Roman tub build (Please help! considering divot method)

[garymaurizi]

Hi Ladies & Gentlemen,

I've been a lurker on this forum for 4+ years while I planned out this project & remodel, and have gained an invaluable amount of knowledge and just wanted to start with a very big thank you! My name is Gary, I've worked as 2nd hand and apprentice in many different construction related fields in my life and built the house I currently live in from the ground up saving this bathroom for last.

I'm in the middle of my very own roman tub build, I've watched every youtube video of similar builds MANY times, and read every forum post on the subject multiple times over.

This is an above slab 'above subfloor' plywood framed roman tub build, all of the framing and ply is done, and the floor joists have been reinforced with sandwiched joistwork extra spanners and extra 4x6 just supports with strong-tie brackets and buried concrete pier blocks. The bathroom is 7' x 7' on an exterior wall and the floor is well supported as far as deflection due to the smaller size and being on an exterior wall, the extra joists supports probably weren't necessary here but I prefer safe vs. sorry.

I have a really good idea on how I 'should' proceed to waterproof this plywood roman tub, currently I have a jones stephens cast iron clamp drain with a purpose built 2" twist and lock roman tub stopper made to fit this drain. From the nowledge I've gained here, my plan up to this point has been to either use a PVC pan liner or hot mop, then cover that with lathe held on with scratch coat & drypack on the horitzontal tub lips as well as lathe fasteneres 6" past the tub lip above the membrane or hotmop, then float the walls and lips of the tub. I have 1/4 notch all around 6" up past the tub lip/arm rest to accomodate a membrane or hotmop and understand the process well enough.

Problem: I'm not very confident on folding a 6x10 PVC pan liner into such a complex shape -- it's a square box with only the back tub wall slanted, but there a few tricky spots and a 6x10 pan liner really wouldn't be big enough. Initially i thought of fixing this by using an EDPM pond liner and I've found a few reports of this working well for large shower builds.

Problem/idea: I've seen 4 videos of people doing plywood roman tub builds by just slapping up wonderboard, a preslope mud bed level to the drain flange, then using just a liquid membrane on the fully cured mudbed in place of any pan liner via reinforcing fabric layers at the drain and plane changes -- I believe it's a spin-off of the divot method without the divot? This method would save me an incredible amount of money headache and work if it's actually something that's going to last 10-15 years? It avoids the issue of holding bent lathe with many plane changes to the walls of the tub and the difficulty of floating the tub walls, etc. What do you think of the usability of this method in my specific circumstance?

I don't like the idea that a conventional shower build like I have been planning up to this point could lead to a constantly HIGHLY saturated mudbed if the tub is used often? A liquid applied mesh reinforced membrane would certainly save alot of work and seems in this specific scenario might be a better build as it avoids the saturated mud bed when the tub is filled often?

Should I consider this pan liner method? Redgard's own spec PDF's do show it approved as a pan liner? And if I did consider this method, would I actually even want to go with the divot method and preserve the drain weep holes? A standard tub drain has NO weep holes?

PS. What provides point load support around the drain when you use the divot method and fill the divot with crushed tile to maintain the weep holes? I'm planning to use a mesh rock type tile on the shower floor.

PPS. I'm aware of kerdi and other surface applied membranes, I am not a fan of their use in this roman tub situation after seeing Isaac Ostrom's flood tests on youtube and hearing schluter's responses to them (they essentially say kerdi membrane is not meant for, or usable in fully submerged applications!)

Also, if I decide to try redgard as a pan liner reinforced with mesh -- either with or without a drain divot -- would my cast iron clamp drain be okay for this? I've only seen the divot method used on ABS clamp drains which may hold the bonded redgard better than an iron flange?

I thought about buying an ABS trip lever kit cutting off the slip joints welding it together and using a 2" threaded coupling to thread in a standard ABS oatey clamp drain as an alternative to the jones stephens 2" twist lock tub stopper, but, I could not solve the problem of finding a way to clamp the overflow drain to a membrane and the watco 500 ABS trip lever kit I purchased to try uses odd thin wall 1.5" ABS piping that standard ABS fittings don't fit in! In relation to this, does anyone know where I could find a threaded bushing that would let me thread in a regular 1.5" twist stop tub drain into a 2" ABS oatey shower drain? I imagine it would be brass and threaded inside and out?

Thank You all so much,
Gary M

 

[Jadnashua]

Had you considered Wedi or Kerdiboard? Noble has some products that could work as well as some of the USG and Laticrete items.

Check out www.johnbridge.com . I agree, a mudbed in a tub is probably not a great idea unless there is proper waterproofing on top of it. While liquid applied ones can work, it's not like painting your wall...the actual thickness of the coats and avoiding runs or pinholes is a real concern.

FWIW, Schluter had a tall container full of water, waterproofed with Kerdi in their office for years...never leaked. For those seams to work properly, you must get at least the minimum overlap, use a premium unmodified thinset, and get the membranes properly embedded. If done right, it works. Get your thinset too thick, have any gaps, or leave notches showing, and it won't. Most of the situations I've seen or read about that failed showed signs of poor workmanship. It's not actually hard, but is very detail oriented...skip one step or misunderstand the reasons for the instructions, and it can fail. FWIW, Schluter does have a drain for a tub, but you have to call them...last I looked, it wasn't in their catalog. They're essentially hand-made to order as I understand it, so not cheap. A Roman tub is not for the casual builder...the whole system will be under stress, and mistakes can take a long time to show up with costly consequences. I think that's one reason why they don't talk about it much, but it is mentioned if you take one of their courses.

 

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[garymaurizi]

The schluter tub drain is roughly $600 without the overflow. I'm for sure on a tighter budget than that in this build...

I'm still open to considering all possibilities. I want to do the best thing I can within my budget for sure!

I've considered the kerdi membrane and board products, I just don't really like the fact that schluter themselves says "don't use our product for a tub" straight out... I've actually called them and discussed it.

I for sure trust PVC membranes and know that EPDM membranes work just as well -- and redgard is essentially a liquid EPDM membrane and liquid epdm has been making big waves in the waterproof roofing industry for 20 years and is well trusted there... I only worry about the drain tie-in in this setup.

I agree with you on the mudbed in a tub situation..

It seems like maybe I'm stuck between either a surface membrane like schluter's or redgard as a pan liner if I'm reading between the lines properly?

 

[Jadnashua]

Wedi sells a bathtub. I'm quite certain that you could use their panels to build a Roman tub. They also can do some custom stuff, but making it up yourself would end up less expensive. https://www.wedi.de/en/products/design-line/sanbath-cube/bath-tub/ If you have sufficient strength in the framing and plywood, you could use their thinnest panel. If your tile are smaller than 2x2", you must use epoxy thinset, though, which adds some costs. Note, thinset is a method of setting tile, and the adhesive could be mortar based, some synthetic rubber, acrylic, an epoxy, or possible other material...most people think of thinset as being a cement based product, and this can cause confusion when someone labels things as thinset and it's not cement based. They're not technically wrong, but it can be confusing.

The foam in Wedi, KerdiBoard, and others is essentially the waterproofing (same stuff, but denser than your foam coffee cup) with a mortar compatibility layer added for strength and reliable bonding. You need to ensure you seal any penetrations properly along with seams. Wedi uses a proprietary material. Kerdiboard can use their KerdiFix, but it's generally less expensive to use KerdiBand and mortar.

 

[garymaurizi]

Wedi sells a bathtub. I'm quite certain that you could use their panels to build a Roman tub. They also can do some custom stuff, but making it up yourself would end up less expensive. https://www.wedi.de/en/products/design-line/sanbath-cube/bath-tub/ If you have sufficient strength in the framing and plywood, you could use their thinnest panel. If your tile are smaller than 2x2", you must use epoxy thinset, though, which adds some costs. Note, thinset is a method of setting tile, and the adhesive could be mortar based, some synthetic rubber, acrylic, an epoxy, or possible other material...most people think of thinset as being a cement based product, and this can cause confusion when someone labels things as thinset and it's not cement based. They're not technically wrong, but it can be confusing.

The foam in Wedi, KerdiBoard, and others is essentially the waterproofing (same stuff, but denser than your foam coffee cup) with a mortar compatibility layer added for strength and reliable bonding. You need to ensure you seal any penetrations properly along with seams. Wedi uses a proprietary material. Kerdiboard can use their KerdiFix, but it's generally less expensive to use KerdiBand and mortar.

Some interesting food for thought there! Thank You!

I'm seeing that wedi sells a sanbath cube, but if you look close this tub has 5 sides (about a 45 corner cut where the shower door would go between the exposed beams) so it's not 100% square -- and it's undersized. When you say I could make my own with it are you thinking of ripping it apart and re-using the panels or using it as is? The only other wedi tub product I see is a foam surround it?

I originally considered just doing an insert but I couldn't even find an RV tub insert small enough for the space and reframing was not an option... and a custom job in stainless or other material wouldn't really go with the decor and would be out of budget...

I'm not at all against considering wedi board for the walls inside the tub, but it still leaves the larger question of what to do with the mortar bed and drain tie-in? were you thinking something along the lines of using a wedi preformed foam base or something of that sort in place of a pre-slope+mud bed and one of their membranes over that foam base for the tub floor (if even necessary?) then say setting a kerdi-like drain into the foam base with thinset? (im sure wedi has a drain similar to kerdi with a mesh+grated flange?)

I would definitely choose kerdifix over kerdi's thinset to bond the kerdiband and maybe even kerdi membrane AND wall panels if i went that route (after watching many flood test results and seeing 1/4 inch water penetrations into the kerdiband with only a 6" column of water) am I off base here thinking kerdifix bonds kerdiband better than their thinset does? but I'm still not sold on schluter/kerdi products in a fully submerged tub installation... If you really think that say 1/4" kerdi board sealed together with kerdifix at the ends/seams supported by the plywood behind it (and maybe kerdiband+thinset over it on top in the corners just as a precaution?) would do the trick in this roman tub install then I'm all for it! This would certainly solve some drain and overflow problems for me and be much less work! (kerdi makes a super low profile 90* offset drain I could use for an overflow that fits in a 2x4 stud wall also!). I'm picturing it in my head and I imagine you would suggest cutting down kerdi's preformed foam pan to fit the bottom of the tub and using kerdifix to seal their wall panels to the foam pan? I don't mind backtracking a bit to take this route if someone with more experience than me trusts it for this type of tiled bath tub use case...

I just don't have enough experience with the product and can only go based on what I've seen in various flood tests from Isaac, starrtile & others.

I could probably make the kerdi drain work with a tub stopper if I found a 2 inch to 1.5 inch threaded reducer bushing or something that let me use a normal tub stopper with the kerdi 2" shower drain, and return the jones stephens 2 screw type roman tub twist stopper.

PS. The kneewall, tub lip & surround and supported by triple stacked 2x4's on top and bottom with sandwidched ertical 2x4's and 4x4's at 6" oc or less all around -- in other words, that 1/2 ply isn't going anywhere!

 

[Jadnashua]

I think that I'd probably just buy 1/4" or maybe even 1/8" Kerdi or Wedi panels to make the whole thing. I haven't looked at the Wedi drains. FWIW, Wedi allows you to use thinset to bond their panel to plywood. Schluter has tested it in that fashion with their Kerdiboard, and should work, too, meaning that there would be no screw fasteners required to hold it in place so you'd only have the seams. I'm thinking as typing, so maybe you'd want to consider thicker panels. Wedi usually bonds their right-angle joints by first making a rabbit. This gives more surface area for the sealant than a butt joint. If the base of the tub is sloped, it should drain. If you were to use their thinnest panel, you could probably get it to bond to a slight curve if you placed weights in there until the thinset cured that would eventually hold it down. I know with Kerdiboard, you can buy it with scored cuts in it so that it will conform to some significant curves, but I think either Wedi or Kerdiboard would bend into a compound curve if you chose a thinner panel and didn't try to make it bend too far.

With either of those, your waterproofing is right below the tile, so no mortar base (deck mud) that would end up saturated. If you did use a liner like that, the entire thing would need to be sloped to the drain, otherwise, it would eventually be totally saturated, keep the grout wet, and promote smells and mold.

I think I might buy a sheet of the material and experiment a little about how well it bends. Flat, obviously, isn't an issue. I think something like sand bags would help it conform to any curves while the thinset cured. I'd probably consider Wedi, but then, I probably wouldn't deal with a tub like that! Too many grout joints to keep clean. I know the thicker sheets can be structural, which is what that tub I liked to is made of.

 

[garymaurizi]

I think that I'd probably just buy 1/4" or maybe even 1/8" Kerdi or Wedi panels to make the whole thing. I haven't looked at the Wedi drains. FWIW, Wedi allows you to use thinset to bond their panel to plywood. Schluter has tested it in that fashion with their Kerdiboard, and should work, too, meaning that there would be no screw fasteners required to hold it in place so you'd only have the seams. I'm thinking as typing, so maybe you'd want to consider thicker panels. Wedi usually bonds their right-angle joints by first making a rabbit. This gives more surface area for the sealant than a butt joint. If the base of the tub is sloped, it should drain. If you were to use their thinnest panel, you could probably get it to bond to a slight curve if you placed weights in there until the thinset cured that would eventually hold it down. I know with Kerdiboard, you can buy it with scored cuts in it so that it will conform to some significant curves, but I think either Wedi or Kerdiboard would bend into a compound curve if you chose a thinner panel and didn't try to make it bend too far.

With either of those, your waterproofing is right below the tile, so no mortar base (deck mud) that would end up saturated. If you did use a liner like that, the entire thing would need to be sloped to the drain, otherwise, it would eventually be totally saturated, keep the grout wet, and promote smells and mold.

I think I might buy a sheet of the material and experiment a little about how well it bends. Flat, obviously, isn't an issue. I think something like sand bags would help it conform to any curves while the thinset cured. I'd probably consider Wedi, but then, I probably wouldn't deal with a tub like that! Too many grout joints to keep clean. I know the thicker sheets can be structural, which is what that tub I liked to is made of.

Thanks! I don't have to worry about curves, I know it's not going to be super comfortable, but tub use isn't going to be the major use case, I'm just gonna K.I.S.S and keep the tub walls flat and only slant the back rest say 22* like it is now

Thank You for the info! I think I'm going to just give 1/4 or 1/8 kerdi board with kerdi fix a try and seal over corner joints with kerdiband and either their suggested thinset or kerdifix under the kerdiband to bond it better. The tip about scored kerdi board is really useful! I avoided compound curves because I didn't know about that product!

Are you sugesting just pre-sloping the plywood base and using kerdiboard on the floor with a hole cut out for the kerdi drain and using kerdifix or kerdi's unmodified thinset mortar to bond the kerdi drain flange to it? or in this (nightmare) installation scenario would you suggest I just use the kerdi foam pan and kerdifix the wallboards to it?

I had no idea I could thinset the thinner kerdiboard to plywood! that would help dramatically! is there any issue with the plywood sucking up the moisture from the thinset? should I seal the plywood somehow first or maybe wet it down before I thinset kerdiboard to it?

Also, what do you think about throwing a few layers of redgard over the ply just as a safety measure ( and it would stop the ply from sucking the moisture out of the thinset that bonds the kerdiboard!) I do worry a little about movement in the wallboards (I am in southern california!) this is why I was thinking of mesh tape+redgard as a pan liner initially... Does kerdi's membrane have any bit of flex to it at all?

I suppose in theory I could fill the cracks in the plywood then pre-slope the plywood tub floor to the drain then throw mesh reinforced redgard on it going up the tub walls, and then proceed to set 1/8 kerdiboard with thinset & glue the corners with kerdifix+kerdiband... Then if I ever get enough shifting/structural movement and a major crack forms somewhere between kerdi wall panels the redgard might help it drain out to the drain... wonder if that would be a 'mold sandwich' situation though...

Thank You soo very much!

 

[Jadnashua]

You will want some slope on the base so that things go to the drain better without pooling unless you want to squeegee it after each use. If you were to use the Kerdi drain, it is designed to sit in a recess so that the top is flush with the rest of the surface. Then, you'd need a ring of Kerdi material around it so that it has the proper overlap of both the drain and then onto the surface of the KerdiBoard. Making that recess might be a little tough (you could do that with a router and a jig, though), but IF you found the sheet thickness closest to the drain edge thickness, you might just be able to cut a nice clean circle where the drain would go and set the drain on the ply. You'd want to use an A118.11 thinset to the plywood, and an unmodified on top unless you chose the right kind of modified. Schluter makes a modified that works, not all modified thinsets will work. Some require drying to work as well as cure (which will happen anyways), some will reach full strength without drying.

It's a good idea anytime you tile something to first take a wet sponge and wipe the surface down. As long as the surface isn't literally dripping wet, things will work. The idea is to supply some moisture prior to spreading the thinset so that the proper mix isn't messed up by immediately losing some to the surface that is dry. Some people try to do that in one step by making their thinset wetter...that's not a good idea as that can make the cement and the aggregates separate and when installing a tile, make it hard to keep them level without sinking into the too soupy thinset. FWIW, exactly following the mixing instructions can make the same thinset function differently than if you wing it. Measure carefully, use a drill motor that can run at the specified RPM, and use a timer...it DOES make a difference. What may at first appear to be too thick, can smooth out after the specified time where adding more water at the beginning may prevent it from working properly, but 'look' the same (often, by not mixing long enough). Especially when using a modified thinset, mixing is particularly important. The modifiers first need to be hydrated which takes time, then, once they're hydrated, you want to coat all of the aggregate with them. That's what the slaking period and remix is all about. Plus, mixing it at the specified speed prevents you from whipping it into meringue (entrapping air) and helps to break down any small lumps so it is smoother. The only way you'll get the strength and texture right is by following the instructions. If you've got really hard water, some purists go to the extent of using distilled water. That's way overkill for most situations, though.

Final thought...you're on uncharted waters building the tub this way. Personally, I'd use mortar and Kerdiband or Kerdi to make my seams. I'm not sure KerdiFix will flow around the fleece as well as thinset. KerdiFix works when sealing edges to things or around say a pipe penetration if you can't use one of their gasket seals, or to fix a hole. It is also pretty expensive stuff compared to mortar. You will want to pick up one of their Kerdi trowels, or one alternate that has the proper notches...it's important to have the right amount of thinset. YOu need enough for it to flow around the fleece, and not too much to provide a path for moisture to penetrate.

In one training class I was at, they made a drink cooler out of a cardboard box with Kerdi thinsetted to it. It sat all day full of drinks and ice that eventually was mostly water. The cardboard stayed dry. Install it right, and it works.

Wediboard, in this situation, might end up easier, as it is designed to be sealed with their sealant only. The coating over the foam is different, but it does have that limitation on tile size which can require epoxy thinset when small. I think that the sheet membrane of Kerdi bonded to the foam ends up providing more strength, which is why it doesn't have the same size issues.

You could probably use Schluter's tub replacement shower pan which would have the slope needed and the opening for their drain. I haven't searched their catalog lately, it may now come already covered with Kerdi from the factory. If you used that, your floor would want to be level since the pan would provide the needed slope. Those come in two flavors, one with the drain in the center, and another with it at one end.

 

[hj]

In this area "tiled Roman tubs" were the rage in the 60s. By now almost all of them have been converted to planters or conventional tubs. They are uncomfortable and cold.

 

[Jadnashua]

The human body has lots of curves...a hard flat surface isn't generally all that comfortable...so, I agree with HJ entirely. Now, a tiled tub over one of the tileable foam boards would tend to warm up quickly with that thermal break/insulation versus one made entirely out of cement based products.