Hello again...
Time to start phase II (hallway, front and back entries this summer) of my tiling project and will be using more self-leveling compound again.

Subfloor will be 5/8 plywood to 3/4 plywood (filling the dip with plywood instead of all SLC)laid over 1x4 planks over 2x10 fir joists on 16" centres (yes, it's pretty solid now).

However, got some conflicting advice - was given to understand that I need to added a layer of mesh on the plywood after the special latex primer. I only need to level my hallway about 3/8 inch at the deepest to featheredge on an area about 16' x 4' wide. Thought the SLC didn't need mesh...only the special latex primer.

Question, do I need the mesh? Didn't use it in Phase I (SLC on kitchen and living room floors but they seem ok and tile is sound.)

Any thoughts?

Paul, when I have poured SLC over plywood, I have always used lath and primer. The brand that I use (Laticrete) calls for lath over plywood, but I have been told that there are some brands of SLC don't don't require lath over ply.

Thank you Rob,
Seems I'm using E-Z Flow self-leveling compound (www.usehickson.com) and the instructions don't mention metal lath. I can certainly consider that of course. I could also go back to building up the floor with thin 1/8th plywood under the 3/4", and use lots of PL400 adhesive and my planer...did that for my other living room floor in preparation for hardwood. Turned out nice, but took half the summer.

Back to SLC: here's a clip from the product brochure...
http://www.usehickson.com/resources/pdfbrochures/EZFlowSelfLevelingUnderlayment_en.pdf

From the manufactuerer's website:

"Wooden Floors – Remove all grease, dirt, oil, dust and any other contaminants from the floor. Nail down loose flooring. Fill any joints in flooring with a stiff mix (mortar consistency) of E-Z FLOW Underlayment, caulking, or other suitable material before applying Primer. Roll on E-Z FLOW Underlayment Primer #100, using a roller cover of at least 1/2" nap or a nap suitable for the surface. E-Z Flow Underlayment Primer #100 is recommended for concrete, wood, tile, slate, terrazzo, brick substrates. In case of doubt, carry out a test application. Pinholes will develop on surface after hardening if improperly primed."

Nothing on metal lath...other thoughts?

Can you actually SEE that your hallway is out of level? If not, I think personally I would not worry about it..if it is flat, I am not sure you would notice it is out of level. I've used a lot of the EZ Flow....I like it..but it does not live up to its name...it doesn't really self level....you have to help it along. The primer is a must...pretty much useless with out it. I've never used it with Lath either...though it does seem like a good idea..in the deep areas anyway. I don't think it would work where you have to feather it. If you do try the lath....Prime the floor first, then install the lath.

Thanks for the advice!
Yes, the hallway has a nice smile in it...using my 6 foot level and tight string from one end to the other.

The reason it is out so much is that this is a hallway that has a sunken living room along one side. The joists under the hallway (lateral) are supported on one side by a 12' header joist on one side, which then forms the step down to the sunken living room. When the house was built 30 years ago the good HVAC folks cut a 30 inch wide cold air return in the header joist ...thus leaving a hallway with no support in the middle. Hence it has a nice smile from one end to the other (amazing what a tight string will reveal). A steel beam in the basement supports the end of the joists under the sunken living room where they terminate under the hallway. Spent a bit of time last summer rebuilding the floor in the sunken living room and my hallway, reinforcing the old header joist with LVL, etc. It's solid now, but the hallway floor still has a bit of a dip left in the middle of its 16' length (tight string pulled from one end of the hallway to the other shows this), and I don't want a dip in the finished floor...

I am deciding whether to correct the dip in the hallway with layers of 1/8th plywood sandwiched between the subfloor and the finish 3/4" plywood (a bit of time with PL400 adhesive and my hand planer), or use SLC on top of the 3/4 and call it a day...if SLC will stick ok on the plywood over the long term.

Whole thing will be covered with Ditra before finally putting down porcelain tile.