor sounds 'hollow' when we walk on it in some areas.
I can see that the tiles (ceramic) were installed on some mesh wire and on thin set (or at least that it what it looks like).
I have done a little research and it looks like this installation is called 'new jersey mud job' and is the worse installation possible. What can I do now to fix this problem?
Can all of it be removed without destroying the floor? I don't think any subfloor was put in before the mesh as the floor is lower than the rest of the house (the seam between the existing floor in the other roomis not finished so I can see the different levels underneath). I can provide a picture if that helps.
Thanks for your guidance.

Jersey mud jobs are common failures ... but are also fairly easy tearouts. If you are experiencing problems there is no fix to it.