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Old 02-23-2015, 11:12 AM   #1
tubber
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Tiling a wooden hot tub?

I have an old wooden hot tub that I wish to line with a waterproof membrane and then tile the entire tub. It is 6' diameter and 4' deep.

I have been reading the mds on various waterproofing membrane/tile systems but I have yet to find one that specifically says it can take a submerged application.

Am I nuts to even attempt this? Don't answer that. I just want the tile to stick.

OK, I'm ready for the stones to be hurled.
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Old 02-23-2015, 11:28 AM   #2
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Welcome, tubber. Please change that permanent signature line to a first name for us to use.

Particularly bad idea in my view, but it's your tub, eh?

The problem is not with the waterproofing membrane being permanently submerged in water, it's the waterproofing membrane being attached, or not attached as it were, to your wood hot tub. No manufacturer of such membranes will approve their being installed directly onto dimension wood even in a dry environment.

But I understand the desire to change from all the problems of maintaining a wood tub to the different-but-equal problems of maintaining a ceramic tiled tub.

My opinion; worth price charged.
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Old 02-23-2015, 11:58 AM   #3
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Thank you for the words of wisdom, CX.

I was afraid of that. The tub is too far gone to fix traditionally with new wood, and I kept getting the sense that something like Ditra would adhere to the wood wall of the tub with the right adhesive, even though they do not recommend submerged applications.

I was willing to experiment however, assuming I found a way to adhere Ditra to a wood substrate.

I understand the risks, but I have a useless tub, and several tons of tile begging to be used.

So, having proved I'm not willing to listen to advice, and totally willing to go outside the box, do you have any suggestions on an adhesive for the Ditra/wood interface?.

And, assuming I was successful in getting the Ditra on the wall and floor, would I still use a non-modified thinset under water?

Sig changed, I hope.
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Old 02-23-2015, 12:29 PM   #4
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You would not use Ditra in any case, Tom, that's not what it's for. Same manufacturer makes Kerdi, which is a direct bonded waterproofing membrane, but I don't know that they recommend it for continuous submerged applications. I do know they do not recommend it for bonding to wood of any kind. You would want to use a thinset mortar recommended by its manufacturer for submerged applications. Not all are.

If the shape of your tub is such that a sheet membrane is feasible, you might wanna contact the Noble Company to see if they might allow such an application with one of their proprietary bonding pookies. You're not gonna get a warranty or a written recommendation, but they might tell you it's likely to work. Or not.

You could also contact the manufacturers of liquid applied membranes to see if any of them will discuss the application with a straight face. You can click on the ads to the side of this page to find some of'em. I think it unlikely, but you never know 'till you axe, eh?

My opinion; worth price charged.
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Old 02-23-2015, 01:58 PM   #5
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I wonder if Kerdi-board might work in this rather unique situation?

I've read the literature and it doesn't say anything about constant submersion into water but bonding it to wood...well, that works fine as it is meant to be bound to stud walls. The wood watertub is a cat of a different skin but it is still wood.

I might call Schluter and talk directly to them...see what they think.
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Old 02-23-2015, 02:38 PM   #6
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I think it's a bad idea but if I were forced to try it, I would use a paint on membrane. Hydroban is made for fountains, etc so I think it would be water tight but I feel the wood tub is going to flex too much behind the membrane when all the weight from the water gets in there.
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Old 02-23-2015, 02:54 PM   #7
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Thank you CX and CPAD007!,

I made some phone calls to Schluter and Noble, and had some frank discussions that were insightful. The issue any of the manufacturers have is application over dimensional lumber and bonding failure to that particular type of substrate. Fair enough, we knew that.

So the biggest impediment is anchoring to the tub wood (1-1/2"X 6" redwood slats, 30 years old at least).

As a base, I intend to use Mapelastic 315 floated over a fiberglass mesh that I will secure at every 12" node with short roofing nails.

Attach Kerdi over that.

4" tile over that using non-modifed thinset with a liquid polymer added.

Cement grout to finish.

All criticisms welcome! The Schluter rep and others thought that this approach had the best chance of succeeding.
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Old 02-23-2015, 03:01 PM   #8
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Hi Davy,

Thanks for the feedback. I'm thinking that a liquid membrane just would not hold up for the reason you mention and a fixed cementitous backing would be more appropriate. Maybe? I dunno for sure and that is why I am here. It is an unusual application and problem. You guys are great!

The tub has 5 iron bands encircling it to help keep it from expanding outward. I'm located in the desert so I don't expect swelling from outside influences to be of importance. If the very old wood does move, it ain't moving much, I reckon. ??
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Old 02-23-2015, 03:25 PM   #9
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Solid wood moves. It doesn't matter if it was cut yesterday or at the turn of the last century.

How much it moves depends on the species. You can look up tables for wood movement and see what you get for good old California Redwood. But the point is, it moves depending upon environmental conditions: Dry winters and it'll shrink and wet summers and it'll expand. Kind of like the door that gets stuck in the summer and moves fine in the winter (or vice versa) or 'that one drawer' on the dresser.
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Old 02-23-2015, 03:31 PM   #10
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As to your cement grout, I think I'd look into something with a bit more flex and perhaps a bit more impervious to staining and such.

Check out urethane grout. Bostik TruColor is one of them. They claim stain resistance, no color fading, and have a bit of flexibility to them. They are also freakin' expensive!!
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Old 02-23-2015, 03:42 PM   #11
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Yes, I've seen the iron straps that go around the tub. Apparently the wood swells and keeps the tub from leaking.

You can experiment and see. Keep in mind that when we tile something, we have to make sure it's going to work or we will get a call back. So we can't do much experimenting. If I were to do it, I would want concrete formed and poured so I could tile it.
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Old 02-23-2015, 03:43 PM   #12
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I think Chris might be onto something here. I would probably attach KerdiBoard with screws & clips. Probably 1/2" with the back scored to let it "bend" around the tub (as JB has done). KerdiBand any seams and tile away.

Small tiles, fer' sure to conform to the tub. Might work....might not. Waddya got to lose?
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Old 02-23-2015, 03:46 PM   #13
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That is an interesting idea, Davy: concrete the whole thing but keep it isolated from the redwood so the wood can move independent of the concrete.
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Old 02-23-2015, 04:02 PM   #14
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I'll give you that one Chris. Wood does move. I'm hoping my desert environment helps in that regard.

I did some calculating on how much a 6" piece of quarter sawn old growth redwood will expand/contract, assuming a 5% change in annual humidity, and came up with .03" or about 1/32 of an inch. There are about 40 of these that make up the tub walls, with the 5 iron bands to hold them together.

That would seem like a lot a movement, and when I think of 40 of them all moving sort of independently, it scares the hell out of me.

But, I'm not new to alpha and beta testing, so if anything it just makes me want to solve this problem.

Clearly I need that initial layer to have some shear strength. That's why I'm leaning towards the fiberglass mesh tacked to the wood and floated with Mapelastic 315 before Kerdi.

I'll check out the grout!
Edit: Checked out the grout. They may have solved the mildew/mold problem by adding antimicrobial ingredients but I certainly wouldn't want to bathe in it. Plain cement won't have the mildew mold problem of polymer grouts or so I'm told.

Great pics on your "Orange tile Project" My bathroom is orange.
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Old 02-23-2015, 04:45 PM   #15
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Chris, I would set forms and rebar and then pour the whole thing out of concrete, doing away with the wood. I just couldn't take the chance of the wood moving and causing problems and then having to do it all over again.

I know a guy that did this years ago. He bought a hay ring like they use for cattle and added rebar to it and then the wood forms around it. Added the plumbing and then tiled the whole thing. Worked well.
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