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Question DetailsAsked on 4/30/2015

Grout lines cracking all over 3 day old professional tile installation. Is it a foundation problem?

Hired contractor to remove and replace my kitchen tiles, thinset, and hardibacker (kitchen located on 2nd floor of 3 story townhome). 3 days later cracks in the grout lines started appearing all over my kitchen floor (thin and thick). Contractor returned and decided to use sanded pre-mix grout (originally used unsanded grout) and layered it all over the original grout. 3 days later the cracks appeared in the same location. This time contractor said it's a foundation problem and that he won't fix until I fix my foundation. I live in a townhome that was built less than 10 years, currently doesn't have any visual signs of foundation issues (no cracks on walls/ceilings, doors open/close fine, no cracks outside of the house). My question is if it's really a foundation issue causing cracks in my grout lines or maybe the contractor is at fault with how he originally mixed the grout or caked new grout over old when cracked. Any insights from the pros out there would be greatly appreciated!

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2 Answers


sounds like too much liquid in the grout which makes it a lot easier for the installer to do the work and clean up but as the liquid dries, the grout cracks. I had the same thing happen to me in a new bathroom re-do and my house is 150 years old and I've done my own tiling on occasion and never had grout cracking problem.
Put the blame where it belongs.....Also, should not grout over grout.. old grout should have been removed first.
Good luck. I am living with the poor job.

Source: my own experiences

Answered 5 years ago by angelwynd7


Believing house settlement just happened to occur same time as a new floor was put in - that is beyond my credibility level.

Floor tiles should (when using cementatious as opposed to epoxy grout) use sanded grout for strength and much less shrinkage - and the high-strength grout mix for floors, as opposed to the finer-grained more water-proof mix (if buying premixed) designed for shower and bath walls. Also, generally grout joints over 1/8" wide (so almost all floor joints except for some very tight mosaic tiles) should use sanded grout for greater strenght and less shrinkage. So highly unlikely he used the right grout in the first place, which added to using sanded as an overlay indicates he is probably not a professional tileman - or at least not well trained, because when you do overlay grout (like on a partial grout job in a shower) you sometimes use unsanded latex or epoxy-modified grout as an overlay on the joint, but never sanded over either sanded or unsanded unless the grout joint is completely routed out (which is very time consuming).

As other comment said, use of excess water will cause cracking and make it weaker - as can failure to wet the tiles and the thinset in the joint first so they draw the water out of the grout.

And putting a patch coat over cracking grout (or concrete for that matter) just fills the crack, does not solve the root problem, and the underlying crack commonly "reflects" through the overlay - certainly if the cause of the cracking is still occurring.

However - given that it took 3 days each time rather than within about 1 day (the grout curing time), couple of other possible causes too - that he oversoaked the thinset before grouting so it really wet the underlying sheathing, which is then shrinking as it dries out and causing cracking - though would REALLY have to have overdone it since you said there was backer board underneath. Usually this happens in a mesh and mortar scratch coat put straight onto the sheating.

Other possible - backer board was not screwed down but was nailed, and it is working up and down on the nails or the nails are working in the sheathing, if thin. Or sheathing is not firmly attached to joists and is working up and down - flexing as it is walked on, causing cracks.

A "bouncy" subfloor can also do this - one with undersized joists or grossly undernailed underlayment sheathing.

My call on this - 99+% chance it is a tile layer problem - and if the previous tile flooring was replaced just as an aesthetic issue rather than because the grout was all cracking up, you have a better argument against his claim it is caused byh settlement. Of course, if prior floor was all cracked up too, then subfloor movement is far more likely the cause. I would call it his problem, cancel payment if possible, and if he will not redo the job (at least TOTALLY remove and redo the grouting) time to talk to his bonding company about having them bring in another contractor. Start documenting your contacts and take photos.

Oh - after-thought while editing, because this is something you just do in the trade without thinking about it - and actually probably at least one of the most common causes of this problem. If he mixed the grout from powder, after initially mixing it you have to let it sit about 5-10 minutes (depending on brand) and then remix it thoroughly (adjusting water to get correct consistency, which should have ended up like mortar rather than pourable batter consistency), so the powder fully soaks up with water and makes a homogeneous mix, otherwise the partly-dry grains of powder in the mix will soak up the water from the mix, resulting in a weak grout because it is short of water needed to set properly. This is called "slaking", or in some parlance "pre-setting" or "soaking".

Two other common crack problem causes too - failing to "stone" the edges of glazed tiles to break off any glaze that ran down the sides of the tiles (which oprevents grout from sticking), and failing to properly "float" or ram the grout all the way down into the joint so it fills it completely - especially common to see only partly filled joints in thick clay (as opposed to true ceramic) and quarry type tile floors, though if the grout is not forcefully floated into the joints when applied can still have lots of air bubbles under it. Should be worked into joints from one end to the other (so air gets pushed out ahead of it instead of trapped under it), then "floated" with a grout applicator (usually rubber or stiff foam rubber trowel-like tool) at 45 degrere angle to the joints to get uniform fill level without peeling the grout out of the joints, which happens when you finish float parallel to the joints.

Answered 5 years ago by LCD

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