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Unread 05-14-2013, 04:50 PM   #1
t2jeff
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Subfloor Advice for Large Format Porcelain Tile

Been lurking on this site for awhile researching my next project. I do have some specific questions for my task at hand. Since this is my first post, here is the back round on what I am doing:

  1. Kitchen Remodel using 12x24x.3/8" porcelain tile
  2. 2x6 floor joists (1.5"x 5.25" actual), 16" oc, unknown wood (looks to be DF though) in good condition
  3. Two 4x6 griders divide the kitchen into 3 spans, longest span being 70"
  4. Deflecto gives me a L 514 (for the 70", which is worst case), thumbs up for ceramic tile
  5. Above the joists sits 1x6 (.75x 5.25 actual) planks, 45 degrees to the joists, spaced 1/8" apart from each other

Plan on placing 19/32's exterior plywood (CCX or better) over the diagonal planks. I plan on staggering the edges of the plywood so there are no areas where 4 corners come together.

Questions #1
Does the plywood grain still need to be perpendicular to the joists since its sitting on the planks? I've seen in the Liberry the post with the bricks on top of the plywood and understand 2 out of 3 plys should be in your favor, but does it apply since its over planks?

What is the assumption the deflecto is using for a thumbs up for tile when it does not know the subfloor? Do I need to consider my planks and exterior ply? I was debating between 19/32's and 23/32's plywood, but will go with the 19/32's if I "already" have the thumbs up to save height.

I plan on using hot dipped galvanized nails (1.5") and construction adhesive under the plywood. I plan to provide 1/8" clearance between plywood sheets and 1/4" around the perimeter.

Questions #2

Are these the right nails for the job?
Any specific construction adhesive?
Is this the correct spacing around the plywood?

I plan on following that up with 1/4" Hardiebacker set into Versabond (1/4 notch) and fastened using hot dipped galvanized nails (1 1/4"). I will stagger the hardibacker edges as to not overlap the plywood edges. I plan to provide 1/8" clearance between sheets and 1/4" around the perimeter. Tape and mortar all gaps will follow.

Finally, use Versabond to set the tiles.

Question #3

Do any of these anti lippage systems actually work? Do they pull the tile off the thinset and prevent 100% coverage?

Sorry for the long first post!! Just trying to get everything out on the table and prevent the standard questions back to a newbie I always see!

Thanks in advance for your professional feedback! Look forward to your comments!

Jeff
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Unread 05-14-2013, 05:41 PM   #2
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Welcome Jeff.

1. Yes, plywood should always be installed with the face grains perpendicular to the joists. 5/8 ply is fine over those planks. Install it like this-

http://www.johnbridge.com/images/mik...-0604.pdf..pdf

First, though, go over the whole floor and replace any cracked, broken or cupped planks, then renail/screw all the planks to the joists. May need to predrill to keep from splitting at board ends.

2. Fasteners for the plywood are in that article. For the backer board, use the fastener recommended by James Hardi - check the Hardi install instructs.

3. They do work. You can read all about the pro's, con's and finer points here

http://www.johnbridge.com/vbulletin/...d.php?t=106061
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Unread 05-14-2013, 06:31 PM   #3
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The article covers it, but DO NOT use construction adhesive between the planks and the plywood. You're trying to decouple the movement of the planks from the more stable plywood, plus, you'd never get full coverage and the ply wouldn't be in intimate contact opening things up for localized deflection of the ply. While construction adhesive on top of the joists with the first layer has advantages, because that area is small, your fasteners can create intimate contact...that will not happen over a larger area.
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Unread 05-15-2013, 10:21 AM   #4
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Thank you for your input. I will adjust my layout to have the 5/8 plywood perpendicular to the joists. I originally had it oriented both ways, just trying to minimalize waste. With the planks under, I didn't think there would be any/minimal deflection of the plywood if nailed with the specified proper spacing.

In the article, it mentions ring shank nails for the plywood. I will go with those, and NOT use the adhesive. Any issues with corrosion since they will be covered with thinset?
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Unread 05-15-2013, 10:32 AM   #5
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Jeff, any fasteners you use on your subfloor should be coated or plated against corrosion. While I much prefer screws for all parts of any subfloor structure, ring-shank nails, preferably gun-driven, will work for that second layer and are readily available in corrosion-resistant finishes. But when they are hammer-driven, chances of damaging the coating on the heads are high.

My opinion; worth price charged.
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Unread 05-15-2013, 09:18 PM   #6
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CX,
Good point about hand driven vs. gun nails. Looks like I need to track down a gun for a few days.

I'm also looking into the Pearl Abrasive anti lippage system. Hopefully this can make a difference at the end of the day.

Thanks for the input.
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Unread 05-16-2013, 07:51 PM   #7
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@CX,

I have read that using electro glavanized nails for the hardi is a no no, but since I may use a coil gun for the plywood subfloor, electro galvanized are ok for the wood, correct?

Planning on using hot dipped for the hardi and driving them by hand. Unless they make hot dipped for the coil gun......thoughts?
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Unread 05-16-2013, 08:08 PM   #8
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I would use a coated ring-shank nail in the nail gun. Usually wouldn't find a galvanized nail, electroplated or hot-dipped) for those, but you never know what you can get these days. But there are lots of gun-driven fasteners that are listed as corrosion resistant, including ring-shanks.

For installing the CBU with a pounder, yes, you want the hot-dipped nails. The Backer-on screws or similar would be my preference if I were to use CBU onna floor.

My opinion; worth price charged.
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Unread 05-16-2013, 08:31 PM   #9
t2jeff
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I was just looking at some electro plated 1 1/4" coiled nails about an hour ago. Didn't think about the ring shank though when seeing what they had in stock. Will have to check again tomorrow.

I hear you about the hardi screws. not having personally driven a hardi screw through hardi without pre drilling and counter sinking before hand, was trying to avoid a multi step process 1200X's. I have full confidence in my screw driving abilities, but not full confidence in the performance of those hardi screws all being sub surface. Maybe it's just a factor of the torque of the tool and using the square driver versions......am I right?
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Unread 05-16-2013, 11:43 PM   #10
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Hi Jeff,

I compliment your parents on giving you such a distinguished and fine name :-)

Regards,

Jeff

On one hand, I'm not "an expert". On the other hand, I've done 2 bathrooms from scratch after a total gut, using natural stone tile (requires VERY stiff floors with no deflection, electric heated flooring, SLC, linear drains and have had no failures at all.

My Opinion is this stream of thoughts:

1. Can you sister the joists from underneath, without tearing everything up? if you CAN ... DO IT! Sistering these is the single MOST important thing you can do to stiffen that floor! You'll use construction adhesive on the top of the sisters as well - and then screw the planking into the sister so that it's pulled into the adhesive. This really won't cost much to do - IF you have access from underneath. And this is the single BEST way to stiffen up your floor. I can't stress this enough.

You didn't mention if you are also redoing your cabinets, etc ... and I'm kinda betting that you might be - along with granite or some stone? That stuff is HEAVY ... and factors into defection ...

FYI - the taller the joist the stiffer it is. If you CAN sister with 2x8s or 2x10s instead of 2x6s ... that is MUCH better!

Simpson screws are great for this (they are called sdw or sds - depot sells them). But ... it'll be tricky to make sure that they are held up in position right against the planks while being sistered - you'll need help!

2. Does the floor squeak? I'm betting it does. Old plank floors do that :-)

So .. you COULD try and screw down all the planks ... and maybe it'll be solid when you are done ... maybe not. If you CAN get it solid as all heck, then glue and screw ADVANTECH 3/4" tongue and groove subfloor - not available at the depot or big box stores but you can get this stuff from places that service to builders and contractors. It is super stiff, strong and water impervious. Think of it as space-age OSB with none of the weaknesses of plywood or OSB. It'll be about $41 per 4x8 sheet. It was $32 a few months ago but the good news in the housing market has shot prices up for a lot of stuff lately.

On top of the advantech, apply latex primer (you need something for thinset to adhere to as it will not do so to plywood etc), let that set. Then thinset, apply a waterproof anti-fracture membrane (I like Wedi subliner or Mapei subliner). Let that set. Then thinset and tile.

2. If you can't get the squeaking out of the planks then you have movement. Movement isn't good as you know. Will this matter with another subfloor glued and screwed to it ...? Well ... PROBABLY NOT ... but no guarantees. It'll be a judgement call that you'll have to make. Ideally, you would rip out the planking, sister all the joists and put down 1 layer of advantech. The only extra labor there is ripping out the planking really ... I would if I were you but ... I'm also don't know the space and you do.

If doing this would make the floor lower than you would like ... then just put a 2nd layer of advantech down - they make it in various thicknesses. Or ... hardibacker.

>> I plan on staggering the edges of the plywood so there are no areas where 4 corners come together.

Yes! good! try and stagger them 4' - so all seams fall onto a joist for full support! glue and screw - around outside and in the field. 2.5 or 3" drywall screws are pretty good for this!


Questions #1
>> Does the plywood grain still need to be perpendicular to the joists since its sitting on the planks? I've seen in the Liberry the post with the bricks on top of the plywood and understand 2 out of 3 plys should be in your favor, but does it apply since its over planks?

Assuming you keep the planks, the 8' of the advantech would be perpendicular to the joists, staggered 4'. Even if you do keep the planking, I'd still do it the same way.


>> What is the assumption the deflecto is using for a thumbs up for tile when it does not know the subfloor? Do I need to consider my planks and exterior ply? I was debating between 19/32's and 23/32's plywood, but will go with the 19/32's if I "already" have the thumbs up to save height.

Assume that it is WRONG and that your floor isn't as stiff as it is desired to be. Planks are just not plywood or advantech. Each of them can move and NONE of them are glued and screwed! Remediation is needed.

Jeff - The LAST thing that you want when this is all done are lovely large format files that will crack, right? You obviously want to DO THIS RIGHT. So do all your prep work now - reinforce that floor (joists first) and you will be confident and happy forever! We're really not talking about a lot of time or work to do it right ... good prep is key!

>> I plan on using hot dipped galvanized nails (1.5") and construction adhesive under the plywood. I plan to provide 1/8" clearance between plywood sheets and 1/4" around the perimeter.

Nails can move. I'd glue and screw per the above. You'll be using some kind of waterproof anti-fracture membrane under the tile so they don't need to be galvanized etc. Some ppl love ditra but it is overkill and very expensive. Wedi, Mapei etc will work just FINE. The main thing is minimizing defection!

Test everything by jumping on it ... you want a nice stiff floor with no movement. Those joists are way small ... and that is your first priority. Sistering these is the single MOST important thing you can do to stiffen that floor!

Questions #2
>> Any specific construction adhesive?

Lots of good stuff available. Don't go crazy ... :-)

>> Is this the correct spacing around the plywood?

No - you'll use tongue and groove - it'll be locked in together except around the very edges of the room - and that'll be hidden by the Base Moulding. Advantech doesn't expand like plywood - you can bring it very close to the edges - just make sure that it is close enough that any gap will be covered by the base that you'll use. 1/4" is probably ideal, and easily filled by a bit of foam to help keep sounds from going down - IF you are concerned about that - otherwise don't bother.

>> I plan on following that up with 1/4" Hardiebacker set into Versabond (1/4 notch) and fastened using hot dipped galvanized nails (1 1/4"). I will stagger the hardibacker edges as to not overlap the plywood edges. I plan to provide 1/8" clearance between sheets and 1/4" around the perimeter. Tape and mortar all gaps will follow.

No need. You will not need hardibacker at all on top of the subfloor - you'll just use a waterproof antifracture membrane. This will also protect from gaps up to 1/8". Ditra can do even more but that is overkill for your application.

>> Finally, use Versabond to set the tiles.

Sure ... or whatever modified thinset you like.


Question #3

>> Do any of these anti lippage systems actually work? Do they pull the tile off the thinset and prevent 100% coverage?

YES they DO work! I'm a FAN! By all means get one!


>> Sorry for the long first post!! Just trying to get everything out on the table and prevent the standard questions back to a newbie I always see!

You are being SMART about this - you are PLANNING and DESIGNING - BEFORE you start! Kudos!!!

I hope this helps! Best of luck to you!!!!
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Unread 05-17-2013, 09:48 AM   #11
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A few more comments, some of which are in contrast to Jeff's (Jefferson17) last post.

While sistering is certainly a nice thing to do to your wood framed floor that will receive ceramic tile, if you've currently got a design deflection of L/514 it would be somewhat wasteful for you to bother sistering the joists to improve that deflection rating. It won't hurt, of course, but even the more conservative of us recognize that there is a point of diminishing return in the joist structure.

Your money and effort would be far better spent on improving the subflooring deflection.

Our Deflectometer does not consider subflooring at all in it's calculation of joist deflection, nor do common dimension wood span tables. Only engineered wood floors consider gluing of a specific subflooring in their deflection specifications.

I agree it's important to re-fasten any existing sawn board subfloor before adding the required enginered wood second layer. I do not agree with trying to glue the OSB to the board subflooring (just doesn't work well in real life) and don't agree with trying to glue any OSB to anything except the tops of your joists with an appropriate construction adhesive.

If your board subflooring is in good condition and well fastened, you must install a minimum of nominal 1/2" plywood or osb over it before your tiling substrate. With the boards oriented diagonally, I would recommend your minimum be 5/8ths" plywoood. I prefer to see plywood used as the top layer of subflooring in consideration of the use of thinset mortar over it for the tiling substrate. Doesn't make much difference if you plan to use a CBU, but if you're bonding anything to the subfloor the plywood surface is preferred by the mortar manufacturers.

Regardless the subflooring materials you elect to use, you do not want to use any drywall screws for the fastening. You want some sort of coated or plated fasteners. Decking screws work well.

And you do not want the second layer of subflooring attached to the floor joists at all if you can avoid it. There is some demonstrable uncoupling of the second layer of subflooring if it is not fastened to the joists, but fastened only to the first layer. How important is that? I dunno. But I recommend you take advantage of the feature if you can. You don't even want the ends of your second layer panels to fall over the joists below.

If you start with new, or in very good condition, plywood subflooring and want to add another layer of plywood subflooring, I'm all in favor of glue-laminating the layers with a full spread of wood glue if possible. In all other situations, I would recommend against trying to glue.

Here is a good article on what I think is the very best method of installing a second layer of structural subflooring and I suggest you follow the recommendations to the extent feasible on your floor.

My opinion; worth price charged.
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Unread 05-17-2013, 03:02 PM   #12
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All comments and input are always appreciated!

I do agree with CX that sistering the joists may have a small rate of return. Longest span is 70" and shortest is 48". I think I am good to go.

Good call CX on refastening the planks before installing the plywood. Consider that done!

Just got back from my local yard and they have 5/8" ACX. I will be using this. Its not tongue and groove. Any issues with that? Not wallet friendly, but the only other option was CDX.

I plan on placing the A side up to accept the thinset before the hardi. Correct?

Thanks again for all input from everyone!
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Unread 05-17-2013, 03:08 PM   #13
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All correct. The T&G is not necessary in that application.

My opinion; worth price charged.
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Unread 05-17-2013, 04:49 PM   #14
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Hi Jeff

>> I do agree with CX that sistering the joists may have a small rate of return. Longest span is 70" and shortest is 48". I think I am good to go.

Does your current floor pass the "jump test"? If you feel flex in areas then it isn't the planking that is flexing so much as those 2x6 joists. Adding a layer of plywood or even advantech does little to remediate a joist that is allowing too much deflection ...

Again - you are there are we aren't. But don't place blind trust in deflecto - do the jump test. deflecto is NOT designed to accurately provide metrics for plank flooring. It would suck to end up with cracked tiles.

You didn't mention it but is there some kind of island etc with stone in the middle of that kitchen? If so, that would place a significant load that affects deflecto's #s.

>> Good call CX on refastening the planks before installing the plywood.
>> Consider that done!

Hey! That was my idea :-)

I would also maintain that you can use drywall screws if you want to - PROVIDED that you use a waterproof antifracture membrane. If you'd rather use coated wood screws ... no worry. Think of the whole thing as an ASSEMBLY - and design accordingly. Personally I would not use nails but you do whatever you think is best and we all do hope that it works perfectly for you.

Bear in mind that this IS a kitchen so at some point there might be a leak, perhaps a bad one. If you don't use a waterproof membrane under your tile, and you don't use advantech ... your subfloor can swell-up etc - and bad things will happen to your lovely tile - and we don't want that.

Best of luck to you!

Jeff
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Unread 05-17-2013, 05:03 PM   #15
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What is the big issue with electro galvanized in hardi? I know its thinner protection, but is that the only reason? Pull out force different?
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