Wolfgang's Bathroom Remodel

[Davy]

Hi Wolfgang, hope you're doing well. I can't say for sure why it cracked but I would remove the cracked grout, regrout it and move on.

[cx]

Have you at any time tested the foundation slab for moisture vapor emissions, Wolfgang?

If that treated wood was in fact dry (a year in unconditioned space would not guarantee that) and you sealed it all around except for its exposure to the SOG, it could begin swelling if your MVER was significant.

The only wood shower curb John Bridge reported having that problem with was one he had sealed completely to a SOG with Kerdi. I've personally seen the problem with any of mine, but most of them were built over my own slabs, which I try to seal well enough never to have a MVER problem.

Your cracking doesn't look quite like what I'd expect from that cause, but it could be just the beginning.

Or it could be something else.

My opinion; worth price charged.

[makethatkerdistick]

Hi Davy,
I am doing well. Have you had any jobs up here lately? I might have to re-grout but before I do that, I want to investigate more.

CX,
Not sure about my slab's vapor emission. This is close to an outside wall, and there is the chance for the slab to pass moisture, too. Not sure if that makes a difference. When I relocated the drain, I found out that a vapor barrier was used under the slab. Again, how effective this 50 year old barrier is, I don't know. Anecdotally, I have never observed aggravated moisture issues that would cause, say, smelly carpet or the like.

I didn't measure the water content of the pressure-treated lumber. But just the fact that it felt identical in weight to regular lumber led me to believe it was pretty dry and ok to use. Certainly a far cry from its wet brethren one picks up fresh from the store. But it's possible that there was more moisture than I assumed. The curb was completely wrapped in plastic, so there should be plastic between the slab and the wood. However, the Tapcons have made tiny holes in the plastic where they penetrate.

When you say this crack doesn't look like one caused by foundation moisture migration issues, does it look like it could have been caused by something else? I guess it's only guessing at this point, but it might still be helpful.

I am still nervous that there is slow moisture creep under the Kerdi seams, given that I folded the corners myself. But I was so very careful when I did that, and I observed the required overlap. I really hope it isn't anything caused by moisture intrusion from the shower proper. That would mean all of my work was wasted, wasn't it?

[cx]

Smelly carpet stage of moisture usually comes from hydrostatic moisture rather than vapor emissions in my experience, Wolfgang. The carpet and pad will generally just let such vapor emissions pass through with no indication at all.

If you wrapped the curb, including the bottom, I doubt much moisture would get in there from vapor emissions from the slab. But any moisture that gets in there will have no way ever to get out, which could cause a problem.

The cracking I see in your photo, especially the horizontal one in the front, would be typical of swelling curb wood, but I would expect it to be much more significant by the time you noticed it. Perhaps you're just more observant than the average shower user?

Or perhaps, as Davy says, it's nothing to worry about and you should pay no attention. I, on the other hand, don't think grout crack just happen, I believe them to have been caused. I hope I'm wrong about the cause of yours.

I wouldn't be too concerned about your Kerdi corners. Thousands of Kerdi showers, including my first two, have been constructed before Schluter even started producing those pre-formed corners. Not to mention all the cardboard box ice chests that were built and used.

The folded corners, done with care, are effective and judging by your work that we have seen I'd expect your corners were carefully done.

My opinion; worth price charged.

[makethatkerdistick]

CX, given the unknown cause which is difficult to assess, I might do the following:

1. Keep showering and watching. If a leak from above were the cause, with the slight crack in the grout, this would quickly exacerbate and make itself known by more swelling.

2. Consider drilling one or two relief holes in the outside portion of the curb. Dependent on finding some sort of decorative mini louvered vent I could put in place to cover it and call it a feature. That way, if (and only IF) the problem stems from vapor from the slab, this would allow for sufficient ventilation. This would mean I am breaching the water-tight construction in this spot, but water never gets there anyway.

One more thought: Maybe, in the course of the past three years, the PT lumber has reached its final moisture equilibrium of sorts, resulting in some additional deformation that caused the crack.

It's a detective story, but one I don't enjoy.

[Davy]

No, Wolfgang. I haven't had anymore jobs up your way. I've been spending most of my time in the Dallas rat race.

[cx]

That PT lumber has a serious habit of changing shape, Wolfgang, but I'd have expected it to do so before now, 'specially it having been a year old before you installed it. I would have expected it to have begun displaying some of that bad habit while it was just sitting idle in your garage.

I think at this point about all you can do is continue using the shower and watching the curb as Davy indicated. I can give you a theory, but I certainly can't tell you for sure what's going on there.

That's great news, Davy! How fun for you.

My opinion; worth price charged.

[makethatkerdistick]

Davy, I am so very glad I can avoid the Dallas traffic. If I hear of someone in need of a new shower, I'll bring attention to you.

CX, thank you for the time you take in responding to my questions now and over the years. Much appreciated, really! I might never meet you in person, but you've contributed much to all of my projects and you have shaped my thinking regarding all things construction.

CX, do you think it would be foolish to drill a vent hole in the outside portion of the curb? I think I want to do that. That way, I can drill some into the wood and judge with my own eyes and fingers what's going on. I suppose one could then also stick one of those moisture meters into the wood if no apparent wetness exists, no?

If I am lucky, and this is not because of a curb leak, then I would have a long-term way of dissipating moisture that might build up from the slab. If it's a leak, then the curb has to be redone anyway. And if it's a leak, then I will be very upset with the Schluter method.

[makethatkerdistick]

I decided to drill a 1 3/4 in hole in the tile, then step down to preserve a flange of Kerdi fabric for sealing, if water ever got around the outside of the curb.
After drilling deep into the wood, turns out it is all bone dry. Thus very, very unlikely I have a leak.
I believe the crack I have is movement stress, however it occurred. I will remove epoxy grout in this area and probably refill with color-matched silicone. I would prefer grout but have to anticipate another crack if expansion/contraction is responsible for this. Probably wasteful to get a mini batch of Spectralock just for this small area. I am still debating this.

So relieved that there does not seem to be a leak. I will install a louvered cover over the hole and will now have an escape route if water vapor from the slab should ever pose a problem. I don’t think that is the culprit in my case.

[cx]

Enlightening, Wolfgang, and probably worthwhile just for your peace of mind. I like the idea of a flexible sealant instead of grout where the cracks appeared.

My opinion; worth price charged.

[makethatkerdistick]

I removed the epoxy grout with a carbide blade and my oscillating tool. Dusty work! As I was cleaning up the joints, I decided to replace the sealant in the short vertical line on the shower curb's inner wall (the inside of the 135 deg. angle). As I poked at it towards the floor, water started to come out. Perhaps not much (maybe an ounce altogether), but this had me worried.
Maybe that's the Achilles' heel of epoxy grout: its inability to let residual moisture dry out.

I decided to leave a little weep hole in this spot and also make another one at the curb to wall transition where some additional moisture wept out.

Anyway, here are three theories why this small grout crack happened in the first place:

1.) moisture buildup by the curb to shower floor transition (Perhaps, long-term exposure over months/years made the Kerdi seam wick some moisture that caused problems in the curb?

2.) foundation vapor transfer

3.) residual shrinking/warping of the PT lumber

I hope that the weep holes will take care of 1.)

Some of you might remember the wicking discussion on Isaac Ostroem's Youtube channel. One of his complaints was that Kerdi that remained wet over extended periods would eventually wick moisture through the seam. He had some good videos to back up his claim. Now, his experiment had hydrostatic pressure through a large vessel filled with water whereas my shower did not. But still....

Anyway, I hope this will settle my issues. I might make one or two weep holes in my other shower as well. Or does anyone see a problem with my thinking here?

[cx]

I find no fault with your weep hole plan, Wolfgang.