cracked tiles and expoxy grout [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-01-2001, 07:54 PM
This winter I installed ceramic floor tile in a bathroom over 3/4" tongue and groove plywood with a layer of 1/2" BC plywood screwed to the 3/4" every 6" and every 4" at seams. The 6x6 tiles were set in Thinset and after 24 hours, I installed expoxy grout. Approximately 2 months after installation, I noticed a straight line crack going across the center of 6 tiles starting from the bathroom doorway. Within another 2 weeks, there was another straight line crack going perpendicular to the first one and following a grout line. Since then, there has been another crack along 8 tiles following a grout line and a diagonal crack going across some other tiles.

This is the first time I have use epoxy grout and I am wondering if that is the problem. If the grout is harder than the tile, would this cause the tile to crack? I am perplexed and very disappointed.

Any ideas as to the cause? Also any thoughts on how to remove the tile? There is about 80 square feet of tile. Thanks.


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Rob Z
07-01-2001, 08:15 PM
Hi Neal

Thanks for visiting the Forum. Hopefully, we can help you diagnose and fix the cause of the problem(s). Here are a few questions. I'm sure the other guys may think of a few others, as well.

Is it possible that the cracks follow joists or where the second layer of plywood overlaps the first layer?

Did the second layer of plywood get staggered from the edges in the first?

What is the size and spacing and span of your joists?

Did you use a latex modified thinset rated for use over plywood?

Did you get good coverage of setting material under the tiles?

We can talk about how to tear it out later. I don't think that the epoxy caused it to crack, but if there were voids under the tile, the epoxy probably would have flowed down in the joint and under the tile. I think that this scenario would result in a field of tiles set over varying strength of material, with different characterisitics thus different affects from a floor that was flexing, for example.

We'll see what the others have to say, too.


Bud Cline
07-01-2001, 10:25 PM
I would think the epoxy grout could be ruled out as the CAUSE of the cracking. Cracking is the result of some type of movement, however minor.

My questions are the same as Robs. In addition, is there any ryme or reason you can see as to the location of the cracks as they would relate to the joints in the underlayment plywood? (Do these crack locations relate to seams you installed in the plywood?)

The diagonal crack is a puzzlement at this point unless the underlayment plywood was cut diagonally at this location.

Means little now but how old is the structure?

07-02-2001, 07:56 AM
I agree with Rob and Bud about the questions.I believe that the 1/2" plywood contributed to the cracks.Also you mentioned setting the tile in the winter.Might be a stupid question but was there adequate heating during the installation and curing? The room temp needs to be above 40 degrees.As Rob pointed out,good coverage is essential ESPECIALLY on plywood although personally I never set tile directly on plywood.I've seen too many installs pop loose even with a latex mod. thinset.

I would remove the 1/2" ply and install cementious backer.Set on a bed of thinset and SCREWS every 6-8 inches.
But we need to be sure that regular old settling isn't the culprit first.What about joist placement,size and spacing?
Bud asked a valid question about the age of the home.

07-02-2001, 12:54 PM
Thanks for all the feedback. Let me see if I can answer some of the follow up questions.

The joints of the second layer of plywood were staggered from the first layer of 3/4".

I thought that the cracks might be following the joints in the first layer until the diagonal crack appeared.

The joists are 2x4 sleepers on top of a 4" concrete slab ( on top of a frost wall), spaced 24" on center. The first layer of plywood is 3/4' tongue and groove southern yellow pine that is glued and nailed.

The home is 20 years old and there has been no sign of shifting or cracking in the slab during that time.

I did use a latex modified thinset that is appropriate for use over plywood and I used a 1/4" notched trowel to spread the thinset. While each tile wasn't buttered, I believe that I got good coverage.

The tile was set in a heated space (70).

I agree that the cracks were caused by some sort of movement. My thought on the epoxy grout was that it was harder than the tile, so the tile cracked. If regular sanded grout had been used, I wonder if the grout would have cracked instead of the tile. However, this doesn't resolve or identity the movement problem.

Any other ideas?

John Bridge
07-02-2001, 02:25 PM
Well, 24 in. centers are one problem. Supports should be closer together.

I don't think we have a bonding problem, since the cracks occur through the tile bodies and not just in the grout joints.

I guess I'd have to say deflection, even though there are two layers of plywood. And there is also the possibility that the top layer of ply was not seasoned and has since shrunk.

I agree that the epoxy grout has nothing to do with the cracking.

Bud Cline
07-02-2001, 04:08 PM

Yep, the twenty four inch spacing of the sleepers is a no-no.

Now those 2 X 4's....where they treated lumber i.e. CCA (I hope not) and how where they attached to the concrete.

I'm afraid your headed back to "square one" here.

07-02-2001, 05:30 PM
Yep, This is starting to sound more and more like a take out/start over deal.

Bud's right,Pressure-treated lumber is trouble.They force the treatment into the wood BEFORE it is cured.So when you buy it and put it in the curing begins and so does the twisting,shrinking and general acts of becoming deformed!!

At any rate,the spacing issue has to be fixed and a sound cementious substrate installed if you are to have piece of mind with a Tile installation.

I still say get rid of the 1/2"ply.If you need another layer make it 5/8" ply glued and screwed then 1/4" backer.

07-02-2001, 07:17 PM
Sounds like I am into a tear out and redo category, with some additional sleepers that decreases the joist spacing. What is the best way to tear out the tile? Grind out the epoxy grout joints, bust out the tile with a cold chisel, and then scrape and/or grind off the thin set from the 1/2" ply?

By the way, the sleepers are not PT, they are fir and are attached to the slab with adhesive and nailed into blocking that has been ramset into the slab.

Bud Cline
07-02-2001, 07:56 PM
OK Neal,

Sounds like your existing sleepers may be salvageable if your adhesive and Ramsets haven't failed. So that's a plus.

Now, without seeing this project I would think your absolute most efficient means of wrecking that tile is to rent an electric chipping hammer. This is in essence a small jackhammer kinda thing if your not familiar with it. With the chipping hammer you usually have a choice of chisel points. I would get the flat chisel (about 3" wide) and mostly a "bushing tool". A bushing tool fits in place of the chisel and looks like a kitchen meat tenderizer (hammer).

Install the bushing tool and go after the tile. Start anywhere and just beat the hell out of it. It should break-up rapidly given you are going to get some flex and vibration out of your wood structure. This vibration should aide in the destruction of the tile.

Don't forget eye protection. I'm not sure how the epoxy grout will react to this invasion but we'll find out. Shovel the spoils into buckets and say goodby to that investment.

Lets see how much thinset remains after this, then it will be possible to plan the next action.

80 square feet isn't that much and this should go quickly for you.

07-02-2001, 10:16 PM
I just helped Derek&Jacqui on a job where they had to remove 500sq.ft. of tile from plywood,clean up the thinset and install backerboard.We used a good floor scraper to remove the bulk of the thinset then got down on hands and knees with a 20grit mason's rub-brick and knocked down all the high spots of thinset.The rub-brick,while tiring,works extremely well .....and fast.BUT...if you're going to do away with the 1/2"ply this step won't be necessary.

By the way, the tile was about 5 years old was set in modified thinset and yet most of it was loose.ONE of the problems was inadequate coverage.I use and recommend a minimum 3/8" notch trowel for 8" to 12" tile.You can't have too much coverage!

07-03-2001, 01:25 PM
I appreciate all your feedback and advice. I think that I will let the weight of the remedy ( tear out and do over) sit for a few days and then proceed. Thanks for your help