I've read the notes on this site and other sites about not using the scratchcoat & wire mesh under tile. I checked my kitchen, bathrooms and foyer and found they are kind like this crappy job, but not exactly same. So I'm confused a lot.

Under my tile, there is a layer of 1/4" mortar with a wire mesh embedded inside and a 3/8" plywood underneath, and then 5/8" plywood subfloor.

It looks like the tile was sitting directly on the additional layer plywood with wire mesh embedded into the mortar, but not using the wire meshed mortar as the substrate.

Could anyone here help me verify if this is the scratchcoat & wire mesh job or another one? If it's the latter, is it acceptable?

Confused me further more is, this house is a newly built house by a builder with very good reputation in quality, and I can see from lots of other aspects of my house, this build did do a good job.

Any input is appreciated.

If there's mesh in there, then it's a scratch and lath job.
As you have read, this is not an approved or accepted installation method by industry standards. It has failed every test when presented.

Even the best builders still have subs install this crap. Why, because it's cheap.In my area the building code actually allows this junk as long as the mortar over the wire lath is a minimum 1/2" thick. Problem is, installers don't do it that way and spread a slurry of the cheapest mortar over the wire just enough to cover it.

There has been some big changes in my area since one builder and the building department were challenged by the homeowner. Ripple effect came right down to the retail level for local stores installing tile flooring. No longer do you see them installing scratch and lath. Now its only "tile approved" underlayments.

Don't know what part of the country your in so I don't know if you have any recourse to follow up on.
If the house is new, you might try approaching the builder for remediation or as a last resort,the local building department to see if any local building codes have been breached.

If you don't get any action from either source then you'll just have to hope for the best.

While I don't endorse scratchcoat installs in any way, with two layers of plywood under there you might well be ok. This hinges on a couple of other factors, such as joist span and spacing and the type of plywood used and installation method for the plywood. For example 3/8" halex plywood on top of a 5/8 subfloor would be an acceptable tile underlay. If a good quality thinset was used, then the mesh does not compromise the quality of the install. Where you really run into problems is where the scratchcoat alone was used to try and stiffen the floor.

Thank you for the reply.

There is still one thing confusing me a lot. I've read and as you have mentioned, when people saying scratch and lath job, they often say the mortal is 1/2" thick or more, but in my house, it's only 1/4". It looks like this layer is the mortar that glues tiles rather than the substrate, and therefore, this is a tiling directly one plywood job rather than scratch and lath job, is it true?

I live in Richmond Hill, ON, do you familiar with the building code of my area?
Thanks!

Hi pistolpete, thanks for you reply. And I have some following questions, hope you can answer, thanks in advance.

I don't know the type of the plywood, cause it is all covered by the tiles. The joist span is 12", Is this ok?

You mentioned "if a good quality thinset was used...", could you be more specific, what kind of thinset is good. And what do you think the purpose of the mesh is here? Is it better than tiling directly on the plywood?

Well I real concern is, I'm going to rip off all the tiles in my kitchen and redo it (cause my wife doesn't like the colour). I hope the new tile will keep the same height level as the current, so the transition to the hardwood floor hall way and family room would be smooth. So I wonder which tiling method should be used to achieve this requirement. Can I use the same way as it was, 1/4" mortar with mesh, or simply without mesh?

Thanks.

Joist span alone is not enough information to determine suitability for tile. Species, grade, and joist size are also important. In the top left corner of this page there is a span calculator where you can enter it all yourself.

With thinset you get what you pay for. You can get standard thinsets for around $10/bag, while modified thinsets range from about $20 to $60/bag. The better thinsets have more acrylic polymer additives that make them bond better and at the same time leave them slightly flexible when cured and thus able to absorb small substrate movements.

As I mentioned before, the mesh does not add a significant amount of strength to the system.

Tile is meant to last 50 to 100 years. It seems a shame to rip up such a recent install. If you do decide to proceed, you might want to find out from your builder what materials were used. If they used a birch plywood underlay like halex, then take it down to that level and re-install with thinset. If they used regular sheeting grade plywood, it should come out.

Check where your heating vents are. A tile specific underlay plywood will have 5 or 7 plies, the other stuff 3.

If your in Richmond Hill, then you have a scratch coat job. It will fail at some point. It's just a matter of time.
The first thing you will see is the grout cracking at the edges of the tile or entire pcs of grout popping out.

Lath started getting used because the builders started putting OSB in for subfloors instead of plywood. Why, because its cheaper than plywood. So to be able to install tile over OSB you need some kind of underlayment. So the answer was, lets just place wire lath and skim it with mortar. Why, because its cheaper than putting another of plywood. Unfortunately in new home construction its all about the bottom line. Builders constantly are looking to lower their costs while boosting the profit margin. This method just happens to fall into that category.

The Ontario Building Code actually covers this and as I mentioned before, the local building department did go after the builder in violation of the code.

I can assure you there is no way that your scratch coat will meet the minimum 1/2" mortar thickness as required by the code.

I've read the Ontario Building Code, and I can see clearly that my floor didn't comply with it by any means. Actually I realized this from the every beginning, I just couldn't believe it, or more accurate, I didn't want to believe it. But now, I see the reality won't be changed no matter you see it or not.

I've started to remove the old tile since I'm going to reset it. I was surprised again. I've done about 20 sq ft, and I found the removing job was much easier than what I expected. The tile could be ripped easily with a ripping bar, and most of the tiles could be kept as the whole piece without cracking. The back of the tile was very clean like a new, only occasionally a little mortar stuck on it. The scratch coat, could be easily removed by pulling up the wire mesh, no any mortar residual left on the plywood underlayment, absolutely zero, only dust left. I'm not sure if the scratch coat should bond on the plywood or not. Any way, I was surprised again. I bought a floor scraper to do this job, but I found there was no need to use it. I can return it to save another 40 bucks.

Now, I'm going to go with Ditra and DIY. I know it's expensive, but it looks this is the easiest way for me to have the job done right and meanwhile to keep the thickness of the finished floor as minimum.

I plan to keep the plywood underlayment. I don't know if it's birch or not. It's 3-layer and 3/8" thick. I think it's better than nothing, since Ditra can be set on top of single layer 5/8" OSB.

I also have two questions,

1. The installation guide of Ditra said that the mortar for setting The Ditra shall be "fairly fluid consistency". Does any one know how fluid it should be?
2. My new tile is 18"x18", what size of trowel shall I use to set it. is 1/4" x 3/8" ok? I wanna keep the thickness of the finished floor as minimum as possible.


RC & pistolpete, thank you very much for your replies. Do you guys have any experience with Ditra, any suggestions or warnings for me?

Any inputs would be greatly appreciated!

Now you know why scratch coat underlayment is garbage. For all the reasons you mentioned.
Judging by the description of the lack of bond to the tile or floor, your floor was doomed anyway. Now your on the right track with the proper underlayment.

What you don't know or can't see is how well the original subfloor is attached. It may only be nailed. If you really want to do this right, the 3/8" ply should be removed and the OSB subfloor needs to be screwed to the floor joists.

Since your trying to match the hardwood height you need to remove the 3/8" plywood. You need to install Ditra XL, not the regular Ditra if you want to be close to the hardwood height.

1.Go to the Schluter web site and view the video of a Ditra installation. http://www.schluter.com/video_zoom.aspx?video=video/schluter_ditra.swf&name=
As for the thinset, over OSB or plywood it should be a modified thinset and the consistency is kind of like yogourt. Too wet and it won't retain the notch from your trowel.

2. I would use a 1/2" notch trowel.

Go to Tilemaster in Aurora for all your supplies.

RC, Tilemaster is the place that I plan to go, thank you. I'll check the subfloor tonight.

However, I have a question about the finish thickness calculation. I know Ditra XL was designed for even hardwood floor transition, and it's 5/16" thick, plus 5/16" tile itself, it's totally 5/8". And then there is only 1/8" left for the two layers of thin-set to make the tile even with hardwood floor. If I use 1/2" trowel, the thickness of the thin-set would be around 5/16" - 3/8", it's a big difference to 1/8". Even with 3/8" trowel, the thin-set would be 1/4", it's still big. This is only about the thin-set for the tile, if take the layer for the Ditra itself, the difference would be further even that layer is very thin. So how could Ditra XL achieve the even transition to the hardwood floor?

I know there must be something wrong with my calculation, but I don't know where. I will appreciate if anyone can point that out.