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Unread 01-14-2021, 03:11 PM   #1
Lee Batchelor
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Re-caulking a shower

Greetings. I’m new here and need some advice.

I installed a man-made marble shower base and wall surrounds about 6 years ago. My question has to do with caulking. I've re-caulked the shower twice and always ended up with mold in the corners of the walls and tray. Each time I remove the old caulking, there is old water (brownish) in the crack between the walls and tray lip. I'm trying to determine where it's coming from. There are two glass doors - one fixed and the other slides on rollers. The fixed door is at the shower head end. The manufacturer says to not caulk any parts of the door on the inside of the shower, only the outside.

1) Is it possible that the water is seeping behind the marble walls where the vertical fixed door framing hardware is attached?

2) Am I using the wrong caulking technique? I have always applied the caulking and then rounded it inward with my finger. I watched a YouTube video about this and the fellow said that was the worst way to do it because it will always leak where the thin part contacts the wall and shower tray. Instead, he suggested using a 45 degree tool to create a more positive bond. That is, the finished caulking would be like a triangle shape instead of an hourglass.

3) When I installed the tray, I made sure it was as level as possible. The subfloor is very sturdy and I embedded the tray in concrete. The leaking area is on an inside wall. There is no significant flex that I can determine.

So, how is the water getting in? I feel I really need to solve this before re-caulking.

I’ve also heard that the GE Silicone caulking is not that good and that I’m better to use something like Mapei caulking. Any thoughts on that? Many thanks...
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Unread 01-14-2021, 07:43 PM   #2
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Welcome to the forum, Lee.

Simply using your finger to tool the joint with feather-thin edges is not the best method. The delicate feather-edges have a habit of fraying and a certain amount of soap & moisture get under there and mold a bit. But it doesn’t automatically mean it will leak. I can say this with authority, as most aquariums I’ve seen are caulked with this exact method and I don’t see most of them leaking.

But I do agree with this unknown YouTuber to use a smoothing tool to give your beads a triangular shap. That’s a great idea. The edges will be more durable...and I think the bead looks much neater. Spraying the bead with a pH-neutral cleaner...or denatured alcohol immediately after gunning the bead and just before tooling really helps to shape the bead beautifully.

I suspect water getting into the walls at the wall-to-pan junction behind the shower door jamb. The first question I have for you is this: when you installed your cultured marble pan and walls, did you caulk all the joints BEFORE you installed the shower doors?

Next, I’ve installed a lot of shower doors over the decades and I’ve never, ever had an installation manual say to only caulk the outside. No, rather the exact opposite: they always have said to only caulk the inside. I’m not doubting you, but I’d like to know who is saying this so I can understand what’s unique.

As an interesting bit: many silicone sealants have mildewcide added to them to hinder the formation of mold. But it leeches from the sealant and is generally gone within 6 months. I had one manufacturer tell me that he can only add a little bit, he says that if he adds any more, the caulk would be under all the regulations of a pesticide and he’s got no interest in that. As far as exact sealants, GE makes several varieties and they are generally good products.

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Unread 01-15-2021, 08:02 AM   #3
Lee Batchelor
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Many thanks for the quick reply, Bubba (if I may) .

Great analogy about the fish tank and where to apply caulking. The door manufacturer is Microtek. Their manual says to not caulk on the inside but only on the outside. You’re the second person to tell me that’s wrong. I agree. Getting back to your fish tank analogy, assuming the structural integrity of the tank is sound and you caulk the outside of the tank, the joints would fill with water – not good.

I caulked all the joints before installing the doors. I uploaded some pics after I removed the old caulking. It's been drying for about 6 days. The caulking joints are 1/8 inch or less. Pic 1 shows the bottom of the marble wall where the shower head is located. I removed the vertical trim piece that holds the fixed door in place so I could caulk all the way through. Pic 2 shows the trim piece in place. I only caulked the outside as per the manufacturer’s instructions. Pic 3 shows the various components screwed to the shower head wall. The piece marked “Not caulked” has a rubber seal but I’ve often heard it said that you should run a clear bead of silicon around the two sides and top, leaving the bottom open in case a bit of water seeps through over time. That way, it can drain.

So, I would conclude that perhaps the water is seeping in behind the wall and tray lip because the door is caulked only on the outside, although that’s hard to figure because that horizontal joint is caulked first and left to dry. The doors are re-installed the next day. Any further thoughts as to why I’m getting water between the tray lip and wall are very much appreciated. Thanks again for the great input !
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Unread 01-15-2021, 08:15 AM   #4
Lee Batchelor
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Here are some more thoughts.

I wish I had taken pics before the caulking removal. The mold was bad in the opposite corner to Pic 1, that is, to the far right where it meets the long marble wall. I wonder if it simply broke down and the water got behind it that way. The long wall also had water behind the lip. I should have mentioned that.

I have developed a ton of skills over the past 50 years including, electrical, plumbing, drywall finishing, cabinet making...you name it. The one thing I suck at is caulking. Could this water problem be caused by simple pilot error?

The caulking I removed was way to wide, on the order of about 3/8 inch on each axis. With the caulking tool, to will be far smaller and more uniform. As mentioned, I really want to find out why there’s water back there before re-caulking. It’s just the wife and I living here now and we have another full bathroom, so I have the luxury of time.
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Unread 01-16-2021, 09:06 AM   #5
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Is the shower head on the left wall and spraying onto the right, moldy, wall?
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Unread 01-16-2021, 09:46 AM   #6
Lee Batchelor
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The shower head is directly above on the wall in the pics. I attached a pic of the whole setup. The shower head is on the left wall, which is also the wall in the previous pics.

Note how I placed the controller valve on the long wall. It has a cover plate with a rubber seal but I wonder if the water is seeping behind it. Should it also be sealed? Is it possible the water is getting in through it? The water was also found over to the seat but stopped under the seat area.

More ideas welcome. I'm ready to caulk. Thanks...
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Unread 01-16-2021, 06:11 PM   #7
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If the sealing ring is the neoprene variety, those seal pretty good if the are compressed nice & snug.

Where is the area with the most mold you were talking about?

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Unread 01-16-2021, 08:01 PM   #8
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There were three primary clusters, as sown in the pic - yellow circles. The rest was clean. If memory serves, I believe the ring seal was a high-grade rubber, similar to neoprene. The fixtures were all made by Riobel. Pretty good stuff, although the water control valve is not great. Thanks!
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Unread 01-18-2021, 12:40 AM   #9
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Oh, man. I wish there was a key identifier to positively point to something. I know you’re ready to caulk, so you might not be interested in continuing to investigate. I’ll share my thoughts on trying to exhaust all possibilities. In no particular order: the screw holes to hold up the vertical shower jamb track. It is a vertical wall, which is much less prone to water infiltration than a horizontal penetration, but a possibility. It looks like you’ve squirted it with silicone before putting the screw in, but that may or may not do the trick. With that track being caulked on the outside, those penetrations will see plenty of plenty of water due to capillary action.

What about that handle by the niche...are there fasteners penetrating the wall for that?

Next, that drop ell with the neoprene-like washer...if there’s any reason to suspect that, I’d run a bead of silicone around that, except for the bottom (as you mentioned).

Next, since new silicone doesn’t stick to cured silicone, how have you been removing all traces of the old silicone before you re-caulk?

Another thought is this: if there really is water getting into the wall on any sort of regular basis, it’s not going to stop after it fills the little crack joint...it’s going to slowly overflow to somewhere else. It would affect the walls or subfloor or framing in terms of moisture damage. If you’ve been finding moisture in the caulked cracks for years, but there’s no other signs of moisture damage, it would be consistent with the caulk simply not sealing the cracks...that water was coming from the front side, not some other funky path. Which makes me ask again: How have you been cleaning all the silicone residue before recaulking?

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Unread 01-18-2021, 07:49 AM   #10
Lee Batchelor
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First, allow me to express my gratitude, Bubba. You’ve been very patient and an enormous help. I promise this will be my last post on this thread.

To your points
  • Screw holes I dabbed them first with clear silicon and then screwed the vertical metal piece on. There could be some slow leakage there. Caulking on the inside of the door piece, as so many have suggested, will be done despite the manufacturer’s guidelines.
  • Niche It is held in place with silicone only. There are two hooks on the underside, where the blue scrub brush hangs in the pic. The hooks are held in place with PL Premium.
  • Drop ell and all other chrome pieces will be siliconed top and sides.
  • Caulk removal I have always run a slit in the middle of the bead and peeled as much away as possible. Then, a new razor blade was used to scrape off the remaining caulk. The surface was then scrubbed with a nylon scratch pad with Vim soap. After a thorough rinse and drying period, I used Isopropyl alcohol 70%, to clean before caulking. Even after all that, I can still feel scant traces of the original caulk in places. It seems almost impossible to get rid of it all. Even after the first caulking where there was no previous caulking, after removing that layer, there was water behind the wall, so I suspect other infiltration points.
  • Underside of the shower is visible from the basement below it. There are no water marks, so I suspect you’re correct about the water getting in but finding a way to ooze back out again before overflowing.
Conclusion
I think my best bet is to caulk using the finishing tool instead of my fingers. Apply caulking to all chrome piece sides and top. Caulk the inside of the shower door trim pieces.

With your help, I’ve discovered several possible flaws in my application techniques and places where the caulking was missed. Despite this being my final post, if you have any other thoughts, please feel free to share. I’ll check back on occasion.

Again, many thanks for your help Bubba !
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Unread 01-18-2021, 11:17 AM   #11
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No limit to questions, Lee! Hang around as long as you like.

For removing all the traces of your silicone, I’d suggest this: use mineral spirits and a white nylon scrub pad (the kind that doesn’t scratch....meaning the cheap ones). The mineral spirits will slowly soften and dissolve the silicone, but it takes time to break the silicone down. So I dip that nylon scrubbie in a small pail with mineral soirits and I wet the caulk residue. Then in a few minutes, I wet it again. As it softens, I gently scrub the surface and it starts coming off in messy bits. You’ll need plenty of paper towels to help out. I keep using the scrubbie unless it gets too gummed up. You might new a few scrubbies. Eventually, it’ll be 100% clean. After allowing any cracks that harbor the mineral spirits (due to capillary action), I clean with denatured alcohol. Then apply the new caulk. The process is slow. However, the good news is that you’ve got a majority of the old stuff off, so it won’t take as long.

Be sure to collect all those mineral spirit-soaked paper towels and dispose of them properly. They are in danger of spontaneous combustion if you inappropriately just stuff them in a garbage or something. I like to simply burn them to eliminate the danger.

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Unread 01-18-2021, 01:07 PM   #12
Lee Batchelor
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Thanks, Bubba! I never thought of using mineral spirits. Good idea! I do have the luxury of time, thanks to this Covid nonsense and one spare full washroom. I can also burn the used paper towels.

Again, thanks for the help !
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