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Old 09-12-2017, 05:55 AM   #46
greenjp
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Hello everyone,
I wanted to follow up on my question 2 above. Based on the tiles and pattern I'm planning to use for the floor, I'm looking at a perimeter gap of ~1/5" on one pair of sides and ~1/2" on another. The 9x12 wall tiles will be 5/16" thick and I'm planning to use a 1/4"x3/8"x1/4" trowel to install them I think this would result in ~1/2" total thickness but not certain.
- Is that going to be OK or could I potentially have an issue with that 1/2" floor tile perimeter gap? Issue like an unsightly gap or any trouble supporting the wall tile during install?
- Should that gap be filled with anything? mortar, backer rod?

Thanks,
jeff
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Old 09-12-2017, 11:27 AM   #47
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That size of a trowel should get you about 1/8 - 3/16" thickness. Leave about the same gap around the perimeter between wall and floor tile.
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Old 09-12-2017, 01:11 PM   #48
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Ok so I think I'm good on the one pair of sides which'll have about a 1/5" gap. The other will have a 1/2" gap, which looks likely to be just about the same size as the combined mortar & tile thickness at the wall. I'd really like to stick with this layout (it results in no tile cutting either at the drain or perimeter) but not if it's going to cause a problem either cosmetically or with the install of the wall tile. Do you think it'll be OK, should I plan for something to fill the gap up, or should I really be looking at modifying the tile layout to reduce the gap? Thanks,

jeff
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Old 09-12-2017, 01:29 PM   #49
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If you have 1/2" gap with a dry layout of the floor tile, you should be okay, since it sounds like the tile and thinset on the wall will be 1/2", maybe a bit less.

If you're in doubt, set the tile on the wall using something about 1/8" thick for a spacer, like cardboard (to account for thinset) then see how it comes out.
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Old 09-15-2017, 09:06 AM   #50
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Continuing to think ahead to the post-shower part of the job, looking at the floor structure. FWIW this is a late '90s townhouse in the Maryland suburbs of DC. Please bear with me this will be a long one

A couple of things I'm fairly certain of:
- the subfloor is 5/8" plywood, observed at the shower drain cut out
- the joists are TJI Pro 120TS, an engineered I-beam type that look to be made of OSB. The house has an unfinished 1st floor utility room from which I can see the structure below the 2nd floor kitchen, and the joists here are 14" tall on 24" centers. Measuring the height/depth between the 2nd floor ceiling and the 3rd floor surface matches an apparent 14" joist height for the bathroom floor was well.

FWIW the kitchen above has some sort of 12" square natural stone tile that's been there for at least 10 years, no cracks. Unsure of the floor prep as it was done before we moved in. It's a wee bit higher than the adjacent hardwood.

Attached is a sketch of the bathroom, more or less to scale, along with a sketch showing the bathroom in relation to the space below. The vanity and shower are against an exterior wall, the tub in an exterior corner. The wall behind the toilet extends down to the 2nd floor and I suspect is load bearing. So I guess you'd say the bathroom is supported underneath on 3 sides.

Also attached is the page from the joists' spec sheet with deflection info.

The purple dashed lines indicate my best guess as to the joist locations. The ones intersecting in the shower I'm certain of, as I could see them when I had everything torn down. The rest are estimates/assumptions based on using a studfinder on the ceiling below. Nominally 24" spacing but with that one set at ~18" running through the middle. Then there are the perpendicular ones at 36" and 48" spacing which would seem to span the width of the house. It would make sense that they'd tighten the spacing underneath the tub, but I'm not familiar with residential design practices.

So, any thoughts or recommendations as to the floor's suitability for ceramic/porcelain tile? I am not sure how to evaluate the span length given what looks like those perpendicular joists at the 3-4' spacing. I'm figuring on 12x12 ceramic if it matters, probably with a Ditra heat type system. Does it need another layer of ply? Thanks!
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Old 09-15-2017, 09:55 AM   #51
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Absent a large beam running left right in your drawing, the cross bracing at 3' to 4' intervals is immaterial for determining the span of your joists. So assume your span is 17'. That still provides an L/480 deflection performance based on the information you posted. Which means ceramic tile is OK, natural stone is not.

As to the second layer of subfloor, see the Ditra heat installation manual. Assembly DH-W24-T-16 calls for a second layer of plywood when the joists are 24" o.c.

BTW, 5/8" floor sheathing is not to my knowledge rated for 24" o.c. supports, the minimum size for that would be 3/4". Are you sure that your floor sheathing is 5/8" and not 3/4"?

Cheers, Wayne
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Old 09-15-2017, 10:56 AM   #52
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You know what, looking at an earlier post I called it ~3/4" of a 5-layer plywood. So let's go with that.

So the deflection looks fine, but according to that install manual Schluter wants a minimum 3/8 plywood in addition to the 3/4". Figure that's sufficient especially considering that one pair of ~18" spaced joists?
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