Concrete on top of slab?

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Old 06-04-11, 02:19 PM
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Concrete on top of slab?

I've begun the tile floor demolition in one of my bathrooms and while trying to be careful and not dig up too much concrete with my hammer chisel, I dug a little too far in one section by the tub. I thought it might have been wood and left it alone while I continued demolition. While I was vacuuming all the dust, I dug around the "wood" and noticed it was actually concrete. I assume it's the slab. Now I have about 1" of concrete on top of my slab that I was just going to use a leveler to fix some of the divets, but I think I need to break everything up down to the slab. I've never seen this before and I'm quite puzzled as to why there would be concrete on top of the slab?? If I break up all the concrete on top of the slap, I'll have a step-down from the hallway to the bathroom, unless I add an enormous amount of thinset.

Can I put concrete board down to make up the difference or should I put more thinset down? I assume concrete board makes more sense, but wanted to make sure.

I'm also planning on putting down radiant heating, so I need to know where this would come into play in this setup?

Thanks!
 
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Old 06-04-11, 02:39 PM
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Tile was laid directly on the slab, so I am not sure what you need to dig further for. Can you post a couple of pictures of the areas you are talking about (not close ups) so we can see what you see. You won't put down concrete board over concrete. http://www.doityourself.com/forum/el...your-post.html
 
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Old 06-04-11, 03:05 PM
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Let's try this

It might be hard to tell from this pictures, but I'll try it.

In the second picture, you can see the edge of my tub with some of the crumbled concrete butting up next to it. The top right corner is concrete (what I asssume is the slab), while the rest is what was directly under the tile. It's hard to tell from the picture, but there is about a 1" lip between the two.

You can also see the old caulk line on the tub showing how much higher the old tile was.



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Old 06-04-11, 03:57 PM
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OK, you don't have a "slab", but you have a framed floor, is that correct? Do you have joisting under the remainder of the house? How old is this house? 1950 or 60's. If so, this was the way tile floors were done back then. A true PITA. Do you have all the tile up? What amount of overall drop do you have? In other words, how much floating will you have to do? It may be that you can float the entire floor and achieve a smooth enough surface for retiling. Others will add their comments, too as all the information starts to flow in. So hang in there.
 
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Old 06-04-11, 07:04 PM
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That's the slab on the right side of the second picture. Typically, a bathtub is placed right on the subflooring when they have wooden floor joists, and the underlayment they put in butts up to the side of the bathtub just like your mortar bed (presumably what it is) did. And then the flooring goes in over the underlayment.

I'm not sure if it's a great idea to put in radiant in-floor heating under the tiling since that concrete slab is gonna suck up heat like a pig. Concrete (and all masonary materials) have a surprisingly low R-value. They conduct heat well; but slowly.

If it wuz me, I'd probably opt for bath mats over top of the tiling to make the floor more comfortable for bare feet. Keeping that concrete slab and the ground under it warm is gonna be an expensive proposition.
 
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Old 06-05-11, 05:02 AM
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The house was built in 1967 and no, I don't have the remainder of the tile up. As far as I can tell, the remainder of the house is slab (or at least what I thought was a slab). The previous owner put an addition on the master bathroom that has a crawl space, but that's it.

If I were to completely remove the additional concrete one top of what I think is the slab, I will have to compensate for about an inch, maybe more. The tile I'm ripping up is pretty thin, but the tile I'm thinking about installing is much thicker so that will help some.

I think it would be easier to use some type of leveler on the additional concrete then put my radiant flooring down, then the tile. However, this new subfloor doesn't seem too sturdy or firm enough. Maybe I'm wrong.
 
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Old 06-05-11, 08:57 AM
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OK, it just looked like an early installation, where the subflooring was set about 2" lower than the remainder of the house and a concrete base was poured, and tile laid on top of that. So, with slab only, as Nestor says, the heating will go up as well as down, and may be more ineffective than a rug.
I'd go ahead and remove the remainder of the tile, float it out and reinstall your tile.
 
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Old 06-05-11, 09:14 AM
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Originally Posted by chandler View Post
OK, it just looked like an early installation, where the subflooring was set about 2" lower than the remainder of the house and a concrete base was poured, and tile laid on top of that. So, with slab only, as Nestor says, the heating will go up as well as down, and may be more ineffective than a rug.
I'd go ahead and remove the remainder of the tile, float it out and reinstall your tile.
Just to confirm - I do NOT need to remove the top layer of concrete down to the slab, correct? I will continue with the demolition of the tile today and will be careful not to dig too deep in the process. My question would be, what do I use to fill in the "holes" that I have made, especially the larger ones (say around the tub which has caused this whole discussion)? Does leveler fill in these types of holes or gaps or is there something else I need to use?

Regarding the radiant heating - isn't there an assumed loss of heat with all radiant heating, both upward and downward? With this being said, the area that I want to heat is only 3'x8' and I would add a thermostat or timer so it's only operating certain times of the day and year. Just curious if the heat loss outweighs the costs associated with installation.
 
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Old 06-09-11, 03:22 AM
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Anyone? I'm just trying to confirm what I'm thinking.
 
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Old 06-09-11, 08:03 AM
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One option is to apply a bonding agent to the pad where you need to build it back up and float out a sand mix (sand/portland cement) 4 to 1 mix which is good for up to 2" of thickness. You can either mix yourself or buy a bag or two of pre-mixed at any big box store. I don't think that self levelling compound material is designed to support a 1 inch fill requirement. It is designed for small adjustments and smoothing typically under 1/2 inch. If there currently for some reason is no heat source in the bathroom you should provide something to meet basic code requirements. A radiant floor will certainly provide what you need, and considering the small area involved and your plan of using it on demand by timer I doubt any downward heat loss issues would be of a major impact on your energy bill. In the end it is all up to what your budget is and what level of comfort you want.
 
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Old 06-09-11, 05:14 PM
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Thanks. I'll look into the fill and how it compares to the thickness of the new tile. I'll be able to make up some of the gap with the new tile and thinset, but not the full amount.

There is already a vent for HVAC, but I wanted to put radiant flooring in as more of a test run for when I redo the master bathroom. I'll have to see how much all of this is going to cost and weigh my options.

Thanks again!
 
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