Flooring Tile - Tiling a sloped, uneven floor (scribe question)

I'm planning on tiling my mothers kitchen for her birthday, the problem is , part of the floor that leads to a bathroom and exit door is uneven and slopes towards the bathroom, it's off by a half inch or so.

Basically the whole kitchen floor is even, except this little area that leads to a tiny bathroom, psuedo mudroom and exit doorway. My plan of attack is to put down backerboard for the kitchen tile (the even part)and then try to put down a leveling compound in the uneven area and feather it out.
I saw a leveling process on Ask this old house maybe a year or so ago, where Tom Silva triangulated 3 pieces of scrap wood and filled them in using a compound of sort , after using a scribe to get the measurements.
My question is does anyone know where I can find this process explained in great detail, maybe a taunton press book or something, or feel free to explain it to me if you know how to do it :D
Thanks Kevin

How about putting the cement board over the whole floor, then mix up some Self Leveling Cement and pour it over the low area. The size of the area and the thickness of the pour will dictate how many bags you need. Can you identify the reason for the slope there, because if it is active and it drops some more after the weight of the tile is added, they will crack or come loose. What is on the floor now? You may also need to beef up the subfloor and/or joists to properly support the tile.

Thanks for the response tileguybob,
The sag/slope is due to poor construction/craftsmanship. The house only had one bathroom (built circa 1918), so this little section psuedo mudroom,bathroom thing was added to the back of the kitchen in the late 1980's, but was done by an amateur. It has been sloped since my we moved in back in the early 90's, and hasnt moved/sunk since, which makes me believe it was not level in the first place.
I went down into basement into the crawlspace ,checked the floor and everything seems to be o.k, structure wise, maybe they messed up the plywood subfloor.
Your idea, is what I am trying to do, but I am not sure completey how, and trying discribe this little addition is tricky, because it has so many little angles, counters,cabinets,etc, and I dont think a pic (even if I could post it could capture the little problem).
The area that is sloped is small, but needs to be fixed. The whole kitchen is level, and I checked the addition/bathroom,etc are/is level , except for where they meet. There is a big bump/slope that divides the 2 areas.
What I wanted to do is scribe a series of wooden shims along the contour of the existing floor, cut them, and then fasten them to the floor. After that I would pour leveling compound between the shims and use something to level the compound.
My question is do I put down the backerbaord down first and than add leveling compound or vice versa. My second question is, is there a book on scribing a uneven floor in good detail that u may know of. The scribing looks a little tricky and it would be nice to know exactly how to do it.
Thanks Kevin

You always set the backerboard first, before using a SLC.:)

Set your backerboard,[don't forget the thinset under the backerboard] then deal with the problem area, if the area is higher than the rest of the floor around it, try and fix that problem before the backerboard, if it's a dip of some sort, do it after, how large of an area are we talking about?:)

You always set the backerboard first, before using a SLC.:)

Set your backerboard,[don't forget the thinset under the backerboard] then deal with the problem area, if the area is higher than the rest of the floor around it, try and fix that problem before the backerboard, if it's a dip of some sort, do it after, how large of an area are we talking about?:)
Thanks R&D, I thought that may not be the way to go:D The kitchen itself is medium size ,the addition to the kitchen is rather small a total of 48 square feet, not including a tiny little bathroom that I will divide from the addition with a threshold.
The working area is really only 22.5 square feet. The difference between the addition's floor and where it connects to the old kitchen is a little over a quarter inch, it's lies somewhere between 1/4 and less than 1/2 an inch. Is that too much of a gap to level with a SLC? I fear that if I laid 1/4 inch plywood down , and than backboard, I may raise the floor too much.

Never use 1/4" plywood in a floor that is getting tiled, only 1/4" backerboard can be used.:)

Trying to picture where the 1/4" gap is, it's between two areas in a straight line?:)

1/4" - 1/2" difference, you can build that up with a thinset-bedded underlayer of 1/4" board and/or old lino scraps stapled down - below the *top* backerboard, that is. Also, any backerboard may sit on a trowelled bed of varying thickness - use different notch sizes: 1/8" to 3/8". Half the notch size is the distance the board may be squeezed down, if you wish. I use straight 2x4s to press the backerboards flat. I also put in a lot of fibreglass mesh joint tape and sometimes loads of staples where an area is built up thick - this prevents cracking and peeling.

To me, bedding the backerboard so it ends up flat seems easier.

You can not level CBUs with extra thinset or vinyl scraps, the thinset is there to only fill any voids under it, that's it. :wall:

Thanks Tileman and Kobuchi.

Tileman, I wish I could take a picture, but the best discription of it I can give is, there its basically there is a line of demarcation between the Kitchen and the small addition. Where they meet, there is a slight bump/ridge that can be seen and felt ( a carpentry error from previous owners, but it is a stable structure), and thats where the slope begins. The small addition slopes from the kitchen, the grade difference is less than 1/2 an inch. I have checked out the additions floor and the old kitchens floor, both are stable, the old kitchen has a plywood backing ontop of an old wood floor, so it's solid, and the addition has a a good plywood floor.

Kobuchi thanks for the info, cool, thats what I was hoping, I checked out the QUIKRETE website the otherday, and it says their SLC is good up to 5/8" so it looks like I am golden. Thats what I want to do, build a tiny retaining wall with 2x4s, and level it with SLC.

So here is where I am at, Both floors have a good plywood subfloor, it's looks like I can just go out and get the backboard lay that out and then work out the Slope/grade with a SLC.
I have a couple of questions left. How much give does does backboard have/ how much can it be bent? Is there anything that has to be done to a floor that that has been leveled with slc first, before going ahead and laying tile?,besides making sure it's dry :D Lastly,what brand of SLC do you recomend.


Thanks for the Help, Kevin

You can not level CBUs with extra thinset or vinyl scraps, the thinset is there to only fill any voids under it, that's it. :wall:

Uh oh. I've been working backward then, taking pains not to bend cement board one way or the other.

What are the reasons not to level under the boards?

You can level under CBU with shaving joists or whatever is needed to get it flat, you can not add extra thinset or use a SLC to do this though, adding extra thinset wouldn't work, when you screw it down it would ooze out and follow the contour of the floor.:)

Letting SLC or thinset dry, then adding the CBU won't work, because, when you screw the boards down, the screws will crack the SLC and or thinset, causing voids between the boards and the floor, this is the same reason CBUs can't be used over concrete floors.:)

What you can do if the whole floor is out of whack, is prime it, set your metal lath, then pour your SLC over the entire area and tile on that, no CBUs needed, or install an isolation membrane over the SLC for added insurance.:)

adding extra thinset wouldn't work, when you screw it down it would ooze out and follow the contour of the floor

Letting SLC or thinset dry, then adding the CBU won't work, because, when you screw the boards down, the screws will crack the SLC and or thinset

I agree on both scenarios. Wrong and wrong. But I don't do either.

What I normally do (and I'm learning this is not normal), is bed the boards down - sometimes with a lot of solid, stable junk to nearly level - and at this stage only drive screws where the board is high. I use a straight 2x4 to check flat, and find that pressing the cement board down with this (by walking on it) can true the boards.

Next day, I drive screws through; these just ensure the bonded mass of cement board and... uh, junk... won't someday lift off the wood beneath. Nothing bad happens as the screws go in because everything's down solid, stuck together, and cured already.

This is backward and probably seems more work, but, to me, forcing flat, stiff cement board to hug the contours of a floor - and then correcting the deformed board - seems like make work.

I do guess I'm wrong, Tileman, and I'd like to know why. :)

VOIDS,VOIDS,VOIDS, it's easier to just level any imperfections after the board is down with thinset or a SLC. :wall:

VOIDS,VOIDS,VOIDS :wall:

I agree. That's why everything under the cement board must be filled solid, and every inch of it has to smush down a bit when the board goes on. Just applying a uniform trowelling of thinset won't work if the board can't flex to meet this under it's entire surface.

The next consideration is: how many times do you want to level?

One could roughly level a subfloor, as you say, "with shaving joists or whatever is needed to get it flat", then screw down the boards so they displace the thinset and deform to fit the roughly flat subfloor, then fix the now deformed boards by levelling a second time on top of them.

Personally, I rather put my time into prepping for the boards so they land flat and supported all over in the first place, and further press them flat (not wavy) while the thinset's soft. I screw them into the subfloor later. They don't move at all while being screwed down. Then I needn't level a second time.

Wet levelling compound and thinset bond well to cement board in any case, top or bottom, so the debate's mainly over the order of operations.

I guess the gaps left by the notched trowel teeth don't fill in as much, the way I do it, as the boards aren't pressed any more than if they were big tiles. Is this the problem of voids you meant, Tileman?

I give up. :wall:

You can not let the thinset or whatever layers of what set up, then screw through it to set the boards, the screws will crack the thinset or SLC below the boards and cause voids, once again, all leveling with thinset or SLCs should be done AFTER the boards are set over unmodified thinset with a 1/4" trowel and set and screwed down per manufacturers directions while the thinset is soft, you also void all warrantees, doing it any other way, end of story. :rolleyes:

the screws will crack the thinset or SLC below the boards and cause voids

I get it. So, for example, if you arrived at a site to tile a board that had already been bedded in wet thinset, which had bonded to the board and cured - properly - and you noticed some areas lacking screws, you would not add screws at this stage, because those screws would create voids under the cement board? What would you do?

I would first ask why it wasn't installed correctly, then see if there is any movement in that spot, then maybe send a screw in or maybe not, then have a written statement on my contract, that because I didn't prep the floor myself, there are no guarrantees what so ever and have it signed by the homeowner, I might even walk away if not happy with the prep work. :D

You can level under CBU with shaving joists or whatever is needed to get it flat, you can not add extra thinset or use a SLC to do this though, adding extra thinset wouldn't work, when you screw it down it would ooze out and follow the contour of the floor.:)

Letting SLC or thinset dry, then adding the CBU won't work, because, when you screw the boards down, the screws will crack the SLC and or thinset, causing voids between the boards and the floor, this is the same reason CBUs can't be used over concrete floors.:)

What you can do if the whole floor is out of whack, is prime it, set your metal lath, then pour your SLC over the entire area and tile on that, no CBUs needed, or install an isolation membrane over the SLC for added insurance.:)

Thanks Tileman, I will take the later approach. Sounds kinda similar to making a mortar bed, and the process you discribed is what I had in mind.

Is there any brands of Latex primer and SLC that you swear by for the job?

Read the directions and follow them to a tee, if a large area and more than one mix is needed, have help and someone else mix while your pouring, have all water pre-measured and on hand to speed things along, this stuff is good , but expensive and takes a little getting used to doing, plug all holes in floor and any openings, I also put an expansion joint around the room first, foam weather stripping works fine for this.:)