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Unread 06-16-2019, 12:40 PM   #1
Janeyk
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New joists?

Hello, I've used your site for years and am very grateful. I'm starting a new bath, 1957 house, 16" oc, don't know span yet. The old tile is on a thick layer of cement over planks over joists. Once I know my height requirements, I will figure out the right 3/4" ext tng plus 1/2-3/4" (?) cc ply with 1/8" gaps, then Hardi or ditra.
Here's my question- contractor spoke of just ripping out joists and starting over, new joists, use joist hangers, and I assume a possible blocking/new beam situation (I will know more tmrw after he takes a look and we talk).
Do you see any red flags here? I want porcelain.
Thank you
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Unread 06-16-2019, 02:36 PM   #2
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After all these years....Welcome, Jane!
Quote:
Originally Posted by Janeyk
...I will know more tmrw after he takes a look....
....Do you see any red flags here?
At first glance, it seems like intense over kill if they have neither seen the joist condition, nor have a reason to suspect some sort of deficiency.
Has the existing tile job failed in some way?
Is it in good condition?
Are you planning on a barrier-free shower or something?

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Unread 06-16-2019, 03:13 PM   #3
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Thank you Planning a corner jetta tub, with probably a partial glass partition on the right side. His reasoning seems to be it's just easier to rip it and put it back instead of working to get it flat- the floor is not flat. Old tile looks ok, but mostly covered in lino so dunno.
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Unread 06-16-2019, 03:36 PM   #4
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Well, joists typically extend into hallways or other adjacent rooms...so replacing them isn’t confined to the bathroom. And rarely are joists spaces exactly at the edges of a room...you’d typically need to leave the last joist on the two sides of the room.

I can’t imagine replacing joists that have an enclosed ceiling below as “easier” than working with what you’ve already got. Perhaps they know more than I. But sight unseen, it’s off the deep end for someone to say that it’s easier to replace joists than to get a flat surface to build upon.

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Unread 06-16-2019, 05:55 PM   #5
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It is only one story. This bathroom is over a crawl space on the ground. But I hear you... I think the joists go across the hall to the other bedroom (making it 13-16'. What plywood situation would work on 16'? (For porcelain) That's why I was considering his proposal...

Also, if anyone here is an experienced tile layer and/or Schulter fan in Tulsa, OK, please let me know!
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Unread 06-17-2019, 08:48 AM   #6
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I'm thinking of just asking him to install new joists in between old joists giving me 8" oc joists which should help me lay porcelain over a 16' span, instead of ripping it out, these new joists will help easily attain the flat/level he's looking for. Does that make sense? I'm meeting with him today...

Also, I'm going to ask him to glue (any glue?) and screw 3/4" tng (exp 1? Cc?)
That has to be long ways across joists, right?
Then I will handle the second layer of ply once I figure out floor height and deflection.
Can I use lowes poly modified? Or get latricete somewhere?
I've used thhermosoft in the past, but folks around here like warmly yours, yes?
Thanks!
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Unread 06-17-2019, 11:15 AM   #7
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Quote:
Originally Posted by JaneNY
I'm thinking of just asking him to install new joists in between old joists giving me 8" oc joists which should help me lay porcelain over a 16' span,
Agree with adding the additional joists but I'd just sister to the existing ones using Locktite PL adhesive and 3" Grip-rite deck screws.

Quote:
Also, I'm going to ask him to glue (any glue?) and screw 3/4" tng (exp 1? Cc?)
That has to be long ways across joists, right?
Either Locktite or Liquid nail sub-floor adhesive will work. Youll want to use T&G plywood similar to 23/32 in. x 4 ft. x 8 ft. Southern Pine Tongue and Groove Plywood
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Unread 06-17-2019, 12:36 PM   #8
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Thank you so much!
Thinset Rec for large porcelain and floor heat?
I keep reading the schluter underlayment article trying to understand...
Both layers of ply are to be perpendicular to joists? Second layer screwed to first, but not joists, and overlapped accordingly. ?? Neither needs to be exterior, and top layer just needs to be cc?
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Unread 06-17-2019, 12:58 PM   #9
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Also, please help me understand proper sistering- proper screws as mentioned spaced ?? And simply screwed laterally into old joist, nothing coming in from the beam into the end of the new joist?
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Unread 06-17-2019, 06:32 PM   #10
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Jane, there are several good thinsets for larger tiles. Kerabond T is one. But let's start at the beginning.
Let's see the joists before any talk of replacing them. Did the guy go into crawl space yet. Maybe they are fine. Wait until he demos the floor.
Sounds like you understand the two layers plywood floor installation.
What floor heat? Different floor heating systems have different requirements.
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Unread 06-17-2019, 07:19 PM   #11
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Sistering joists needs to be long enough to cover a minimum of the center 2/3 of the joists; I typically go to within 12” of each end.

I do a heavy bead of the adhesive in a serpentine pattern. I place the screws in a alternating sides pattern about 12-15” spacing. If I’m screwing into old joists, I’ll put 1/4” washers on the screws as shown in the photo below.

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Unread 06-17-2019, 07:24 PM   #12
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Second layer is typically a BC grade like this one:

https://www.homedepot.com/p/15-32-in...6030/100012720

Re you the orientation of both layers, you are correct. Long way goes perpendicular to the joists.

You have a good understanding of the screw pattern for attaching the second layer. The number of screws (“schedule”) is one every 4” along the edges and 8” in the field with lines spaced at +/- 4” of center line of joists.

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Unread 06-17-2019, 08:16 PM   #13
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Thinset: versabond white or grey. Your choice of color at Home Depot for around $15
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Unread 06-17-2019, 08:17 PM   #14
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Thanks for the info! Ripout the joists guy didn't show up but another guy did- he was very open to all my silly requirements. He agrees about sistering, but he thinks the sisters need to sit on top of a perimeter beam, and that he may even need to add a beam on some concrete piers under the joists to raise up the sunken areas. Still don't know my joist span, but you guys are saying put a 14' sister on a 16' joist I think... If all that makes any sense...

Haven't decided on floor heat. Don't know how to decide that.

Also... I have 3 1/4" total. 1/4-1/2" plus tiles leaves 2 1/2" or so of ply. Do I add a third layer of 3/4" ply? Or just two, but thicker first or second layer?

Does Hardi get put under the tub? For height reasons? Or just ply, then Hardi up to edge of the tub?

Lastly, he asked me why not just pour two inches or so of concrete over the first layer of ply. How do I answer that?
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Unread 06-17-2019, 08:28 PM   #15
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Welcome, Jane.

I'm not understanding the part where you're planning new joists, but still lack 3 1/4 inches in finished floor height. Why would you not simply install the new joists at the proper height for the subfloor, substrate, and tile installation you want?

If there is some reason to keep the subfloor at the lower level, you also have the option of using reinforced deck mud to raise the floor to the perfect level to accommodate your tile installation and make it very flat for the installation.

But If I were to install new joists, I'd want to make the joist tops as perfectly in plane as possible and as close to the correct height as I could.

My opinion; worth price charged.
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