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Old 06-28-2013, 09:23 PM   #1
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thinset over plywood or cement board


What's better and what would last longer.

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Old 06-28-2013, 09:31 PM   #2
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thinset over plywood or cement board


1/4 cement board.
Far more important what's under the floors.
Joist width, free spans, spacing, how thick the subflooring and underlayment is and what it's made of.
No particle board or 1/4 plywood allowed.

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Old 06-28-2013, 09:36 PM   #3
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thinset over plywood or cement board


Thinset, CBU, Thinset, tile. on plywood subfloor.
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Old 06-28-2013, 09:46 PM   #4
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I have joists 2x8x12 every 15 or so inches I'm going to add a extra joist ever other joist and set it in place and screw it to another. There's 1/2 or 3/4 x 6in subfloor with 23/32 plywood over it. The floor will be nice and solid. I've been reading that sometimes u can use thinset with an additive over plywood. I want to see if I can eliminate the cost of the backer board. I'm using 18x18in porcelain tile. Also what's the best thinset to use. I heard modified takes for every to dry and I'll be on a time restraint of 2days to get it dry and able to walk on it.
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Old 06-28-2013, 10:11 PM   #5
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Well I found the answer to applying thinset over plywood. It said u need a modified thinset but it takes a lot longer to dry. That's no go for me. So I'll just use backerboard.
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Old 06-29-2013, 12:09 AM   #6
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thinset over plywood or cement board


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Originally Posted by crash525 View Post
Well I found the answer to applying thinset over plywood. It said u need a modified thinset but it takes a lot longer to dry. That's no go for me. So I'll just use backerboard.
You still must have thinset under the backerboard.
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Old 06-30-2013, 03:29 PM   #7
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thinset over plywood or cement board


Thin set - DITRA - Thin set - Tile.
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Old 06-30-2013, 10:34 PM   #8
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thinset over plywood or cement board


Crash,

Something tells me you're not completely up to speed about your project. Please take the time to explain what materials and method you're planning.

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Old 07-01-2013, 10:37 AM   #9
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Here's what I have going on. I'm laying 18x18 1/4in porcelain tile in my kitchen. It's 10'x14'. With the floor joists they span about 10' of the 14', 10' across the floor. Then the other 4' is 12' joist that go to the center support beam. I have added sister joists every other joist. 2 12' and 3 10'. The subfloor is screwed to the joists. The sub floor is 1x6 and the length varies due to it being placed at an angle. Then there's 23/32 plywood thats screwed to the subfloor. Were using mapei brand thinset and grout because that's really the only brand that I can get. I read that modified thinset can be used over treated plywood. I thought the plywood I bought was treated but it is not. I wanted to use it over the plywood for cost reasons. I had called and talk to mapei and they said for my tile size they recommend at least an 1.25 in floor before laying the tile down. Currently I'm using 1/4 hardi backer. I'm going to lay thinset down under the backer and screw it down and then lay the thinset then tile. I needed the thinset to dry in a day and mapei said that the large floor tile thinset they offer sets in 24 hours and it is a modified thenset. I was going to use unmodified because of the dry time is so long for for modified but since they said it sets that fast I'm ok with it. Also mapei recommends a 1/4 trowel for the tile size. I have a 1/4 and 1/2 trowel. I'm going to backbutter the tiles for better fill and adhesion. If I'm missing something please let me know.
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Old 07-01-2013, 09:44 PM   #10
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Crash,

If you use unmodified thin set to install your porcelain tiles, you will indeed earn the name "Crash".

You can use unmodified to install the Hardie over the 3/4" plywood, but not the tiles. (unless you use Ditra instead of Hardie, better but more $$$).

Your original idea of installing the tiles over plywood was a bad idea and sounds like you're over that.

1/4x1/4x1/4 trowel is too small for your tiles. You'll probably need 1/2x1/2" but that's if the floor is very flat. Have you heard about the BBB? Back Butter Buddy. Have you checked just how flat the floor is?

Where did you get the info about drying time etc.? Why the big rush?

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Old 07-01-2013, 09:57 PM   #11
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I got my information about the grout straight from Mapei customer support. They said I could use unmodified thinset but best to use modified. They also said they recommend 1/4x1/4 trowel for the tile with that thinset. Could u explain why u suggest a 1/2x1/2 trowel? The floor has one low spot from the plywood not being made correctly on one of the corners. I'm going to be putting thinset, backer, thinset, tile. One question. How long should I wait to lay tile when I put the thinset and backer down? Could I start right away or do I need to let it set?

I'm off work from the 4th to the 7th and I'm putting up new drywall. I'm starting to tear down the walls and put new ones up immediately. Once the walls are painted then I'm going to start the floor. I can wait to lay tile or grout it until a later date but I just want to get this done in one shot.

Why is ditra better than backer? I also heard that using a modified thinset it will take days to week to dry with ditra compared to backer.

Last edited by crash525; 07-01-2013 at 10:00 PM.
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Old 07-01-2013, 10:59 PM   #12
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thinset over plywood or cement board


Crash,

I'm not concerned about the grout, thin set for now.

Referring to your conversation with someone at Mapei;

Quote:
Originally Posted by Crash says that Mapei...
They said I could use unmodified thinset but best to use modified. They also said they recommend 1/4x1/4 trowel for the tile with that thinset.
If that's what they said, I'm thinking you got the wrong person.

Quote:
Originally Posted by Crash
How long should I wait to lay tile when I put the thinset and backer down? Could I start right away or do I need to let it set?
You can start right away, unless the big game is on.

Quote:
Originally Posted by Crash
Why is ditra better than backer? I also heard that using a modified thinset it will take days to week to dry with ditra compared to backer.
Ditra does several things CBU's can't do. Ditra is light, thinner, it uncouples the tile work from the substrate eliminating the #1 or #2 reason for failures.
Ditra can be seamed in a way to make the floor waterproof. It's faster too. It does cost about 2.5 x more than most CBU's though.

Jaz

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