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Unread 09-22-2020, 05:30 PM   #1
weronika
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Advice for first time tiling project

Hello,
I'm in the process of doing my first tiling project and I'd be very grateful for advice. I have very little knowledge on the topic - only what I've been able to learn from googling around - so please bear with me

I bought 8x8 ceramic tile (1/2 inch thick) for my 6x7.5ft laundry room. Previously there were two layers of linoleum there which I took out, I also took out the 1/2 inch particle board that was underneath that (from what I understand particle board is not suitable for tile installation).

Underneath that I found a 23/32'' thick plywood. The rows of nails int he plywood are spaced 16'' apart which I figured is what the o.c. joist spacing is - am I correct?

Under the tile I'd like to use Ditra, it seems much easier to deal with than cement board.

I have a front loading washing machine that shook the floor a decent amount with the old flooring. I'm wondering how it will behave with Ditra and porcelain tile. Should I plan on adding more plywood to help with the washer vibration and/or making tile cracks less probable?
Ditra installation handbook says that with 16'' joists spacing the minimum plywood thickness is 5/8'', so mine is a bit thicker than the minimum, but I'm wondering how the presence of the washer impacts the situation. When i walk on the subfloor it seems relatively stable but it does squeak a little bit. Ideally I'd like to avoid having to add more plywood but more importantly I don't want to end up with cracked tiles.
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Unread 09-22-2020, 06:05 PM   #2
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Welcome, Veronica.

If you have squeaks, you're likely to have a failed ceramic tile installation. Squeaks = movement; movement = bad for ceramic tile.

Yes, the nailing pattern most likely indicates the joist spacing and direction. Does not, however give you any indication of the joist type, size, condition, or unsupported span. Those are things you need to know.

Can you determine that your subfloor does/does not have tongue & groove edges?

While Schluter does indicate the use of nominal 5/8ths" subflooring, that assumes near perfect conditions and I would not tile over that on a bet. Yes, you have more than that, but your subfloor is old, damaged, and likely not properly fastened as indicated by the squeaking, and you will be subjecting it to some serious vibrations.

Entirely up to you what you're willing to tile over, though.

Check out your joist structure and as an absolute minimum get some deck screws and re-fasten that subfloor to see if you can make the squeaking stop.

My opinion; worth price charged.
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Unread 09-22-2020, 06:12 PM   #3
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Hi Veronica,

Looks like you've done your homework and prepped your floors properly by removing everything except for the plywood/OSB subfloor. If the nails are 16" apart, your joist spacing should be 16" on center.

If your floor squeaks, start by grabbing a box of #8 or #9 by 2-2.5" deck screws and run those screws along the nail pattern every 8" or so to really secure the subfloor and minimize squeaking.

Ditra is a good idea and based on your description, your floor is within spec. For thinset, I'd recommend Custom's Flexbond (Home Depot) for use under the ditra and Mapei's Kerabond T (Floor and Decor) over the ditra. I don't think you'll have a problem with the washer vibrating but I would refrain from reinstalling the washer over the fresh tile for a week or two to let the thinset really cure (maximum strength achieved at 28 or so days).

This is a little unconventional, but you could also set your washer on a .25" rubber gym tile or something similar to act as a vibration damper (make sure to raise the feet on the dryer so the heights match).

Good luck with your project.

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Unread 09-22-2020, 11:38 PM   #4
weronika
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Thank you for your replies, I appreciate it! I'll definitely start with adding some deck screws and go from there.

I'm not sure how to find out the joist specs you mentioned - would I have to go into the crawlspace and check them out? I'm also not sure about the tongue & groove edges, would there be any written indication printed on the plywood about that?

Thank you for the thinset suggestions, that's very useful. Do you have any recommendations on what to use for floor levelling? I also wondered if using a floor levelling product would change recommendations regarding which thinset to use for under Ditra (from what I understand you need to use different types of thinset for different types of subfloor material).
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Unread 09-23-2020, 07:22 AM   #5
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You'll be amazed, Veronica, how much those deck screws will tighten up the floor. As Ali advised, run them in every 8" or so. If you can add another layer of 1/2" ply on top of the existing ply that would be a good idea for the laundry room with spinny machines.

You can probably tell if the plywood is T&G from above. Ply is typically 4X8 so locate the "long" edge (any edge longer than 4'). There will likely be a small gap on the long edge where two panels meet. Use something thin, like a wire clothes hanger, to poke into the gap. If the hanger goes in more than, say, 3/8" the plywood edge is not T&G. Test it in several different spots.

You do need to determine the length and height of the joists. Sometimes you can approximate the length by the size of the house, interior load bearing walls, and other tell-tales. Figuring out joist height can be more of a challenge. Sounds like a visit to the crawl space is in your future.
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Unread 09-23-2020, 08:50 AM   #6
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I'm not a pro, but an extreme DIY'er and I've probably tiled about a dozen bathrooms. Every single time I tile a new bathroom, I always add a 2nd layer of OSB 3/4" on top of the subfloor. I glue and screw it onto the existing subfloor, unless concrete, then I use a self leveler if needed. Yes, it'll raise the floor 3/4", but in my experience, it either raises it level to the rest of the floor in the house or you can easily transition with a marble threshold. The 'new' subfloor will make a very nice bond with the Ditra.
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Unread 09-23-2020, 09:33 AM   #7
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Quote:
Originally Posted by Michael
I glue and screw....
What kind of glue do you use, Michael, and where do you place the screws?
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Unread 09-23-2020, 10:29 AM   #8
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If you add that second layer of 1/2" plywood, I seem to recall the following recommendations:

1. Run the 2nd layer "the other way".
If the existing plywood sub-floor runs "up and down" the room, run the new plywood "left and right".

2. Overlap joints.
This really might be the main purpose for going "the other way".
But the main point is to NOT have joints in the 2nd layer of plywood lining up with joints in the 1st layer.

3. Don't nail/screw thru the bottom layer to floor joists.
While you want the bottom layer screwed to the floor joist to help prevent squeaks, the top layer should only be attached to the bottom layer rather than thru the bottom layer to the floor joists.


Keep in mind, I'm just a DIYer like you, so I'd appreciate any of the pros stepping up and pointing out anything I'm missing/forgeting.
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Unread 09-23-2020, 10:45 AM   #9
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Think we need to review some of this advice a bit.

Michael, while I'm a big fan of gluing everything to everything in a wood framed subfloor, the ceramic tile industry actually recommends not gluing the second subfloor layer to the first. That's a requirement, actually, if you're bonding directly to the second layer, but probably a good idea in any case.

I'm also not a fan of using CBU for the second layer simply because it's a poor choice of material for bonding with anything, including thinset mortar. Indeed, some manufacturers prohibit bonding with their products to OSB. If the tiling substrate is to be a CBU where not bonding to the subfloor is required, the OSB surface would be fine, of course.

I don't see a need for anything thicker than nominal half-inch plywood for the second layer and I think for anything thicker than that, pre-drilling for screws is a necessity to prevent screw-jacking.
Quote:
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1. Run the 2nd layer "the other way".
If the existing plywood sub-floor runs "up and down" the room, run the new plywood "left and right".
Joseph, that's not a difference of opinion, I'm afraid, that's just incorrect! All layers of structural subflooring must be oriented with the strength axis perpendicular to the joists. No exceptions to that at all.

There is a good article in our Liberry showing what I think to be the best method of installing the second layer of subflooring (mislabeled underlayment) and I recommend following the recommendations there.

My opinion; worth price charged.
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Unread 09-23-2020, 12:46 PM   #10
weronika
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Checked the subfloor like Dan suggested and it does seem to be T&G. I also scanned through home inspection report from two years ago for any info about the joists and the only thing I found said:
Joists/trusses: 2x8
Would this be the size of the joists?

In case I decide not to add any extra plywood on top of my subfloor I was wondering what prep I need to perform on it before laying down Ditra. I'm attaching a few pics where you can see the surface has some superficial damage (dents etc.). I was wondering if I should fill all of those with something?
In also not sure what the white film is, do I need to remove it?
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Unread 09-23-2020, 01:10 PM   #11
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Quote:
Originally Posted by CX
Joseph, that's not a difference of opinion, I'm afraid, that's just incorrect! All layers of structural subflooring must be oriented with the strength axis perpendicular to the joists. No exceptions to that at all.

There is a good article in our Liberry showing what I think to be the best method of installing the second layer of subflooring (mislabeled underlayment) and I recommend following the recommendations there.
Thanks for the correction.
I've seen the Liberry article, but it's been a while and I was trying to go from memory.
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Unread 09-23-2020, 01:38 PM   #12
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Veronica, if the inspection report says the joists are 2X8's then it's a pretty safe bet. Safer still, of course, would be self-verification.

And still, you don't know what the free span of the joists are. The joist size and span are critical information to know for a tiling job.

As to the divots, a patching compound is available at your local Depot/Lowes/Menards/etc. Yeah, you'll wanna fill those. The white film is likely paint over-spray from when the house was built. They spray the walls and ceilings with lousy paint before installing the flooring. Yes, you will want to remove as much as you can. No, no one will want to help.
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Unread 09-23-2020, 01:51 PM   #13
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Or you could elect to use a CBU as your tiling substrate in lieu of the Ditra, Veronica, and not worry about the condition of the surface of your subflooring. I'd still strongly recommend a second layer of nominal half-inch subflooring, though.

My opinion; worth price charged.
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Unread 09-23-2020, 02:33 PM   #14
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Whoops, Dan and CX's response hadn't loaded when I typed mine.

For 2x8 joists, it will be important to identify the wood species and the length of the unsupported span your laundry room is located in to make sure your structure is adequate for tile. I would measure the distance between beams or from exterior wall to beam depending on where your laundry room is located. The joist size, span, and species can be plugged into the delfecto-calculator on the site to give you an output. You need a minimum of L360 to install tile without risk of failure.

I also see a lot of primer and joint compound on your subfloor. That must be mechanically abraded before you can install ditra. The thinset will not bond well to what's there right now.

My recommendation is to rent a flooring edger from home depot or similar with 36-80 grit pads and grind off the layer of 'white' to expose fresh OSB. Make sure to use a good dust collector with hepa filtration as that OSB dust is nasty stuff. Alternatively, you can layer 1/2" plywood over the existing substrate as previously mentioned and install your ditra over that.

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Unread 09-23-2020, 02:53 PM   #15
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Quote:
Originally Posted by Ali
You need a minimum of L336 to install tile without risk of failure.
I'm thinking that's a typo on Ali's part. The ceramic tile industry requires that joist deflection not exceed L/360 for a tile installation. That's 1/360th the length of the unsupported span of the joists, measured in inches.

The part about being "without risk of failure" must be his own personal warranty, but I can tell. You might wanna give him a call, Veronica.
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