Bathtub installation -- order of installation (end pony wall, tub, heated floor)?

[jch]

I took out the toilet drain stub tonight and then could see that the cracks go all the way through the SLC.

Also, now that it's been 10 days, no more new cracks have appeared. Now I can see a pattern--they're approximately over top of the structural members--joists and blocking. Which tells me the 3/4" T&G exterior ply is "hammoking" between joists.

Regardless, the SLC is firmly bonded to it.

Put down the Ditra tonight--using their 4.5mm square notch trowel--worked really well. Thanks for all the advice.

For laying the 12x24" tiles, do I make all my cuts before I start thinsetting them down? Or do you recommend I cut as I go??

[jadnashua]

Gluing the subfloor to the joists when nailing or screwing it down can help a lot with this. What you see is one reason why they require TWO layers of ply for natural stone installations. The edge of a board will act like a lever when there's deflection between the joists. That's also why you don't line up the joints on sheets - the top layer should be 1/4-span past a joist. This can also happen if the subfloor is not installed perpendicular to the joists, as it is much stronger across the joists due to the face grain. If your joist spacing is within specs, you'll probably be okay. Ditra can help if the subfloor is within specs. This is one reason a lot of pros like to install a second layer of ply regardless of whether it is for ceramic or stone. INdustry standards call for a minimum of 5/8" ply on 16"oc joists, but again, most people don't like the minimum, as it leaves little margin for error.

As long as there's no vertical displacement on the cracks, you should be okay.

Precutting sort of depends. Any little miscalculation can be exagerated when setting. On a small room, probably not a big deal - it can be huge on a large install. Off by 1/32" over a row of 32 tile, is an inch, which would likely be unacceptable. But, if you have layout lines and are constantly correcting as you go, it's not as big a deal. Depends on how many, if any, critical things you have in the middle. If it is a clear, unobstructed job, since you need a gap at the edges, being off a little isn't a big issue as long as the baseboard will cover it.

[jch]

That's what's puzzling about this.

- I glued and screwed the 3/4" exterior t&g ply to the joists and the blocking using deck screws and construction adhesive (PL400)
- I ran the ply's face grain perpendicular to the joists (see photos earlier in thread)
- the cracks are not at the plywood joints--instead they seem to roughly follow all the joists and blocking
- I have a layer of 1/2" ply that I was about to install over the 3/4" (using the staggered offset you describe) but the TCNA and Ditra manuals convinced me that it wasn't necessary. In hindsight I should've eaten the extra headroom and used it. I won't know until the tile is installed over the Ditra whether this was a critical error.



On another note, I mixed 1/3 bag of thinset when putting down the Ditra and it wasn't enough. Had to stop part way through and mix more (which is much harder than mixing entire bags).

Trying to figure out whether I should continue to mix small batches and cut tiles as i go when laying the tile or whether I should precut a bunch so I can lay a lot at once.

Would it work better to lay the uncut field tiles first in one big batch, then go back and do the cuts for the perimeter tiles and then lay them as a group???

[chefwong]

Depends on what works for your flow....

You could consider installing ditra, prefilling the waffles, run your chalk lines and then decide on a starting point and lay that tile true.

[johnfrwhipple]

Always better to mix your setting materials in smaller batches as you go. If you open the bag up most drill bits will fit into the bag so you can dry mix your thin-set. Make sure to follow the mix ratio's when you mix small lots.

[jch]

I don't know whether I'd have the nerve to run my mixing paddle in the dry bag... Visions of tearing through it and having powder everywhere. :-)

But I agree that it'll end up being small batches. It just seems to put a lot of air into the mix when there isn't enough to completely cover the mixing paddle. I'm using a Makita fixed-speed mixing drill (600 rpm) with a double-box paddle.


In terms of layout/lippage, leaning towards using QEP's LASH system with 1/8" spacers. Tiles are 12x24" porcelain, rectified, with a beveled edge:

Would it work better to lay the uncut field tiles first in one big batch, then go back and do the cuts for the perimeter tiles and then lay them as a group???

In particular, if I did it this way, how would I minimize lippage between the uncut field tiles that i set initially and the trimmed perimeter tiles that I set a few days later? Do I install LASH ties on the perimeter edge of the field tiles during the initial set so they're there for when I install the perimeter tiles??

[jch]

In terms of layout/lippage, leaning towards using QEP's LASH system with 1/8" spacers. Tiles are 12x24" porcelain, rectified, with a beveled edge.

In particular, if I did it this way, how would I minimize lippage between the uncut field tiles that i set initially and the trimmed perimeter tiles that I set a few days later? Do I install LASH ties on the perimeter edge of the field tiles during the initial set so they're there for when I install the perimeter tiles??

I just called QEP and they told me this:
- When ending a row for the day, make sure your edge tiles are level
- Slide some LASH wedges under the free edges to support the tiles at that orientation
- Once they're supported, use a LASH clip to dig out the still-wet thinset from where the clips will be installed when you resume tiling.
- Don't leave these clips there--you won't be able to get them straight enough. Just make room for them.
- When you resume tiling, slide some fresh thinset under the existing tiles' edges (where you tunneled the thinset out previously), install a LASH clip, and continue tiling.

I haven't tried it, so I'm not sure how much of a pain this would be, but that's their recommendation.


So, would you people recommend for or against my idea of setting all the full-size field tiles in one pass, waiting a couple of days for it to set, then measuring and cutting all the perimeter tiles?

[johnfrwhipple]

I've done this before. It is a solid plan of attack. You might find it's nice to break up the routine by cutting some tiles.

Just start and see how you feel - there are no tile police going to be checking on order of events.

One thing to remember with those Lash clips is that they do hold the tile a little of the floor so if you have a corner where the tile needs to be quite tight to the floor you may need to trim the clip bottom. The Raymondi system is similar to lash but a little flatter - I've just not seen it sold here in BC.

JW

[jch]

Thanks. I think I'm having problems with whipping too much air into my Kerabond thinset.

I'm using a fixed-speed Makita 1/2" mixer drill and the double box paddle that came with it.

Instructions on the bag say: mix 5 minutes at 250 rpm, slake for 10 minutes, then mix for another 2 minutes.

My mixer only goes at 600 rpm and the thinset seems like whipped cake batter by the time I've run it for 5 minutes, especially on a small batch.

Should I change to a different paddle? If so, what type?

Walking on the 2-day old Ditra, I'm getting crinkling sounds, which to me sound like the thinset underneath crumbling(!).

[johnfrwhipple]

Try mixing for four minutes and then mixing by hand for one. Use a broom stick and hold the bucket between your knees while your kneeling.

When we mix we do so like this;

1). Read the instructions! Then. We add all the liquid and one half the thinset and spin it for a half minute. This makes a very wet slurry coat.

2). Then we add in 25% more thin-set and spin it again for 30 seconds. Stiffer but to thin still

3). Then we add in the last 25% slowly will mixing.



If your adding to much air you might find that your working time is dropping. The second mix is to extend the working times. How does your working time fit with the printed instructions?

The crinkling sound might just be the Ditra itself. There are air pockets between those dovetails.

[jch]

Maybe. It just seems like the second (smaller) batch I mixed is more crumbly. Kerabond White with water. Trying to follow the bag instructions to the letter.

Would an egg-beater paddle be better than the double box when mixing thinset??

[johnfrwhipple]

John it's hard to determine what you got there without seeing it and feeling it. You should never have any thing rocky or crumbly in your thin set.

Did you check the date code on the KeraBond?

Is the product store right and not wet?

Can you post a video of your mix?

JW

[jadnashua]

600 RPM is just too fast, I think, regarless of the paddle you use. They recommended a paddle shaped more like a spiral when I took the class. Too much air will also make the stuff weaker.

[jch]

Thinset is very smooth after mixing. The crumbliness/crinkle sounds appeared 2 days later when stepping on the bare Ditra (with thinset underneath).

Date code says it was manufactured this month. Used it the day I bought it.

Unfortunately, the mixing drill I bought only has one speed: 600 rpm. It's the Makita 6013BRX1 kit sold at home cheapo. http://www.homedepot.ca/product/maki...t-mixer/969317

Now what? I can see if I can get a spiral paddle....

[jch]

The Mapei rep said to talk to Schluter. Schluter said the sound means that the fleece is not embedded in the thinset. Told me to cut a 1 foot square and try to peel up the Ditra--to see whether the whole square would come up, or whether the orange plastic would pull off its fleece backing.

The whole square came up, fleece and all. :-(

Coverage was 100% and you could see the grid pattern in the thinset, so mechanically it was installed right.

Schluter told me the problem was that I followed the mixing ratios on the thinset bag (!). Even though Mapei's instructions say "do not over-water", Schluter wants me to add so much water that the thinset ridges slump when troweled.

Ripped up the entire membrane (which stretched the plastic so that it would no longer sit flat). Schluter comp'd for free replacement Ditra :-) so now I just need to figure out how to get the floor flat before I reapply a membrane.

The original thinset (kerabond unmodified) is now 2 days old.

**What's the best way to remove it so that I'm back down to my nice smooth flat SLC layer?? I bought a big scraper, but it's really slow going....