Ask Your Question

Angie's List Answers is the trusted spot to ask home improvement and health questions and get answers from service companies, health providers and consumers. For ratings and reviews on companies in your area, search Angie's List.

Top 30 Days Experts
Rank Leader Points*
1 kstreett 240
2 Guest_9020487 110
3 Guest_9190926 105
4 GoldenKid 100
5 ahowell 95
6 KnowledgeBase 95
7 skbloom 80
8 Guest_98024861 70
9 Guest_9311297 70
10 Guest_9400529 70

*Updates every 4 hours

Browse Projects By Category

Question DetailsAsked on 6/14/2014

Basement shower has grout missing at base, and MOLD

A large spot of black mold recently appeared on the floor tiles of the basement shower.
I just noticed that about a foot of grout is missing between the wall and ceiling. Naturally, we
want to re-grout. But the worry is that the shower dampness may have gotten into the wall behind
the shower tiles. Should we cut into the wall to be on the safe side, or just re-seal the grout.
Also, this shower was installed by a contractor 3 years ago. Does this possibly mean that the installation
was not done correctly?

Do you have the same question? Follow this Question

2 Answers

Voted Best Answer

Lot of what ifs in your case, and of course without hands-on checking hard to tell, but here is my shot at it, having torn into a LOT of moldy showers and baths - my Dad was a tile and countertop contractor, so I spent time working with him and commonly when young got the tearout and regrout jobs.

You say mold on floor tiles - generally black mold is because of constant high humidity and lack of cleaning, though can at times be a sign of water seeping through from behind. Probably due to floor not being scrubbed clean of soap scum and shower and not being aired out - doors left open when not in use and fan not run for 15-30 minutes after shower/bath. Bathroom showers/baths commonly have more mildew/mold issues due to geneally higher basement humidity, plus commonly not used as often so no soap or shampoo to help keep it under control and wash away the mold spores before they start a colony. And possibly D/S bathroom humidity is consistently too high - if so, you will eventually have brown or black mold on walls too, generally starting at top of walls over the bath/shower area, or on ceiling in that area if ceiling paint is not bathroom rated or does not have mold resistant additive in it.

Missing grout for a foot between wall and ceiling - that I don't visualize - you should not have bare grout (except joints) anywhere, so do you mean missing a foot of tile, or maybe you meant a foot of plaster has come off ? Or do you mean about a foot of grout has fallen out of one or more joints, or maybe grout at the top edge (which should be caulk, not grout) has come off. Or maybe you have tiled shower ceiling and you mean a foot of grout at wall/ceiling interface - which should not be grout. Reentrant corners like that should be caulked, not grouted - or grouted half depth and surface caulked, because house and wall shrinkage and expansion WILL crack those joints.

(Photos would certainly help here - you can provide additional info or response to answerer on a question if desired using the Answer This Question button right below your question, and there is a tool to add photos there too).

If you had loose tiles it would be easy to drill a hole in the backer board with a hole saw and test / fiber optic inspect for moisture/rot behind the tile. You can still do that from behind the wall (other side) depending on what is there, but takes 1/2" hole typically for fiber optic scope, more like 4 inches for mirror and moisture tester. Can also get an idea, indirectly, using thermal IR scanner (non-destructive) but costs a lot more to have done.

Not seeing your situation makes it hard to make a call. If I were you, but this is because I have two fiber optic inspection tools (wand and camera type) I would try to access the wall from above the tile in the shower (if does not go to ceiling) or from back of wall if easier to patch there and check through 3-4 holes for leakage through the backer board or water barrier. This would not tell you if there is water getting behind the tile or not, but would tell you if getting into the wall and starting to rot. Could also inspect from below to check under wall, drill through base of wall into bottom part of wall where water would accumulate, and under shower base by going up through downstairs/basement ceiling. Can sometimes reduce drywall hole repairs, especially in ceilings, by getting tricky and going up next to deenergized light fixture electrical boxes so patched hole is covered by light fixture base or by going through similar existing openings like under HVAC vent covers. Of course, all inspection holes should be repaired in kind - meaning with waterproof grout or sealant if through the bathroom walls, drywall compound if through other drywall.

Some plumbers have inspection tools, a very few thermal IR cameras - normally insulation auditors who have those. Can rent fiber optic inspection tool/camera for about $20-25/day at tool rental and some auto supply stores (used for looking into engines and such through drain plugs or sparkplug holes), or buhy at Amazon or places like Harborfreight Tools for about $40-50 for manual (hold to eye) type or under $100 for color camera type (has 2-4 inch screen on tool plus some can download to digital storage or computer).

Answered 6 years ago by LCD


Thanks for the awesome, detailed response, LCD!

I'd wanted to edit that "foot of grout" sentence, but was unable to. I'd meant a crack suddenly appeared along the base, where the shower floor meets the wall. You're probably correct about the house expansion and shrinkage. It's an old house, and we had an unusually long, cold winter followed by massive rains.

I'll hunt around to try and fine someone in our area with the inspection tools that you mention. Wish you were in Queens!

Thank you again.

Answered 6 years ago by 1960


As you found out, you can only edit a question while preparing it for entry - after that, using the Answer This Question button, as you did, is the right way to keep followup details, photos, thank yours etc on the same thread.

If your walls are prefab "surround" panels with a prefab tub or shower floor this location usually does not do more than get grundgy, because IF property installed, the wall panels overlap INSIDE the outer lip in the tub or shower liner - in other words, the tub or shower pan has a roughly 1 inch or higher lip (called the "tiling flange" around the outer edge that you don't see once installed - and the surround or backer board and tile SHOULD come down inside this lip almost to the tub/shower base - just like sheets of roofing felt or house wrap overlap top over bottom layer. Looks like diagram in this blog - down page from the first photo -

So, unless you really back the water up at the edges of the tub or shower liner (more than standing water onlip from showering) it cannot leak up over that outer lip even if the bottom wall joint is totally open. Will get moldy and such, though, and eventually bottom of surround or tile may start breaking off backer board if water gets back there.

If a fully tiled shower, with tiles shower base and walls, the shower pan (under the tile) should still come 4 or more inches up the wall behind the tile and bottom edge of the backer board, so a true "leak" outside the pan from this wall/floor joint should not happen, though that water will go down under the tile itself through the concrete mat underneath until it hits the liner or pan and gets diverted to the drain - out of sight to you. This will eventually deteriorate the tile and can also start smelling really septic. To prevent this I like to put in an equivalent to a shower edge lip tile all around the edge of the shower floor - as well as sloping to the drain of course, so even if the bottom joint opens up the water has nowhere to go. Looks like the diagram here, except where is says

"tub deck" that is the floor, and instead of an integral lip that is high-lip reverse bullnose tile, with the wall tile coming down to and on top of the flat part of the bullnose. Some manufacturers make special tile for this, some you have to use the highest bullnose or base they have. Wall tile should always overlap wall - wall tile should not go down behind the edge of floor tile.

My philosophy - reentrant (inward-bending) wall corners (the two back corners in normal bath or shower), all shower/tub door frames and vertical door/glass enclosure panels (inside face anyway - clear silicone OK for outside joint for appearance purposes, though tends ot discolor and show dirt easier), and bottom joint between wall surround or wall tile and the tub or shower itself - should ALL be done with the grout or adhesive or whatever is adheringti to the wall at the back of the joint (as applicable), but a good mildew resistant Tub and Tile Caulk (I like the siliconized latex Dap products) should be used for the front 1/4" or so of those joints - and for all inside joint caulking on door frames and where vertical glass panels meet wall or tub. These joints have too much movement from seasonal changes in wood and metal, and also from heating and cooling from the shower (1/8 or more movement just from that at times over the length of a wall) for glue or grout to stay uncracked - so a flexible caulk is needed, and commonly needs at least partial gouging out and redoing about every 5 years or less (though mine now needs it due to start of mold behind the caulk lips, though zero cracking, after about 15 years with Dap), especially in the reenterant corners and around tub spout which tend to open up the most easily.

Answered 6 years ago by LCD

Related Questions

Terms Of Use
Privacy Policy