Subfloor Not Flat - Please Help.

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  #1  
Old 05-10-09, 02:06 PM
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Question Subfloor Not Flat - Please Help.

I have a gutted full-bath that formerly had tile on a bed of cement. The remaining subfloor is 1/2" ply.

The existing subfloor is not flat due to a joist running the length of the center of room just shy of 1/2" high at it's worst point. Could be a combination of one high and the neighboring two low but a hump just the same.

I am not saying that the floor is not level, I am saying that it is not flat.

The joists are 2"x10", 16"OC with a span of 10'

Here was my original plan and I would like to know how you suggest I modify to address this issue:
1) further secure the existing subfloor to the joists with corrosion resistant screws

2) Add a layer of 3/4 BC ply (clean-side up)
- laid across the joists
- no 4 corners meeting
- no glue
- 1/8" caulked gaps
- secured by 1-1/4 corrosion resistant screws (6" around perimeter / 8" over the field).

3) Unmodified Thinset (1/4x1/4 square-notch trowel?)

4) Concrete board & tape following manufacturer instructions

5) Thinset/Tile as normal (12" tile)
I feel like SLC is going to be a true hassle... sounds like I would need to plug every escape, deal with lathe and flood the room.... and I feel like it is over my head to rip out the subfloor and replace.

Can I just put some thinset with a notched trowel down between the existing 1/2" and 3/4" I am about to lay to fill the voids? Seems like the same reason you put it between the ply and concrete board but I don't know if the moisture between the wood layers will cause problems.

Someone please tell me that I can do nothing and by the time I get to the tile that the 3/8" will be diminished by the layers of thinset
 
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  #2  
Old 05-11-09, 06:10 AM
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Adding plywood is not going to flatten your floor, although I agree that with 1/2" subfloor you do need more plywood. Remove the plywood subfloor over the crowned joist and plane it down so that its flat to the other joists. Reinstall the plywood subfloor, add a second layer of plywood minimum of 5/8" exterior glue bc or better (no thinset between layers), then either 1/4" cement board or an isolation membrane.
 
  #3  
Old 05-11-09, 07:25 AM
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Thank you for the prompt response.

My best guess to do what you are saying would be to run my skillsaw down the center of the neighbooring joists with the depth set to 1/2 and pull out a long 32" panel over the problem joist.

Snap a level line on the joist and plane it... possibly with a belt sander or maybe screw a temporary fence to the joist and use my saw or maybe a router with a flushtrim bit.

Then patch the opening with a new 1/2" piece of ply and continue with my plan of putting down 3/4" over the entire floor.

Will that suffice or will a thin strip patch like that seriously affect the strength of the floor? I don't know that I can pull out much more of the subfloor than that because it runs under the walls around the room and under walls that make up the closet & surround.

Here are some pictures if they can be of any help:
Looking into the room from the door:
Bath 001 on Flickr - Photo Sharing!

Looking at the door from the back:
Bath 004 on Flickr - Photo Sharing!

At floor level:
Bath 002 on Flickr - Photo Sharing!

3/4 View:
Bath 003 on Flickr - Photo Sharing!

Arial View:
Bath 005 on Flickr - Photo Sharing!
Thanks!
 
  #4  
Old 05-11-09, 09:22 AM
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I wouldn't cut the joist. The compression/tension is in the top and bottom 1-1/2". Put self-leveler on the sides. The high center meets the doorway correctly now.

Glue between sheets to strengthen the floor and act as one.

Nails are 2-1/2"min. or screws, stagger the ply edges and joints.

Is the joist span (not the same as bathroom length) 10', that's short for 2x10's?

By your copper waste and metal recept's, is your house 1950-1960 built? Are you sure it's 1/2" ply, not 5/8?

If access under, could you sister that center joist, after cutting partway from top down, to lower it slightly? Be safe, G
 
  #5  
Old 05-11-09, 09:31 AM
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Hi Michael, just wanted to add a comment as I have a floor with a similar lift. What is causing the lift? You may want to be sure you understand why the hump exists so you can be confident it won't continue to increase over time.

Bud
 
  #6  
Old 05-11-09, 11:02 AM
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Is the joist span (not the same as bathroom length) 10', that's short for 2x10's?

The far bathroom wall is an exterior wall and the near bathroom wall is shared with a hallway wall on the 1st floor which I assumed was load bearing. If it is not, then it would presumably be the next wall (otherside of hallway) which would make the span ~14'.
By your copper waste and metal recept's, is your house 1950-1960 built? Are you sure it's 1/2" ply, not 5/8?
Correct, 1950s. Re-measured, still 1/2".
What is causing the lift?
I cannot be sure, but judging from the discoloration on the ply I had assumed it was moisture related because there is a stain running over where it is swollen that appears to originate near the toilet flange
Small point of clarification, the joist does not appear to be high at either end for about 2ft... just the 8ft in the middle of the room.

If I had a low spot I would have filled with SLC, but being a high spot I am concerned about the volume and damming I am going to need to do to bring up the whole level of the entire room to the high spot.

I am happy to do this the "right way" but can't the thinset under the concrete board and the thinset under the tile do enough to make this workable? By workable I mean have the tiles not pop. The right side where the drop is most apparent is going to have two sinks over it so I am ok aesthetically with the room being a little off kilter. The tile does not rock on the bare floor except at the peak of the hump and even then not more than the height that the thinset would be.

If not, anyone else care to chime in on planing the joist vs SLC?

Thanks,
Michael
 
  #7  
Old 05-11-09, 11:07 AM
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missed a question:

If access under, could you sister that center joist, after cutting partway from top down, to lower it slightly?
I do not think I could sister the joist if the sister needs to end on load bearing supports. If it simply needs to be fastened alongside the length that I plane, then yes.
 
  #8  
Old 05-11-09, 11:11 AM
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If you decide to use a self leveler (slc) and you will be installing tile, the self leveler must be installed on top of the second layer of plywood, not in between the 2 layers. Additionally, you must use a portland cement based leveler. Most slc's require a minimum of 1/2" at the thinest part of the pour over plywood, so it will be thicker at the low ends, perhaps 1" or so. The top layer of plywood will have to be primed with whatever primer the slc manufacturer indicates, then galvanized diamond metal lath stapled to the plywood.

Slc is expensive, and if you haven't worked with it before it can be a costly learning experience so you should read up on it before you decide to go this route.

GBR, I'm just curious, not a structural guy here, just a lowly tile guy. Are you suggesting that planning 1/2" off the top of the high joist will substantially compromise the strength of the joist? I've done this quite a few times before, and if I shouldn't be, Id like to know about it. Thanks
 
  #9  
Old 05-11-09, 01:20 PM
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Jonney, if you rip 1/2" of a floor joist in the middle 1/3 of it's length, it weakens it to the next size down. 2x10 to 2x8, etc. Certain size holes can be drilled almost anywhere, but no notching or ripping in the middle 1/3.As I said the compression/top, and tension/bottom stresses are the greatest there.

UBC (2320.8.3) and IRC [502.8.1] do not allow this.

http://arch.umd.edu/Tech/Structural_..._Guide_A11.pdf Be safe, G
 
  #10  
Old 05-11-09, 01:41 PM
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Good to know, thanks. I would not have thought that planning1/2" off a 2x10 would have made that much of a difference. So sistering that one joist after its been planed should work, yes?
 
  #11  
Old 05-11-09, 06:26 PM
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Is it a high joist or some next to some crowned down? You can sister and bevel one edge only at the ends at bearings, roll it in, with glue between and lots of nails.

I'm not a S.E., just a carpenter,with 36 years in residential and an avid book reader.

This is a great site, just enter the subject, pick a book that has Preview-- in red:

Audel Complete Building Construction - Google Book Search

Be safe, G
 
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