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Why does my shower tile grout keep cracking?

I just redid my bathroom and the grout keeps cracking and falling out between the tiles on the window sill. I just redid the grout for a 2nd time last week and it's already cracking. I've taken two showers in there so far. I sealed the grout too. What am I doing wrong? The grout is from Home Depot along with the sealer. The sealer is the exact one the grout mfg recommended.

Please help me!!!! I'm going nuts with this bathroom.


Re: Why does my shower tile grout keep cracking?
Re: Why does my shower tile grout keep cracking?

Sorry.......but the pics are blurry (cell-phone?) and so I can't tell exactly where the cracks are, etc.

Evidently, this window is rightin the shower-stall. ???

Where exactly is the grout cracking (in what location)?

What material comprises the window sill? Wood, vinyl, or...???

Without more info about the best I can offer at the moment is that you may be trying to grout where grout simply won't hold up because of material movement (differing amounts of expansion and contraction between two materials). Locations such as this should be caulked, not grouted. You can likely get a color-matched caulk for your grout from the same manufacturer as the grout.

If there is wood involved and you tiled right on top of it, that could be the problem. Applications like that will benefit from the use of an isolation membrane (like Ditra) between the wood and tile.

Re: Why does my shower tile grout keep cracking?
goldhiller wrote:

If there is wood involved and you tiled right on top of it, that could be the problem. Applications like that will benefit from the use of an isolation membrane (like Ditra) between the wood and tile.

Yes, it's wood for the window sill and I tiled right on top of it. It's treated/waterproof. I guess that is my problem. Thanks. I'll look into the caulk.

If you look at the pics the cracks run along the edge of the tiles that lay flat.

Blue RidgeParkway
Re: Why does my shower tile grout keep cracking?

A few things.

As goldhiller indicated whenever you are abutting differing materials which move, react to temperature, moisture, etc. differently you have to allow for that movement not join them directly - vinyl window vs. wood vs. tile field significantly different therefore you need an isolation joint in this case as suggested caulk.

whenever you have a change in plane that is a different directional orientation from one tile field to another - for example two walls meeting at a corner, each has a different orientation of the vertical plane directionally (90 degrees corner) that intersection needs to be caulked not grouted - as the tile field is connected to a wall - and the walls will move/react and each tiled field will in the best case act as a monolithic structure (single field) and mounted to different orientation support so you have to let it move and its stresses not transmit to the other wall field so we caulk that joint or else we get failure.

the same goes for a transition from a horizontal surface to a vertical surface [your tiled window stool being horizontal to its cap being vertical, then its underside being horizontal (tiles facing floor) then the shower wall itself underneath being vertical].

Now when we tile a field upon a substance which can move (swell, shrink with moisture, swell or shrink with temperature) more than the tile field itself we also have to manage this with some sort of isolation (of the movement, moisture and temperature) transition membrane to) prevent or reduce this movement at least to buffer or transition it. Tiling directly on solid wood usually doesn't work, then we go to plywood an engineered wood with layers with graining in perpendicular opposition and glued - considered more stable regarding reactions to movement but tiling directly upon this also a problem so either a thick "mud" base but still prone to failure so now we use membrane products and to promote adhesion use modified thinset mortar to install the membrane then set tile upon thinset mortar.

We want a stable non moving base field for setting the tile and to keep it monolithic to connect the tiles (parts) to one unit (whole). This is why using real thinset mortar is most important (not adhesive). As the mortar cures it hardens and bonds making a strong field allowing little movement, this is important as we then apply grout between the tiles, which if there is any movement of the tiles will have failure. Depending on the strength of the grout and the strength of the tiles and the level of forces affecting it something will fail if there is movement, either the grout, the tiles or both.

Wood warms and cools fairly quickly (meaning it adjusts and responds to changes of temperature) and reacts (swells, shrinks) significantly when moisture levels increase or decrease (direct water exposure, humidity, etc.), vinyl reacts even faster to changes in temperature and moves significantly and quickly with those temperature changes much more (expands and contracts) but hardly reacts at all to moisture, tile, mortar, etc. are slow to adjust to changes in temperature (takes long time to warm up or cool off). grout and tile are not water proof either. The walls behind the tile obviously at least one of them are exposed outside walls - the floor beneth the shower or tub may also be moving - another reason a gap/overlap lip and caulk needs to be used between tile wall and shower pan/tub - as the pan/tub may move up/down with the floor. If the showerpan/tub are not well supported, bedded and flex with load (water weight, weight of user) this too can cause problems the stresses may be broadcast throughout the tile field and cracks could show up on the opposite side - if the tile field is acting like one monolithic structure.
Another common DIY error is to fail to waterproof the washed walls and/or shower pan prior to installing tile. thus allowing moisture behind the tile field (direct fluid water via micro cracks, condensation, water vapor) again grout and tile are not waterPROOF or impervious to water, moisture, etc. there is always some level of porousity even to stone, and even if doing so not providing for a drainage plane/path behind same for any collections of condensation, etc.

Bottom line, proper selection of materials and installation; installation on stable surfaces; dissimilar materials need isolation from temperature, moisture and movement (membranes/caulk); real thinset mortar or modified thinset mortar to set tiles (ANSI 118.1 or 118.4), and avoiding shocks. We can't know where the wink link in the chain is, but from your description and the photos it looks like there are several problems (tile ontop of wood window stool of a vinyl window - no caulk for change of planes in tile - movement - moisture - temperature extremes/shocks, plus the unknown of other installation factors could lead to some of your troubles.

finally you can do everything perfect and still have issues with a tiled over corner lip of a horizontal tile field over a vertical edge (window stool/sill or a countertop edge) which is why there are rounded over or cap tiles these are part of the top or horizontal field, you caulk between them and the top vertical course below and let their vertical backs float out a bit but set the horizontal backs (on the flat field) in mortar. A very good resource is John Bridge's web site, and his tile forums.

Hope that helps somewhat as you look towards identifying and addressing your concerns.

Re: Why does my shower tile grout keep cracking?

Thanks for the responses. Those helped a ton. Now I understand why what's happening is happening.

I used DensGuard directly behind the shower tiles and fiberglass, not paper, drywall in the rest of the bathroom.



I will see if I can find a caulk that matches and caulk the corners and the window sill.

Thanks guys!

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