The plastic mesh he's talking about is made by Mapei and it's called Mapelath. When they first came out with it 4 years ago, their rep came to our local Dal warehouse to demonstrate how to use it. During q&a afterward, I asked him what the difference was between this and the old lath ans scratch method, also known as a "Jersey mud job" which had been found by the TCNA to be at fault for many failures. He couldn't give me a straight answer. As a result, I won't use it, even though Mapei, who is a reputable company, warranties it. I would imagine the latex he's going to put over your plywood is also Mapei's, called Keralastic, which is some of the best stuff around for this kind of installation.

The 5/8ths ply over 1/2" is fine, just make sure it's screwed down well.

Concur with Bill, plastic mesh is uneeded.

For the SLC primer, I use "SLC primer". From your text I'm not sure if your guy is using SLC primer or regular latex admix.

Bill, a Q for you, it's something I've never really thought about, but is SLC primer the same formulation as a regular liquid latex admix for modifying dryset? I've never thought to compare the MSDS's to see what's what.

Back for the OP, I'll usually apply a coat of SLC primer to the subfloor and let it dry. I'll then install my mats and/or cables. I'll then apply another coat of SLC primer, out of a garden sprayer. This coats the cables/mats, etc, and gives nice adhesion to everything.

There is an "open time" or working time with the SLC primer, so once I spray on the second coat, I have a certain amount of time to get the SLC mixed and set down over it.

Thanks...!!

He did say it was the same stuff you add to the bags of dry thinset mix, so I am sure it was not the SLC primer you mentioned. Thanks for that information, I will use the primer made for SLC.

I read on this site, installing tile to plywood with thinset is bad because it eventually fails. Does the SLC layer provide this protection being it goes on first, then the thinset, then the tile? Can SLC fail if on top of plywood? Does it remain flexible and stable as a backerboard would? I know if flows like liquid and reaches a level surface. I guess it is super strong stuff then.

I have to also ask out of curiousity...a Jersey mud job? How did it get that name? Is it related to NJ State? In my sisters home, a metal mesh was nailed to the plywood and then the thinset was worked into the mesh, troweled and then tiled in one shot. And.....she lives in NJ.

I guess this was a Jersey mud job? Is a better way to do this is to pour SLC over the mesh, then thinset and tile?

Bill, a Q for you, it's something I've never really thought about, but is SLC primer the same formulation as a regular liquid latex admix for modifying dryset? I've never thought to compare the MSDS's to see what's what.

Let me put it this way-- if you ask any particular company rep, they'll tell you you need to use the bonding agent specific to that SLC. That being said, I know of plenty of contractors who've used Mapei's Keralastic, Hydroment's Flexalastic, and Laticrete's 333 latex as a bonding agent with no ill effects. I'll let you decide from there. :-)

I have to also ask out of curiousity...a Jersey mud job? How did it get that name? Is it related to NJ State? In my sisters home, a metal mesh was nailed to the plywood and then the thinset was worked into the mesh, troweled and then tiled in one shot. And.....she lives in NJ.

A jersey mud job consists of nailing down wire lath to the subfloor, and then skimming it with a "scratch coat" of thinset, prior to setting tile (hence the real name of the method, lath and scratch). It's a bad method for two reasons. First, if you overlap the wire, it's next to impossible to get a nice flat floor out of it, without building the floor way up with thinset, and thinset's not made to be used in that kind of thickness-- it shrinks as it dries, way too much. Secondly, if you DON'T overlap the sheets of wire lath, now you've created weak points between the sheets, and as a result, the floor will fail, more times than not. The reason it's called a "Jersey mudjob" is because this method seems to be used more in and around New Jersey than any place else in the country.

"I'll let you decide from there. :-)"

Well there's one less product I need to have on hand. And a smiley face right back at you!

How thick should the SLC be so it does not crack, how does it stay together without a mesh. I am envisioning concrete and rebar...or am I off with my thinking?

I read on this site, installing tile to plywood with thinset is bad because it eventually fails. Does the SLC layer provide this protection being it goes on first, then the thinset, then the tile? Can SLC fail if on top of plywood? Does it remain flexible and stable as a backerboard would? I know if flows like liquid and reaches a level surface. I guess it is super strong stuff then

installing tile to plywood with thinset is bad because it eventually fails.

Although you really need to know what you're doing, I'm in the minority saying that's not necessarily true. It IS, however, a very temperamental installation method, and if you mess up even a little, it's done.

Can SLC fail if on top of plywood?

not so long as you prime the plywood properly, and mix the SLC according to the directions.

How come no one is suggesting dietra? Just wondering cause I have the wood floors and I am reading all this and wondering what is different?

Ditra's also another possibility.

When I read your post, the first thing that jumped out at me was "no underlayment!" The ensuing discussion about SLC and mesh covers was enlightening, as I've never used them, but the need for an underlayment never came out (notwithstanding Bill's comment that some really good tilers can skip it).

So yes, make sure he uses an underlayment. I'd recommend Ditra (only 1/8" thick and better technology than cement board), which you'd put over whatever mats/SLC/mesh combo you end up using.

What is the uncoupling membrane if SLC is poured on plywood? Wouldn't it be a better install if mesh indeed was used?

SLC serves as the transition material when going from plywood to tile. You don't need Ditra with SLC. Think of SLC as a transition material like cement board.

While SLC is normally used to level floors, it's also quite common to use it over radiant mats and cables. It encapsulates them nicely (and easily) and eliminates the chance of cables being damaged when trying to thinset and tile directly over the cables/mats.

With 5/8" underlayment over the 1/2" ply, it's an adequate base for tiling.

SLC as underlayment...I learn something new every day. Thanks!

This is new to me too, but good news !!!

So the 5/8" you are referring to is the original posters 5/8" plywood on top of the 1/2" plywood, correct? Not 5/8" of SLC...just clarifying.

That being said, how thick should the SLC be? Just enough to level the floor, or some other thickness?

I heard on this post people installing Ditra, then SLC, then a heating mat, then more SLC, then thinset, and then tile. It appears this is all overkill.

Correct. You'd need two layers of engineered wood (plywood, OSB, Advantec, etc.) underneath the SLC.

What makes SLC so good..versus metal lath and thinset. Wouldn't it be better to pour SLC over the metal lath, or is that overkill? Do you need 3" like a mud bed job?

The SLC would be MUCH better than thinset, because of the fact that the SLC will be much easier to work with, and it won't shrink nearly as much as the thinset while drying.

And no, you don't need 3". In fact, Most SLC manufacturers won't allow pours in more than 1/2" at a time. All you really need, is to cover the heating wires.