Latex-modified thinset for shower bed
FHB has a real interesting article on building a leakproof shower pan. Aug/Sept. 2001.
http://www.taunton.com/finehomebuilding/how-to/articles/installing-a-leakproof-shower-pan.aspx?ac=fp
In the article Tom Meehan likes to pitch the shower floor before he puts the membrane material down. So the first thing he does is “to bond the mud layer to the plywood subfloor, I first apply a thin layer of latex-modified thinset to the subfloor. The mud mix is spread on top of the thinset, leaving a pitch of 1/4″ per ft. from the outside perimeter to the drain.”
My question is: how thick is this thinset layer? And do I let the thinset set up at all before I add the mud layer? And thirdly isn’t there a mortar that will bond to the subfloor and create the sloped mud bed instead of using two different products?
Replies
I'm not sure what the point is of adhereing the mortar pre-slope to the underlayment via thinset. The thinset is acting as a primer. It will adhere to the plywood and the mortar will adhere to the thinset.
The pre-slope mortar is effectively trapped between the wall bottom plates and the bottom of the vinyl liner that has a couple of hundred pounds of mortar and tile in it. I don't see where a mortar pre-slope is going to move to under those conditions.
Thinset has a limitation on it's applicable thickness...somewhere around 1/4". That would pretty much rule it out as a preslope material.
Tim does a few kooky things..just my opinion. May be a regional deifference thing too.
Eric
[email protected]
Greetings mlawrence,
This interesting subject deserves more attention,
so by placing this post, in response to your question, the thread will be 'bumped' through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
Peace out.
like Eric ... I disagree with the guy from time to time.
anyways ... I start by putting a layer of felt paper down over the ply.
then my drypack preslope starts on top of that.
helps keep the ply from suching the little bit of moisture outta the drypack and in my mind helps for a better cure.
I also think it helps as an isolation membrane between the two different materials.
Toms way of bonding would seem to add cracking and breakdown of the mudbed.
Jeff
Buck Construction
Artistry In Carpentry
Pittsburgh Pa
I'm with Jeff on this. Sorta. I like the system described by Kerdi: Plastic or felt, stapled down with diamond mesh on top, then mud. But if you use Kerdi, there's only one slope anyway. Like this:
View Image
But, I don't think Kerdi was around in 2001 so, with the advent of Kerdi, the article is officially "antique". ;-)
If I was doing what you plan, I'd just thinset like I was going to do tile, spreading it with a 1/4" notched trowel. I'd let it set up and then do the preslope. The notches in the thinset would key the preslope into place.
That said, unless you're doing an open plan shower, I don't see much need to bond the shower floor to the ply -- it can't go anywhere since its a 400 lb weight sitting in a walled-in enclosure.
Bottom line: use Kerdi and don't worry about a preslope, bonding to the ply, etc.
Mike Hennessy
Pittsburgh, PA
I tried to understand the kerdi system and the websites don't answer the basic question for me.Would you mind explaining each step briefly?I don't understand or agree with the thinset slope idea either. Bob's next test date: 12/10/07
Kerdi is different than the standard install. With a standard install, you build a mud preslope, then put a liner on that directs water to the weep holes in the drain unit. (This is needed because tile/mud is not really waterproof, and some moisture gets through. The liner catches it and directs it to the drain weepholes.) You put your base and tile on top of that.
With Kerdi, the Kerdi -- a completly waterproof membrane -- is applied with unmodified thinset on top of the mud and walls, directly under the tile. It has a "fuzzy" surface that allows thinset to stick to it so it can be bonded to the substrate and the tile. With Kerdi, no moisture gets beyond it to the deck or the backer. In fact, Schluter recommends just using drywall for the walls since it's protected from moisture by the Kerdi.
A Kerdi drain is more like a standard floor drain (as opposed to a shower drain) -- it doesn't have (or need) weepholes. It does have a flange that is "fuzzy" similar to the Kerdi, so the Kerdi can be bonded to it for a waterproof installation.
So, with Kerdi, you don't build a preslope -- you just build a sloped shower floor. Or, alternatively, you can use a pre-made pan from Schluter -- it's on their site.
The Kerdi site also has some nice videos. Check them out if you haven't yet.
If you want to look into the Kerdi system more, Mongo posted a nice sequence here a few months ago on doing a Kerdi shower -- look it up with the search function. You can also go to the John Bridge tile forum. There's a ton of Kerdi info there.
It's nice stuff -- you should consider using it.
Give a holler if I haven't answered your Qs.
Mike HennessyPittsburgh, PA
Here's the Mongo Kerdi Shower link: http://forums.taunton.com/tp-breaktime/messages?msg=86714.1
Edited 1/9/2008 10:34 am ET by MikeHennessy
I think you answered it. The key bit of knowledge was that tile is installed directly to the fuzzy side of the product. How much extra cost does Kerdi add? In the traditional, the waterproofing membrane is run only on the bottom floor. I get the feeling that Kerdi will double or triple the costs compared to a traditional dry pack. Incidently, I've never seen anyone install the membrane over a sloped bed. Instead, the membrane is laid on the level subfloor. The drypacked mudbase is installed over the membrane and sloped to the drain. That's how I've done it but I'm no expert. I know a little bit about framing though. Bob's next test date: 12/10/07
Actually, both sides of the Kerdi are "fuzzy". One side to bond to the substrate, and the other to bond to the tile.
"How much extra cost does Kerdi add?"
Hard to say. Depends on how much you charge per hour for your labor. Overall, I think it's a bit quicker than traditional, so "cost" may be less, but YMMV. TileProtection.com has an all-included kit for a 30" X 60" shower for aroung $400. (The Kerdi costs more, but you don't need cement board for the walls or mud for the floor or a seperate drain since one is in the kit.) So that's what, maybe $200 more than standard for materials?
IIRC, the Mongo thread addresses this Q as well, but it may have been some other thread.
IMHO, the minimal extra cost is more than offset by the results.
Mike HennessyPittsburgh, PA
You probably told everyone but what does your date on the bottom mean?(Bobs next test date)?
Hey on tile I think the reason to pre slope is to keep from raising bugs.
Bob and I have trouble communicating in the same language. We occasionally give each other a test to see if we are on the same wavelength. Lately, we seem to be somewhat. Are you saying that there are bugs growing in every shower pan not sloped? If so, I know of ten million pest control jobs in MI. I've never heard of anyone having a bug problem. I think your point is that the water that filters down into the shower pan doesn't run. I'm not familiar with how much water seeps through but I would assume that it would evaporate if it didn't run. Perhaps shower pans installed over concrete slabs are different. I've never done one in a basement. Bob's next test date: 12/10/07
"Are you saying that there are bugs growing in every shower pan not sloped?"
yes ... at least every one that I've torn out.
which is quite a few.
bugs, mold, mildew and just plain years of stink ... usually black slimey stink at that.
old tech was lay the lead or copper pan flat on the subfloor ...
new tech is preslope ... may membrane ... then mudbed and tile.
in this case ... new tech is gooder.
helpes the water that made it's way to the waterproofing find the weepholes in the drain.
not much more work ... slightly more plumber bitching ... better end result.
even newer tech is the Kerdi ... I haven't done one yet ... but plan to.
looks to be the way of the future.
Mongo did his Kerdi over cement backer ... not sure how comfy I'll be ...
but seems the whole point is less labor ... which drywall would be ...
so pretty sure when I go and do one ... I'll trust them.
famous last words ...
Jeff Buck Construction
Artistry In Carpentry
Pittsburgh Pa
I'll take your experienced words for it. I'll look for them if I ever tear one out. How come the bugs never go anywhere outside of the shower pan? I never saw any hanging around my last one. Bob's next test date: 12/10/07
they have set up home in the wet and mold....
most of the bugs ya find are lunching on the mold...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
"I never saw any hanging around my last one."
You'd need a microscope!
in lieu of a microscope ... I use my nose.
and those flat old pans stink!
Jeff Buck Construction
Artistry In Carpentry
Pittsburgh Pa
Jeff, Without a doubt, go with Kerdi over drywall. No worries. Mongo
I'm kinda thinking like a swimming pool that never gets cleaned, lot's of good stuff to munch on if your hungery or wanting to start a 1918 pandemic.
I know I pulled up some pretty nasty old shower pans/culture generators.
"Mycotoxins. Some molds are capable of producing mycotoxins, natural organic
compounds that are capable of initiating a toxic response in vertebrates.21 Molds known
to potentially produce mycotoxins and which have been isolated in infestations causing
adverse health effects include certain species of Acremonium, Alternaria, Aspergillus"
Hmmm don't know if it killed any of the past residents. Actually not all that pleasent when remembering it. How come I can remeber that and can't find the pencil I just had.
Maybe I'm not too worried because my wife and I are regular bleachers. The bleach and water solutions must penetrate the pores and soak down into the bug zone. Do you think a weekly dose of bleach will kill these pests?I've heard that there are critters living everywhere...on our skin, in our eyes, mouths, etc. Bob's next test date: 12/10/07
I was just sayin but since I'm sayin on this issue another great piece of work on some tile and kerdi is the small addition listed in photo Gallery. If you haven't followed it the tile stuff is around the ? 200s http://forums.taunton.com/tp-breaktime/messages?msg=99042.17&redirCnt=1
As for the bleach? I'm just a grunt DA but I do know how to work the goggle.
Plus I followed some of your old threads, and kinda view you kinda as a transformer god.
A carpenter shows up to the job site(you) and next thing you know he transforms into the cellulose comping circular saw with no base that zooms around creating huge piles of sawdust. When you can finally see through the settling dust ? a house appears.
I don't know what got into me but I couldn't put down this book on bugs and what appeared to me the transition to modern medical practice.
The Great Influenza:
I'm not following your last post too good. I'm kind of thrust into the arena where I need to start looking into products like Kerdi....so I'm interested. I'm also trying to understand the "problem". When they talk about bugs....I'm thinking silverfish, centipededes etc. Lets say I accept the premise that a sloped mortar bed is better. I still could create the slope, put the old fashioned membrane down, then remud. That creates a two day installation...or does it? Remember, I'm still a fan of the dry pack because I think it fast, easy and cheap. The thinset crowd mixes a bucket of thinset and lays cement board (or not). I mix a bucket of drypack and toss it in and smooth it to a shallow slope. I just don't see the need for cement board or thinset. I do accept the premise that the membrane needs sloping.From a microscopic view, this topic intrigues me because I'm a germaphobe. Bob's next test date: 12/10/07
Jim,The "bugs" are microorganisms, not insects. I agree with Buck, the old flat-bottomed mudbeds are nasty. Ones with a preslope are less nasty, but still stinky. Kerdi jobs should be dry, but I've never torn one out.Bleach is unlikely to kill all the foul stuff in a shower floor mudbed, unless you block the drain and the weeps and flood the thing, submerging it for a whole day. That would be hard on the other components, too. Bleach is corrosive to metals.Kerdi is the way to go, IMO.Bill
I'm on my 10th Kerdi shower, and I have nothing but positive input.
From a cost perspective, I would assert that, since the kerdi system eliminates a couple of steps in the construction (backerboard and a mudset over a PVC liner) that the labor savings makes it a wash.
The Schleuter drain system is terrific.
And the piece of mind is priceless.
One of my friends did a kerdi shower, but used the TEC product (similar to RedGard) to waterproof the walls. I don't know that he saved any money, but it is an alternative worth considering.
I did one with kerdi over drypack on the floor, and GP Denshield tile backer on the walls & ceiling. It was in my own house and, since I have had good experience with the Denshield over the years for walls, I wanted to try this hybrid as an experiment. So far, it's worked out OK. Saved a bit of time and $$, but it hasn't been in long enough for me to recommend it to anyone else.
View Image
Mike HennessyPittsburgh, PA
To be honest, I haven't done one with any kind of gypsum board, but all of mine have either been native stone or slate and, IMO, needed a heavier wall base.
Nevertheless, I would feel comfortable with the Densheild for most tile products.
I always hated dealing with the PVC liners and fiddling around with the framing to compensate for folded PVC trying to get nice crisp corners for the tile base. Or on larger showers, hoping all the glue joints were good.
The kerdi pretty much eliminated that hassle.
The first one I did left me with a sense of confidence in the waterproofing and the tile bonding.
"Nevertheless, I would feel comfortable with the Densheild for most tile products."
Yeah, I like the stuff. It's one of those products that generate a lot of "great product/junk product" arguments. My take is that those who think it's junk haven't tried it, and trash talk it simply because they aren't convinced that a gyp product can be used successfully in a shower.
But I've used it for years as tile backer -- some salesman talked me into trying it when it first came out -- and it's been great. It's the same concept as Kerdi -- it has a totally waterproof membrane on it's surface that thinset will stick to. So moisture never gets any deeper than the thinset and you don't have to worry about what's going on behind the backer. That's why I wanted to try the hybrid install -- the products seem to compliment each other.
As for a heaver base, it don't come much heavier than a 4'X8' sheet of 5/8" Denshield. Umgfh! ;-)
Crisp corners are a bit of a challenge with Kerdi as well, but not nearly as bad as with PVC liner, since Kerdi is thinner.
Mike HennessyPittsburgh, PA
I use the pre-formed kerdi corners, which work for a range of angles and eliminate folding except where the kerdi sheet is turned up the wall.
I'm soon to build another shower for myself, and may try the densheild.
I used it for tile backer and in a pump room on a house a build several years ago. It's held up well, but my memory of it was the unanticipated fiberglass itch I got from cutting it. :-)
"but my memory of it was the unanticipated fiberglass itch I got from cutting it."
Oh, yeah.
Just like the other paperless gypsum products, but maybe a bit worser. ;-(
Mike HennessyPittsburgh, PA
So...I was back in the shower today thinking about the base again. Again, I was thankful for the fiberglass and the lack of bugs.....Anyways, I got to thinking that I could frame a sloped osb pan in about ten minutes in any shower that I've ever built. Would this be a good base for kerdi? Bob's next test date: 12/10/07
I would think so, although I usually use treated plywood....which is overkill, but the treated ply I get here is all good Doug Fir and I usually get AC for a smooth surface.
Whatever you use, I think you will discover. like others and I have found, that the kerdi is really a good waterproofing material. If it's recommended to put over drywall, I'm sure OSB would be fine.
In reality, if your shower is to be within a certain range of sizes, you can get presloped pans from Schleuter and others that are actually styrofoam. I've only used one of those, and, while they have a good track record as far as I know, I really prefer a mud base over the plywood to lay the kerdi on.
Blue,
You don't want to adhere Kerdi to plywood or OSB on a shower floor. You can frame the floor flat, then do a drypack preslope, then Kerdi right over the preslope and tile over the Kerdi.
Here's Kerdi thread. Should be enough there to put you to sleep.
Mongo
I've worked with Denshield, but I didn't even notice the fiberglass. After all, it only comes in 3X5 sheets (that I know of) so it's easy to handle and one side is the moisture barrier. Maybe I was working in cooler weather and was wearing long sleeves, I don't remember.
3X5 is how I originally got the stuff. Now, I can only get it in 4X8.
Mike HennessyPittsburgh, PA
One of the selling points of the kerdi system is that water only penetrates just below the tile and stops at the membrane. This allows the shower to dry out faster which should largely prevent the growth of mold and nasties. A CBU or floated mud wall shower can get wet all the way through to the vapor barrier and take a long time to dry, giving stuff a chance to grow. I've done a few showers using regular drywall and/or densarmour. Used CBU on the fixture wall. If there is going a leak, that's where it will be - coming from the valve body area.
On the crazy circular saw ? I was thinking you used to be Blue ? If not that's why it doesn't make sense. My bad but I though I saw a note at one point on some of your posts?
On to the shower pan, again there are many way more expert then me. I think the theory is the standing water.Depending on the frequency of use leads to the accumulation.
The time involved to slope is going to be extra no mater what. But depending on your material you can still use dry pack on top of the sloped membrane.
As far as bugs go there's big ones and there's little ones. The little ones are the killers or less if your lucky. Bactria and fungi. Not really bugs, see told you I don't know squat.
I am blue.I had a new found appreciation for the fiberglass shower pan I was standing in tonite when I showered. I'm going to investigate this kerdi stuff in the flesh. Bob's next test date: 12/10/07
"I had a new found appreciation for the fiberglass shower pan I was standing in tonite when I showered.
I'm going to investigate this kerdi stuff in the flesh."
uh ... put yer clothes on first.
Jeff Buck Construction
Artistry In Carpentry
Pittsburgh Pa
Well Ya I was referring to you cutting off /modifying the base of your saw and using it as a Multi tool. Just funnin. But kinda thinking after being forced to watch some movie ? transformer or something.http://www.transformersmovie.com
Well it was kinda like being forced after about 20 minutes.
The membrane HAS to be sloped.
No exceptions.
It's code, and these days it's not just a code violation, it's an invitation to a lawsuit.
Mongo