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Unread 05-16-2013, 03:23 PM   #1
nowwhatnapster
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Kitchen remodel, Subfloor deflection question for porcelain tile

I have vinyl floor in my kitchen that is in poor condition, ugly and cracking along plywood seams. It is asbestos free. My wife and I were thinking of replacing it with porcelain tile. I have a few questions regarding subfloor deflection which will probably answer many other questions. I used this sites deflection calculator but I'm just unsure.

Here are the numbers. Joists are 2x10's, 16" on center, span is 14' or less (I will take exact measurement of joists this weekend). Current floor is made up of 3/4" thick 7" wide tongue and groove boards on 45 degree angle to joists. On top of those is 5/8" plywood (5-ply, unknown grade) The crappy vinyl is adhered strongly to the plywood. The kitchen floor is flush with the adjacent oak floor in hallway.

***See the attachment on this post for room dimensions.***

Tile is intended for the eat-in area and kitchen and transition to oak floor in hallway. Let me know if you need additional information.

Deflection leads into my next question.. Plywood... What thickness/grade/glue/type are the minimum and what is excessive. Please be specific, a link to a manufacturers plywood product would be helpful.
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Last edited by nowwhatnapster; 05-16-2013 at 11:48 PM. Reason: Wrong joist dimensions, they are 2x10's
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Unread 05-16-2013, 08:28 PM   #2
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Welcome Steve.

I think you probably read the Deflecto right. You'll need the joists to be spanned down near 11' to even get in the ballpark with the best joists. And that's for ceramic/porcelain tiles.

Let us know what you get for the maximum unsupported span(s), and try to get a look at the condition of the joists. Might snap a few photos while you're down there too.

Are you planning on ceramic/porcelain tile or natural stone?
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Unread 05-16-2013, 11:47 PM   #3
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oops! They are 2x10's NOT 2x8's. I think I still fall short on the deflection.

I was planning on ceramic/porcelain tiles.

I'll get the exact span measurement and a few photos this weekend.
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Unread 05-19-2013, 04:15 PM   #4
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Span is just shy of 13', from beam to sill plate. They are 2x10's. 16" OC. It's a pine of some sort.

Behind the furnace is the chimney which has cinderblock supports on either side that the center beams rests on. The joists at the edge of the chimney are sistered. There are 4 joists that are shorter 11'8" because of the chimney. They are toe nailed at the chimney, no brackets. Their load, I would assume, is carried over to the sistered joists.

There is blocking/strutting down the center of the span between the joists.

With these new measurements the deflectolator says I have L\350. Just shy of the L\360 required for ceramic/porcelain.

I would assume it would be wise to beef up the joist either by sistering or the attaching 2x4 or 2x6 to the bottom of the joist to create a T beam. There are a decent amount of obstructions to work around. So sistering would be a bit of PITA, but it is doable I think. Only obstacles I can't move are some pipes near the fireplace that run through the joists. Most of the wiring I could remove and reattach.

I think this lends well to the T joist approach. Opinion?

By the way, if you right click the images and click view image, they are larger.
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Unread 05-19-2013, 05:00 PM   #5
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Steve, I can't see well enough to grade those joists, but they look like Yellow Pine to me. And I'd guess grade #2. I'd not be concerned to tile over those at your indicated span.

Have you removed the plywood from your sawn board subfloor? I'm confused about your plywood question.

My opinion; worth price charged.
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Unread 05-20-2013, 06:13 AM   #6
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Hi cx,

Sorry for the confusion. I have not removed the existing plywood with linolium on top. I wanted to know what grade and thickness should be used to replace the old plywood. What would be the minimum grade/thickness and what grade/thickness does it become excessive.
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Unread 05-20-2013, 09:34 AM   #7
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The minimum requirement over sawn board subflooring is nominal 1/2" exterior glue plywood with no face of grade lower than C. But with your diagonally placed subfloor boards, I'd want a minimum of 5/8ths" plywood.

You'll want the plywood properly fastened only to the board subfloor, not into the joists, which does not appear to be the case now. Here is a good article on what I think to be the best method of installing the second subflooring layer.

My opinion; worth price charged.
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Unread 05-30-2013, 11:50 PM   #8
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hi cx,

I am concerned the new tile floor may be too thick for a reasonable transition to the adjacent hardwood floors. The hardwood flooring is 5/8" thick, plus the 3/4" planks for an overall height of 1-3/8".

Scenario 1:
3/4" planks, 5/8 ply, 1/8" thinset, 1/4" CBU, 1/8" thinset, 1/4" tile
Overall height: 2-1/8"
Transition difference: +3/4"
So i looked into ditra....
Scenario 2:
3/4" planks, 5/8 ply, 1/8" thinset, 1/8" ditra, 1/8" thinset, 1/4" tile
Overall height: 2"
Transition difference: +5/8"
Those are the bare minimums I could come up with. Please correct my numbers if they are wrong, I tried my best.

1/2" transition is too much in my opinion. The wife is not even happy with the idea of 1/4". So I started thinking about removing the planks, but I'm not sure how feasible that is since there are walls and structures built on them. Are there any other ways to get the floor height down?

Also, I might as well bring this up now. I am doing the bathroom floor in tile as well. I just removed the plywood and vinyl on monday. I would assume everything discussed in this thread applies to the bathroom as well. I'll double check the joist span but I think its the same. Does the deflection matter as much if the bath is only 5' wide?
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Last edited by nowwhatnapster; 05-31-2013 at 08:54 PM. Reason: corrected numbers
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Unread 05-31-2013, 12:05 AM   #9
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Steve, the height difference between using a CBU and using Ditra will be no more than about 1/8" maximum.

Changing from 5/8ths" plywood under the CBU to 1/2" under the Ditra isn't realistic. If it'll work under one, it'll work under the other. The (nominal) 1/2" plywood is the minimum thickness recommended by the tile industry, but that presumes the boards be laid perpendicular to the joists (and they're really supposed to be T&G), the recommendation of the thicker plywood is my own based upon the unsupported span of the diagonal boards being much longer than with perpendicular boards.

Aside from removing and replacing the sawn boards with plywood, I really don't know of a good way to reduce your finished floor height and still have good tile installation.

How much horizontal distance do you have in which to make this transition from tile to hardwood?

My opinion; worth price charged.
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Unread 05-31-2013, 07:01 AM   #10
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If height becomes critical, think about switching from CBU or Ditra to Greenskin which has the thickness of a used dollar bill. GS is self stick and gets adhered directly to your plywood (in good condition)
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Unread 05-31-2013, 10:42 AM   #11
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cx, Thanks for clearing up the 45 degree vs perpendicular. I understand your 5/8" recommendation better now. I'll update the numbers in my post.

As for the transition area, I'll snap a few photos this weekend, but in the mean time I'll do my best to explain. If you refer to the graphic in my first post, the bathroom transitions takes place at the door threshold. You could easily put up to a 4" wide transition strip and not have it look awkward. I am less concerned about height of this transition.

The kitchen transition on the other hand is out in the open and its not a straight line. It's an inverted L shape. The hardwood from the hallway extends past the office wall into the kitchen by about 4 inches. I believe they did this because without it the transition would take place inside the living room doorway. I will need to do some mitered transition or cut out the hardwood on an angle to eliminate the L shape. This transition is the one I want to minimize the height and width of the transition.


Paul, the green skin product does seem legit. I found a long discussion thread on this forum about it. Looks like it can eliminate a layer of 1/8" thinset and reduce the membrane to ~1/16" for an overall floor height of 1-13/16" and a 7/16" transition. Better, but pretty far from the wife's expectations. I believe the green skin is only an uncoupling membrane and not a waterproof membrane, correct? So maybe not a good idea for my bathroom, but the kitchen would probably be ok?

Here is another scenario I cooked up. Since, I have to refasten those planks to the joists, why not counter sink the nails and screws and hit the planks with a 36grit belt sander. It would level any cupped boards and reduce the height of the floor by 1/16"~1/8". Then I could skip the blocking, although it couldn't hurt to add some. That could get my overall height with green skin down to 5/16~3/8" which is about where I would want to be for a reasonable transition.

Thoughts?
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Unread 07-28-2013, 06:00 PM   #12
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Grade markings

Jumping back to deflection....

While removing staples and other obstructions from the joists in preparation for sistering. I found some grade markings on the joists. I was hoping someone here might be able to determine if the lumber is douglas fir?

I double checked the span measurements. The kitchen at the widest span is 12'10" and the bathroom is over a 14' span. If it is douglas fir then the deflectolator says I'm good for ceramic tile in both locations.
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Unread 07-28-2013, 06:13 PM   #13
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GS is waterproof but they didn't bother to get the certifications as their chosen market strategy is for flooring and not showers. We use it in bathroom floors all the time. A 2 inch overlap, well pressed into place then covered with a liquid waterproofing for added insurance is the GS recommended method.
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