Return to the Bathrooms Forum | Post a Follow-Up

 o
areas of dark grout lines in new shower

Posted by metcarl (My Page) on
Sun, Sep 15, 13 at 18:38

Our shower has just been redone (because of mold/leaking/improper tiling job). It looks beautiful, except that the medium gray grout lines are staying dark. Immediately after showering, most of the grout appears wet. Several hours later and even 4 days later, the are multiple areas where the grout remains dark. They are in different areas - along the edges, some by the drain and others near neither the edge or the drain.

I discussed this with my contractor and tiler who first questioned if we were using the fan. Yes, we are using the fan and leaving it on for hours and days and leaving the shower door open. Then, the tiler came back out and said that the grout is staying wet because of the mud base becoming saturated and remaining wet. As the mud becomes more saturated, the darker areas may even begin to change. He said that when demo-ing some showers that haven't been used in weeks to months that the mud base can still be wet. (yes, but were they supposed to be?)

My main concern is mold becoming a problem. If the tiler's explanation is basically that the grout is never drying out because the mud base remain wet, then won't there be mold problems?

I have been reading the forums and know to ask about adequate preslope (not just slope) and clogged weepholes and what mortar mix was used. I just wanted to make sure that this wasn't an adequate explanation before I proceeded.


Follow-Up Postings:

 o
RE: areas of dark grout lines in new shower

Ask him if the membrane is sitting flat on the subfloor, or if it is sloped to the drain. By code, the membrane itself needs to be sloped.

He should have:

1) on top of the flat subfloor, set a SLOPED layer of deck mud that is sloped to the drain.

2) the membrane then gets set on top of that sloped mud. Note the membrane is sloped.

3) On top of the membrane goes another layer of mud, by it sitting on top of the sloped membrane, the surface of that top layer of mud will also be sloped to the drain.

4) Then you tile.

With this type of construction, the drain used is known as a clamping drain. It "clamps" over the membrane. The drain has weep holes in the lower part of it, you can't see them after the shower is built unless you pull the drain cover grate and look down the drain opening. They'll look like pinholes in the cylindrical walls of the drain.

When you shower, most of the water will sheet over the tile and grout and go down the drain.

However, some water may go through the grout and get into the mud. As it "percolates" through the mud, it'll eventually hit the sloped membrane. It will then follow the slope to the drain and go through the weep holes and then down the drain.

Problems are usually twofold:

1) Quite a few installers simply install the membrane itself flat on the subfloor and put a single layer of sloped mud on top of it, and tile over that mud. Water that gets into the mud will then hit the flat membrane and simply sit there. That's why code requires the membrane itself to be sloped.

2) Clogged weep holes. Conscientious installers will surround the weepholes with a handful of pea gravel, some use tile spacers. Then they pack the layer of deck mud over the gravel. The goal is to keep deck mud from clogging the weep holes, the gravel allows moisture to flow through the holes a little easier.

And another thing. You mention dampness "...in different areas - along the edges, some by the drain and others near neither the edge or the drain."

If the floor/wall intersection remains wet, that can be because the floor slope has flattened out by the wall and it's not draining well. Around the drain, it can sometimes be because the same thing, or because the drain grate sits slightly higher than the tile and it holding a bit of water around the edge of the drain.

If there is a simply a damp ring (not standing water) surrounding the drain, that can sometimes indicate that the membrane is sloped...that moisture in the mud layer is indeed following the slope of the membrane to the weep holes...but the weep holes are clogged so the moisture can't escape.

And lastly, the mud should be made from sand and portland cement. On occasion I've come across a few showers where the fool installer used a bagged mortar mix. Mortar mixes can contain lime, and lime can cause the "mud" to hold water.

And lastly....sealers. If the floor was sealed and too much sealer used, sometimes sealer can get down into the mud and screw things up.

So there are a lot of possible issues here.

Here's a little photo primer from Harry Dunbar regarding sloped membrane showers and weepholes.

" If the tiler's explanation is basically that the grout is never drying out because the mud base remain wet, then won't there be mold problems? "

There could be. The fact that your tiler seems sort of apathetic about this is what worries me. Along the idea of "I built you a shower that will never dry out, and that's the way it is".


 o
RE: areas of dark grout lines in new shower

So, the shower has been drying out for 10 days with a humidifier, with no change. There are still some areas of dark grout. However, the lines do not disappear with a hairdryer as well.

Our contractor has talked to others about this problem and most have had this happen on occasion and they all feel that the job was done correctly (not sure how they know this). They thought that If the mud bed was wet at all, all of the grout lines would be darkened. And that all of the moisture should have been pulled out by the humidifier.

Not sure where to go from here.


 o
RE: areas of dark grout lines in new shower

So, the shower has been drying out for 10 days with a humidifier, with no change. There are still some areas of dark grout. However, the lines do not disappear with a hairdryer as well.

Our contractor has talked to others about this problem and most have had this happen on occasion and they all feel that the job was done correctly (not sure how they know this). They thought that If the mud bed was wet at all, all of the grout lines would be darkened. And that all of the moisture should have been pulled out by the humidifier.

Not sure where to go from here.


 o
RE: areas of dark grout lines in new shower

Mongoct, now I get it! Great information in your post and the link was very informative too.


 o
RE: areas of dark grout lines in new shower

Enduring, thanks.

metcarl, did you find out if your membrane is flat or sloped?


 o
RE: areas of dark grout lines in new shower

What ended up happening here? We are having a similar problem in one of our showers?


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Bathrooms Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here