Ceramic Tile Advice Forums - John Bridge Ceramic Tile

Welcome to John Bridge / Tile Your World, the friendliest DIY Forum on the Internet


Advertiser Directory
JohnBridge.com Home
Buy John Bridge's Books

Go Back   Ceramic Tile Advice Forums - John Bridge Ceramic Tile > Tile & Stone Forums > Tile Forum/Advice Board

Sponsors


Reply
Thread Tools Search this Thread
Unread 12-04-2022, 08:50 PM   #1
Tiledadd
Registered User
 
Join Date: Dec 2022
Location: Hudson Valley, New York
Posts: 6
wood fired sauna subfloor advice for slate tile

I am mid-build on an outdoor Wood-fired Sauna. The structure is about the 8X12 with two rooms. Approx 8X8 hot room and 4X8 Changing room. I'll be tiling all the interior spaces with 12X24 slate. The floor underlayment is 3/4" pressure treated plywood and I have laid hardibacker and fixed it with the hardibacker screws at 8" increments. I did not use mortar for this step at the advice of a friend.

The hot room has a drain in the floor. My goal is to make a waterproof floor so any water that is spilled on the floor or any condensation in the walls will end up in the drain rather than in the studs. Ill also have a vapor barrier in the wall between the cedar and studs.

To make the floor waterproof my current plan is to use Kerdi Band to tape the hardibacker seams using thinset mortar. And use Kerdi corners and kerdi band up the edges (about 2.5") onto the wall studs. Then use one or more coats of Aqua Defense on the hardi backer.

The issue is that with added costs of - kerdiband, aqua defesne and kerdi corners, are easily approaching the cost of using Ditra on top of the hardibacker
I suppose I can use a less expensive tape on the seams of the hardibacker than Schluter brand.

At this point I am thinking of returning the kerdi band and bucket of aqua defense and just using Ditra which will be truly waterproof and may offer some defense against cracked tile with the wild swings of temperature from below freezing to 150 degrees F regularly through the winter. We are in New York State.

Is there any argument to stick with the original plan? Hardibacker plus aqua defense? Or would the Ditra on top of Hardibacker be a better choice for this hot and cold room?

If I use Ditra on top of Hardibacker should i use the uncoupling membrane mortar on the layer between the hardibacker and the Ditra? Can i use unmodified thinset on top of the Ditra? Or is the uncoupling mortar meant for below and above the Ditra?
__________________
Jonas
Tiledadd is offline   Reply With Quote
Sponsored Links
Unread 12-04-2022, 09:29 PM   #2
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 96,417
Welcome, Jonas.

If you don't add a geographic location to your User Profile, the information will be lost before we leave this page.

Without knowing your joist structure, it's not possible to help determine whether it is suitable for a natural stone installation. The industry requires the joist structure meet L/720 deflection criteria for natural stone, twice as rigid as the requirement for ceramic tile.

I wish you had not used the pressure treated plywood for your first layer of subflooring. It will do more shrinking than you want for your purposes. And the tile industry requires two layers of plywood subflooring, each properly and differently installed, for a natural stone tile installation.

Quote:
Originally Posted by Jonas
I have laid hardibacker and fixed it with the hardibacker screws at 8" increments. I did not use mortar for this step at the advice of a friend.
He may be your friend sometimes, but this was not one of those times. The CBU manufacturer requires the panels be bedded in a layer of thinset mortar before being fastened with mechanical fasteners. The manufacturer also requires that the joints be taped with alkali-resistant mesh tape and filled with thinset mortar before tiling.

But not having use the mortar will make it easier to remove the the Hardiebacker to install your second layer of plywood. Maybe he was your friend after all.

I'm not real familiar with Yankee saunas, but it sounds like you intend to treat this as a wet area. Do you plan to slope the floor to the drain you spoke of? And not only a wet area, but more like a steam shower, in which case you'll really want a vapor barrier membrane on the walls and ceiling.

Let's start with that and you can give us more information.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is online now   Reply With Quote
Unread 12-04-2022, 10:16 PM   #3
Tiledadd
Registered User
 
Join Date: Dec 2022
Location: Hudson Valley, New York
Posts: 6
Thank you in advance.

The base of the building is made up of 2x6s. On the perimeter the 2X6s are doubled up. The joists, are 2X6s nailed on hangers, 16" apart. The base of the structure has a "bottom" to keep critters out of 1/2 plywood, taped and caulked. Then and on top of thus base is a 3/4" subfloor, tongue and groove plywood.

It all sits on a pad of 6" of 3/4 stone between a larger frame of 4X4s.

Yes we're treating the room like a wet area. No, we wont be sloping to the drain to simplify the structure and theres not as much water as a shower. The occasionall spray down and we can squeegee to the drain.

We'll be using a foil vapor barrier popular in saunas, so from inside out it goes cedar tongue and groove, foil vapor barrier, studs with rockwool insulation, then 3/8 plywood, housewrap, then metal siding.
__________________
Jonas

Last edited by Tiledadd; 12-04-2022 at 11:27 PM. Reason: more about vapor barrier and drain
Tiledadd is offline   Reply With Quote
Unread 12-04-2022, 10:19 PM   #4
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 96,417
Without knowing the species and unsupported span of the joists were still not able to begin the evaluation of the structure, Jonas.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is online now   Reply With Quote
Unread 12-05-2022, 08:23 AM   #5
Tiledadd
Registered User
 
Join Date: Dec 2022
Location: Hudson Valley, New York
Posts: 6
images to show joist structure

see attached for images -

We may end up returning the stone and using ceramic or porcelain if our base is not stiff enough.
Attached Images
File Type: pdf Joist structure.pdf (1.26 MB, 22 views)
__________________
Jonas
Tiledadd is offline   Reply With Quote
Unread 12-05-2022, 08:41 AM   #6
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 96,417
With no foundation, I suspect you'll experience a good deal of twisting in that floor over time, Jonas. Not a good thing for a tile installation.

You still haven't answered the question about species and grade and such for your joist lumber. It appears in your photos that the unsupported span is about nine feet. You'll be borderline if you meet the required L/360 deflection at all.

A bigger problem still is the incorrect orientation of your plywood subflooring. Those panels needed to be oriented perpendicular to the joists. As it is, you'll really need a second layer of subflooring, oriented in the proper direction, even for a ceramic tile installation.

If you plan to use a waterproofing membrane, such as the Ditra you mentioned, there is no need for the CBU at all. You bond the membrane directly to the plywood subfloor. That's usually sufficient for an interior application, and it appears you'll be fully enclosed.

I think changing to a ceramic tile in lieu of the natural stone is a good idea, but I suspect you're looking at some potential problems even at that.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is online now   Reply With Quote
Unread 12-05-2022, 09:29 AM   #7
Tiledadd
Registered User
 
Join Date: Dec 2022
Location: Hudson Valley, New York
Posts: 6
For the species of wood for 2X6 it was souther yellow pine, pressure treated. Premium grade. The building 8' 8"wide. The joists are 8' long.

Considering the stone pad is there any type tile floor that would be more forgiving over time? Would the ditra membrane be more forgiving?
__________________
Jonas

Last edited by Tiledadd; 12-05-2022 at 09:35 AM. Reason: added grade and span
Tiledadd is offline   Reply With Quote
Unread 12-05-2022, 12:22 PM   #8
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 96,417
Quote:
Originally Posted by Jonas
Considering the stone pad is there any type tile floor that would be more forgiving over time?
The only thing I could suggest is that a porcelain tile will be a bit more resistant to cracking than other ceramic types.
Quote:
Originally Posted by Jonas
Would the ditra membrane be more forgiving?
Difficult to say. Problem there is that there is no tile industry standard for uncoupling membranes. Never has been. The difficulty there is that no one has yet come up with a test to verify just what this "uncoupling" actually does. All we have is the manufacturers advertising claims to go by. In your particular application, I can't say that a CBU, properly installed, won't give you more protection from the type of movement I foresee. Just don't know.

I can say your pressure treated framing and pressure treated and incorrectly installed plywood subfloor are prone to introducing some shrinkage, warping, and deflection issues. The presence of the plywood on the bottom of the joists is certainly in your favor as far as resisting the overall twisting of the structure, but I'm not engineer enough to say just how much of an advantage that will be.

I'm sure a number of us will be watching for a report a few years down the road.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!

Last edited by cx; 12-05-2022 at 12:29 PM. Reason: typo
cx is online now   Reply With Quote
Unread 12-06-2022, 08:52 AM   #9
Tiledadd
Registered User
 
Join Date: Dec 2022
Location: Hudson Valley, New York
Posts: 6
Appreciate all your advice. Will return the slate and get a porcelain tile that designed for heavy traffic. my original question was about creating a water barrier underneath the tile do you have any recommendations for this? Is there a membrane that works better than Aquadefense painted on hardibacker? To keep water from getting into the wood below? My guess is any water freezing in the joists would encourage twisting. My current plan is to use ditra but a thinner membrane is preferred. And if the uncoupling claims are questionable I’d prefer to not have the added height.
__________________
Jonas
Tiledadd is offline   Reply With Quote
Unread 12-06-2022, 09:15 AM   #10
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 96,417
Quote:
Originally Posted by Jonas
And if the uncoupling claims are questionable I’d prefer to not have the added height.
Well, the claims are currently not supported by any known testing, Jonas, that's what I was pointing out.

As for height, the Ditra is thinner than the CBU you initially proposed. And there are sheet waterproofing membranes that are thinner than the Ditra. The liquid-applied waterproofing membrane you proposed is thinner even than the sheet-type membranes, but it cannot be applied to the plywood directly. In that application you'd definitely need the CBU.

I'm a bit confused by the whole waterproofing concept. Perhaps that's because I've seen a total of one sauna in my whole life and that was more than 40 years ago. I thought they were always made of wood, usually a cedar or similar, and no attempt was made to make them either waterproof or vaporproof. So, I think you're building something with which I'm not at all familiar. I can only advise on the tile installation and the waterproofing associated with a tile installation.

If what you're building is to be closer to a steam shower, we need to back up a bit and make some different plans, I think.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is online now   Reply With Quote
Unread 12-06-2022, 11:46 AM   #11
Tiledadd
Registered User
 
Join Date: Dec 2022
Location: Hudson Valley, New York
Posts: 6
There are many ways to make the floor to a sauna. Depends on budget and aesthetics. These are the most popular:

- wooden floors with gaps between the floorboards. Can see the ground beneath the floor. Provides very good ventilation but has poor insulation. No need for drain.
- insulated floor with poured cement floor and usually has a drain in floor
- tile floor with drain in the floor.

We're choosing the third for aesthetics and ease of maintaining. Wed like to spray it down once in a while and have a drain in the floor.

There is water and moisture in a sauna but not nearly as much as a shower.

The steam you make in a wood fired sauna (by pouring water on hot rocks) creates condensation on surfaces etc and theres a bucket of water in there. It could spill. You spray it down every once in awhile with a hose to clean it.

So a drain in the floor is advantageous. Tile is advantageous.

The walls are cedar with foil vapor barrier between the cedar and the studs.
so I am trying to make the floor waterproof and the vapor barrier on the walls meet a moisture barrier under the tile.

If the aqua defense on CBU is a good method ill stick with that. My concern is the cost of taping all the seams and edges with kerdiband (need 80 feet for all the seams and edges, plus the pre-made corners?) and painting it with Aqua Defense

to me it seems larger sheets of waterproofing membrane might be more waterproof and easier to apply?

I think treating this as a steam shower is a good benchmark for waterproofness but it wouldn't suffer the heavy rain of a shower system pouring into the room.
__________________
Jonas
Tiledadd is offline   Reply With Quote
Unread 12-12-2022, 10:25 AM   #12
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 96,417
Quote:
Originally Posted by Jonas
If the aqua defense on CBU is a good method ill stick with that. My concern is the cost of taping all the seams and edges with kerdiband (need 80 feet for all the seams and edges, plus the pre-made corners?) and painting it with Aqua Defense
Problem I see there is that you have nothing to which to bond any membrane on the walls, Jonas. Using KerdiBand doesn't make any sense to me if you're waterproofing with Hydroban liquid. Use of a reinforcing fabric with the Hydroban would make sense, but, again, only if you've got a CBU going up the walls to which to bond the fabric and membrane, and it sounds like you don't plan to have any such.

The extra problem with steam showers is not the shower part, it's the steam/water vapor part that is more difficult to contain. Same would be true in your application as you describe it. Are your walls to be insulated at all?

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is online now   Reply With Quote
Reply

Stonetooling.com   Tile-Assn.com   National Gypsum Permabase


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Tile on wood subfloor norskemann1 Tile Forum/Advice Board 2 10-06-2022 12:49 PM
Just fired my tile installers, need further advice lutus8 Tile Forum/Advice Board 17 02-04-2015 12:28 PM
Slate tile over wood subfloor bobandsandi Tile Forum/Advice Board 7 08-18-2012 07:06 PM
Newbie here in MO. I need WFO (wood fired oven) help! Faith Tile Forum/Advice Board 6 10-08-2011 09:34 AM
Raku fired tile TwoSisters Tile Forum/Advice Board 3 07-17-2005 06:03 PM


All times are GMT -6. The time now is 11:38 AM.


Sponsors

Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2023, Jelsoft Enterprises Ltd.
Copyright 2018 John Bridge & Associates, LLC