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jelly 07-14-2008 09:52 PM

Tiling on Above sub floor radiant heat
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I am putting radiant floor heat in our upstairs bathroom which is 5 x 11.

I first laid the moister paper down and then staples a wire mesh over the paper. Next I tied down 5/8" pex tubbing to the mesh 6" on center.

I then poured 1-part mortar/3=part sand over the tubes barely covering them.

I let it dry over the weekend and today I went into the bathroom and noticed it did not dry very smooth. Because its mainly sand, I am able to rub the high spots down with my boots.

1) Does it sound like I mixed properly? Can I use thinset on this mix?
2) In some spots I can see the pex, is this okay?
3) I have 12" tiles, How do i tile over this? first a thick layer of any kind of thinset? use a deep slotted trowel and lay the tile with some spacers?

I did the backspalsh on the kitchen wall but I was told the process is a little different when tileing the floor.


26yrsinflooring 07-14-2008 10:42 PM

The best thing you can do know is Ditra over it, this floor will fail drastically if you tile over it.

angus242 07-14-2008 11:29 PM

Another vote for Ditra over. :thumbup1:

Check this out:

Termite 07-15-2008 08:35 AM

Ditra is a good recommendation. Radiant flooring is typically covered with flowable lightweight (somewhat self-leveling) concrete, and the tubing should be concealed in it.

jelly 07-15-2008 09:28 AM

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Thanks for the tip!

Do they sell Ditra at HD? If not, where do I get it?

angus242 07-15-2008 09:54 AM


Originally Posted by jelly (Post 139471)
Thanks for the tip!

Do they sell Ditra at HD? If not, where do I get it?

Yes they do but it's kind of expensive there. Check out the prices here to compare:


26yrsinflooring 07-15-2008 02:24 PM

You can also get it here from me, at the best price on the net.

jelly 07-16-2008 05:47 PM

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1) Based on how soft my mud is, do you think I screwed up? As stated above, I mixed 3 parts sand to 1 part portland cement. You can see by the photo below how soft it is.

2) Thanks for the Ditra recommendation. The Ditra packaging says to use modified thinset under the ditra and unmodified over the ditra. I have 3.5 gal but it does not say which type it is. I know the modified type has latex but I do not see any indication on the bucket.

3) My next step is to sweep up the loose sand on my floor and pour a bag of leveling sand and let dry. Apply a layer of modified thinset. While wet, lay the Ditra. Let dry before laying the unmodified thinset and tile.

Sorry for all the questions. I have not been able to find any firm answers from my HVAC guy, Schluter or online. Thanks again for yout time....

jelly 08-04-2008 06:40 PM

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Bud Cline 08-04-2008 09:23 PM



DITRA will not work over that mess you have there. Don't even try it!

That also is not the right thinset, DON'T use it either.

This is the type of thing that has you in this mess now.

Where on earth are you getting these ideas?


jelly 08-05-2008 06:13 AM

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My HVAC guy told me to lay the tubes and mix the mud. It is so soft, should I remove it?

Pleas help, my bathroom has been in this condition for almost a month.

ccarlisle 08-05-2008 07:04 AM

Oh, Lord! :( You're going to have to start again; IMO there is no fix for this. Start by reading up on how to lay a tile floor because I'll tell you there's more to it than the average HVAC guy knows...go back in this forum, or go to the John Bridge Tile forum, or buy a book. But reserach first, then come back.

Then return that premixed thinset junk and get a refund. Take our word for it, you don't want that stuff within a mile of this job...prepare to make a mess cleaning this up before you get to start again - and consider it a lesson well learned.

Sorry, can't be more diplomatic, but you came here just in time...:yes:


javan 08-05-2008 11:04 AM

I 2nd the idea of starting over! Thankfully, this is a small room.

I also 2nd the idea of John Bridges website. It is a wealth of tiling knowledge. It really helped me do my floor.

read read read and ask tons of questions. You will get there.

jelly 08-05-2008 11:44 AM

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Thanks for confirming I need to remove this sand mix. After I remove, Can I just pick up a couple bags of cement mix and pour?

My HVAC said many times that I should put a little amount of water in the mix. I should be able to make a ball with it and my hands should not be wet.

So confused what to pour over the tubing. There are so many different types of mortar, cement. I don't even know the difference. I was on the John Bridges website over the weekend. I will look around there some more.

If someone could just advise which bags to pick up at HD and if I should follow the mix directions, that would be a big help.


ccarlisle 08-05-2008 12:24 PM

Check over there on the John Bridge forum and most installers who put down hydronic (i.e water running around tubing - compared to electric) radiant floor heating will probably tell you to use either Self-Leveliing cement ("SLC") or thinset. SLC is I think the preferred option. But there are specific parameters to follow so as to get the maximum contact between the pex and the cement...there's no point in having voids, is there?

And you should follow the manufacturer's instructions ON THE them then add the appropriate amount of water. Not a "bit", not "enough", but the exact quantities they recommend. That's the way out of your dilemma.

Apart from the SLC, you'll be needing unmodified thinset, maybe some modified thinset, for the application of the Ditra, and the tiles. But wait till you have the floor down level and heating is working before you get into tiliing.

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