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Unread 02-24-2005, 02:01 PM   #1
kstaffor
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Ditra and heated floor

I am putting down limestone 12 x 12 tiles over 3/4" plywood with 9.5" I joists on 16" centers with a span of 8' in the front hall. I want the tiles heated so I am putting down the 220v electric heating cable and I also was thinking about putting ditra. My questions are the following:

1. Is my support structure enough
2. Is ditra really necessary since the floor won't see a lot of water
3. If you don't put ditra what is the alternative (peaople have suggested a mesh and scratch coat)
2. Does the heating cable go down before or after the ditra/scratch coat
3. What's the best way to put the heating cable down to avoid damage ( some people have suggested to cover the cable with floor leveler)

Thanks in advance,

Kevin
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Unread 02-24-2005, 05:16 PM   #2
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Hi Kevin.

For natural stone tile you will need a double layer plywood floor. I'd say another layer of 1/2" ply (minimum) to bring it up to 1/ 1/4" total. Then your heating system and if you go with Ditra, it will follow on top of all that followed by the tile.

There are so many different kinds of electric heating systems for use under tile, each with manufacturer provided installation instructions which must be followed, so until that decision is made you may not be able to get much in the way of specific advice on that aspect of the project.
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Unread 02-24-2005, 09:29 PM   #3
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Thanks for the info on the extra layer of plywood. I will be using the Alcatel heating cable. If I put a 1/2" layer of plywood, then the alcatel heating cable with some floor leveler in order to protect and embed the cable (roughly 1/8"), and then the ditra (1/8") and finally the thinset & tile ( 3/8"), I figure I am 1 1/8" above the original 3/4" plywood. I will be putting 3/4" hardwood outside of this room and I am concerned about the transition which would be roughly 5/8" to 3/4". Is this too much of a transition or am I worried about nothing.

Thanks,

Kevin
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Unread 02-24-2005, 10:30 PM   #4
jd77
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Kevin,

That is the best heating cable around (IMO). We do it all the time with lath over the plywood ( I think the 3/4 should be enough) then the cable - then prime - pour the SLU - install the Ditra and tile. You MUST have expansion material around the entire perimeter before you pour the SLU.

Here is a pic...
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Unread 02-24-2005, 10:32 PM   #5
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Then poured and tiled - sorry - didn't get a shot of the Ditra going down.

BTW - ever install this heating cable before?
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Unread 02-25-2005, 06:33 AM   #6
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Is that Nexans cable? If so, I had a hard time with it, only used it once though. Its very thick cable........like the size of the cable that you get cable from..........cable t.v that is.......
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Unread 02-25-2005, 07:57 AM   #7
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I have the impression floor leveller (SLC) must be minimum 3/8". And you need the wire mesh to hold it together. And you need the extra layer of ply, I guess to decouple the SLC from wall movement. Ditra on top of that may not be required, but I plan to use it for peace of mind, plus protect floor from water damage.

I will have a hell of a transition, but better that than the POS tile job this will be replacing....
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Unread 02-25-2005, 08:40 AM   #8
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JD, are you saying that I don't need to add the 1/2" plywood...just put the wire mesh over the 3/4" ply, attach the heating cable and then pour the SLU. What product do you use for SLU? What about the expansion material? After that, the ditra and then the tile. Someone earlier mentioned for natural stone (I am using limestone 12x12) that you need 1 1/4" ply. Does the wire mesh & SLU count for some of that including the use of ditra?

Thanks,

Kevin
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Unread 02-25-2005, 03:13 PM   #9
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Kevin,

I'm not an engineer but according to the deflection calculator your floor is purty steef (L / 1389) and is approved for both tile and stone. Maybe someone with better knowledge can confirm.

It is best to install some 1/2" foam @ the perimeter before the lath. Cut strips from a sheet of foam and stand them on end attaching them to the clean plywood with silicone or caulking. Do this all the way around and accross doorways etc. Also tape or caulk joints between the plywood so the SLC won't leak. Think of it as a shallow pool that you will be pouring water into.

Then the lath must be installed with big staples (1" crown X 1" or more depth) on 4" centers at the perimeter and 6" everywhere else. I use a pneumatic stapler for this and install the cables with it as well. Since your cable install will be putting in quite a few staples you could leave a few out whilst installing the lath. Oh - don't overlap the lath. Use self furring galvanized without the paper.
If you can't use staples you can use galvanized ring or screw shank roofing nails. Then use galv. fencing staples for the cable. Both are a pain and could damage your cable (or your thumbs) if you slip.

Once you have the lath and cable down (make sure to test the cable constantly) you are ready for the SLC. Make sure you have the time to complete the job before you start. You will need help - the more the merrier.

1) prime with approved primer using long nap roller (1 1/4") or sprayer - no pooling

2) allow primer to dry

3) mix and pour SLC per manufacturer specs

4) allow to cure then trim foam carefully with a blunt tool (margin trowel)

5)Install Ditra per spec then tile.

Don't forget:

test the cable at all times

floor sensor

protect doors and walls from SLC

mix outside if possible


Good luck!
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Unread 02-26-2005, 09:35 AM   #10
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Quote:
Originally Posted by RandyL
Is that Nexans cable? If so, I had a hard time with it, only used it once though. Its very thick cable........like the size of the cable that you get cable from..........cable t.v that is.......

How many kool-aids did you have?
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Unread 02-26-2005, 06:02 PM   #11
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Too many JD........too many.............ha!
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Unread 02-28-2005, 07:59 AM   #12
kstaffor
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Thanks for the advice JD.

What is the primer for? What type/brand of primer do you use?

Thanks

Kevin
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Unread 02-28-2005, 10:09 AM   #13
sean riha
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primer is needed so the underlayment doesn't suck all the h2o out of the SLC. custom makes 'rapid set' SLC available at HD, and they usually have their primer right next to it (can't remember the name right now).
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