Can I put a heated tile me mat under my backer board?

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Old 01-30-11, 06:53 AM
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Can I put a heated tile me mat under my backer board?

I want to heat the tile I am putting in a bathroom I am remodeling. But weight is a very big concern (2x6 joists) so I don't want to do the normal sandwich of backerboard, heat mat, leveling compound, and tile. Can I skip the leveling compound and put the heat mat under my backer board? I figure that if I keep the wires in as large of loops as possible and mark the loops i keep from putting a screw through it. And then just tile on top of it.
 
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Old 01-30-11, 07:04 AM
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I'd hate to know I had to miss the mat with my screws that I am putting in every 6" across the area of the cbu. 2x6 joisting is not sufficient support for tile anyway, unless you have direct support below to the ground. What is that situation like? You won't be saving anything by doing it that way, and will be delaying heat dissipation when it has to go through the thinset, cbu, thinset, and tile. Others will chime in here with more information, so stay tuned.
 
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Old 01-30-11, 01:48 PM
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You dont need the cement board. You can install the heat mats over the plywood, then pour slc over that, then the tile. An isolation membrane over the slc and then the tile is even a better solution. Installing cement board over the heat mats is definitely the wrong thing to do.

As chandler pointed out 2x6's may not cut it for ceramic tile. What is the on center spacing of the joists, and what is their unsupported span?
 
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Old 01-30-11, 08:13 PM
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Im more worried about weight, I was going to use greenboard (not the shower greenboard the brand greenboard backerboard) because it weights just a few pounds per sheet.

The joists are 2x6 red oak (the old good stuff) spaced every 16" and with a 12' span
 

Last edited by Nurumkin; 01-30-11 at 08:16 PM. Reason: add more info
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Old 01-31-11, 05:58 AM
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Span tables I use indicate that those joists are good for about 8'. If you expect the tile installation to last, you defininetly have to do something to stiffen those joists, or shorten their span.
 
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Old 01-31-11, 08:39 PM
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Span tables I use indicate that those joists are good for about 8'.
Yes, and that's if they are grade #2 in excellent condition. If they're #3 in perfect condition the span needs to be under 6' 2".

Jaz
 
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Old 02-06-11, 09:03 AM
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I am confused as to how that span is so low. There was a very large bathtub in the area before that had been there for years (though it did cause a little bit of sagging). But if I am potentially almost double my rated span how has the floor not had problems in the last 100 years? I do know that 2 of the previous owners were not light people (one was eventually bedridden because of his weight).

What are my options? should I just continue with wood in the bathroom? because I cannot support it from below without basically destroying my lower floor.
 
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Old 02-06-11, 05:38 PM
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Are you sure the span is 12 ft.? If they're 100 years old they are probably a true 2" by 6", which will rate better than the modern size of 1.5 x 5.5, but they are 100 years old and so are they in good condition? Even so I'm sure the floor is not up to par. You've said so yourself. It sagged. Large people will NOT make a proper floor sag. Maybe 10 large people all in the bathroom at the same time for a long time might.

You've got the wrong idea about loads over a wooden structure. Wood bends, that is why it so good. If it was brittle and it snapped, the bathroom would have been in the floor below years ago.

Double check the span, you can sister the joists by removing the subfloor and exposing it. Otherwise a nice vinyl floor can work.

Jaz
 
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Old 02-06-11, 07:32 PM
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They are definitely true 2x6's and they are in very good condition (no cracks or splits) the span is 11' 5" (inside to inside). I am going to sandwich another 2x6 to the joists under the shower (where I obviously have to use tile) but the rest of the bathroom is over the kitchen which is not really practical to pull out. I was actually already thinking about vinyl tiles. Do any of you have a recommendation of some that look good, cost is not really an issue I just don't want it to look like a linoleum floor.
 
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Old 02-06-11, 08:03 PM
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How did you measure the span? I thought the bottom was finished or something. Kitchen is it?

No cracks or splits is not a plus. They're not supposed to be cracked.

I am going to sandwich another 2x6 to the joists under the shower
Sandwich, how you gonna do that?

I was actually already thinking about vinyl tiles.
I don't recommend that is a bathroom.

cost is not really an issue
OK, then remove the subfloor and bring the floor up to standards. Or have someone do it.

I just don't want it to look like a linoleum floor.
What does linoleum look like? I suppose you meant sheet vinyl. There's all kinds of patterns available in every type of flooring.

Jaz
 
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Old 02-07-11, 11:22 AM
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I don't think that even if you sister all the joists that the joist system will be stiff enough for ceramic tile. While sheet vinyl might not be the best choice for a bathroom, it might be your only choice.

What was on the floor originally, not ceramic tile, right?
 
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Old 02-07-11, 11:47 AM
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The alternative I can think of is kind of spendy but not when compared to ripping out the subfloor to create the right environment for tile is a product called Snapstone - it's ceramic tile on a rubber/plastic backing which also has its own flexible grout so you can use it in places where the flooring is not stiff enough for a traditional ceramic installation. It's going to cost you upward of $10/square foot. I also don't know how that backing would hold up to the heating mat.
 
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Old 02-07-11, 06:26 PM
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With Snapstone, the heat mats would definitely be out. Its probably not a good solution for a bathroom either, as seting the toilet over Snapstone would result in constant movement of the toilet, and eventual failure of the wax ring. Also, setting a vanity with plumbing and countertop on Snapstone could be a problem. I've never used Snapstone but have read about it a little. I suppose a product like that might have a place, but probably not in a bathroom.
 
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Old 02-08-11, 06:26 AM
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I didn't know Snapstone moved that much - I'm going to have to do some more research and maybe quit recommending the product

What I know about it comes from a buddy who manages the floor and window coverings department at a big box store and he says he's never gotten a complaint back on a sale of it
 
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Old 02-09-11, 09:24 PM
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I guess I'm just going to have to do it the hard way and rip up the entire floor until I get get to the support in the middle of the house. If I were to sister all of the joists would that make it stiff enough for tile? My line of thinking is that if a normal 2x6 is strong enough to stay up for 100 years then a 4x6 should be strong enough to add 3 or 400 lbs of tile+thinset.

Also does it matter that the bathroom is very narrow. so the tiled area only comes out about 8 feet from the wall at the widest point and most of it is only about 6 feet wide. So the weight is spread out over about 9 joists
 
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Old 02-10-11, 06:24 AM
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There is another thing that I never really worried about but probably should. The shower itself sits over another room that I have to remove the ceiling anyway. The shower will consist of about 140 sq ft of tile+ the 100 lbs floor pack I used (had to use a little on the edges of the schluter)+ 160 lbs of thinset (4 bags for the kerdi + tile= at 3lbs per foot of ceramic tile this comes out to about 680 lbs in the shower.

I kind of messed up when I was first starting this because I wasn't expecting to be removing the ceiling below, so I just sistered a 6' piece of 2x6 from above the shower to stiffen up the floor. Would sistering another 2x6to each joist give me enough strength? I will also probably add a couple 2x4's down the wall (there is balloon framing). Or is there a better product to use then a plain old 2x6? something that may be stronger that I can buy
 
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Old 02-10-11, 07:14 PM
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Ok I had a thought today, tell me if this would work. If I were to just knock out the ceiling in the room below and sister 2x10's and essentially drop the ceiling on that half of the house 4" would that solve my problems? I figure I could just run another 2x4 down the wall to support it on the outside (down to the foundation) and notch the side that is supported by the support in the center of the house (and attach the 4" that hang below with a joist hanger of some sort)

One thing I would like to do if I go through all this extra effort is put a bath tub in as well. With this extra reinforcement would I be safe to do so?
 
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