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Old 06-18-2018, 07:46 AM   #1
Steve C.
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Tile Floor Job for Daughter (Sub floor and other questions to follow)

Hi,

My daughter and son-in-law purchased a home and we are tiling the kitchen, family room, hallway, and dining room (About 800 Sq. Feet). We plan on using 1/4" Durock.

https://www.lowes.com/pd/American-Ol...-in/1000379207

The joists are 2x10 16" OC with 13' Span. Not really sure what grade the joists are though. I'm concerned about the sub floor as it is less than 3/4" thick. Bigger than 1/2" though. And it is slightly torn up after removing the previous hardwood flooring and a million staples.

Cost is important...but secondary to making sure we do this right. Should I put down another layer of plywood and if so what thickness and quality. Want to do this right...but need to keep the price down.

Does the Durock preclude needing a better sub floor? If I do install another layer...do I butt the edges or leave an expansion gap?

Also, is cheap non-modified thinset good for under the Durock?

Thank you.
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Old 06-18-2018, 08:18 AM   #2
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1. I would. Nominal half-inch exterior glue plywood with no face of grade lower than C.

2. Absolutely not. Durock, or similar CBU or tiling substrate has no structural value.

No, you install per material manufacturer's instructions, which usually call for a gap of 1/8th" between plywood sheets.

3. Yes.

My opinion; worth price charged.
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Old 06-18-2018, 11:22 AM   #3
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Plywood at Lowes

Thank you CX.

With me, every great response gets rewarded with more dumb questions

Since you say that no worse than C on either face, that eliminates CDX. What I find is that most local places go from CDX to sanded which is about $10 more per sheet or so. Do you have a recommended grade (Lowes and HD don't do a good job providing this info).

I saw this: https://www.lowes.com/pd/Plytanium-1...-4-x-8/3010149



I know that I don't want to connect the "underlayment" sheets into the joists and that they should be staggered from the existing sub floor. Do I use any adhesive or should I just nail/screw down?

Thanks again.
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Last edited by Steve C.; 06-18-2018 at 11:34 AM. Reason: Added link for plywood with pic of specs.
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Old 06-18-2018, 12:33 PM   #4
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Hi Steve,

Sanded plywood is fine, and so it Sturd-I-Floor, which is tongue and groove. CDX is used only for roof and siding sheathing, never for floors.
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Old 06-18-2018, 01:27 PM   #5
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Sturd-i-Floor

Thank you John.

I called GP and they gave me some numbers who gave me some numbers and after about 10 calls, nobody around here has the Sturd-i-Floor unless I want to buy a truck load verse 25 sheets. And trying to find 1/2" or 5/8" or 15/32" or 23/32" plywood that isn't CDX isn't working any better either.

The reason I want to keep this as thin as possible is because the adjoining family room is going to have carpet...and after I add a 1/2" underlayment and then 1/4" Durock and then the tile...the tiled floor will be much higher than the carpet. And I really don't need to beef up the sub floor under carpet.

Best I can find so far is this at Lowe's...but I have no idea of the veneer rating to know if this works or not.

https://www.lowes.com/pd/American-Ol...-in/1000379207

Any other ideas? I'm going to measure the subfloor when I get home...but am pretty sure it's the 5/8 or 23/32 which won't be sufficient for the tile job.

EDIT: Just found 1/2" square edge or 5/8" T&G Underlayment Grade which is probably better than the Lowe's.

Thank you....I truly appreciate this web site. I use it for all of my projects.
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Old 06-21-2018, 11:39 AM   #6
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Choices of Plywood

Hi,

There is a local lumber yard that has the following:

5/8 Yellow Pine for $28.72 and Fir for $33.71. For 25 sheets, it's probably best to get the Fir.

More questions as always. Quick summary. Putting 6x24 ceramic tile in kitchen and family room and dining room...total of 700 Square Feet. 2x10s with 13' span and 16" OC. Subfloor is only 5/8 and has lots of staple holes from hardwood flooring that was removed. Want to beef up the subfloor with a plywood underlayment.

Initial plan was to add 5/8" underlayment...then the 1/4" Durock and then the tile. Worried about height which is why I am leaning towards 5/8" verse 3/4". I've read the article about underlayment that CX recommended in a different post.

1. Do you think the 5/8" is sufficient as the underlayment with the 1/4" Durock?

2. If I went with Ditra...do I still need Cement Board. If not, is it better to do 3/4" Underlayment (Plytanium or Sturd-i-floor) and then Ditra and then tile? DITRA is expensive as you all know.

Cost is a factor (it's my daughter's house)...but still want to do a job that will look professional and last. I would appreciate it if you can answer in 2 ways:

a) Will #1 be sufficient...and if not, what would you do if adding ply underlayment and then CBU?

b) What would you do if this was your house?



Thank you.
Steve
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Old 06-21-2018, 02:56 PM   #7
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Steve, you're adding structural subflooring with your second layer of plywood, no matter what it's being called in various things you read. If you're not bonding ceramic tile to it, it's not your tiling underlayment. The CBU or similar will be your tile underlayment.

A second subfloor layer of nominal 5/8ths" should be fine. You can actually use nominal 1/2" if height is a consideration.

Your local home center should carry an exterior glue plywood in AC or BC grade, which would be suitable for your application.

I would recommend the fastening schedule recommended in that article your referenced. I prefer screws for all parts of a subfloor structure, but deformed shank nails are also suitable for your second layer of subflooring.

You don't need any adhesive between the subfloor layers, but if you elect to do so you want a full spread of wood glue rather than anything out of a caulking gun.

You do not want to install a CBU if you're planning to use an underlayment such as Ditra.

2,b. I would add nominal half-inch plywood and Ditra.

My opinion; worth price charged.
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Old 06-21-2018, 05:59 PM   #8
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Steve,
Laticrete makes an unoupling/anti fracture mat similar to ditra but I think it has some advantages. It allows you to use a modified thinset o to set the tile, it is much cheaper, and they clain it is an anti fracture and the other guys say uncoupling. You can call Laticrete and you will get someone in tech. support that knows their bussiness. Before install make sure to prep your second layer of ply to be very flat. Then the mat will be flat and you are going to really want that when installing them big boy tiles. The product is called strata mat..
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Old 06-22-2018, 12:29 PM   #9
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Next Steps

Thanks everyone. My daughter nix'd the Ditra (~$1500) so we will be going with either nominal 1/2" or 5/8" subfloor reinforcement and 1/4" Durock underlayment.

For the subfloor, the article recommends every 6" which equates to about 150 screws per 4x8 board. I have a Senco gun and can use collated so was going to go with the Wood to Wood 1 3/4" screws. They come in lot of 4000 for $85.

http://www.senco.com/fasteners/woodtowoodsfctyz/

I would prefer the 1 1/2" so they don't penetrate as far, but they only come in lots of 1000 and would be slightly more ($120 for 4000). I can use these for the extra $35 if you recommend. These are sharp...the 1 3/4" are Type 17. I've googled and don't really see a comparison that tells me what is better.

http://www.senco.com/fasteners/woodtowoodsfshyz/

Thank you.
Steve
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Old 06-22-2018, 03:40 PM   #10
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Steve, your application won't benefit much, if at all, from the Type 17 point, but it won't hurt. It might actually help prevent screw-jacking, but I can't prove that. Do stand with your feet directly on either side of your screw when driving in any case.

The 1/3/4" screws are a bit long for your application, but that shouldn't create a problem. The 1 1/2" would be the more appropriate length.

My opinion; worth price charged.
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Old 06-24-2018, 07:11 AM   #11
Steve C.
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Thanks CX.

Going to go with the 1 1/2" screws.

Last question (that's a lie)...if I use T&G, I believe I leave 1/8" gap at the ends. But how tight to I jam the tongue into the groove. Do I jam it with a hammer and 2x4?

Do I run this layer in the same direction or perpendicular to the existing layer? Based on the article, I would guess the same direction with the ends 4" (1/4 of 16" OC) and the long edges 1/2 the distance from the existing floor (e.g, 24").

For my understanding, how come you have to leave a gap for square edge for expansion but you don't need a gap with T&G?

Thanks again.
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Old 06-24-2018, 08:31 AM   #12
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There is no need got center-matched (T&G) edges on your second layer of subflooring. Square edge is fine and that's all you'll find in half-inch material.

You must orient all layers of structural subflooring with the strength axis perpendicular to the joists.

You gap the subflooring sheets as specified by the manufacturer. Some T&G material is gapped, some is "self-gapping." Do what the manufacturer says, but you never hammer the sheets together.
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Old 06-26-2018, 01:18 PM   #13
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So I went to get the 1/2" under-layment grade plywood. All they have in 1/2" is yellow pine. Is yellow pine okay?

For the screws for the Durock, I would like to get collated cement board screws for the Senco...but they are only Size 8 whereas the others are Size 9. Are 8's sufficient?

I worry too much about things I shouldn't worry about!

Thank you.
Steve
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Old 06-26-2018, 02:45 PM   #14
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Yellow pine plywood is OK for your application so long as it is exterior glue and of the correct face grades.

#8 CBU screws should be adequate.

My opinion; worth price charged.
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Old 06-28-2018, 11:13 PM   #15
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Thanks CX.

Getting BCX 15/32 yellow pine tomorrow. Will post some before pics soon.
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