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metcarl_gw

areas of dark grout lines in new shower

metcarl
10 years ago

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.

Featured Answer
  • MongoCT
    10 years ago
    last modified: 9 years ago

    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".

    Comments (28)

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