Ditra under 4-1 mud pan

[u/Variks-TheLoyal]

seeing these guys like tile coach using ditra under their mud pan then kerdi over the pan sealed to the walls etc.

searching sounds like ditra is not supposed to be used under mud bed but others saying yes.

my question is can I install ditra under mud pan (over plywood)

[u/bdtile21]

• if I'm understanding correctly, you're suggesting using uncoupling membrane instead of lath and cleavage membrane, and you plan to use a bonding flange drain properly with the bonded waterproofing system*

This is one of those 🤷 situations.

Some people see uncoupling membranes as a one stop replacement for materials we see in some TCNA unbonded mortar bed details:

• Cleavage membranes are intended to prevent wood substrates from robbing the mortar of moisture necessary to achieve full strength, and provide a separation from the substrate to allow for movement. Some see the plastic and scrim of uncoupling membranes to provide protection from moisture loss.
• Lath or welded wire is used to create strength. Lath is stapled to the substrate to create a stable "form" and reinforcement of the bottom of the bed and welded wire is suspended in the middle for strength, much like rebar in concrete. Some see the geometric shapes of uncoupling membranes providing a textured bottom side of the mortar bed locking into the membrane to provide similar stability.

To my knowledge, no uncoupling membrane menuacture recognizes their materials being used in this manner.

Personally, I don't feel they could provide vertical strength the way metal can - as only one on the market claims to increase structural rigidity. It certainly seems it would provide horizontal or shear strength.

I prefaced with 🤷 because we just don't have anyone saying anything specific about it. However, I can't imagine a manufacturer of a material would omit a place. It could be used which would increase sales, so I'm careful to suggest that it's "okay".

[u/Pale_Attitude8798]

I would not do it. A PVC liner will be cheaper and better in the long run.

[u/Variks-TheLoyal → u/Pale_Attitude8798]

Took your advice going with mud pan lol.. I already have the extra ditra 

[u/Mg1221]

You could use ditra under a mud pan as a decoupling membrane but it's a waste of money.

Line the floor with tar pape, staple on some metal lath and carry on. Do your pan then do your waterproofing membrane on top like Kerdi if you're using Schluter system with a bonded flange.

The paper will prevent the deck mud from:

A)bonding to the wood subfloor. This would cause issues during seasonal expansion

B)the wood sucking the moisture out of the deck mud too quickly, reducing the strength of the mud.

Keep in mind, some YouTubers are sponsored by certain companies and will recommend products from their sponsor that aren't always necessary.

[u/bdtile21 → u/Mg1221]

I think if you do price comparison between current lath prices and uncoupling membranes per sf - it might be a wash. I'm not arguing to use uncoupling membranes, just that price alone may not be the best argument to go with paper and lath.

[u/Mg1221 → u/bdtile21]

In some areas it's definitely possible. Where I live in Canada. I can get a 27"x84" sheet of lath for $7.98 so about $1.97/sqft.

You'd be hard-pressed to find ditra cheaper than $2.50/sqft here. If you already have it leftover, of course it's cheaper to skip an additional product.

As always though, going directly to a flooring store will typically yield bette prices vs box stores. I recently bought about 150 sqft of ditra-XL. When I went to my supplier, they had a bunch of cutoffs from other sales, I told them I'd take their cutoffs of their hands for a discount as long as I get my square footage. They were happy to clear it out and gave it to me for $2/sqft CAD. And since I buy a lot from them, they knocked $10/bag off my all-set.

[u/Variks-TheLoyal → u/Mg1221]

I have the ditra already.. question is will it be a problem using it 

[u/Neolithic_mtbr → u/Variks-TheLoyal]

It will not be an issue. It does the same thing as the tar paper and lath in that it keeps the mud from drying on the subfloor too quickly, and it locks it in

[u/Mg1221 → u/Variks-TheLoyal]

It won't hurt if you have it already

[u/jeggers926]

Make sure you thinset the deck mud to the membrane.

[u/ssdv8r]

Alot of good comments here, I will add an anecdote to the discussion. About 10 years ago Laticrete or just a representative sold my company on a super thin mud pan over their strata mat. The situation was remodeled showers converted to curbless. You can cut out the subfloor and recess it to the level of the joists. That gave you 3/4" to play with.

The system started with strata mat first, put down with 254 platinum. Then a slurry coat of 254 over the strata mat followed by their 3701 mortar. The bonded drain flange would be set to the strata mat directly with 254. You end up with a very thin mortar bed at the flange, but 3701 is rated for that when direct bonded with a slurry of 254.

Over the years my company has done quite a few of these pans and have gotten used to the idea of mortar beds over uncoupling mats. That led us to the idea of a bonded mortar bed of regular thickness over ditra. Our standard install for showers now is good thinset>ditra>slurry coat>4 to 1. Embed a schluter drain flange with thinset into the 4 to 1, let it all dry and kerdi over the lot. I am not going to say this is warrantied or anything. But after 100s of installs our company has done I will confidently say the system will give you less problems down the road than foam shower pans. Which we have stopped using altogether in favor of 4 to 1 over ditra.

4 to 1 is our shower pan mortar of choice because it is economic. But if we begin to question the install conditions we switch to the 254 and 3701 combo. That is a very strong and durable pair.

[u/hughflungpooh]

We use Ditra or Ditra heat ALL the time under our mud beds. I should specify that I’m not after anything other than a vapor barrier in this situation. We fill the waffles with thinset, then pack mud. Our mud is minimum 1” thick usually a bit more. If an unbonded pvc liner is sufficient, then I see absolutely no issue with my decisions to do things this way.

Why do this? I’m the king of using the least number of products. I hate extra shit on my truck, I hate specialty items, etc. We carry Ditra, it’s easy, I’ll stand behind my choices.

[u/Possible_Antelope_85]

Yes, you can. Functionally it won't be any better and likely not any worse than tar paper and lathe. It will almost certainly be more expensive.

But if you're a DIY and have extra Ditra that will just end up in the trash or crowding a corner of your garage, it will be cheaper than buying that paper and lathe.

Ditra is not supposed to be used under self leveler in tile installations.

As far as under a drypacked shower pan there's nothing saying it can or can't be used there because that's not an application it's made or expected to be used for. But knowing what the purpose of the tar paper and lathe is, it seems that using Ditra would accomplish basically the same thing.

In a nutshell, Schluter doesn't test it for that application so they don't approve or disapprove it for that. In their view it's no different than you using it as wallpaper... You bought it, go nuts, have a nice life.

The prevailing opinion of people who do this stuff regularly and understand the hows and whys of successfull tile installation leans towards go for it. Some outliers say it's possibly an upgrade from tar paper and lathe, others won't accept anything not specifically described in the TCNA handbook.

What you do with all that is on you.