TCNA handbook (bible for tile guys and girls ) mandates silicone caulk at change of plane.

It is not optional, it is THE LAW!

If grout is going to crack at change of planes, then the substrate is not sturdy which is allowing the differential bouncing.

Grout and tile were never waterPROOF. Tile helps water resistance but that and grout are porous materials nonetheless. Look water WILL creep around any joint in a bathroom. The idea with tile and grout is to allow the water a way to breathe out and not get trapped in a moisture sandwich beneath your finish walls and floor.

Silicone will not resist water that is trapped behind it. It will discolor with mold and crack.

Make your substrate good and solid in construction, you could opt to use a plastic sheet between stud and cement board. Over the cement board you HAVE to use liquid applied waterproofing membrane (redguard, laticrete 9235, etc..). Then you put on your mortar bed for the tile/stone finish. Your GC might even purposely make little weep holes for water at the base of your wall before it hits the tub/shower floor.
Some installers cut the cement board wall 1" ABOVE a shower mortar bed so as to prevent capillary action of water from wicking up the wall. They cover over the 1" gap with tile/stone.

Here's the deal, if your walls are going to bounce, cracked grout is the last thing I'd worry about. I'd worry about the waterproofing membrane behind the wall no longer being a continuous membrane.

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:We are getting estimates to renovate our bathrooms, and every contractor we have spoken to (who all came highly recommended on Checkbook) has said that they use grout at changes of planes. This runs contrary to everything I have ever heard/read/experienced; my understanding is that because grout isn't flexible, it is bound to crack in this application. Am I going crazy? If just one contractor would say this I would assume that they are cheap/lazy but everyone I've talked to has said the same thing.

So what I have learned is that silicon prevents the “dripping” of water down at the base of showers and bathtubs so that the hardy board in the back absorbs the water.

We have had a couple of our showers destroyed by this practice already.

This is correct. Use grout it allows the water to go back into tub or shower base.

This is so incorrect it's barely even wrong. Grout is cosmetic. The waterproofing has to be behind the tile.

You can have water proofing behind, and still have grout, that diverts 99.9% of water toward a drain. Redundancy works.
Grout is not only cosmetic. It can certainly provide a waterproof surface.

The issue is not always waterproofing, it is managing what happens to moisture after it migrates through/around a certain material or surface.

Any design that relies on the waterproofness of grout is flawed.

For a proper job, after the waterproofing is installed you should be able to plug the drain, fill the shower with water up to the edge of the curb and leave it for 48 hours with no leakage. A shower sees thousands of gallons of water a month, a design that only stops 99.9% of the water is allowing gallons of water a month into the walls and floor.

As others have noted, contractors get shower waterproofing wrong all the time.