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Unread 03-14-2021, 02:10 PM   #1
Randall5
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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.
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Unread 11-08-2021, 09:26 PM   #6
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Resurrecting an older thread, but the hour is at hand to start the floor renovation. We are starting demo of the kitchen floor in short order, and that means that we will be sistering the joists below. Now, when the existing flooring material comes up, I have a high degree of confidence that the underlayment consists of particleboard, which will also then come up. That would leave me with the following: double 2x8 joists, 16" on center, with an unsupported span of 149" (edge to edge). The subfloor is 2x12 pine boards. Once the particleboard is removed, I would re-secure the pine boards with new fasteners, then I want to add new underlayment. I would think that 1/2" plywood, glued and screwed (but not to the joists, only the pine boards) would be sufficient, unless 3/4" is preferred. I was hoping for the 1/2", as it will better allow for minimizing the transition to neighboring floor surfaces. After the plywood, it's Ditra, then tile.

Does that sound like the proper approach?
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Unread 11-08-2021, 09:56 PM   #7
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The nominal 1/2" exterior glue plywood, with no face of grade lower than C, is the minimum requirement, presuming the boards are oriented perpendicular to the joists.

I don't recommend you try to glue the second layer of subflooring to the first sawn board layer.

My opinion; worth price charged.
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Unread 11-08-2021, 10:38 PM   #8
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So, just screw the plywood to the 2x12? Is gluing not necessary, or not practical? Curious, as always, as to the reasoning behind the recommendation. Which is not to say I disagree, just interested in the thought process.
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Unread 11-08-2021, 11:12 PM   #9
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Even if gluing was practical (it’s not because of the uneven surface), I wouldn’t want the movement of the solid 2x12’s trying to manipulate the plywood that would otherwise be “balanced” with it’s almost equal number of perpendicular layers.
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Unread 11-09-2021, 08:52 AM   #10
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Randy, I'm a big fan of gluing all parts of a wood subfloor structure and I generally do just that, including the layers of engineered wood subflooring.

In discussion with one of the authors of this article from our Liberry, I've been convinced that they can achieve "almost the same performance" using their closer fastener schedule as with gluing the two layers. And it eliminates the fairly major PITA of properly applying the full spread of wood glue involved in the gluing method. And not fastening into the joists with the second layer also is alleged to provide some very small measure of uncoupling of the top layer from the joist structure. So I've elected to give them that point. Couple pretty capable guys, there.

But with a sawn board first layer of subflooring, I would not have tried gluing the second layer anyway, for the reasons Goldstein mentioned. Just doesn't work well.

My opinion; worth price charged.
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Unread 11-09-2021, 09:56 AM   #11
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All of that makes sense. As I understand it, the "gluing and screwing" method is best for direct attachment of subfloor to joists, instead of between layers of a subfloor assembly, which is what I would have. If it were new construction, you could/would run a bead of glue on top of the joists, drop the subfloor down and then screw the two together. Ties the whole thing together. But in remodel, where that assembly already exists, the approach might be to use screws on the sawn boards to the joists, after pulling up the particleboard, as the nails that are in there may have movement from their now 50 year age. Also, since I am sistering the joists, I may be able to add some subfloor glue to the top of the new joists as I put them in place. That could create a solid assembly, and then the plywood on top of the planks would be screwed to the planks, not the joists. Sound about right?
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Unread 11-09-2021, 10:01 AM   #12
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Yes.
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Unread 12-06-2021, 06:55 AM   #13
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Follow up question after an enjoyable day of getting joists into place. If the area that I am supporting consists of 14 "bays" spaced 16" on center, if I am able to get 12 of them properly sistered to existing joists (glued, nailed, adequate bearing at both ends...), can two of the bays have a new joist placed on 8" centers, and still provide the necessary support? There are some obstructions in these two areas, and I can get the board in, just not directly attachable to the existing board.
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Unread 12-06-2021, 08:50 AM   #14
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If you can support both ends of the new joist, sistering to an existing joist is not a requirement. You'll actually gain rigidity in the subfloor by reducing the between-joist span on those bays where your new joist is added near the center between existing joists.

My opinion; worth price charged.
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Unread 06-15-2022, 09:15 PM   #15
Randall5
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Finished product

Wanted to update the thread with "after" pics. So, after much work bolstering the structure with new sistered joists, and plywood subfloor, we got Ditra, Ditra heat and tile installed. Managed to not damage the cable when cleaning thinset out of the grout joints. Must say, and the missus would certainly agree, I had NO idea just how much work it would be to get this installed, and the level of respect meter for day to day pros is off the charts.

This was a F*&^ton of work.

My sincerest thanks and appreciation for advice and knowledge gained from this entire community.
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