My opinion? For lightweight shower thinset construction, it's best to caulk changes in plane. For true mud jobs with reinforced corners, it's okay to grout those corners.

If caulk is over grout, the grout can be wetted from behind. The caulk seals the moisture within the grout, not allowing it to dry back in to the shower. That could be the cause of your discoloration.

If you caulk the joint with no grout, water can't penetrate caulk, so no water will be trapped behind or within the grout.

As far as some spots discoloring and others not, it can be how water hits the wall, it can be air circulation or light exposure in that some areas get a better chance to dry, it can be voids in the grout of thinset, it can be areas that have accumulated hair care products or sloughed off skin cells, it can be hocus pocus.

Mongo, thank you for such quick help.

I don't know whether my shower is "lightweight" or a "true mud job". From what I recall when the house was built, it was framed with 2x4s, lined with some colored drywall-like boards, and the tile was added on top of that. I was told that there was a shower pan under the floor tile, but I wasn't specifically looking at how it was constructed. I trusted the GC. This is a semi-custom, mid to upper end home.

Given that we are trying to get rid of these black stains, would you re-do it as grout only or as caulk only?

Can you comment on the "water behind the tile" issue? If moisture got behind the wall tile somehow and we use caulk only at this joint, would it trap the water and cause mold and then we'd be back in the same position again?

Thanks again for your advice.

If you walls were built with "drywall-like boards" then that would be "lightweight" construction.

Normally there is a vapor barrier in the wall, between the cement board or drywall-like boards and the wood framing.

Moisture does get through the grout and tile by various means. If it's insignificant, it'll dry back into the bathroom by coming right back out through the wall.

If it's significant or long-term, it'll eventually condense on the vapor barrier and run down the wall, between the vapor barrier and the cement board.

At the bottom of the wall, the vapor barrier is lapped over or in front of the portion of the sloped floor membrane that also runs up the walls. Typically the pan membrane is run up the wall about 8" to 10".

Once the moisture hits the floor membrane, it "flows" through the floor mud and down the membrane slope and out the secondary weep holes that are built into the drain, then down the drain.

Most floor moisture problems are caused because the floor membrane is installed flat on the subfloor instead of sloped to the drain. A flat membrane will simply catch and hold water, saturating the floor mud. This can be indicated by one of several things. Spots on the floor that don't seem to dry. Discolored grout at the floor-wall juncture, or discolored grout along the bottoms of the walls.

So long story semi-short? I don't advocate using caulk over grout. If the grout gets wet, the sealed grout can't dry back into the shower due to no exposure to free air.

Since your shower is lightweight construction, I recommend caulking the joint. Caulk will provide flexibility at the joint, and with it being full-depth, moisture won't get trapped behind it.

Regardless, just ensure that the joint, whether grouted or caulked, gets properly tooled. You want a nice flowing cove from wall to floor. If they overtool the joint and create a slight recess, then water can pool there and cause future problems.

I'm not trying to skirt the issue but there really are no guarantees against future discoloration.

Go Pats!

We definitely have slope toward the drain. The floor tiles don't exhibit this discoloration, only the joint between floor and wall.

So, it sounds like we need to remove the caulk AND grout from this joint and replace with caulk only.

Our discoloration is black. Is this mold, mildew, both, neither? Just curious.

Thank you very much for your help. I can at least now discuss this intelligently with the contractor.

(1) My contractor grouted the corners of my bathroom and I had wanted them caulked. When I told him this, he said to wait for the grout to crack (if it does) the caulk at that time, whether it be months or years from now. (My grout is unsanded TEC Accucolor with grout lines as close as possible to 1/16" (subway tiles were not the same size). I asked him if caulking over the grout now would be a problem and he said no but I am not sure based upon the postings I have read. Advice? (Bathroom was gutted and furred; building is old and is located in Northeast)
(2) Is grout instead of caulk around the tub OK?
(3) What if the tub has already been grouted?
(4) If caulk is better, is it easy to chop out day old grout?
(5) Is it important to caulk after re-glazing rather than before?

My contractor is coming tomorrow to finish grouting.

Thank you.

As my questions are requests for clarification/confirmation of previous postings, I thought I'd post some pix. (My window sash will be replaced in 2013 but sill, frame and molding is new.)

Thank you for writing again what was written previously.

Here is a link that might be useful: Bathroom Progress Pix

1) remove the grout first. The caulking needs the joint to anchor itself, or it'll peel back off later.

2) Not at all. It'll crack out pretty quickly. Caulk it.

3) Score out the grout and THEN caulk it.

4) relatively speaking, yes. Hit it with a utility knife, and it should come out pretty easily.

5) Not sure what you mean, but when the tile is done, the grouting should be completed, and that joint left empty, and then it should be caulked as the last step of the tile installation. If you're saying the tub is getting reglazed, I would think that should've been done before the tile got installed.

Thanks, Bill.

I talked to my contractor this morning and he said:

1. He used silicone at the corners of the sheet rock. He also said the reason he doesn't like to use caulk at the corners is that even though it is supposed to be the same color as the grout, it really isn't, plus the caulk will crack if the building moves just like grout cracks. I asked him about grout behind the caulk and he said he recommends keeping the bathroom dry by using a squeegie/towel where needed, particularly along the top of the tub. The grout looks so nice I guess I'll wait to see if it cracks. It probably will as the roof needs more work and I guess I'll caulk at that time.
2 and 3. There isn't grout at the tub line. It just looks like it as the grout is the same color as the empty space. (That's what I get for looking at it at night.)
4. OK
5. Tub reglazing was put last on the schedule so that it wouldn't get damaged during the other stages. I am going to have them cover all of the walls up to the tile line, and the floor, with plastic.

Dang it! I ordered what I thought was TEC Accucolor Caulk and instead received Colorfast's version.

Could you please tell me if you've used Colorfast's product and if the colors do indeed match TEC's colors?

Thank you.

They do. I've had this happen directly from Daltile's warehouse, and the caulking has always been right on. Nothing to worry about.

It is sad to see so much misinformation being given by "experienced" contractors. Especially questionable was the installer for "biker chick" who told her to use grout and only when it cracked to cover it with caulk! Removing old grout is a difficult job and it would need to be completely removed to get a good quality installation of caulk. Always grout the wall tile and when there is a change of plane,( corners and floors) use the best quality silicone caulk for baths and showers that you can find, The shower should be caulked only when it has been unused and is completely dry for a day or two, After you caulk, wait the recommended amount of time on the caulk label before using the shower. If the instructions are followed, your caulk will be in good shape for a long time. You can purchase the caulk in colors to match the grout both online and in the big box stores.

EPHROSS, you do realize this post is 8 years old, don't you?

Thank you Ephross--STILL helpful!!