Expanding tile?

[Dinamight]

We have a tiled floor downstairs, ground level, which seems to have expanded and come off the subfloor. There is a definite elevation change and it is peaking in the middle - the floor sounds hollow and flexes when we walk on it. The edges are solid and it doesn't look like there is anything pushing the tile up but it's hard to say.

As far as we know tile was put down directly onto the concrete pad after the existing vinyl tile had been scraped off. I know the job was done by the previous home owner, and when we removed tile from another part of the floor there was not much thinset on it. Could it be that they didn't put on enough thinset and the whole thing has come off its base and expanded upwards?

I know wood floors expand and contract but can this happen to a tiled floor? We are not walking on it to prevent cracking it - am wondering if anyone has experienced this and what the best fix is.

[Carey]

Proper base prep may be what was missing.

If there is any residue from the adhesive on the vinyl tile, it can cause improper bonding between the thinset & concrete pad.... A good thinset application actually forms a cystalline bond with the base concrete, even a light oil film can impede the bond. The area that is not bonded will have the potential of trapping water vapor that migrates in the base and tile... this trapped vapor can be your problem.

ETA: fix: take up the tiles that are not bonded (hollow sound) grind the base & reapply (you may be able to salvage the tile that is not bonded, but if you do not, you can look for replacement tile or contemplate a mosaic....)

[Kapohocat]

When you are prepping a concrete floor for tile, dye or paint, it is a good idea to use a muriatic acid solution to wash floor after it has been thoroughly cleaned of debris.

You can buy various versions at Home Depot.

Catherine Dumond
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[Carey]

I would put a caveat on the acid etching.

The thinset I use does not recommend acid etching... so I grind. I have seen sites that contradict each other on this, some strongly recommend against acid etching because of the chemical/structural changes in the base concrete for the thinset bonding, others recommend acid etching, if grinding is not an option.

Have not seen anything against grinding, so I do (and it is a supreme pain in the as..er....knees) plus I have had a lifetime of commercial acid exposure, and I really do not want to add more acid load (if you do decide use acid, take my advice and definitely wear all of the protective gear, including an acid respirator - not to do this will wear down your respiratory system & teeth.... not worth it for a floor...)

[Kapohocat]

quote:

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Originally posted by Carey

I would put a caveat on the acid etching.

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It is not etching.

If you are etching, you have too strong a concentration which many home owners always think more is better. The strongest solution available is about 34% which you then dilute as per instructions and yes wear the protective gear.

Grinding can still leave particulates in the pores and on the surface of the concrete that allows the thin set to not bond properly.

Bleach and Muriatic acid are in the same family.

But again this is much like people saying using hardiboard in the shower as backer board is okay. The damage by not doing it properly may not appear for a few years as dinamight is seeing.

Another issue that can cause improper bonding is thin-set mixed in too thin a mix because it is easier to work with, or too little thin set under the tiles. And conversely, allowing thin set to harden slightly before applying.

Getting the concrete slab a little damp before laying the thinset and tile will increase the bonding between the thinset and the concrete.

[Dinamight]

Thank you so much for the information! I was in Home Depot today and their tile man told me there was no way tiles expand, so it had to be something that pushed through the subfloor. I was depressed all day thinking we had huge foundation problems, but I cheered up the minute I read your advice, Carey and Kapohocat. I will ask my tile man if he can remove some of the raised tile with a grinder and we'll have a good look at it. It was a common tile at Pacific Island Flooring, so I may be able to buy some more, even if the dye lot is different it will create that artistic look ???? If not, well, I'll cross that bridge when I come to it.

The raised area is just so uniform as if it's being pushed up by a layer of air or vapor as Carey says. It does not look as if a tree root has grown underground. It would have had to go under a big area of concrete outside the house and reach out to the middle of this floor without damaging any of the concrete outside nearer to the trees. That would be a real fluke.

I'll let you know what I find when we do take up some of the tile. Thanks again!

[DanielP]

When setting tile over concrete, it is always best to use an isolation membrane. If the slab cracks or moves or sweats, it won't effect the tile.

Dan

[hotinhawaii]

quote:

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Originally posted by DanielP

When setting tile over concrete, it is always best to use an isolation membrane. If the slab cracks or moves or sweats, it won't effect the tile.

Dan

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I second that. I will also help if there were any spots where the concrete was stained with oil.

[konadave]

How soon after the concrete slab was poured that you set your tiles on it? If less than a month or two it could be that there is still moisture escaping from the surface of the slab.

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[john the architect]

There is some floating tile flooring for sale (recycled/donation) on the materials part of craigslist at one of the Habitat for Hamsters locations. That stuff flexes and would ride out the subfloor problems possibly. It's only $2 psf if they still have it in stock. Saw the ad today.