Video /
Jan 7, 2021

How to Waterproof, Steamproof a Spa Bathroom

Custom Builder Nick Schiffer walks through the process of waterproofing and steam-proofing a Boston-area bathroom renovation.

“The client had incredibly high expectations and wanted to transform their bathroom into a high-end spa,” the founder of NS Builders says. “This primary suite bathroom includes a waterproof and steam proof ‘wet room’ with giant slab tiles.”

Watch as Schiffer walks you through the steps on how the company made the bathroom come to life.




I'm Nick Schiffer and I own NS Builders. I get to work with a team of wildly talented craftsmen, building and renovating some of the coolest homes in Boston. We have this renovation project that we're working on with Cambridge Seven Architects. It's an extremely modern primary suite renovation. There's a lot of detail and an immense amount of forethought that is going into this project, but specifically I'm talking about the shower, or what we're calling the wet room.

It's a really oversized shower with a bathtub, it has four windows in it, and it's also being prepared for steam, and not to mention the curbless entry. Knowing that the attention to detail was gonna be so critical, it was really important that our team as well as our subcontractors, were on the same page and had a clear understanding

of how we were gonna approach this project, equally, the vendors and working

with an all encompassing system, that was going to allow us to not only waterproof this room, but also steam proof it.


So that's exactly why we worked with Schluter. They had the entire line of products

that were going to allow us to achieve what was designed.

First step on this project, after demo,

we flattened the entire floor.

They sistered every single floor joist

to make sure the entire space was flat.

We knew that this jar was going to be curbless,

so we need to make sure that we were setting ourselves up

with a flat floor, that we could then transition

to our signature move, where we're recessing all the sub

floor within our shower space.

So the reason we do that, is to prepare it later on,

for our pitched shower pen.

We actually have to get pretty far along in this project

and do things a little bit of out of order,

where we're almost 90% complete with the entire project,

before we get into waterproofing, nevermind tiling,

this space.

Rough plumbing and electrical have been signed off

and we're going to start working

on our Kerdi board on the walls.

So the Kerdi board is actually an all-in-one substrate

for our tile, but it's completely waterproof

and steam proof.

Has this felt membrane applied to it,

that is setting the base for this waterproof system.



We installed all these panels with screws

and it's really important to use the wide washers,

because the panels are light they're made of foam

and the wide washers actually helps spread that weight

out and hold these panels tight against the framing.

We're going a little bit above and beyond here,

we're actually applying a Kerdi fix

to the backside of these panels,

so once they're pressed up against these studs

and the screws are in place,

that Kerdi fix is just adding another layer

of holding power to our framing.

We spent a lot of time making sure these walls

were ultra flat and preparing for a nice straight wall,

especially with this large format tile.

So once the panels are installed,

we need to seal up the seams, the corners

and the screw heads.

And we're gonna do that with the Kerdi band

and that Kerdi band is installed with a thin set.

We're using the Schluter, all set, troweling that on

and then applying the Kerdi band over that.

We're using just a, a knife to basically screed out

the excess and make sure that that's really flat.

So we're not getting any waviness or bubbling,

underneath what will be our tile substrate,

once it's cured.

It's really important that we prevent any moisture,

whether it's water or vapor,

getting into any of these crevices.

So remember the drop sub floor we talked about?

This is exactly where this comes into play.

We have a curbless entry to our shower.

So our sub floor is at a certain level,

that drop sub floor in our shower area,

allows us to now mud that area.

And it's really important that you use a fortified mud here

because it needs to be able to screed down

to just an eighth of an inch.

So our high spot is essentially our base sub floor level,

and then our low spot is gonna be at the linear drain.

Once the walls are done, we're gonna get into the floor,

we're gonna be installing the Ditra mat.

And the Ditra mat is actually gonna be doing two things.

It's decoupling the tile from the sub floor.

And what that means is the sub floor can slightly move,

expansion and contraction, it's wood,

it's a different material than a tile.

So that's giving the opportunity for the sub floor

to move separately from the tile,

so if something were to move or shift ever so slightly,

that felt backing on the Ditra mat allows that movement

to happen without cracking our tile

or our grout joints.


The second thing, is it's laying a track

for our radiant heat cable.

Signature move for us, is we're gonna run

that radiant heat cable throughout the bathroom,

and then into the shower.

The Ditra actually is waterproof, but once you add a cable

to it, especially in a wet area, like a shower,

it needs to be waterproofed again, to prevent that cable

from being exposed to moisture.

We need to waterproof the floor to the walls,

so we're doing the same thing as we did on the seams,

we're taking that Kerdi band,

applying an all set to that space

and then screeding that Kerdi band into place.

We have two layers of waterproofing.

So what we're doing is we're actually using

the Kerdi membrane and going over that cable,

making this a monolithic and cohesive waterproofing

and steam proof system from wall to floor

That heated floor is not only in the bathroom,

but all the way continues throughout the shower,

which is super nice, especially when you're standing

in the bathroom, getting ready to jump in the shower,

you're not going from a nice warm floor, to a cold floor.

One of the biggest challenges we dealt with in this space,

is the four windows that end up inside the steam shower.

From the outside looking in, the windows had to appear

as though we didn't change,

because it's actually a historic home.

On the inside, Cambridge Seven actually designed

this killer detail, where they tapered the tile

into the glazing, and there was actually

no window frame exposed from the inside.

So there was a lot of forethought that went into this.

We couldn't just taper our waterproofing

or our tile into this space.

We had to really consider the layout all the way through.

Waterproofing detail, continuous from the Kerdi

onto our glazing.

And then we did that by Kerdi fixed adhesive

to span from that Kerdi board,

to the glazing, giving us

that continuous waterproofing layer.


Using the Kerdi band all the way up to the glazing,

to span from that Kerdi board

to the glazing tenuous waterproofing layer.

So essentially if we had water on that glass,

it was going to run down, and you know,

ultimately hit the tile, but if it were able

to get behind the tile, it would go right

into our waterproofing layer and be protected,

so we're not running the risk of damaging anything inside.

The fact of the matter is, it's an architectural detail

that wasn't designed around how easy

we can replace the glass.

Is it replaceable?

Of course it is.

We take out the custom may pieces of tile

that taper into the window,

we break the window out and we put a new piece of glazing in

and we re waterproof and we re-tile.

So it's doable, it's just not easy,

but it wasn't designed to be easy,

it was designed to be beautiful.

So on a traditional project, once we're tiled,

we usually Venn template for glass and install our glass.

We templated and installed the glass before tile.

That allows for all the glass to be buried

into our finished surfaces.

It's pushed up against the finished floor on the outside,

pushed up against the plaster on the walls and the ceilings

and really gives this illusion that the glass

is just sitting there with no support whatsoever,

besides the fact that it sits floor to ceiling.

And what's really key here, is that we have a hinged door

on one of these panels,

and if there's no structural clips holding that glass

into place, we need to structurally support it somehow,

and that's exactly what we did with a structural silicone.

So the glass gets set three sides, ceiling, wall, and floor,

with a structural silicone that will dry hard enough

and strong enough, to support the swing of our center door.

We'll do the same thing on the other panel.

Even though it doesn't have any weight,

we want that panel to feel strong,

and when you lean up against it, not have any chatter in it.

Once that glass got installed, we basically get it

into place, make sure everything's plumb,

level and prepared, and that glass track actually

has a flange on it.

It's the Schluter glass track SG.

So it's part of their aluminum extrusion profiles,

and that flange actually gets set in a Kerdi fix.

So that's structurally holding it

to our Kerdi waterproof panels,

but then again, we wanna make sure that we're,

we're taking an additional step and actually

installing another layer of Kerdi band over that flange.

So we're waterproofed behind the glass track,

we're waterproofed again,

with the Kerdi fixed behind the glass track,

and then we're waterproofed on top

of the glass track with our Kerdi band.

And then that final piece will be the tile,

pressed up against the glass track,

takes an incredible amount of forethought

because you are putting this glass in

way before anything else, before finishes

and you're working around it.

So if this wasn't complex enough,

the tub also didn't fit through the window,

nor did it fit through the door for the shower,

nor could we increase the width of the door of the shower.

So this tub, also had to come before glass

and we already talked about how glass

was coming before anything else.

So now we're bringing this really expensive,

nice freestanding tub, putting it in place,

before we even have glass installed,

nevermind the waterproofing and tile details

and a lot of maneuvering and moving it back and forth

while we tiled.

So we knew that was going to be really challenging

to work around, but it was a necessary evil

for this project.

The actual install of the tile we're dealing

with large format, we're talking 48 by 48

and 48 by 96 inch tile, it's essentially a micro slab.

And we chose to take a more countertop approach,

where we were templating wall by wall, piece by piece,

and then bringing it to the fabricators shop,

cutting it on the CNC, fabricating it as a piece,

and then bringing it back to site.

It was a much slower process.

Everything had to be templated one by one for the majority

of what was going on from a fabrication standpoint,

it was being done in a shop which nets a great result,

it's just very different from our typical approach,

where we're able to use tools and materials that are onsite

which we could have done, but we just knew that the level

of execution, everything really needed

to be absolutely perfect, so we wanted to make sure

we were approaching it with the very best intention.


Overall, this project was extremely complex,

but that's exactly why we were eager to do this project,

work with the client.

Their expectations were so high,

same with the architect.

We collaboratively knew that a lot of these details

were designed in a way that would be difficult

or challenging to execute, but that's really the fun

in a project like this.

This takes a tremendous amount of thought and consideration

on how things go together and who does what first

and that in itself is so incredibly rewarding.

And to see the project come to a completion at this point

and stand back and see the fruits of our labor

and just how things ended up coming together,

all those micro details that we get to enjoy now,

as we look at the entire space,

the team did an incredible job,

and working with our subcontractors, our guys in the field

and companies like Schluter, it really just makes

for a much more rewarding project,

when we know that we're working at the very highest caliber,

and working with the very best products.