04:58AM | 04/16/03
Member Since: 04/15/03
5 lifetime posts
I want to build a polished concrete bathtub in a commercial wooden floored loft building. The walls of the tub will be 4" thick. There are several issues that concern me. One is waterproofing, in relation to the steel reinforcing; I plan to use plastic shower pan material, imbedded in the concrete with all rebar and wire mesh "outside" of the plastic pan material (because of rust potential resulting in spalling of the concrete surface) with the "inside" of the tub going unreinforced, but contained within the steel reinforced part of the concrete tub.

Has anyone attempted anything like this? Any other issues? Caveats?

[This message has been edited by NeoLuddite (edited April 16, 2003).]


05:30AM | 04/16/03
Member Since: 01/14/03
264 lifetime posts
I can't say much about the tub idea. I've never heard or seen anything like that. But I can make a comment about weight. You mention that this will be constructed in a wood frame building? On a loft? If you're constructing such a thing in a wood frame building, I'd suggest getting some professional advice on the weight carrying characteristics of the existing frame, and the anticipated weight of the tub, plus water, plus person(s). You don't want to build this thing only to have it end up in the basement...


05:30AM | 04/16/03
Member Since: 01/14/03
264 lifetime posts
Double post monster......

[This message has been edited by treebeard (edited April 16, 2003).]


05:45AM | 04/16/03
Member Since: 04/15/03
5 lifetime posts
Thanks for your reply. Yes, weight is also a concern. I calculate the tub + water + 1 person will weigh around 3500 pounds.

The building is a commercial loft building, it's not being built on a loft.

Joists are 3" x 12"s 16"oc. running from an adjacent, outside brick wall to a steel I beam around 16 feet away. We may put in some steel between the two outside brick walls in the corner into which this tub will be placed.

However, waterproofing vis a vis the rebar and structure of the concrete in the tub are my main concerns at this point.


06:01PM | 04/17/03
Member Since: 11/14/00
333 lifetime posts
I would not use the plastic insert for the very reasons you noted.

Rebar works to reinforce concrete by becomming a part of the stones and cement "fabric". The rebar does not provide a foundation for the concrete, but becomes and intergral part of the concrete: that is why it needs to be in the middle of the concrete, surrounded by concrete, not at the bottom or on one side of the concrete. Moreover, if you isolate the rebar support from the interior water in the tub, then that will only make the inside of the tub that much more susecptible to cracking and failing. With a plastic liner, the interior concrete will shift off the plastic and fall off as the concrete fails (because it lacks support of the rebar to keep it together).

Instead of putting the water barrier INSIDE the concrete, you want the barrirer to be on the SURFACE of the concrete. Your solution is to, first, trowel the heck out of the interior of the tub so as to milk the finer sediments to the surface and create a smoother surface. Second, you can waterproof the surface with either a sealant or waterproof paint, depending on how you wnat the surface to look.

There are non-glossy sealant product out there to provide somewhat of an "invisible" seal.

[This message has been edited by Lawrence (edited April 17, 2003).]


10:14AM | 04/27/03
Member Since: 02/22/03
23 lifetime posts
water proof with a PVC liner available at a tile supply store- the same as used in tile showers. You will need to build a pre-slope mortar bed with a diamond or expanded metal lathe. Install the PVC liner over it with the pre-fab corners-- then put another mortar coat on top of that.. THat is the traditional way.. BUT, one way people are doing it now (I did this) is to build your form, then do the pre-slope with a regular mortar (Or portland cement with a polymer additive and fine sand)-- then install a fiberglass sheathing over the top of it-- much easier than the PVC liner.

I would like to talk to you about your concrete tub. I build concrete counters and do decorative concrete overlays and have always thought about doing a tub, but hadn't decided the best way to build it.. Are you doing it with a gunnite and rebar? Curved? Straight edges? Email me


03:23AM | 06/14/03
Member Since: 04/15/03
5 lifetime posts

OK, here's what I did. I poured a concrete floor which will be polished and used as the finished surface in the bathroom. Where the tub would be, I sloped the floor towards a previously installed shower drain/pan attachment. I had the plumbers install a shower pan, as if we were constructing a curbless shower/handicap shower, with no curb on the two outer walls. I then formed the two outer walls with plywood. Within that I constructed a cage of fiberglass rebar, and carbon fiber mesh. To that I attached pex tubing, fed by the hot water heating system, for nice warm baths all winter, and then I suspended a well reinforced plywood insert to form the interior of the tub.

I used a special concrete including several additives to give a strong, dense, waterproof mix, even without surface or penetrating sealers.

The tub will be a dark graphite color and the floor a natural concrete. Both will be polished to a high gloss.

I'll let you know how well it holds water.


01:18PM | 06/21/03
Member Since: 04/15/03
5 lifetime posts
I pulled the forms, did an initial grinding to expose the aggregate a bit, in preparation for polishing, and filled it with water, first for an hour or so, and then overnight; no leaks or even damp areas. Now, I've left it full of water for the weekend.

It holds around 80 gallons to the bottom of the overflow. It looks great.


03:20AM | 07/25/03
Member Since: 04/15/03
5 lifetime posts
It worked! I left the outside of the tub rough after grinding off the surface of the concrete, and polished the top and inside to a high gloss.

You can see some pictures of the construction and finished tub here:

Edited to fix URL.

[This message has been edited by NeoLuddite (edited July 25, 2003).]


04:27PM | 09/12/03
I have a uncompleted cast-in-place concrete tub, which i planned to line with a membrane, then floated with cement mortar over metal lath.

How do you stopper a 2" shower pan drain?
Any ideas on mastic to use to glue membrane to tub walls?
What drain, stoppers & overflow hardware can be used to sandwich the membrane thru the 3/4 to 1" of floated mortar?

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