Strike One~ No waterproofing.
Strike Two~ Mastic.

With no poly attached to the studs or Kerdi or Hydroban applied to the Durock surface, there is nothing to prevent the studs from rotting away eventually.

Mastic is an organic adhesive and will re-emulsify in the presence of water. The tiles will probably come loose before the studs rot.

He is no Tile Mechanic...he is a hack if that's his procedure for a shower build.

I hesitate to ask what he did to build the shower pan.....!

This is a tear-out and re-do with a competent installer.

Sorry~

My contractor said he planned to do the same thing, which I posted about recently. I found an installation pdf on the Durock website that said Durock is water resistant, but for a waterproof installation, you need a different product. It didn't mention adding a plastic liner, but referred to another Durock product. If you need something to show your contractor, those installation documents might help.

Here's the thing...manufacturers are, for the most part, only going to tell you how to install their product. In the case of Durock, they'll tell you how to install the boards, what backing is required, how many fasteners to use, how to treat panel joints, etc...but then they'll get fairly ambiguous about how their specific material should relate to the other materials used.

Most of it is liability related. Plus there are national, state, and local building codes. USG and other manufacturers can't play to all parties involved. They don't want to tell you you have to use waterproofing, where to use the waterproofing, or what waterproofing to use. They'll just tell you to use it if it's required.

So...is Durock waterproof? No. The USG literature will probably tell you it's "resistant to water damage" or something like that. Durock is cement board. Cement is porous. Expose Durock to enough moisture and the moisture will pass right through. But the Durock itself won't be damaged. Think of it as having the structure of a sponge. Sponges undergo repeated wetting and drying cycles and are pretty much undamaged by water. But water can pass right through a sponge. The same hold true for cement board.

So there are all types of membrane materials that are used in conjunction with tile backer boards like Durock. Probably most common and least expensive, but at the same time adequate if properly detailed, is installing either tar paper of 6-mil poly sheeting between the Durock and the studs.

More expensive, and in many ways better performing, is using a topical membrane along the lines of what the original poster mentioned; Hydroban or Kerdi.

As to the adhesive used, the mastic? It's technically allowed in a shower surround on the walls, but not on the shower floor. But using it, even though it is allowed, doesn't make it a best, or even really a "good" building practice. Mastic is it something that I'd ever use in a shower. But technically, it is allowed on shower walls. Now if he used it on your shower's floor tiles, that's an outright "failure to perform" type of thing for the exact reasons that Stonetech mentioned. Mastic is essentially water soluble.

What do I recommend? Call or visit your local building office if you have one. Ask if any waterproofing membrane, or vapor retarder/membrane is required in a shower where the walls consist of tile over cement backer board.

If it's required by code and he didn't install anything behind the cement backer board, it's "failure to perform".

As far as the mastic, technically and legally, if use only used it on the walls, he's technically and legally okay. But if he used is on the tiled shower floor?

Now I'm sort of walking a tightrope with this reply. By posting this I sort of fell like I'm intentionally hitting my thumb with a hammer. I fully agree with the spirit of StoneTech's reply; that you should have a waterproof membrane in the wall, and that mastic shouldn't be used in a shower.

But legally? "Legally correct" can be different than "morally correct".

As to the adhesive used, the mastic? It's technically allowed in a shower surround on the walls, but not on the shower floor.

The hell it is. Every pail says it can be used. But every manufacturer's rep will tell you it can't be done.

Thank you for the advice, everyone. I feel sick over this.

Yes, this is the same contractor who ruined my kitchen too, which I recently posted about. :(

So 1) how would I go about finding out what local building code is? 2) Does he have any liability or am I just screwed and I have to eat all that money + hire someone else?

kmcg, when you showed that literature to your contractor, did he agree to do it correctly?

And just to clarify, mastic should NOT be used at all? Is thin set okay? Clueless novice here...thanks!

I had a similar problem when they were doing my showers last November, except my contractor used Fiberock. I spoke with Steve Rausch with USG, and he was very helpful. You might try contacting him and see if you can have a three way conversation with him and your contractor. His email is Srausch@usg.com and his cell phone is 404-281-2218. Good luck getting this resolved.

laila, I haven't talked to my contractor about it yet. But I'm lucky to know about this in advance, and will simply insist that he has to do it this way, and I will pay for the extra materials/time in order to make it happen. He already thinks I'm a little bit detail-obsessed, so I doubt he'll be surprised.

To find out about building codes, you can look for your city's codes online, but the easier way might be to call the building department that's staffed by people who answer these questions all the time.

"The hell it is. Every pail says it can be used."

Geez, Bill, your comment made me go look. Maybe your Laticrete pails read different, but for the two mastics most readily available near me; OmniGrip and AcrylPro, they both state they can be used on shower walls and they both specifically prohibit them from being used on shower floors.

All,

Thanks for your helpful advice.

My contractor used mastic everywhere he installed new tile for me--kitchen floor, foyer, etc. Is it okay in these areas since they aren't generally wet, or is this still a no no?

mongoct, I interpreted Bill's comment to mean that even though the pail says you can use it on the walls, the rep's will tell you it can't.
"The hell it is" was referring to the claim that it is okay to use on the walls.

But maybe I'm misinterpreting.

Greg, thanks for that re-interpretation. I was certainly surprised and apparently confused by the wording of his comment.

"My contractor used mastic everywhere he installed new tile for me--kitchen floor, foyer, etc. Is it okay in these areas since they aren't generally wet, or is this still a no no? "

Laila, it depends. On your substrate and the size of the tile used.

Substrate: Some manufacturers restrict the type of material that you can spread mastic on. Example, many prohibit OSB and chip board types of subfloors or underlayments.

Tile size: Mastic cures by drying, so it needs exposure to a certain amount of free air. Some restrict the size of the tile you can install on floors and walls. Floors size is usually more restrictive due to the weight of walking on the tile. If the mastic can't see enough air the mastic can remain soft.

One mastic I've used has I a maximum of 6" square tiles on floors and 10" square on walls. Another manufacturer restricts tile to 12". Some prohibit setting natural stone tile on floors with mastic.

So within the entire family of mastics, each manufacturer may have their own limitations due to how they formulate their specific products.

Thank you mongo!

Kind of good news: I called the contractor and he said that he did NOT use mastic on the floors...he used thin set mortar. So that's at least a relief!

Bad news is that he DID use mastic on ALL bath/shower walls. Even with the heavy 13 x 13 porcelain tile we picked. ARGH! I'm thinking both bathroom's walls need to be completely redone with proper water proofing and thinset instead of mastic. What a ridiculous waste of money!

Laila I'm so sorry for your situation.

I am a remodeling novice and one way I try to protect myself is by getting city permits on my remodeling jobs. (I'm in Oakland, CA). It adds to the cost of the job but I actually like having a building inspector come out at various stages of the job and take a look at what my contractor is doing and sign off on it. It's not foolproof - I'm sure there's stuff that can slip by but if you're heading for a re-do you might consider it.

No self-respecting installer would use mastic. Here, in Georgia anyhow, tile is considered finish work and can have only a taillight warranty. That should be changed---

Why did you dig up a 5 yr old posy for that tidbit Lynda?

Did you have any trouble with the bathroom years later? https://psthisrocks.com 

I’d love to hear what happened. I’m in a similar situation. Can you share the final outcome?

Same as mine and that dude refused redo it when i asked him to retile and left in the middle of the job.