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Old 05-15-2015, 05:13 PM   #1
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Plywood Subfloor Questions


My husband and I are older and live in a rural area. We are not close to any big towns. We are presently getting bids on have tile installed. I have been doing a lot of research so I am an informed consumer and hopefully will choose the correct installer to put down the correct products.

Subfloors: (1) ¾ plywood in good condition (not excellent)
Trusses: 2 x 12 pine on 18” centers.
Location: Near water in NE Oklahoma, where seasonal temperature can vary greatly.
Area Tiling: 834 sq. ft. - laundry, craft, hall, 2 piece bath, kitchen & dining. Some rooms are adjacent. Tile would be continuous.
Tile: 7.87 x 15.75, Porcelain

Leveling: Floor is not level or flat. A portion of house was ‘lifted’, creating issues. New plywood was installed in places,shimmed & braced, but still have issues. It will be impossible to get all the floors level/flat to each other throughout. Some rooms have no issues in THAT room, but not level or flat to the hall. Example: 10’ construction level centered on the threshold to bath and reaching into hall appears to read that the hall is a little under ½” lower. The level laid in the bathroom only is flat. The level laid in the hall only, hall floor is flat. The hall turns and goes into the kitchen area. Kitchen floor is about ¼” lower than the hall floor at end of 10’ level.

Our goal has to be flat. Could never achieve level. I have about 1 1/4” I can add to my floors. Would have to cut off room doors, address plumbing in bath and install a threshold leading into living room. All entry doors would be OK. (I think). Probably only have room to add ½” plywood. Know this would add some strength to my floor, but would I have enough room to then install Ditra or backer board with a 8mm tile & thinsets necessary? I presume I would still have to make sure flat with some product.

Ditra XL 5/16: I have not found a contractor in my area that is familiar with Ditra (yet). I have read many threads on self leveling compounds (SLC). If use a SLC, it will be a big job. (If can’t find Ditra guy, I wonder about finding one familiar with this process?) I note that you have to cover entire space for consistency. Can I use leveler in one entire room and not in another room? If us Ditra, could change bonding thin set to subfloor easily. Am I correct that if use SLC (cement based product) that I consider my floor to be cement & use unmodified thin set to attach Ditra to subfloor? I am considering Ditra XL 5/16 if don’t add more subfloor. One contractor felt this would work.

Tile Board ½”: Am I correct that if I use this product, I level after installing so that I do not destroy the leveler by putting in the screws? Would you use a SLC to make sure flat or just work on problem areas and sand edges. What type of product?

Any suggestions would be greatly appreciated. We only get to do this once and my father used to say, “Anything worth doing once was worth doing once RIGHT”

Last edited by Te-teh; 05-15-2015 at 05:19 PM.
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Old 05-15-2015, 05:24 PM   #2
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Lots of questions---I need one answer--what is the unsupported length of the floor joist? You mentioned 18" centers--16" is the standard--is it 16 or 18?

With that one of us can check the span chart and find the deflection and see if you are safe for tile.

A diagram would help--showing the rooms --the orientation of the tile--and which rooms go down hill---

A few answers----Self leveling compound---use it only where needed--no need for a continual SLC surface.

1/4" backer board,set into wet thinset(like a huge tile) and nailed or screwed is a good backer---Ditra is also a fine backer and is thinner---
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Old 05-15-2015, 06:07 PM   #3
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My husband corrected me. 16" centers.

Dining Room & Kitchen area is 19' 3"Wide x 26' 11-1/2" long with a cement pillars running down the center. He believes trusses approx. 1/2 of 19' 3" sistered & resting on cement column, maybe 10" long. The last 10' approx. of dining/kitchen is over a half-basement. The joist there are on 12" centers and are TGI's. There are metal posts supporting (Just a storage basement).

The Craft room is 17'3" Wide x 10' Deep. There are cement column supports down center. I am guessing those are about half of 17' 3". So probably around 10' as well.

The bath backs up to back wall of kitchen. That is where the house was jacked up. I am assuming the same as kitchen-10'. There is TONS of metal posts set in lots of cement in that location. The bath is only about 5' x 7'. The joists run under the 7' length.

I don't know how to post a drawing. I have a drawing on my computer. It is an excel document. Can I post and excel document?

I am a handy female, but joists are a little above my pay grade. If I have not answered correctly, please let me know.

Thanks so much for you VERY quick response!!

Te-teh
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Old 05-15-2015, 06:43 PM   #4
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Te-teh,

Will you please post your location since it'l probably be helpful to better answer your questions.

The size of the rooms is not that important in regards to joists' span. Mike would like to know the distance between the supports, although from your answer it looks like you may be ok.

You mentioned both "trusses and joists". Do you have both?

Yes, lots of questions so let's start with the framing and get that over with.

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Old 05-15-2015, 07:59 PM   #5
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OK, as I said, in over my head. I believe I have ALL Trusses supported by cement supports, except basement. However, tomorrow I am going to go under the house & verify all the trusse information. I want to be accurate in my responses. You guys can't help me if I don't provide totally accurate information. My husband believes it is two 2x12 with plywood in the center, glued and screwed. I will verify tomorrow.

Thanks Jaz.
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Old 05-15-2015, 08:21 PM   #6
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Sure would be nice if you took a camera down there with you.

Jaz

These are trusses;
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Old 05-17-2015, 05:18 PM   #7
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Downstairs Drawing (18-8).pdfSee pdf attached

Our house is supported by 3 separate rectangles. Each is totally separated by cement walls and not accessible via the other. These areas are represented by the Red, Blue & Green rectangles on the attached drawing. The brown lines are stud walls. The red rectangle is much larger, but due to KB limitations, I could not include in drawing. I went under the house, however the floor is insulated and has 2 vapor barriers. I could see columns and center support. Was able to measure the unsupported length and distance between trusses, by measuring from/to nails attaching vapor barrier.

RED Rectangle & BLUE Rectangle are both under 20’ wide. There are cement columns about every 8’ (closer under Blue rectangle) running North/South down the middle of both areas. Resting on columns is laminated 2x10. These are bolted together to create length and where joined are resting on columns. On top of laminated center and running East/West, are the trusses. They are on 16” centers and bolted together over laminated center support (according to hubby, couldn’t see). No truss in these areas is unsupported for longer than 10’.

GREEN rectangle represents basement walls. I earlier gave misinformation on the basement trusses. We had height issues. Hit solid bedrock. To allow for 8’ ceilings on West side of basement, raised the floor of the office. (one step up from kitchen to landing of stairs). Used on West side, TGI on 12” centers. The East side, under dining room, is 2 x 6. There is a support pole 4’ from South basement wall, centered E/W. Running N/S is laminated 2X6. Attached by joint hangers are 2x6 on 12” centers, running E/W. These are 6’10” long both sides. The is a tool room, supporting floor in rest of area. Room is about 15’ x 20’.

SUN on pdf: This indicates where floor was jacked up. I must explain that my husband and I have been working & living in this house for a number of years. With periodic help, have done all the finish work (sheetrock, trim, hardwood floors, etc. The flooring in this area & the kitchen cabinets are all we lack to complete. The floor issue developed early. I had the framer move the North wall of the guest bath 1’ to the South. This moved support wall off column below. I then loaded the small bedroom above, floor to ceiling, with VERY heavy boxes. Next I installed a commercial range on kitchen side & a large tub in master bath to the East. OOPS! The floor moved under the ALL the weight. We had the house jacked up, poured a lot of cement & put in metal supports all along that wall.

ISSUE: If I lay a 6.5’ level half in bath & half in hall, the West side of the level at about 58" floor has drops about ½”. If I rotate the level (N/S), staying center of guest bath door but reaching into kitchen/dining, the floor has dropped ¼” at 6’. The hall is flat to itself. The bath is level to itself. The craft room has a low corner, but less than 3/16” out. The kitchen/dining room floor slopes slowly to North, but never out of flat more that a 1/8”. It looks pretty good. None of the floors appear to move and feels very solid.

Oh-Mike:
1st: If you use SLC & Ditra, what is the appropriate bonder to subfloor? I thought I read that if you used a cement based SLC you used a different bonding for Ditra because it was cement based.

2nd: I thought that 1/2” hardy board was required for floors?

I live in humid area. NE Oklahoma near water. Temps in OK can go from 20 degrees below in winter to 100+ degrees in summer months. This location, not this house, has been in my family for approaching 100 years. It will be passed down and will most likely be a summer destination. I believe they will keep HVAC on year round, but you never know. Does this change what I use for subfloor prep?

Took me 2 day to figure out how to create a PDF & then make it small enough. Who said “you can’t teach old dogs new tricks!” Homework accomplished.

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Old 05-17-2015, 07:24 PM   #8
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You may want a company come in and pump SLC on the entire area to make them flat and level. I can't be positive that's even possible though from here. Remember you'l need to prime and install lath and the min. thickness has to be ⅜" and so some areas will be much thicker.

Another alternative is to hire a crew to do a "real mud job" in preparation for the tiles.

Quote:
If you use SLC & Ditra, what is the appropriate bonder to subfloor? I thought I read that if you used a cement based SLC you used a different bonding for Ditra because it was cement based.
You always use the type of thinset that is appropriate for the substrate.

Quote:
I thought that 1/2” hardy board was required for floors?
No, just the opposite, unless you want the extra thickness for some reason.

Personally I would not use Hardie and especially on such a large area. Hardie has a 15' expansion joints spacing requirement and it can get tricky. I would use Ditra, but then again the material costs more $$$. However it's better and cheaper (labor) to install so in the end the cost is similar if you hire a tile setter. If you do it yourselves, it's easier but does cost more.

Jaz
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Old 05-18-2015, 08:59 AM   #9
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Laying SLC in entire area is a big job. Finding someone out here to apply is probably an equally big job, however nothing is impossible if you put your mind to it. Knowing how to do correctly, that is an education best learned by doing. Don’t feel competent to do ourselves.

We will use Ditra as you suggest.

1st: We are going to remove 2 pieces of plywood at front of bath door that were replaced after house was jacked up and see if we can shave the trusses. That is a really bad area! Will check out that entire wall E/W.

2nd: Guest bath is low. We are considering putting hardwood (shimmed) in that area. We could use a threshold to offset height issues and transition to hall tile.

3rd: I don’t believe that level can be accomplished in living/dining. I think flat N/S & E/W (within tolerances) might be possible with SLC, but will have to maintain a gentle slope to the North. I have to beware of entry doors and not raising floors too much. Room doors are easily shortened, but issues with threshold on entry doors.

4th: I feel like I am very DENSE, but am still confused about Ditra and SLC. After apply SLC, is my subfloor considered cement or does is it still considered plywood?

I was not aware you could use SLC with lath. That was great info’. I will search for more information.

Have an installer coming tomorrow. With ALL our issues, he may say “Thanks, but no thanks”. With your help, I do feel that I am a more informed consumer and will have a better idea of his competency. I am sure I will be checking back in before beginning this process.

Have a good day.
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Old 05-18-2015, 09:05 AM   #10
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Laying SLC in entire area is a big job. Finding someone out here to apply is probably an equally big job, however nothing is impossible if you put your mind to it. Knowing how to do correctly, that is an education best learned by doing. Don’t feel competent to do ourselves.

We will use Ditra as you suggest.

1st: We are going to remove 2 pieces of plywood at front of bath door that were replaced after house was jacked up and see if we can shave the trusses. That is a really bad area! Will check out that entire wall E/W.

2nd: Guest bath is low. We are considering putting hardwood (shimmed) in that area. We could use a threshold to offset height issues and transition hall tile.

3rd: I don’t believe that level can be accomplished in living/dining. I think flat N/S & E/W (within tolerances) might be possible with SLC, but will have to maintain a gentle slope to the North. I have to beware of entry doors and not raising floors too much. Room doors are easily shortened, but issues with threshold on entry doors.

4th: I feel like I am very DENSE, but am still confused about Ditra and SLC. After apply SLC, is my subfloor considered cement or does is it still considered plywood?

I was not aware you could use SLC with lath. That was great info’. I will search for more information.

Have an installer coming tomorrow. With ALL our issues, he may say “Thanks, but no thanks”. With your help, I do feel that I am a more informed consumer.

Have a good day.

Te-teh
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Old 05-18-2015, 01:06 PM   #11
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I heard you the first time.......

I heard you the first time.....

Talk more later, no time now.

Jaz
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Old 05-18-2015, 05:32 PM   #12
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Sorry about posting twice. It was an error. I apologize. Never been in a chat room. Still learning.

No big rush. This is a a process not an event.

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Old 05-18-2015, 07:00 PM   #13
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No problem posting twice, sometimes it just happens I think, I've done it myself.

Yes it's a big job installing that much SLC. Not a DIY job for most people for sure.

A level floor is nice to have but sometimes almost impossible and not absolutely necessary for tiles unless it's too much which would spoil the whole job.

But you keep going back to SLC. You can't use SLC unless you're trying to achieve a level floor, the stuff will flow to the low spots and in the end if you pour enough material it will be level, or darn close. You can also mess it all up by not being prepare and not working fast enough, hence the no DIY recommendation.

Quote:
I feel like I am very DENSE, but am still confused about Ditra and SLC. After apply SLC, is my subfloor considered cement or does is it still considered plywood?
You're doing just fine, young lady.

Obviously a floor with SLC is a Portland substrate and Schluter recommends unmodified, the same floor without the SLC would require modified thinset. I think the confusion came when something was said about just applying SLC on part of a room, I think it was Mike. Use the thinset appropriate to the substrate.

Read the date sheet of the SLC or patching materials you may be using. I think you'l find they all want you to install lath (SLC) and the min thickness is ⅜".

Take good notes on what the installer tells you. Make sure he has lots of experience doing tile work the right way, (just lots of years doesn't necessarily count), and is licensed if required. Hopefully in the end before you decide, you'l run the details by us.

Jaz
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Old 05-21-2015, 07:45 AM   #14
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I think you must visit to a good interior decorator.
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Old 05-21-2015, 05:40 PM   #15
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Quote:
Originally Posted by mariadelgado View Post
I think you must visit to a good interior decorator.
and the reason for that would be?
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