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Unread 10-24-2020, 08:40 AM   #16
HouseOfJoe
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I believe he’s saying “in real life”, CX.
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Unread 10-24-2020, 01:14 PM   #17
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Borescopin'

I just had an idea, found a borescope (little 1/4" camera on a bendable wire) that I was using for engine diagnostics at my studio, going to try and drill a tiny hole in the subfloor and scope out what the joists are actually made of so I can finally use the Deflecto to get a deflection rating! Here's wishing for < L/720!
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Unread 10-24-2020, 03:09 PM   #18
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It is VERY rare in a residential building to have L/720 unless the original design planned for natural stone as it adds potentially, significant costs for no benefit. Now, how easy it is to retrofit, depends.

There are two components of deflection that must be taken care of...along the joists, and in between them. Subflooring is tasked with in between, the joists take care of along them. A tiled floor is a distributed load, whereas point loads can be problematic as well. In a well constructed structure, as long as you don't overload it, it should work.

Another thing to consider is that long-term, wood is more fluid than you'd think. Picture a bookcase with a simple board as the shelf. Install it, put some weight on it and it bends, but over time, the warp continues to increase, and if it sits long enough, becomes bent into a semi permanent curve (flip it over, and it will bend back, eventually). So, what might work initially, can fail eventually because of this creep. Picture an old barn or other building. Over the years, it's not uncommon to see the ridge line no longer straight. Now, put a rigid tile on that surface and over the years, you'll either break the bond, or break the tile or both. Ever been to Salisbury Cathedral? The granite columns around the bell tower have a very distinct bow to them...they were straight when installed. As they decided they wanted a taller tower, the structure was overloaded and over hundreds of years, the stone literally bent and was reinforced. So, as is very apparent visiting that place, the rocks in the crust of the earth are also bent over time. Your house is not in the same time scale, and movement will not be tolerated. Testing has found you need a certain level of strength for a tiled installation to survive. Ignore that at your own risk.
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Unread 10-24-2020, 07:22 PM   #19
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Excellent structural info, jadnashua!

I finally got a peek into the subfloor using the remote camera, as I suspected it looks like the joists are engineered "Silent Floor" brand stamped on the side, with Laminated Veneer Lumber in the center, not OSB. They are 16" high, around 2" thick at the top and bottom, thankfully just a few holes for electrical cable. I'm taking the span should be around 20 feet for the entire width of the building.

So the Deflecto is still technically no good as it does not work with engineered lumber, but would the engineered joists be stiffer than the SYP or Doug Fir of a similar size? I get L/678 using the same dimensions and spacing on the Deflecto.

Also trying to reverse read these tables for a similar joist, and looks like the lightest-duty 16" joist at 22' span would give you greater than L/480 according to the table at 19.2 spacing...

I also just found that the "Silent Floor" was a system trademarked by Truss-Joint, who is now owned by Weyerhaeuser, so that table is for the current version of the product. Who knows if it was the same in 1991 when the building was built.

Still too sketchy for slate with 1.5" of subfloor and underlayment?
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Last edited by risotttto; 10-24-2020 at 07:52 PM. Reason: found joist manufacturer
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Unread 10-24-2020, 10:21 PM   #20
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As I read those tables the longest span you could get away with for for 16" TJI 110s at 19.2" spacing and a 20psf dead load would be 20 feet, 1 inch to achieve L/480 deflection. You may have a little less dead load than that, but you also don't have an accurate joist span. "Around 20 feet could be a bit more or a bit less, eh?

But that's still only buys you a deflection of L/480, which is a long, long way from L/720. And you've still got a 19.2" joist spacing instead of the required 16" or less.

Again, it's your floor and your stone tile and you can tile over whatever you feel comfortable with.

My opinion; worth price charged.
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Unread 10-25-2020, 09:27 AM   #21
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so the span is exactly 20' 9". I figured the joists cannot be the TJI-110's as they don't make them in 16". So the the 210 is worst case scenario joist, and that comes up as 22' at ~L/480 with 19.2" spacing.

Coming to realize my slate dreams may be shattered, looking into a ceramic or porcelain tile, which should work at L/480. Looking at 'fake' slate, but I just hate the fact that they print 4 patterns for each type of tile, and your floor will look like a bad photoshop collage inkjet printed stone tiles!

Any recommendations on a good slate knock off?
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Unread 10-25-2020, 09:51 AM   #22
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I think it all comes down to your tolerance for failure, S. One major tile installation materials manufcturer, Laticrete, recommends a subfloor structure with as much as L/480 deflection for the installation of natural stone tiles. I don't recall just what products are required, but I'm sure they'd be happy to tell you if you were to contact them.

Are their products actually better than that of other manufacturers at tolerating stress, or are they, the manufacturer just better at tolerating the stress of failures? I dunno. But if you wanna roll the dice, that might be worth looking into.

Presuming, of course, that you actually meet an L/480 deflection in both your joist structure and subflooring.

My opinion; worth price charged.
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Unread 10-25-2020, 01:44 PM   #23
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It's my understanding the Schluter did some tests at less than industry standards deflection with their Ditra product, but found that while it worked, everything had to be perfect with no margin for error, so they, being conservative, decided to keep the status quo. That included the joists all being up to snuff without improper holes, notches, fastening, subflooring installed perfectly, and thinset coverage essentially perfect. IOW, conditions you'd almost never encounter. If you throw in a situation where you may exceed the initial loads (throw a party, move a monster freezer on a dolly into position, decide to put up a center island with a 3cm granite top, etc., that could easily exceed the design load) then all bets were off.

For lack of a better one, the test generally used is the Robinson floor test. This is a weighted roller that runs over the floor numerous times with weight added in increments until failure. The number of times and the weight then classify the suitability of the tile for different conditions from residential to heavy commercial. Now, you're not going to be driving a tractor trailer over your tiled installation, but it might need better than a typical residential rating, too when you throw in some of those outlyer conditions mentioned above. That Christmas party might just do the tile in!
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Unread 10-25-2020, 08:21 PM   #24
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So it's better to safely overbuild than risk the Christmas Party Tile Massacre. Counting on everything being installed perfectly will never happen, henceforth a decent safety factor. The weighted roller test sounds like a fun IRL test, just not in my kitchen! Assuming around L/400 with just the subfloor conservatively, going to beef up the underlayment for safety.

So the plan is:

Install 23/32" (EXT or Exposure 1, will see what the local Lumber Yard has in stock) AC or BC ply over the subfloor, offset and strength grain perpendicular to the joists, screwed every 6", not glued, gapped with some caulk between the sheets.

Flexbond and 1/4" Hardiebacker on top of that.

A decent ceramic or porcelain tile as the final layer, install as required for that tile.

Work out a nice transition to the floor, probably Schluter Schiene edge then wide oak reducer stained to match the floor. The bathroom drops 7/8" with no bevel, so shooting for a much smoother transition.

Thanks again to jadnashua and CX, learning a lot!
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Unread 10-25-2020, 09:05 PM   #25
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Quote:
Originally Posted by S
Flexbond and 1/4" Hardiebacker on top of that.
Flexbond under the CBU is not overkill, S, it's overspend. The purpose of the thinset mortar under a CBU is not to bond it to the subfloor, it's to provide a 100 percent footprint for the CBU panel. The mortar holds it up, the mechanical fasteners hold it down.

One of the few areas where buying and using a cheap mortar is fine.

My opinion; worth price charged.
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Unread 10-26-2020, 12:12 AM   #26
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I’d suggest investing some additional time looking for additional tile choices. There are plenty of manufacturers who produce great looking tile that mimics stone. And there are plenty of manufacturers that produce a lot of different tile prints. I’d recommend shopping at as many real tile shops as possible to find something you’ll really like.

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Unread 10-26-2020, 07:11 AM   #27
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Was actually thinking of driving out to Floor and Decor in Long Island to look at some in person. I like that they have small panels set up and boxes on the floor.

Some other tile shops you only get to see one tile, then when you buy the box you realize they are only 3 printed patterns!

Looking online is no comparison to seeing and feeling in person...

Also thinking about 11x13 cermaic hexagon, no need for a printed tile if you have a unique pattern!
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Unread 10-26-2020, 12:30 PM   #28
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While a little more complex to figure out quantities and layout, there are some interesting tile patterns that utilize various tile sizes that can add interest to the floor, if that's what you're interested in. Pinwheel and Versailles come to mind as two that use a combination of sizes, along with herringbone, and others that are a more interesting layout. Should you go with one of the first two, you want your tile sizes to be modular, IOW, designed for that layout, or while it can work, because of the tile size and grout line, the pattern can walk. NOt an issue unless you want the pattern to remain perfectly in line across the floor. Another way to look a that is, you generally can't just cut the tiles up into smaller pieces, and if they are modular, you must pay very close attention to maintain the designed grout line...the smaller tile cannot be just say 1/2 the width of the larger one, if you want their outside edges to line up, since there needs to be a grout line in between the smaller ones, too - they need to be slightly smaller than the 1/2 or 1/4 or whatever the pattern calls for by 1/2 of the expected grout width for to, or whatever, so they all add up to the larger tile when stacked.
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Unread 10-28-2020, 11:43 AM   #29
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Good to know with the shaped tile grout application, layout and measure twice, before you lay down! I like the flexibility of the 'rhombus' shaped tile if I can find it in a large size, there's quite a few options to lay them out! Will see what strikes me at the store. Maybe black hexagon with gray grout or checkerboard!?

I got some A/C Exterior rated ply in the kitchen acclimating before I lay it down for new underlyment. Is there are rhyme or reason as to what side to face up? I would guess the A side, then slightly dampen it with a sponge before laying down the thinset underneath the CBU.
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Unread 10-28-2020, 11:47 AM   #30
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Put the A side up. You will have dampened the surface when you wipe it down with a damp sponge to remove any dust and that is sufficient.

My opinion; worth price charged.
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