DITRA and SLC ?-Sagging/and Repair Option?

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Old 01-09-07, 06:58 AM
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DITRA and SLC ?-Sagging/and Repair Option?

I've got a (2) 1/2" plywood sheets over 4" wided 3/4 subfloor boards with a dip of about 3/4 in the middle of the joists span in a bath. Joists are sagging but I will jack up slightly from basement and install a perpendicular load wall beneath so they don't sag any further. 8" joists 16 OC

I can't jack up too much to sister because of new tile work directly above that wall on 2nd floor. Don't want to loose that. So I decided to make a perpendicular wall int eh basement as part of a laundry which will also get snugged up w/lolly columns and stop the sag from progressing and built w/ adouble 2X6 plate on top.

Question:
I want to level the dip in the middle of the bath and use ditra. How couuld I do this? SLC over plywood then the ditra? How would you use SLC w/ DITRA? I"ll already be over the hallway transition by 3/8" and need a saddle to bridge the difference.
THanks for any help.
 
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Old 01-09-07, 07:24 AM
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Where is the dip, in the middle of the room or by the door? If its in the middle of the room, you could use slc and feather it at the doorway. You could then use ditra over the entire floor. The most important thing here is to figure out why the floor is sagging, and solve that problem first.

If the dip is by the door, youll either have to correct the framing problem or deal with the height difference at the door transition.
 
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Old 01-09-07, 07:43 AM
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There is a perpendicular wall that runs across the mid span of the joists (hallway wall) and on top of that a 2nd floor hallway wall. So the load is pushing down mid span and has caused the dip. THat is why I can't jack up much w/out damaging 2nd floor and why I'd like to put a basement partition wall up under the sag. Within the basement wall I intend to put a couple of screw post lolly columns to "snug it up" before putting in the 2X6 wall studs. THe dip doesnt' affect the door operation as the door is perpendicular to the joists also.

So can I assume to use SLC over the plywood then thinset Ditra thinset tile?

I am asking becuse I'm not a pro and have not used DITRA before But I like the fact it is thin due to a transition issue at the door.
 
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Old 01-09-07, 08:13 AM
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Yes you can use slc, then ditra, then tile. Make sure you spend some time researching slc. It can be a daunting task if you havent done it before. The most important thing to do here is read and follow the instructions on the bags to every detail.

Heres some good info on slc's.

http://johnbridge.com/vbulletin/showthread.php?t=1807
 
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Old 01-09-07, 08:20 AM
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Ditra is the priemier uncoupling membrane:This means it will allow movement under it and keep your tile surface solid.
I use it all the time. I love it.
Be sure to backfill your dovetails fully while you are setting the mud,this will require troweling opposite directions until they are filled.
Alway use unmodified thinset on top of the Ditra
You can carry in 300 ft of Ditra on your shoulder.Try that with CBU.
You have also a moisture barrier.

Mapei makes some if the best SLC on the market. Try Novoplane 2.There is a primer required to insure a bond with the wood.As Johnny stated feather the edges. BUT... Good SLC cannot be feathered properly so use some Ardex or Plani Patch on the feathering.

If the whole floor is SLC use Unmodified thin set. If wood is showing use Modified. Use 1/4 V notch trowel
Follow all directions on the bag of SLC unless it become redundant then apply common sense
 
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Old 01-09-07, 08:32 AM
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When you state the above, not quite sure what you mean regarding wood showing?

I think you mean the SLC not covering the entire floor. I think it will. pretty good size dip to fill.
Also, can you elaborate on the dovetaling? I've only tiled 1 other bath floor before as I'm a new homeowner and not a pro.

As far as the feathering compounds, very useful info had not thought about feather. I expected to be able to use the SLC.

I will post pictures as the project progesses. I'll put some on tonight to show where I'm starting from.
Thanks,
 
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Old 01-09-07, 02:15 PM
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Ditra has small dovetail squares that the mortar locks into. The thinset doesnt actually bond to the ditra, it fills in the dovetail and hardens, locking the thinset into place. This is what holds the tile to the ditra.

You can feather the slc at the edges - nothing additional is required.
 
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Old 01-09-07, 04:59 PM
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If the whole floor will be covered with slc you will not need to feather anything but your wifes feet
Johnny is correct about the Ditra dovetails.

It looks like this /__\|/__\. Sometimes I will flat trowel the dovetails until they are filled,then used the notched side to set the mud for the tile.

When you mix 5 quarts of water with one bag of mud as required for Novoplane2 you get a soup that will dry to a 4200psi.(It is hard to feather soup in my world)

I have a few pics if you need some more info.
 
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