Do it Yourself (if you must)

[cx]

It's pretty tough stuff, Skyler, but clean up your cuts as much as you can, just on general principal, anyway, eh?

[zinctoo]

I mentioned on an earlier post a plumbing problem that caused me to have to remove the CBU I'd installed. That problem was that I had a (very reputable) plumbing company out to do some work, and they made a mistake and flooded the stud bay right next to my new shower. The water splashed all around and got under the pan, thoroughly soaking my preslope. The plumber said it would dry out in a few days, and I took him at his word.

Well, because I've got the CBU removed and the pan liner pulled up at the corners, I can see that the preslope was much darker than it should be, indicating it was still damp. I stuck a box fan on it over night and it dried and lighted up in color. However, if I pull the pan back further, closer to the drain and the curb, I can see that the preslope is still dark, still damp.

Thank goodness I used western red cedar heartwood for the curb.

My hope is that the moisture that's under the PVC pan liner will evaporate out through the exposed area of the preslope. I can't pull the pan back any further than I already have because of the drain clamp and the mud curb that's built over it.

Will the preslope dry out in time? If the preslope doesn't fully dry, how boned am I?

[cx]

Should dry out in time, Skyler, but I'd still wanna leave it open as long as I could 'till it just had to be closed up again. A dehumidifier in the room would help, too.

My opinion; worth price charged.

[zinctoo]

CX, thanks a lot. That's reassuring. I hope you don't mind all the questions, I've got a few more

This bathroom floor was previously leveled with leveling compound. Unfortunately, there are a few spots where the leveling compound pulled up with the previous tile. I think that I need to bring these areas up to the height of the surrounding floor before I lay new tile.

I've mixed small batches of leveling compound before and had a lot of trouble with it. It's difficult to mix such small amounts and if I don't get it just right, it's a terrible pain to grind it away once it's dry.

My question is, can I fill in these low spots with thinset? My plan is to use AquaDefense over the floor area as an isolation membrane prior to tiling the bathroom floor (note I'm talking about the bathroom floor, not the shower floor). I'm thinking I'd patch these spots with thinset, let that dry, AquaDefense over it all, let that dry, then tile over that.

[cx]

That's not an appropriate use of thinset mortar, Skyler, but you can do it if you want. It's not an approved use according to either the product manufacturer nor the ceramic tile industry, but it's done. There are many cementitious patching compounds out there that are made for the purpose and would be more appropriate.

My opinion; worth price charged.

[zinctoo]

Alright, something more appropriate than thinset it is. Thanks for the quick reply!

[zinctoo]

How long after creating my top layer of deck mud must I wait before tiling it?

I'm pretty sure that I read an earlier discussion on the forum that said you could tile the next day but I can't manage to find it via search or my browser history.

As always, thanks in advance.

[cx]

For tiling on "cured" mortar beds the industry recommends a minimum of 20 hours cure time, but indicates more cure time is desirable and as much as 10 days being preferable. Real life? In a shower-size installation you can tile over your mud as soon as it's solid enough to work over.

Cured mortar bed, by the way, means as opposed to wet-setting over a still workable mortar bed using the old "splash and dash" thick-bed method used for many, many years before the advent of thinset bonding mortars.

If you've just completed your mortar bed, I'd recommend you wait at least until tomorrow to tile it. And I'd recommend you cover it with polyethylene sheeting or similar until then.

My opinion; worth price charged.

[zinctoo]

Thanks for your quick reply, CX. I actually completed it on Monday. I did not cover it, unfortunately, but because of the weather we've had here lately, the room has been cool and dark, so hopefully that had some beneficial effect.

Interesting info about the older way of constructing these, by the way.

Also, I should say, I'm glad I asked if I needed to notch out the studs further by the pan liner. I absolutely did. The CBU is now perfectly plumb and it looks really great. I'm aware that some people don't notch at all, and that sounds completely insane to me now that I know just how much you have to notch out to get it to look good.

[cx]

Cool and dark is OK, but damp is what you really need for curing any Portland cement mix. You don't want any drying at all, you want it to cure first.

Notching wasn't a necessity in the old days when mud walls were the norm. You just made your mud fit what you had to work with. 'Specially true with one-coat mud where you had a half-inch space at the bottom anyway.

[zinctoo]

CX, about covering the deck mud, that's good to know. If I do this again, I'll be sure to do that. Thankfully, not covering it doesn't appear to have had an adverse affect. The surface is strong and I can't easily dent it (caveat I haven't gone out of my way to try to dent it). There were some crumbles on the surface, but those were easily vacuumed away. I've stood on it and it holds my weight and doesn't show any real visible signs from me being on it.

Looking around now, I see folks recommending covering the deck mud after floating it. I pretty much used https://www.johnbridge.com/how-to/deck-mud/ as my how-to, and I re-read it over a dozen times before I did this work. Would it be possible to update this article to mention that step?

[zinctoo]

In an earlier reply, CX, you said not to paint the bottom edge of the CBU with waterproofing (the part that faces the pan liner) because if water got into the CBU, it would need a way to drain into the pain. I did not paint the bottom of the CBU edge for this reason.

I started to wonder though, how typical is it that water gets into the CBU? If the walls are coated well with waterproofing (like AquaDefense or RedGuard), should that not prevent water from getting into the CBU? Or is it safest to assume that some water will get in regardless, and to provide a path for it to escape?

[cx]

Originally Posted by Skyler

Or is it safest to assume that some water will get in regardless, and to provide a path for it to escape?

That's been my assumption and experience for at least 50 years, Skyler. And when it's easier to provide the escape path than to close it, it makes even more sense to me.

Where will the moisture come from that is likely to enter the CBU when a direct bonded waterproofing membrane is used? Likely from the back side, but there will always be at least a little moisture vapor pass through the membrane when the hot shower is in use and the surrounding walls are cooler. Not much mind you, the amount depending upon the perm rating of the particular membrane and the temperature differential, but some. It'll condense somewhere. Give it room is my approach, based upon theory and experience with other waterproofing methods.

If you paint the bottom edge of your CBU wallboard, will you ever have a problem? I doubt it. Will you even know? I doubt it. Would I leave it open, anyway? Yes, I would.

My opinion; worth price charged.

[Kman]

Originally Posted by CX

That's been my assumption and experience for at least 50 years...

All these years, I thought you were older than cement board.....

[cx]

Oh, I am, Kevin, much older.

But my moisture experience pre-dates even my construction and tile experience, although it didn't actually begin until maybe 60 years ago. I just shortened the time span so's you wouldn't think I was braggin'.