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Do I have correct materials and procedures installing tile over 3/4" plywood sub

Do I have correct materials and procedures installing tile over 3/4" plywood sub

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  #1  
Old 06-25-17, 06:36 PM
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Do I have correct materials and procedures installing tile over 3/4" plywood sub

Hi,

I am getting ready to install tile on the ground floor of the house. Subfloor is new reinforced from the bottom 3/4" plywood subfloor. Most likely will be using either 1/4" "Wonderboard - Custom Building Products WonderBoard Lite 5 ft. x 3 ft. x 1/4 in. Backer Board-FLB60L - The Home Depot or 1/4" Durock - DUROCK Next Gen 1/4 in. x 3 ft. x 5 ft. Cement Board-170219 - The Home Depot. I suspect Durock is probably not as clean of the cut, but provides more grip for the thinset, Wonderboard is probably easier to cut. I prefer not to use any power tools to cut it.
I read in one of the posts here that you should use unmodified thinset - Custom Building Products CustomBlend Gray 50 lb. Standard Thinset Mortar-CBTSG50 - The Home Depot between the whatever board I decide to use and the subfloor and fortified thinset - Custom Building Products VersaBond Gray 50 lb. Fortified Thin-Set Mortar-MTSG50 - The Home Depot
to lay the tile over the board.


Do I have right materials and procedure? Any other suggestions? Like should I put building paper or anything else on top of the subfloor or just lay it right on top? Do I need to wet the subfloor first?

Thank you in advance,
 
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  #2  
Old 06-28-17, 01:17 PM
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followup

Well,
since there was no takers after 65 views, I thought of adding more questions to maybe make it more appealing

When I start laying/gluing my cement board, should I lay it diagonal to the floor joists or in the same direction? If one way is better than the other, what are the benefits?

Thanks,
 
  #3  
Old 06-28-17, 06:21 PM
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Not a tile guy but I will give my 2 cents.

Your materials is exactly what I have used and have had very good results. No reason to lay diagonal, just stagger the joints of the cement board and plywood. Also use cement board screws in addition to the thinset when laying the backer on the plywood. http://www.homedepot.com/p/Backer-On...3400/100143730
 
  #4  
Old 06-29-17, 04:02 AM
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Thank you Ironhead!

Not needing to do diagonal layout helps a lot actually. Maybe I am overdoing it, as usual. I was going to use longer screws at least scattered somewhere between the Backer-on, just to make sure I catch the joists (i marked them on the walls) as well when screwing on my cement board. I think the longest Backer-on they sell is 1 5/8" so not sure if that's enough penetration to get both 1/4" cement board and 3/4" plywood on solid.
 
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Old 06-30-17, 03:16 PM
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You are really attaching the backer board to the subfloor, not to the joists. 1 1/4" will get you enough penetration into the subfloor.
 
  #6  
Old 06-30-17, 04:50 PM
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I have always used 1/2" cement board / wonder board to get to that 1 1/4" thickness that always is stated. For 40 years every tile job came out perfect so its cheap insurance!
 
  #7  
Old 07-01-17, 05:49 AM
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The reason I wanted to catch the joists was becasue the plywood was nailed not screwed to the joists. I used liquid nails in addition to the regular nails to hold it down though.
I agree it's a cheap insurance to use 1/2" board instead of 1/4", the problem is, I will need even longer screws then and my transitions from carpet will be even higher. Or should I go back and screw down the plywood first and then install the cement board?

Thanks,
 
  #8  
Old 07-03-17, 11:45 AM
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Doing the same thing here, but thinking of using Ditra vice cement board.
Not going to hijack your post.
Start at the bottom: if your subfloor has any movement in it, it needs to be addressed. Doesn't matter if it is nailed or screwed, as long as there isn't any movement.
The cement board is supposed to be a way to allow the wood to expand and contract normally without it effecting your tiles on top; it is a uncoupling membrane (not just something to stick the tiles to).
The cement board is marked with where the screws are to be placed, for proper installation, they may or may not line up with the joist. These screws aren't there to hold your subfloor to the joists, that is what the nails were supposed to do...
Yes, wet the plywood prior to applying modified thinset, it will keep the thinset from drying to fast or not adhering to the subfloor.
Make straight lines in your thinset, don't use zig-zag pattern or spiral pattern. If you are laying tile with any one side longer than 15", back butter the tile.

Now, I am not a tile guy, this is just what I have read and looked up, thus far into my own project.

Good luck.
 
  #9  
Old 07-03-17, 05:39 PM
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Thanks

Hey, thanks for the reply.

Honestly my biggest problem is not understanding the logic why things are done one way or the other.
I made sure the movement is minimized, but on this kind of foundation there is no way of eliminating it. One of the foundation contractors, on another property, called them "walking foundations". The reasons why I wanted to catch the joists was becasue I have no faith in nails no matter how many there are, and there are a lot. Is there any harm if do catch the joists?
If I am laying cement board on the plywood using thinset (CustomBlend white 50lbs) , pretty much gluing cement board on top of plywood, where is the uncoupling happening? Inside the board? I switched to 1/2" btw, the 1/4" felt too flimsy, I've been wrong before, but that 1/4" just didn't feel right.
 
  #10  
Old 07-04-17, 09:49 AM
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Newbie. The success of your installation is not going to be dependent on whether you use quarter inch or half-inch cement board. You need to make sure that your joist system and subfloor are adequate. Cement board is not structural. If you need to make your floor stronger you need to add plywood, not cement board. The only reason you may want to use half-inch cement board is if you want the additional height. The thin set under the cement board is meant to fill any voids between the cement board and the plywood. The screws are what will hold the cement board to the plywood subfloor. If you are concerned that the plywood subfloor is not attached well to the joists feel free to add as many screws as you need to the plywood subfloor to make sure it is attached properly. The cement board should be attached only to the plywood subfloor. Use screws about a quarter inch longer than the thickness of your cement board, thin set and subfloor combined.
 
  #11  
Old 07-06-17, 07:37 PM
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Thank you HeresJohnny,

So if I use the screws and accidentally do catch the joists, should I reposition the screw to make sure I am not sandwiching it all together? Also why is it dangerous?

Also, since I will be using Durock cement board, I see in some places it's recommened to leave a 1/8" spacing between the boards, in some places it says to butt them to each other. What is the correct method and why?

Thanks you,
 
  #12  
Old 07-07-17, 12:08 PM
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As I said, use screws that are about a quarter of an inch longer than the total thickness of the cement board and plywood. Don't worry if you hit a joist here or there, but don't intentionally screw along the joists. The cement board and the plywood will expand and contract at different rates. The screws willmechanically fastened the cement board to the plywood but will also allow each to move somewhat independently. The unmodified thinset between the sandwich is not meant to bond the two layers but rather fill any voids between them.

Leave a small gap between the cement board sheets. The idea is that you want to allow thinset to squeeze into the joint between the sheets when you are taping the joints. This makes the Top surface of cement board one monolithic unit. Leave a quarter inch space around the entire perimeter of the room for expansion. Tape the joints while you were setting the tile. That way you won't have to worry about having any high spots that your a tile will rock on.
 
  #13  
Old 07-07-17, 01:28 PM
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Thank you again.

So let me try to understand what are the physics of the tile installation.
We first level the joists as much as possible, then attach the 3/4" plywood to these joists sometimes with addition of the "liquid nails" to make these components monolithic, then we attach the cement board to the plywood with screws and thinset and make that monolithic. Is the goal of it to make the installation somewhat "floating"? If yes, where is the movement?
Please understand, I am not questioning your logic, just trying to understand how it actually works.

btw, do you wet or dampen your cement board before installing the tile?
We are likely to have 90 degrees temperature tomorrow...
 
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