leveling sloped suspended slab sloped in preparation for porcelain tile

[gitrdone]

I am looking for advice for options on leveling an interior suspended concrete slab over a conditioned space. The slab is 6-8 inches thick and slopes to the center of the room. There was once a drain which is no longer needed. The area to level is about 314 Sq feet and has a 4 foot by 13 foot hole in the center for a future staircase. Using a rotary laser level the outside perimeter is off by about 7/16 of an inch and slopes to the center by about 2 inches. Have found this forum to be extremely helpful, reading up on pros and cons using dry pack versus self level products. Need to decide what is best way to get best finished job taking into consideration time, labor, and material costs.

[jadnashua]

A bonded mudbed over the slab will probably be the least expensive, especially if you are not paying labor, but an slc pour will be much faster. Both would provide similar quality results IF the installer knows what they are doing. SLC maybe should be called self-smoothing verses leveling...it isn't like water, it needs some help to become level. Once you understand and have the right tools and techniques, it can be very level and smooth, but it is lots more expensive in materials.

[gitrdone]

Thanks for the reply Jim. Having this large and deep of an area to level, factoring in the cost of materials, and getting help from others, it probably makes the most sense to go with a bonded mudbed.

[cx]

Buck, for an above ground concrete slab you're limited to no more than a 100 square foot area using that bonded mud method. And your mud must be a minimum of 3/4" thick at the thinnest point and no more than 2" thick at the thickest.

If you want level using mud in that application, I think you'd be required to level with a bonded mud bed and then install a cleavage membrane and a minimum 1 1/4" reinforced mud bed over that.

There are special requrements for you bonding mortar in those suspended slab applications, too.

My opinion; worth price charged.

[gitrdone]

Is the reason because there could be deflection? Because I would think the thickness of the slab and the span between supports would also need to be put in the equation and not just Sq footage. Following what you outlined would raise my finished floor height and not work in this situation. Maybe slc would be the best way? Thanks CX.

[cx]

It does not have to do with deflection, Buck. More towards the other stresses known to exist in those above grade applications, including flexing and vibration as I understand it.

Some or all of these stresses may or may not apply to your individual situation and I have no way of knowing that. All I can tell you is what the current industry standards say. What you do with the information is entirely up to you.

My opinion; worth price charged.

[dhagin]

Welcome Buck.

I'd suggest enlisting a professional engineer to make these decisions. Once a slab is elevated, everything changes and with that large an area, the weight alone would cause me concern. As mentioned above, weight may be the least of your concerns.

[jadnashua]

FWIW, the place where I worked before I retired had suspended concrete slab floors. Big large open area. If someone who was heavy hitting on their heels while they walked, you could feel the floor vibrate 50' away. This could make for a major problem trying to install tile (that area was covered with a commercial, low-loop carpet).

[gitrdone]

I had involved a structural engineer prior to cutting in the hole for the staircase. The added I-beams installed below along with the removal of the old mortar bed and flagstone puts me well under the weight specs. So my only major concern now is getting the best possible finished product that will last taking into consideration cost and labor. I am going to try and get some estimates for a stained overlay...problem is there are not a lot of contractors in my area that do that work. Thanks for all the great advise.