gaps between each 4x8 ply?

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Old 02-25-10, 11:31 PM
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gaps between each 4x8 ply?

Here's me being paranoid again. But is there a need to leave gaps between 4x8 plywood subfloors? I know I should leave about 1/8" at the wall for expansion. But between each sheet? If so, how much of a gap? Thanks in advance.
 
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Old 02-26-10, 05:48 AM
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You should be using T&G subflooring anyway, so the gap won't show. On the flat ends, you can use a 1/8" gap to take into consideration expansion and contraction. Stagger your joints by 1/2 sheet. If this subflooring is going directly on joists use an adhesive like PL400 to glue it down, then either nail with ring shanked nails or screw it down to the joists.
 
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Old 02-26-10, 10:03 AM
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Rayyu,

I have a feeling what you're installing is not the subfloor, but an underlayment. There wouldn't be any walls if it was the subfloor unless you removed the old and are re-building.

Please confirm what you're doing and what kind of flooring will be installed.

Jaz
 
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Old 02-26-10, 06:57 PM
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Hi Chandler,

So 1/8" at the perimeter where the ply meets the dry wall? And if this is my second layer of ply, would I still need adhesive?


Hi Jazman,

I suppose I might have my term wrong when I say "subfloor". I'm laying down granite tiles (and yes I have reinforced the joists with 8x2 to meet the deflection standard). I have already glued and screwed one layer of 5/8 ply on the joists. And now I am laying down another layer of 5/8 ply before my hardibacker and my granite.

So, for this second layer of 5/8 ply, should there be any gap between each sheet, and between the sheets and the dry wall at the perimeter?

Thanks all,
and cheers!
 
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Old 02-26-10, 08:01 PM
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Yes, underlayment is spaced min. 1/8" between sheets and would be smart to leave a bigger gap (1/4"), at the perimeter and all vertical objects.

Do NOT glue the second sheet to the subfloor, AND do NOT screw the second sheet into the joists. Fasten it only to the subfloor. You should be using 1 1/4" galvanized deck screws which would take care of that.

Jaz
 
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Old 02-26-10, 10:10 PM
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I have some Kwiki flooring screw. 1-1/4 screw length should hold the second layer just right without fastening it to the joist.

Thanks Jazman.
 
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Old 02-27-10, 05:19 AM
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Go with Jazman's recommendations as it is not "subflooring" as you stated in your OP. Glad he realized it was underlayment. Things change with the layers. The reason for no glue and no screws into joists is to allow some movement, although minimal, between subflooring and underlayment.
 
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Old 02-27-10, 01:47 PM
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Thanks Chandler for pointing that out.

Also, my friend has a couple of bags of polymer modified mortar (Ultraflex 2, Mapei brand). They are unopened, but has been sitting in his garage for over 2 years. Are they still good for laying down hardibacker and granite? Or should I get a new batch? Thanks.
 
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Old 02-27-10, 02:08 PM
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Just a guess..but if its still a powder after 2 yrs..it can prob still be used. I'd be surprised if its not one big solid chunk.

Whether its the right thing or not..I couldn't tell ya.
 
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Old 02-27-10, 02:51 PM
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ya, the couple of bags do feel solidly chuncky. Guess I shouldn't even try to break it up with a hammer eh?
 
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Old 02-27-10, 02:58 PM
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Nope...if its not a pwder..its no good as far as I've been told. I mean sure..light hand pressure is one thing..but having to use a hammer...nope!
 
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Old 02-27-10, 04:11 PM
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It's probably no good even if it's still powder. Sometimes it looks and feels OK, but when used will not set up.

Take it to the curb.

Jaz
 
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Old 02-27-10, 04:14 PM
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Do you want to trust your job to a product that is questionable and only $15 a bag?
 
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Old 02-27-10, 09:43 PM
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Haha, good point Chandler. I've torn up my floor, reinforced my joists, removed my cabinets, hauled home the plywood sheets. To save some dollars on couple bags of mortar is probably sensely.

But the type is correct, no? Polymer modified mortar is good for setting hardibacker?

Also, I'm using t&g ply for my underlayment right now. And I have knocked the t&g pretty tight. That's ok right? I did leave 1/8" on the ends for expansion.

Thanks again.

Cheers.
 
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Old 02-28-10, 01:10 PM
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T&G is correct. Thinset should be modified if one of your stratum is pourous which durock/hardie backer is. Unmodified if neither is pourous such as linoleum (not recommended anyway, but done).
 
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Old 03-01-10, 09:22 PM
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Moving my new thread here to consolidate things as suggested by JazMan.

Originally Posted by rayyu View Post
Hi all,

Just trying to calculate my floor height offset. What is the height of 1/4" hardibacker with mortar under and above? (basically, what is my height increase minus the tiles?) Thanks.
Originally Posted by JazMan View Post
Rayuu,

It would have been better if you had asked this question in the other thread you have going on this same project. The info contained there may be relevant to this thread and they will soon the separated forcing people to ask the same questions again.

But since you're here.

You can figure about 1/16" for the thin set under the CBU. Don't really know how much it'll raise the tile since we don't know what tile you're using. Generally the thin set to install the tiles is from 3/32-1/8".

Jaz

So to be more specific, if my granite tiles are 3/8" thick, what will be the total height taking account of cbu and the 2 layers of thinsets. Actually, more importantly, how will I know how thick of a thinset I'm trowelling on? Does a 1/4" trowel automatically leave a 1/8" thick layer?

Also, I'm screwing in my 5/8" ply underlayment right now. I'm putting in screws 6" apart at about 1" from the edge of each sheet. And also putting in screws 8" apart in field. Just want to confirm I'm doing it right. Thanks. again.


Cheers.
 

Last edited by rayyu; 03-01-10 at 09:49 PM.
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Old 03-02-10, 12:45 PM
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That fastener schedule should be fine.

Your granite tile should be 1 cm thick, (.3937 inch) which is a hair over 3/8" (.3750).

Since the backs of the tiles are flat, 1/4x1/4 trowel is plenty as long as the substrate is flat within specs. Total tile thickness installed will be very close to 1/2".

Jaz
 
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Old 03-02-10, 01:14 PM
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Hope you aren't using drywall screws.....

Just jumping in with that......
 
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Old 03-02-10, 01:24 PM
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Hi Jazman,

So I'll be getting about 3/8" from the cbu, and 1/2" from the tile, is that a close estimate? Guess in total I'll have a 1" raise from the underlayment.

Hi Gunguy45,
I'm using 1-1/4" Kwiki flooring screw for my plywood underlayment. For the hardibacker, some web page suggests 1-1/4" corrosion resistant screws. What exactly is that? Galvanized screws?

And what type of caulk should I use for gaps between the hardibackers and the walls?

Much appreciated.
 
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Old 03-02-10, 01:53 PM
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Ray

No caulk is needed around the perimeter of the floor. Leave that space open for movement.

Their are screws made to be used with cement board and fiber cement board, like this. HD, Lowes and others carry them.

http://www.itwconstruction.ca/files/...0Backer-On.pdf

The square drive screws are easier to set flush with the top of the board. Phillips heads can be a pia.
 
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Old 03-02-10, 02:29 PM
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Yea, about 1" total, actually I think a bit less, but close enough.

Use the special screws. For large areas I use galvanized roofing nails which also meet specs for CBU's.

Jaz
 
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Old 03-02-10, 02:39 PM
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ok, getting prepped to do put down the hardibackers. One more little detail I'm confused about. For screwing down the hardibackers, is that done before or after the thinset is dry?

And I read the screws should be 8" apart with staggering pattern. Please tell me if that is wrong.

Thanks.
 
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Old 03-02-10, 03:14 PM
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Follow the pattern avoid screws on the corners as shown.

You gotta screw right away, if you're alone do one sheet at a time. Best to start in the center and work outwards.

Jaz
 
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Old 03-02-10, 03:15 PM
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Ray

is that done before or after the thinset is dry
Its done immediately, as soon as you notch the thinset, put the board down and start screwing.

This is from the James Hardie website installation instructions.

3. Attach HardieBacker cement board to subfloor
• Apply a supporting bed of mortar or modified thinset to subfloor using a 1/4”
square-notched trowel.
• Embed HardieBacker cement board firmly and evenly in the wet mortar.
• Use the fastener pattern as a guide. Fasten HardieBacker cement board with specified
nails or screws (as listed in “Materials Required”) every 8” over the entire surface.
Keep fasteners 3/8” from board edges and 2” in from board corners.
• Set fastener heads flush with the surface without overdriving.
 
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Old 03-04-10, 08:27 PM
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Ok, I have just put in the hardibackers. Couples things I wanna run by your guys. First, I have some coppoer pipe protruding from the ground. So the mortar is in contact with those pipes. Is this dangerous? Is there anything in the mortar that might corrode the copper pipes?

Second, when setting in the hardibackers, it was hard to keep the 1/8" and 1/4" gaps in between sheets and around walls. Some sheets moved around, and the gaps ended up not exactly 1/8" or 1/4", but were either a little more of less. Is this ok?

Thanks. I'm getting close to finishing my kitchen reno.
 
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Old 03-05-10, 07:10 AM
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Ray

Id not worry about either issue.

The cement board gaps dont need to be perfect. They'll be completely filled with thinset and taped over.

Leave the perimeter gap around the room open. It'll get covered over with base molding when your done.
 
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Old 03-08-10, 02:22 PM
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So for my 3mm granite tiles, what trowel size should I use? 1/4x3/8? Thanks.
 
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Old 03-08-10, 02:41 PM
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Ray

Is the tile really 3mm?
 
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Old 03-08-10, 05:23 PM
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sorry Johnny, I got my numbers mixed up. My tiles are about 3/8" thick (a tad over actually), which you pointed out to be 1cm to be more exact.
 
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Old 03-09-10, 09:04 AM
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What Jazman said in the post above.

Since the backs of the tiles are flat, 1/4x1/4 trowel is plenty as long as the substrate is flat within specs. Total tile thickness installed will be very close to 1/2".
If your not getting full coverage, you can move up to 1/4x3/8x1/4 trowel.
 
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Old 03-09-10, 10:02 AM
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Sorry Johnny, I don't know how I missed that part of your reply.

I don't quite understand what you mean by "full coverage". Do you mean that the tiles get even amount of thinset on all area? How do I tell? And for mortar, is polymer modified mortar (Ultraflex 2, Mapei brand) ok for granite tiling? Thanks.
 
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