Backerboard needed over SLC?

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  #1  
Old 01-12-08, 07:21 PM
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Backerboard needed over SLC?

Hi all,

I am fairly new to DIY home renevations and this website, and am currently starting a remodel on my master bathroom, which is basically an empty shell right now(down to the subfloor/framing). While this has been an over-all frustrating project to this point already, my wife and I are going to attempt laying 12" ceramic tile for the flooring.

The issue I have is that the floor in this 6x24ft room has shifted out of level the narrow way, dropping around 3/4 of an inch over the 6 feet(we did not rip up the floors except to replace a small section of water damage by our old tub). I know I am supposed to lay backerboard down under the tiles, but that will not fix my level problem, so I am considering using a self-leveling compound. My question is do I have to lay backerboard down on top of the SLC?

Also, how many bags do you think I would need to level this floor out(144 Sq. feet of space)? I have looked at some bags of SLC at Home Depot, and they say a 50lb bag covers 50 sq. feet at 1/8"., but I don't know how to account for the slope.

The subfloor is 1/4 inch exterior plywood over top of 3/4 inch ext. ply, with 2x6 joists 16" OC.

Is there an easier approach to level this floor out? Don't think I can do too much to the subfloor itself because it is sitting on a concrete foundation and I am afraid if I shift the floor it will shift the new roof on it also.

As I said, I am fairly new to renovating and any help would be greatly appreciated. I expect to be spending a lot of time at this site, as we are re-doing the entire house

Thanks,
Sam.
 
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  #2  
Old 01-13-08, 08:15 AM
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If you can get away with the height change, you might think about ripping up the 1/4" underlayment and adding a new 3/4 plywood base.

Lay plywood sleepers of various thickness perpendicular to the joists and lay the new plywood on top. Adjust the thickness of the sleepers to level the new plywood.

If your setup won't allow the additional floor height (probably 1/2") another option is to use plywood pieces as fillers before using the leveling compound. On the end that is 3/4" down you could probably get away with 5/8" or even 3/4". Size the width and thickness of the plywood to get a surface near level and then just use leveling compound to smooth the transitions between the different thicknesses.
 
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Old 01-14-08, 06:00 AM
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Originally Posted by SpAmSoNiTe View Post
Hi all,
Also, how many bags do you think I would need to level this floor out(144 Sq. feet of space)? I have looked at some bags of SLC at Home Depot, and they say a 50lb bag covers 50 sq. feet at 1/8"., but I don't know how to account for the slope.
I have limited experience using SLC, but I think I can provide some calculations that can help yoiu make an educated guess on how much to use:

If 50# bag covers 50 sq ft at 1/8" (or .0104 ft), that means that 50# will provide a volume of .52 cubic feet ([L X W] X D, or 50' X 0.0104').

If your floor drops that 3/4" (0.0625 ft) uniformly over the 6 feet, then you basically have a wedge shape that you need to cover. So, I'd calculate the area of the triangle part of the wedge, then multiply by the length to get my volume.

The area of a triangle is 1/2(H X W).
In your case 1/2(.0625' X 6'), or .1875 sq ft. Multily that by the length of your room, so .1875 X 24=4.5 cubic feet.

So, at 0.52 cu ft/bag, you need almost 9 bags of SLC.

Again, that assumes that the drop is uniform. For example, if the 3/4 drop is over the last 2 feet instead of the whole 6 feet, then you'd need 1/3 as much.

Hope this helps
 

Last edited by GaetanoL; 01-14-08 at 07:46 AM. Reason: math correction
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Old 01-14-08, 10:36 AM
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Hi Spam

3/4" in 6' is really a lot. Whats going on there that you have this much of a slope on your floor? Give us the details of exactly what you have there as to the floor framing. We need to know the size of your joists, there on center spacing and unsupported span. Also give details as to the support structures for the joists and their condition. We need to understand why your floor is sloped 3/4" over 6'.

By the way, you need to remove the 1/4" underlayment that you have there currently. There is no 1/4" plywood underlayment that is acceptable in a tile installation so it has to go.

To answer your question. You would need a lot of slc to correct such a problem and it would be very expensive and not so easy for a diyer to do. You need a minimum of about 1/2" in the shallowest part of the pour so you would need 1 1/4" on the low side. That would require either more than one pour or that you add aggregate to the pour. If you use slc on the floor there would be no need for cement board.

You really need to find out whats going on with that floor structure before you go any further.
 
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Old 01-14-08, 04:48 PM
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Mud job.
 
  #6  
Old 01-15-08, 06:19 AM
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Once your sure that you have no more movement, a mud job will work. But that will add substantially more height to the finished floor. You'll need minimum 1 1/4" on the high side so 2" on the low side. Lot cheaper than slc though.
 
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