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Unread 03-14-2021, 02:10 PM   #1
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Joist measurements for deflection

So, when measuring joist span, is it from edge of support to edge of support? Or is it full bearing? For example, I have 2x8, 16 o.c. joists that bear on sill plates over a poured concrete foundation at one end, and over a beam at the other end. The span from edge of sill to edge of beam is 12'4". Obviously, that span is greater (approx 13') when including the amount that is in contact with the supports. Either way, the deflecto is thumbs down for tile. So, this leads to the question of: is there anything that can be done to bring the floor into compliance? Subfloor consists of 2x12 pine planks with particle board on top (1.5" total). I would replace the particle board if I can get the rest of the assembly to be acceptable. Interested in any feedback

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Unread 03-14-2021, 05:58 PM   #2
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Welcome, Randy.

The edge to edge measurement is the correct one for the unsupported span of your joists.

Your common options are 1) sister each of the joists with a similar joist, or add a mid-span support to reduce the unsupported span of the existing joists.

What's below this area to be tiled?

My opinion; worth price charged.

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Unread 03-14-2021, 06:45 PM   #3
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Classic New England basement, circa late 50's-early 60's. 24'x34' with a center beam (single piece of wood 5-1/4"x9-1/4") with steel columns, poured concrete foundation walls and a poured concrete floor. Also, there are wood 1x cross braces mid-span.
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Unread 05-06-2021, 02:57 PM   #4
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Couple questions

So, I am preparing for an upcoming project (kitchen and bath remodel). The deflection issue mentioned above will be remedied before doing the floors. We also will be doing a shower in the bathroom. Naturally, there are boatloads of questions and this site is a tremendous resource. But, the wealth of information can also lead to overload so, if possible, I wanted to ask a few questions to get some insight on how to proceed:

1. We have struggled with the selection of the floor tile for the kitchen. The Mrs. knows the general color, but the space is a 14x13 area with a hallway measuring 10' x 3' leading away from it. We feel that the 12x24 tile which seems to be the NUMBER ONE size these days is not the best choice, especially down the hallway. We have found an image of what looks like 4x8 laid in herringbone that works well down the hallway, and I can't quite determine whether it would look good that way in the whole kitchen. What factors go into determining the best pattern and size for a room? Curious as to the thoughts behind the designs.

2. I have read hundreds of shower construction threads, and wanted to clarify a few things before proceeding on the work:

a. Floated mud walls and floor, done properly, is the BEST surface to install tile on (True/False)

b. There needs to be a vapor/moisture barrier somewhere in that assembly, such as tar paper behind the mud, OR a liquid waterproof (Redgard/Hydroban, etc.) on the surface, but not both, correct?

c. Same with floor. If you install a PVC pan liner, on top of pre-slope, and below mud bed floor, a liquid waterproof on top of mud will create a "sandwich" that traps moisture, and that is not preferable, correct?

d. Edges can be finished in one of several ways: bullnose, miter, manufactured trim pieces, etc. Is there a preference, or does the tile selection determine that? If a tile doesn't come with a bullnose, that is out of the picture, for example.

Just a little musing, but really interested in how the final product is determined, and the decision making process. Any input is very welcomed.
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Unread 05-06-2021, 04:24 PM   #5
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1. In that hallway, unless the tile you chose is REALLY flat, that tile size wouldn't work well. The generally accepted offset on large tile like that is no more than about 30%, and you'd end up with a 50% offset which is the worst thing for lippage unless the tile are very flat.
2a. If done with skill, a floated wall will give you a perfectly flat and plumb surface to tile to. You can achieve that with other methods, too. Floating a wall takes some skill, and you may not get your best result without lots of practice.
b. Yes, one moisture barrier or one waterproofing layer. My preference is a sheet membrane versus trying to get things painted properly with a liquid one.
c. True, you generally do not want to deal with two waterproofing layers. If the top one isn't perfect, OR, if the drain backs up and moisture can enter via the weepholes, it may take forever to get back out. Again, my preference is a single sloped bed and a sheet membrane on top...then, nothing beneath the tile and thinset should ever see any moisture.
d. Schluter's first products were profiles...their shower products came later. The industry has been removing edge finishing tile as part of their tile families for ages, so you had to do something to treat the edges. The profile is more than just for looks...it performs a necessary function of helping to prevent chipping the edge. A few companies make profiles, but Schluter seems to have the largest variety in styles, colors, and materials from plastics, to anodized aluminum, to stainless steel. Whether a profile is your best choice depends on your ultimate goal. Hiding and protecting the edge without a profile or trim tile can be tricky.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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