Schluter Ditra, Hardie board, Cement Board

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Old 02-27-12, 07:48 PM
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Question Schluter Ditra, Hardie board, Cement Board

I will be installing 12 x 24 porcelain tile in my kitchen. My house is almost 20 years and sits on a crawlspace. I am buying, what I think is a decent quality tile at $4.75 per sq. ft.

I am uncertain what to use below the tile, Ditra, Hardie board, or cement board I am drawn toward the Ditra since it is very thin. The place I am buying the tile from is trying to dissuade me from Ditra and is recommending a similar material (spider mat, I think). He made it seem like it is difficult to correctly install the Ditra, so he recommended a very similar product or going with the hardie board.

Of course people are going to recommend the product they sell. So...I want to reach out to other DIYers and see what they recommend.

Thanks for your input.
 
  #2  
Old 02-28-12, 02:40 PM
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I think the membrane you are talking about is Custom Building Products "SpiderWeb". I have never used it and so cannot comment on its performance. I will tell you that Ditra is a product that has been around for many years and there are many miles of successful installations out there. Its a great product.

For tile that size, you will want a proper joist structure and substrate. Give us the details as to the joist size, on center spacing and unsupported span of the joists. Consider adding an additional 1/2" of exterior glue plywood over the subfloor, and then using ditra.

For that size tile, you will need a dead flat floor, and little to no movement. You want to resolve any high spots or dips in the floor before you install the ditra.

If you will be installing the tile in a brick pattern, you will want to check the tile to make sure they are perfectly flat. You can do this by doing a test layout on a dead flat surface, and checking the height of the tiles where 2 ends meet the middle of the tile next to them. If the tiles are cupped, they will not match up well and you may have to rethink your pattern. Minimum grout joint size for these tiles is probably 3/16" or bigger. It'll depend if they are cupped, tile size consistency, how flat the floor is, what the edges of the tile look like and maybe some other factors. Consider using a leveling system like the Lash System for minimizing lippage.

It would be better for you to use ditra (over a second layer of plywood), than cement board. Ditra does a better job of uncoupling the subfloor movement than does the cement board. Additionally, cement board adds no structural strength but takes up more height.
 
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Old 02-29-12, 08:34 AM
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Johnny's right - you left out the most important information, we don't know anything about your existing subfloor or structure beneath it.
 
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Old 02-29-12, 04:42 PM
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Schluter Ditra

Thanks to you both. This weekend I will get in the crawl space and measure the distance between each joist and the height and thickness of the joists. I don't know what you mean about the "unsupported span of the joists."

Do you mean the greatest distance between where the joist rest on the concrete block foundation around the perimter and the smaller stacks of block scattered throughout the crawl?

I know that I have some slight high spots and dips in the subfloor. They are very slight. I'm not certain how to resolve these since they are so slight. I suppose I can use more screws (if its on a joist) to lower slight high spot.

How do I resolve a slight low spot? Is that the purposeof the recommended second layer of 1/2 plywood?

Would using a 12x12 tiles instead of 12x24 reduce the potential negative impact of imperfect subfloors? Also, still recommend another layer of plywood before the Ditra if I go with 12X12?

I really would rather not add the height another 1/2 of plywood before the Ditra. With more plywood, Ditra, and the tile itself, it would be higher than the carpeting of my living room and the hardwood floor of my dining room.

Thanks again.
 
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Old 02-29-12, 07:50 PM
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Let us know about what you find in the crawl space this weekend. The unsupported span is as you described, measure to the inch. Check their condition and see if you can read the species and grade, it makes a difference.

Also tell us what kind of subfloor you have. According to normal recommendations a single layer of properly installed 5/8" or thicker ply if sufficient esp. if the joists are 16" o.c. Single 5/8" scares me, but it meets specs in most cases. I like min. 3/4". It's always better to have more if possible. And yes of course the tiles area might be higher than an adjacent room. Don't like that? Put tiles in all the rooms. Sounds like the other rooms are done already.

Yes, smaller tiles are more forgiving and easier to install. I like and use Ditra whenever practical and when the customer wants a premium job.

Jaz
 
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Old 03-04-12, 01:54 PM
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Went into my crawl space on a fact finding mission.

Floor joists are 2 x 8 and are spaced 16" on center.

My kitchen is located in the back right corner of my house, on a crawl space. The kitchen measures 20 X 11. One 20' side and one 11' side sit on the outer perimeter of the foundation block. There are two columns of block supporting the other 20' side and one column on the other 11' side. There are no columns directly under the kitchen floor other than at the edges described above.

My subfloor is APA Series Blue Ribbon 24CC 23/32" "Mobile Home Flooring". If my math is correct, this is 1/16" thinner than 3/4". It's particle board that is sprayed blue on one side. And "No", my home is not a mobile home, so that has me a bit concerned. My home is your typical studs and vinyl siding home, sitting on concrete block.

Any input regarding adequate preparation for the 12x24 tiles would be appreciated. I could go with the 12x12 if its in the my long-term interest but the 12x24 look so much better. I plan to use the Ditra. I just read up about the QEP Lash Leveling option, that is pretty slick, so I may use that for good measure to prevent lippage.

Thanks for your help.
 
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Old 03-04-12, 03:54 PM
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OK, so what is the unsupported span of the joists, species and grade of the joists?

You say your subfloor is particle board, are you sure? According to my info Blue Ribbon is OSB, not PT. All sheets measure 1/32" less than their stated thickness.

You may want to call Georgia Pacific (GP 1-800-284-5347), see if they will give the go ahead to install Ditra over the blue. Tell them you'll be using a good modified thin set mortar that meets A118.4 and A118.11 Hopefully the person you speak to knows what Ditra is. They will probably tell you to use their Denshield instead.

Jaz
 
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Old 03-04-12, 04:03 PM
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What constitutes "unsupported?" My entire kitchen floor has support structure around the edges. The kitchen is 20 x 11.

The joist appear to be regular 2 x 8. I thought the species focus was on the subfloor, not the joist.

Is particle board compressed pieces of smaller chips? If so, definitely I have particle board. I have provided the specs. I am not sure what OSB is, please educate me.

Thanks for the advice.
 
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Old 03-04-12, 04:41 PM
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Does it look like this? Georgia-Pacific Oriented Strand Board

PT looks like tiny particles instead of flakes.

The span is the distance between the supports that hold a joist. The size of the room has nothing to do with it. It's usually the distance between the outer supporting foundation and a beam near the center.

Jaz
 
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Old 03-05-12, 03:04 AM
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Yes JazMan, that is exactly what I have, the Blue Ribbon OSB. Regarding the unsupported span, the joists run 10' from the back foundation wall to the center beam, which is supported by block columns.

What do you think, will I be OK with Ditra and 12x24?
 
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Old 03-05-12, 04:01 AM
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What do you think, will I be OK with Ditra and 12x24?
Well.......maybe. The subfloor portion of the equation certainly meets minimums. and I recommend Ditra although the other products will work too.

But you still wanna keep the species and grade of the joists a secret. So I can't be positive, but probably yes you are close to meeting L360 max deflection for the joists. I tried a few species and you are very close, but just barely in some cases.

People don't think about it but here's an example.

To meet L360 at 50/20 live/dead load;

1. Southern Pine - 2x8 - grade #2 - 16" o.c. can span up to 11' 5"
2. SPF (south) same specs can span up to 10' 0"
3. Douglas Fir Larch (north) can span up to 10' 6"

That's why I keep axing. So no definite answer for you. If you've got your heart set on 12x24, go for it. The spec are the same, just make very sure the floor is flat like your kitchen table.

Jaz
 
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Old 03-05-12, 06:24 PM
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You keep axing???....and now you trippin' JazMan.

I told you that I thought the grade and species question was regarding the subfloor, not the joists, so when I was under the house I didn't look for a species or grade on the joists, I simply measured the joists and the spacing between them. Why would I keep that a secret if I am asking for advice? I was reluctant to say my subflooring says "Moile Home Flooring" on it, not that there is anything wrong with a mobile home. Again, why would I keep a secret about the joist species?

Would 1/4" hardibacker board be a better move than the Ditra?
 
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Old 03-05-12, 06:40 PM
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Why would I keep that a secret if I am asking for advice?
Ahhhhhhh. I still don't know the answer. You should assume that your joists system probably just meet minimum recommendations. It may all work out fine. You could add a supporting beam to reduce the span, or sister the joists.

Would 1/4" hardibacker board be a better move than the Ditra?
No, Ditra is a much better way to go, but Hardie will also work.

Jaz
 
  #14  
Old 03-06-12, 11:18 AM
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Your floor joists are at best bare bones minimum, and the same for the subfloor. Consider sistering the joists. More important in my opinion, consider adding an additional layer of 1/2" eg plywood over the osb, and then the ditra. You will be spending a lot of money and time. Why take the chance that it may be ok.
 
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Old 03-06-12, 08:04 PM
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Jaz....that's two of us that still don't know what kind of joists I have, since I have not been back under my house to check.

You are a weird dude if you think I am going to ask for advice and then keep secrets about the floor joists.
 
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Old 03-07-12, 03:27 PM
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You are a weird dude if you think I am going to ask for advice and then keep secrets about the floor joists.
You obviously don't understand what I was really saying. Please take a "chill pill".

Early in this thread you had been asked to measure the "unsupported span and spacing of the joists. You speculated what "unsupported" meant and I said you had its meaning right. To which I wrote:

Let us know about what you find in the crawl space this weekend. The unsupported span is as you described, measure to the inch. Check their condition and see if you can read the species and grade, it makes a difference.
Later you said you thought when I said check the species you thought I meant of the plywood and not the joists we were talking about. well dahhhhhhhh. But OK, no problem, get back down there so you can get all the info right.

If i were you I would not accept any free info from any weird person, especially over the internet. :NO NO NO: After all, you're not a dimwit.

Jaz
 
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Old 03-08-12, 04:15 PM
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The funny thing is that you don't seem to believe me when I told you that I thought you all were asking for the grade and series of the subflooring. Why would would keep that info a secret if I was asking for advice? That's why I called you weird.
 
 

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