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Old 01-13-2018, 05:05 PM   #1
rkhanso
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getting ready to install tile, but have sub-floor questions

I've searched and found a lot of info. I'm a bit confused on what the searches found.

I have a multi-level house and the front entry floor is above a crawl space. There's the front entry, a small bathroom, and family/TV room that doubles as a small office area. At the rear of the house there is a patio door out the back. The existing flooring on this level has always been solid. We've not notices any give or creaks/squeaks in any of the flooring on this level.

I'm going to tile most of it - all of the higher traffic areas, leaving carpet at only the TV area where the couch is. I have the Quiet Warmth thin heating mats for under tile floors that I'm going to install under most of the tiled area. This adds a small "credit card" thickness and is not set in floor leveler or anything. It has an adhesive that sticks it to the sub-floor and thinset and tile go right over the top of it. The ceramic tile is a wood-look that is 6"x36".

My sub-floor appears to be 1/2" plywood and there's a 5/8" particle board over the top of it. I made a drawing of what I measured for thickness and clearances of the front door. I removed the existing 2 layers of laminate squares first. I measured the distance from the sub-floor top to the bottom of the door, both with and without a piece of tile just setting in place. To determine the thickness of the sub-floor, I drilled a 3/8" diameter hole and measured the layers.

Now, I know that the particle board should be removed because it's not a suitable underlayment for the ceramic tile. I plan on removing it and putting in 1/4" Wonderboard type material in it's place (I suppose, with the thinset underneath it). Then the heating mat and tile.

Does anyone see any major issues with this? Will my clearances be OK - even if we want to add a rug over the tile at the front door?
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Old 01-13-2018, 06:25 PM   #2
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Welcome to the forum, Roger.

If you have only 1/2" plywood as your subfloor, you have a problem. It would be woefully inadequate for tile, or most anything. The bare minimum is 5/8" plywood, and we would recommend 3/4" to be safe. You don't mention your joist spacing, so you may need more than that.

I would start by running the joist specs through the Deflecto in the blue bar at the top of the page. Once you've verified your joists are adequate for tile, we can move forward to the subfloor issue.
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Old 01-13-2018, 06:30 PM   #3
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IF the layer beneath the particle board truly is 1/2", yes, you have a problem! The minimum thickness subflooring that has been tested for tile is a nominal 5/8", and that's new, not after you've removed something nailed on top of it. And that is over 16" OC joists...if they're wider, that won't work.

But, beyond that, you need to determine the strength of your joist system. You can do that by inputting the numbers of your actual materials in the 'deflecto' tool in the blue bar at the top of the forum.

No CBU is structural, so do not count on its thickness to provide any strength to your subflooring. It's both brittle and will bend to conform to the substrate beneath it over time.
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Old 01-14-2018, 12:52 PM   #4
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16" on center
2x10 (1.5x9.25)
plywood subfloor
12' length to center of the house

Thank you for using the John Bridge Forums Deflect-O-Lator :-)

For joists that are SYP or Douglas Fir, in good condition, 9.25 inches tall, 1.5 inches wide, 12 inches on center, and 10 feet long between supports, the deflection calculated is 0.105 inches.

This translates to a deflection of L / 1142.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile or Natural stone, Congratulations!


I'm not sure what this is telling me - I'm still ? the height clearance (see diagram on my first post) and what I can do for a tile installation here.
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Old 01-14-2018, 01:42 PM   #5
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Can you take a pic of what you consider particle board?
Like others said the 1/2" is basically treated as if it isn't there. Personally I would remove the 5/8" then make sure what you have is indeed 1/2" below that. If thats the case then you can either remove that or treat it lime it isn't there and go over it with 3/4", followed by cbu or underlayment of choice
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Old 01-14-2018, 01:51 PM   #6
rkhanso
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The particle board was painted with something black. I took 2 pictures - one with a flash and one without.

If I leave the 1/2" plywood there and add 3/4" and then 1/4" wonderboard or similar, then the heat mat and the thinset and tile, am I going to have enough room under the door and hopefully have room for a rug?

Or, can I just remove the particle board, add 1/4" or more Wonderboard or similar and then finish with the heat mat, thinset and tile?
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Old 01-14-2018, 03:19 PM   #7
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I think you misentered the info into the deflectolator, you put in 12" o.c. instead of 12' length between supports. The information you gave:

16" on center
2x10 (1.5x9.25)
12' length to center of the house

gives L/558 for "SYP or Douglas Fir, in good condition." This assumes there is a girder or bearing wall at the "center of the house" so that 12' is your unsupported span.

Cheers, Wayne
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Old 01-14-2018, 03:30 PM   #8
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I did have the wrong distance on-center
Here are the correct numbers:
For joists that are SYP or Douglas Fir, in good condition, 9.25 inches tall, 1.5 inches wide, 16 inches on center, and 10 feet long between supports, the deflection calculated is 0.140 inches.

This translates to a deflection of L / 857.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile or Natural stone, Congratulations!

There is a center beam down the center of the house. Steel in the multi-story part of the house and wood in the crawlspace area (which is where this tile floor will be above - the Crawlspace).
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Old 01-14-2018, 05:26 PM   #9
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The only way to get the minimum height is to remove everything to the joists, install 3/4" plywood, and start from there. The 1/2" plywood won't really do anything for you.

What is the thickness of the tile?
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Old 01-14-2018, 07:19 PM   #10
rkhanso
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I did have the wrong distance on-center
Here are the correct numbers:
For joists that are SYP or Douglas Fir, in good condition, 9.25 inches tall, 1.5 inches wide, 16 inches on center, and 12 feet long between supports, the deflection calculated is 0.258 inches.

This translates to a deflection of L / 558.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile, Congratulations!

There is a center beam down the center of the house. Steel in the multi-story part of the house and wood in the crawlspace area (which is where this tile floor will be above - the Crawlspace).
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Old 01-14-2018, 07:21 PM   #11
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The tile is 1/4"
I'm putting Quiet Warmth heat mat under much of the tile (not all)
http://www.quietwarmth.com/products/...tick-for-tile/

The tile is 6"x36" wood-look ceramic.

What would happen if I just put 1/4" or 7/16" Wonderboard over the 1/2" plywood and then the tile over that?
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Old 01-14-2018, 07:38 PM   #12
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Pretty good chance you'll be starting over again in less than 6 months. Your first layer needs to be a minimum of 5/8" Tounge and groove. I prefer nothing less than 3/4" when I install.
Like mentioned earlier cement board offers no additional strength, it is a surface to adhere to. It doesnt matter what wonderboard thickness you use.
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Old 01-14-2018, 09:24 PM   #13
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Your base is inadequate for installation of any tile. The minimum base subflooring is 5/8" plywood in good shape...your 1/2" stuff has lots of holes in it, and is too thin. Deflection has two components: along the joists (yours appear to be okay for ceramic, not natural stone), but the between the joist deflection is inadequate for tile. The first layer needs to be thicker, or, you need a new layer on top of it that is thick enough all on its own. That might put you above your available height, especially if you want a door mat there.

The most reliable thing would be to tear out the existing subflooring to the joists, level things if required, then install new subflooring. If you level the joists properly, you should have a dead flat floor which is a pleasure to tile onto. NOte, 5/8" subflooring is the minimum, which is why most people prefer a thicker layer for a bit more margin.
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Old 01-15-2018, 09:48 AM   #14
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OK - so, say I remove everything in the part that I'll be tiling - but not where I won't be adding tile....the carpeted area. I instead, put 3/4" plywood on the floor joists and then 1/4" Wonderboard over that. Will that give me enough clearance for the heat mat (their website says it's less than .03" thick), the thinset and tile and still have room for a entry-type rug at/under the front door?

I'll be taking out 1 1/8" and putting back in 1 1/4" if I do this. I did put some measurements of what I currently have in my first post above.

Or, can I get 5/8" plywood subflooring instead and that be good enough?

And, does it have to be plywood, or is OSB adequate? Tongue and groove? Or just plain? Something like this?

I'm trying to save some $$ because I didn't anticipate this expense and the project is already over what I was prepared for.

And, would I just cut with a sawzall or circular saw to remove what is there? Maybe a sawzall by the walls and circular saw in the middle of the room? I'm guessing the walls are not sitting on top of the sub-floor, but they are built over the floor joist? I'm not a framer and don't know this.
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Old 01-15-2018, 10:26 AM   #15
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Walls that run perpendicular to the joists will be fine. Those that run parallel would hopefully have some cross support, or be resting on a joist. Otherwise they'll likely sag over time. Once you start taking out the subfloor you'll be able to see that.

You would need to add blocking between the joists around the perimeter of the room to support the plywood (yes, plywood instead of OSB) edges. The tongue and groove of the plywood will take care of the support everywhere else. You should use 3/4" plywood, which is in some cases cheaper than 5/8".

If you want to save some height, use a tile membrane like Laticrete Stratamat. It's just about as cheap as installing cement board, when you factor in the cost of the screws and mesh tape, not to mention the membrane is so much easier to work with.

Quote:
Originally Posted by Roger
Maybe a sawzall by the walls and circular saw in the middle of the room?
That would work.
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