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Unread 05-11-2011, 02:03 PM   #1
SDangerfield
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Wedi as Substrate for Lime-Plaster (Tadelakt finish) shower?

I am planning a bathroom remodel and will be attempting most of the finish work myself. The idea is to do the shower and the walls of the bathroom in tadelakt finish lime plaster. I've been researching various substrates and waterproofing options, including Kerdi or other membranes over concrete board and have found myself drawn toward Wedi owing to the promise of water-proofness (without the hassle and newbie-installer error-proneness of lapped membrane) and what looks to be a truly easy, user-friendly system (with the possible exception of the drain assembly.

The main question is: How appropriate is Wedi board as a substrate for the application of tadelakt, meaning (1) a scratch coat of Portland cement, followed by (2) a coat of lime plaster, followed by (2) at least two coats of tadelakt mix (lime plaster with calcium carbonate granules of varying sizes, which is compressed when still wet and treated with olive oil soap to produce a largely waterproof, yet breathable finish)?

Subsidiary questions are: (A) Would it be possible/advisable to apply the layers mentioned above directly onto the Wedi without worrying about adhesion (i.e., is there any concern that all or part of the mortar/plaster layers separating from the board and even collapsing)? (B) Would it be better to screw rib lath onto the Wedi board using the Wedi fasteners and washers and sealant method.

I think lath is by far the safest way to go, but have concerns. The major one is that the more fasteners that go through the board, of course, the more possible entry points for water and/or vapor. And fastening the lath even with the special Wedi screws and washers likely will not of course be the same as sinking the washers straight into the board. I suppose this can be mitigated by putting the sealant on the studs and squeezing out a drop where each lath-fastening screw goes in (and letting it go tacky first), but wanted to see what the smart folks here think.
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Unread 05-11-2011, 05:50 PM   #2
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Welcome, Sebastian.

Three questions:

1. What does the manufacturer of that product recommend as a backing? I'm not currently prepared to wade through that kind of website to try to find any information. If you can provide a link to their Data Sheet for the product, that might help. Just spell it out, one of our moderators will light up the link for you.

2. Who is expected to clean this shower?

3. Are you married to this person?

My opinion; worth price charged.
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Unread 05-11-2011, 06:00 PM   #3
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Interesting. http://en.wikipedia.org/wiki/Tadelakt
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Unread 05-12-2011, 12:40 AM   #4
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http://www.tierrafino.com/pdf/Tierra...tone%20TDS.pdf is a spec sheet from one manufacturer.

Did some reading from the wiki link Joe posted. Really interesting.

Based on my zero experience with Tadelakt.....My first thought is that I'd feel safest going over some good thick floated mud walls. It seems like flex, even minimal flex, would be the enemy of this type of finish.

I don't see any issues getting it to stick to anything you'd build a tile shower out of. We know that thinset sticks to Wedi/Kerdi/Hydroban/Wall Mud/CBU/Etc/Etc. If needed, you could do a "scratch coat" of thinset and then your lime plaster would key into the scratch. Just my first thoughts. I'm sure there are lots of ways to skin this cat.
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Unread 05-12-2011, 05:37 AM   #5
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Follow-up info

Many thanks for the responses and interest. It is an amazing surface that I fell in love with on my first visit to Morocco. I couldn't for the life of me figure out what it was. It has the hardness and feel of stone (duh, with full carbonation I guess that's what lime plaster becomes) but it also has a softness and lustre unlike any other surface I've encountered, even "Venetian" plaster.

Ennyways, in answer to the questions:

For the only tadelakt product I can find within the US, the advice is this: "The ideal substrate is new plaster composed of lime, a little cement and sand. It can also be applied over old substrates as long as there is no crumbling and it has been treated with a primer." I have alsoe heard that it can work over brick and mortar.

A product sheet can be found at stuccoitaliano dot com (sorry, I apparently can't post a link) scroll to "our materials" and click the drop down menu for tadelakt and then scroll to the bottom of the pages for appliacation instructions. There's a link there for the data sheet.

On cleaning, my understanding that if (and that's a big "if") the tadelakt is properly applied, treated (with the black olive oil soap -- a soap the consistency of butter or vaseline, heavy in potassium), tadelakt is fairly easy to keep clean. No solvents or caustics can be used. Just the same kind of olive soap or marseille soap. I can attest from expoeriernce that good tadelakt is quite waterproof --- it's used in tubs, basins, showers, and hammams (public baths) throughout Morocco.

If anyone has thoughts, I'd be grateful. I realize that lime plasters are not exactly the prime topic around here, but figured folks on these boards would be as likely to have good advice as anyone. (And I do plan to tile the floor, so I can at least claim that this is marginally tile-related.) Thanks again.
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Unread 05-12-2011, 05:40 AM   #6
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Product sheet

Can't link but can attach. Here tis.
Attached Files
File Type: doc tadelakt0509.doc (79.5 KB, 407 views)
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Unread 05-12-2011, 08:52 AM   #7
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Quote:
Originally Posted by Sebastian
"The ideal substrate is new plaster composed of lime, a little cement and sand....
This is what a wall would be floated with in a traditional mud shower.
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Unread 05-12-2011, 09:50 AM   #8
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That's a safety data sheet (MSDS), Sebastian, not meaningful to this discussion.

You now have enough posts to permit you to post links if you can find one.
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Unread 05-12-2011, 10:05 AM   #9
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Re Mud float underlayer

Deckert: Thanks. Indeed, a thick mud float seems to be the best bet. As you note, flex has to be prevented at all costs, else catastrophic cracks will develop. (Small hairline cracks -- like crazed ceramic -- are both inevitable and often desired -- they are repaired through gradual calcification from within).

Also, there is a bit of cross-purposes involved in the necessity for waterproofing underneath combined with the requirement that there be a thirsty and damp substrate that will help the tadelakt to dry very slowly, which is important. (For traditional Moroccan homes built with rammed earth/adobe, no worries on that front; adobe and plaster breath, and the climate is plenty dry.) Seems to me that a good deal of mud over the waterproof board/membrane -- at least 8 mm -- will fit the bill.

I keep coming back to the possibly paranoid thought that a thick -- say 8 mm or so -- undercoat of mud + the layers of tadelakt on top might prove to be a bit much for keying solely through a layer of thinset.

Maybe I'm just being paranoid, but that brings me back to wondering about having some metal lath underneath the mud. Certainly can't hurt, so long as I can maximally guard against water/vapor intrusion at the points where the fasteners necessary to secure the lath penetrate the board. (Again, maybe I'm being a bit paranoid about that, too, as Wedi seems to believe that applying sealant over screw-heads does the trick.)

How about this for two belts and suspenders? 1. Coat studs with some kind of waterproofing (mastic, synthetic sealant, what have you), so that there is something above the wood where the screws penetrate to form at least some kind of seal. 2. After insulating the voids, cover stud wall with a good barrier (Home Wrap, roofing felt perhaps), which is both glued to the studs by the waterproofing material and nailed/stapled tight to the studs. 3. Coat the stud lines over the liner with some kind of waterproofing. 4. Install Wedi boards (gluing them to the stud lines in the process b/c of the waterproofing layer). 4. Apply Wedi sealant to spots screws will go in. 5. Apply metal lath, using the Wedi stainless screws and washers. 6. Apply sealant over the fasteners. 7. Throw lots of mud.

Am I overthinking the waterproofing? (And the whole keying issue for that matter?) I live in mortal fear of water intrusion, particularly given the existing work on the house (a *small* brick 1910 row house worked on by baboons for decades; don't get me started). And, as insurance against Noob errors in installation, I want to make sure that the whole assembly is both water-tight (or as much as is possible) and super structurally solid (I plan to shore the floor joists even though it's largely redundant, given how narrow the house is -- there are no load bearng walls other than the brick; I don't mind some extra steps and expense. The tadelakt is water-resistant, but not quite waterproof. Some water will be absorbed and will eventually be released, but it's certainly possible for it to start migrating--and those fastener points seem like prime candidates.
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Unread 05-12-2011, 10:09 AM   #10
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D'oh!

CX: Sorry 'bout that. I sent before looking at it.

The Tierrfino data sheet posted upthread is far more meaningful, and their product looks very good. The Stuccoitaliano product has a bit of acrylic in it and is therefore not so traditional and chemically different -- might affect the carbonation/calcification process.
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Unread 05-12-2011, 11:13 AM   #11
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I'd want to avoid penetrations into your waterproofing membrane as much as possible. That said, a traditional shower with mud floated walls sounds like the way to go. Follow that up with your Tadelakt finish and you should be good.

Are you planning on doing this yourself or hiring out? Sounds like a fun project.
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Unread 05-12-2011, 12:23 PM   #12
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They appear to be very concerned with the stability of the backing for that product, Sebastian, and I think the very best you could likely do is a two-coat mud installation. That involves attaching roofing felt to your studs, then 2.5lb (or 3.4lb) metal lath, then a scratch coat of wall mud, then a brown coat of wall mud.

That will get you very flat, very stable walls with an acceptable water containment for whatever aesthetic coating you wanna apply. Your plaster coat should go onto that quite easily and stick very well.

The tadelakt coating sounds like something you might wanna practice a little with before you commit to doing your entire shower. Don't think a fella's likely to get it exactly right on his first pass, but maybe I just lack sufficient talent.

My opinion; worth price charged.
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Unread 05-12-2011, 12:53 PM   #13
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Smile Thanks for the advice!

CX and JGleason: Many thanks for the help. Stability is definitely the key.

I am planning on -- more or less -- doing this myself. I'd love to find someone who's good with mud/plaster to do it with (probably causing them to charge more on the "double if you watch, triple if you help" principle of labor rates!) but I'd definitely like to have my hand in it. I'm also planning on doing quite a bit of practice first. In fact, I'm on my way to Morocco, where i'll be taking a short course in the method. If anyone here is in the mid-Atlantic area and is interested, I'd certainly consider hiring on some help, since i doubt I'll be able to bring a Moroccan maalem (master) back with me.

Any other thoughts would be welcome. And once I get this thing off the ground -- it will be a while, have to gut my little cave out first -- I'd be glad to post on the project and all tribulations involved.

BTW This is a wonderful forum. Thanks to all who put it together and maintain it. The archive is a trove of wisdom.
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Unread 05-18-2011, 05:33 PM   #14
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Kerdi board

Have had good track record with couple dozen Tadelakt installs our customers have done using Wedi over past 3-4 years. Just attended a one-day Schluter seminar and am now thinking the Kerdi Board system is what we will be recommending for subsequent installs of our Tadelakt material. Was impressed with most aspects of their system including the joint fabric because cracking of joints is what worries me most on these type of installs.

We may try working with the Schluter people in the future to help create a spec for these types of wet area lime plaster installs. For early adapters right now, but I think this will be getting more popular in the future.

I'm no tile guy so take my advice with the proper amount of skepticism, please.
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Unread 05-25-2011, 08:05 PM   #15
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Tadelakt, Wedi, Kerdi, lath?

Hi,
Took a tadelakt workshop using the limes.us products, Saint Astier NHL. Great fun, beautiful finishes achieved by all in the workshop, including 3 generation pros and first time plasterers.

Your suggestion of two coats of wall mud for a stable firm base. What about two coats of wall mud over wedi or kerdi for the ultimate h20 proof? Will the mud, portland or lime, stick to the wedi/kerdi board? Or will it need lath?

Thanks
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