Flooring Tile - Levelling Concrete Slab for Ceramic Tile

I just remove 2 layers of vinyl tile from the concrete slab in our 150 year old carriage house. (The vinyl tiles themselves came up easyily but the adhesive was a nightmarish to get off.) What I assumed was major settling problems in the slab turned out to have been purposely constructed with a drain at the lowest point (which of course has been sealed over long ago). Anyway, it still has to be levelled.

I have read people struggling with self levelling thinset, especially if they are using it for the first time (which I am). It looks like the low spot around the old drain will require quite a lot of SL thinset. Should I consider another product or forge ahead?

Additional info: Total area of floor is 212 sq feet. There are some other smaller levelling isues and hairline cracks.

Thanks for any response. All past advice in this forum has been most helpful.

Mark let's first clear up a little confusion. Thinset IS NOT Self Levelling Compound, they are two entirely different products, procedures, and costs.

Speaking of "costs", are you aware of the cost and coverage of SLC?
SLC costs around $30 per fifty pound bag and one 50# bag will only cover about 35 to 50 square feet at 1/8" thick. The cost of using SLC's could quickly get out of hand.

SLC's are very easy to use and I can't imagine why anyone would think any different.

One other option for you may be to install a new 'mudbed' that would level everything for you and the cost would be very very low comparitively. The new mudbed would however require an overall minimum thickness of 1-1/4", but this would solve all your levelling needs in one fell-swoop.:)

Forgetting THAT minimum thickness requirement for a moment: Can you use some creative mathematics and a little imagination to estimate the volume of product you would require to level everything you have to level? Assume you were to start at the existing highest point now and level the entire area, what would be the volume of product required?:)

Bud,

Here is the creative math: (FEEL FREE to check my calculations! I figured total volume by using the dimensions from the lowest point and then dividing by 2; I used a divider of 1728 to get from cubic inches to cubic feet.)
*The kitchen is on two levels. The lower level with the biggest levelling problem has a square footage of 125 square feet. I have taken measurements, rechecked them, and averaged them several times. Generally, I was getting measurement from the highest corner of 1" in 150" on one wall; 2" on the opposing 150" length, 1" on the 134" width, and almost flat on the opposite 134" wall. I did not account in my final calculations for a step and refrigerator platform but just erred on the low side.
So, I am coming up with calculation of 9 to 10 cubic feet of volume to be filled to make a level floor.
*The upper level is 82 sq ft and has some areas that are about .250"out of level that would be about 1 cubic foot of material.

Bud, the idea of a new mudbed adding 1.250" of height adds some other complications. I am hoping that my calculations give you enough information to propose another alternative.
Would it be possible to build up the floor with the cheaper, traditional concrete and finish it off with a SL concrete?
If so, is there a fast curing concrete that can be used so that we are not out of commission in our kitchen for weeks?
And, how do you handle the low end of the floor where I will be adding the most concrete? (i.e how do you handle where the wall board and the floor meet at the low end of the floor...forms?)
I am somewhat appalled at the extent of the level problem. Is it naive to think that being flat but "slightly" out of level would be an acceptable solution to my problem? ( I guess that would kill the idea of using a self levelling concrete.)

3:00pm-Went to HD, looked at various Quikrete products and checked Quikrete's web site. They are recommending one of their products called "Sand Topping Mix" that is appropriate for 2" thick down to 3/8" thick. Any opinions?

Sorry for all the questions...you can tell I am stressed...your advice is much appreciated!

OK Mark I was afraid of that. Ten cubic feet is a lot and would preclude the use of SLC in most peoples thinking do to the cost. Ten cubic feet is approaching a half-yard of concrete and in the world of SLC that can be a lot for a project of this size.

I can't see your project and if I could I may think I could tweak things just a little. By "tweak" I mean I would be tempted to lower the minimum thickness of a mudbed to not less than 3/4" since the full 1-1/4" is appearing to be prohibitive. Don't misunderstand me, 1-1/4" is the industry recommended minimum thickness for a mud bed and I don't particularly like to go against that standard but the truth is I have, and successfully I might add. Now whatch, somebody is going to come along here and clean my plow for me for suggesting such a thing.:)

I don't have much time right now but I will give you something to think about. The standard recipe for a mudbed mixture is 4 or 5 parts of sand (sharp sand) to 1 part portland cement. The premixed "sandmix" is usually 3:1 but I have never found that to be a problem. There have been jobs that I used to order sand from a dump truck and bought portland in 90 pound bags but I'm not getting any younger and those days are gone. I now use sandmix.:)

Thers' more to this approach but I'm outa time for now.:)

Bud, Thank you very much for your time and expertise.

What do you say Mark?
Where do we go from here?:)