Back-buttering every tile?

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Old 01-27-09, 09:41 PM
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Back-buttering every tile?

I plan to lay a tile floor in my kitchen ~180 sq ft, 12x12 tiles. I am putting down underfloor heating wires (mesh) and am concerned about damaging the wires with either the notched trowel or when I am cleaning excess mortar from the joints before grouting. I am planning to back butter EACH tile as opposed to spreading the mortar onto the floor first. I know this will make the job go slower, but I have found in previous jobs that not only does the area that I've spread the mortar on start to dry out (skim), but I also am inconsistent with the thickness of the mortar. I feel that I can be consistent with the amount I comb onto each tile and avoid too much excess mortar filling the joints. Is there any reason why backbuttering every tile would be a problem? Any help would be appreciated. Thanks.
 
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Old 01-28-09, 01:04 PM
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It will be difficult to do what you propose. Even a skilled tilesetter will have difficulty doing it that way. The best way to approach this is to pour self leveling compound over the cables, then an isolation membrane over the slc, then set the tile.
 
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Old 01-28-09, 07:04 PM
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Not a good plan

I agree, that is not going to work so good. You have to make the floor flat before you install the tiles. SLC, then membrane such as Ditra or Noble CIS then tiles.

Jaz
 
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Old 01-31-09, 08:44 AM
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membrane?

I plan to put down backerboard on top of 3/4 in TG plywood. Why would I need a membrane?
 
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Old 01-31-09, 09:06 AM
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With the heat cable, you'll have extreme temperature changes causing movement. The membrane will help to isolate that movement between the slc and tile. Is the membrane absolutely needed, maybe not, but if it were me, its cheap insurance.
 
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Old 01-31-09, 03:07 PM
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Membrane

I can understand using the membrane if I use SLC, but if I'm just using hardibacker, then is the membrane necessary? I thought the hardibacker was stable and not prone to microcracking.
 
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Old 01-31-09, 04:37 PM
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So what will you be covering the cables with?
 
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Old 01-31-09, 05:35 PM
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Cables

The cables are woven into a mesh that is rolled out. The installation instructions say that thinset can be applied directly on top of the mesh. Alternately, they say that you can use SLC, but I'm a bit hesitant to use SLC. I have used SLC on a small area under a bathtub, but my kitchen is about 15 x 15. With SLC, would I need to do any tooling, or would I simply pour it out? Do you have any experience with these heating wires? If I were to decide on the SLC, I assume I would not need the hardibacker.
 
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Old 02-01-09, 08:53 AM
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Yes I have installed mats like you are describing. I have installed them in bathrooms which are smaller than your kitchen space and I have always used slc. If you use slc, then you dont need the cement board. Pouring slc on a floor that size will require a helper or 2 and yes you'll need to do some "tooling". It's not an easy task if you havent done it before. You'll want to read up on it as much as possible before you start.

You can do the installation over cement board the way you are describing, but I have not done it that way. I've seen some installers do it with thinset, but they actually skim over the cables one day and get it as flat as they can, then come back the next day and set the tile over the skimmed bed. Thinset is really not made to screed like this so its not all that easy to get a flat surface for tile. The problem I see with the installation method that you are proposing is that you will not be keying the thinset into the cement board which is really a necessity. Also, you may be leaving voids under the tile which could be a problem, with floors, you want to strive for 100% coverage. Additionally, when working with trowels over mats or cables, its easy to damage them and not know it.
 
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Old 02-01-09, 09:26 AM
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Some additional comments here.

Thinset is meant to be applied no thicker than 1/4". More than that, and the tile can actually sink as the thinset cures and shrinks. It may be hard to get an acceptable level of lippage from tile to tile if you try to set the way you propose.

Right now, there is another thread going from Anthonyputz. He is wanting to remove tile over in floor heating system. Im not sure what kind though. If he used ditra over slc or lightweight concrete, he'll be able to remove it possibly without damage to the heating system. If he did not use ditra, it may be a difficult task to remove with no damage.
 
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