Mortared shower pan on slab foundation

[BryanG]

I am remoldeling my master bath and making it all shower. I have everything out and the walls done with durock. I want to make a mortared shower pan since the shower is an odd size. Everything I read about it is talking about doing it over a subfloor. I need to know the procedure for a slab floor.

[jimbo]

You still need to builed a preslope foundation, covered with a membrane layer, then the tile.

For best advice, try this forum: www.johnbridge.com

[geniescience]

only that. not deck mud.

You need only a slope, a liner and tile.

Therefore you could (even) have a sunken shower floor, by cutting away some of the slab concrete. You do not need to raise the floor by adding any cement product.

If you build the slope on top of the slab instead of cutting the slab down, all the height (or thickness) of "new" cement you need is from ZERO at the drain, and from there UP with the slight slope to whatever thickness is needed by the slope. Two feet from the drain, you need a half inch height.

You do not need to start with any greater thickness at the drain. My memories of the jb forum are not happy, with this subject: nobody ever said what i have just said above, and yet they claim to know a lot. Maybe today someone over there will confirm the above...

The point is, you asked about a slab and how it differs from a wooden subfloor. This is how it is different. It doesn't need any "deck mud" or thick layer that is designed to hold together and be stiff enough... All that is for wood buildings.

A slab has enough strength already.

The concrete product that you will use to make your slope will be whatever the local concrete product manufacturer sells for this purpose. I cannot name product names, since they vary a lot from place to place.

David

[jadnashua]

You want to bond the deckmud to the slab. There are several ways to do this...you can mix some thinset runny and almost paint it on, then get the deck mud on top of it quickly before it skins over. You can sprinkle dry cement on the floor then sprinkle some water on it then dump the deck mud, and there are other techniques.

Deck mud is sharp sand and portland cement mix in the 4-5:1 ratio. Think sand castle that hardens. You can taper it to zero at the drain, but that will often mean digging a bigger hole to recess the drain and getting it supported is harder. It may be worth it if your goal is an absolute minimum height floor. A Kerdi shower would provide that as well, since you only need one layer - the slope, then the waterproofing membrane, rather then the preslope, membrane, top slope, then tile.

SO, preslope, liner, then final slope, then tile. Unless you use something like Kerdi (you should check this out at www.schluter.com). The advantage of using Kerdi is that there is no thick cement layer on the walls or floor to get saturated...the waterproofing layer is right under the tile. You can also cover your walls and curb with normal drywall, which sticks the Kerdi in place well and provides a fine surface for the waterproof membrane.

[geniescience]

Deck mud is sharp sand and portland cement mix in the 4-5:1 ratio. Think sand castle that hardens. You can taper it to zero at the drain, but that will often mean digging a bigger hole to recess the drain and getting it supported is harder....

all wrong here.

Also, not true that using Kerdi is the way by which

you only need one layer - the slope, then the waterproofing membrane, rather then the preslope, membrane, top slope, then tile

also not true is

The advantage of using Kerdi is that there is no thick cement layer on the walls or floor to get saturated...

also no good is

You want to bond the deckmud to the slab

Sorry to be so clear about it. Over at the world's friendliest web site, they would fudge the issues so no-one would ever know.


David

[jadnashua]

David,
If you have a gripe with them over there, fine. The information comes from the Tile Council of America. They set the standards for the codes that dictate best practices. Many locales abide by their recommendations. They spend big money to test these and have a proven track record. There is often more than one way to skin a cat, but saying one is all wrong is plain disregarding long term testing and proven methods.

You build yours your way, and I'll build it mine. They both may last a very long time, but I can sleep with the knowledge that I'm not reinventing the wheel, and that it has been life-tested.

Building a sloped floor with stuff like concrete is tough. Plus, the goal is not a nearly waterproof layer, but one that will allow any moisture to percolate to the weep holes, assuming you are doing a liner and clamping drain.

Kerdi is a whole other concept, where you actually make the tileable surface totally waterproof. Therefore, there isn't any need for the deckmud underneath, but as said, it is far easier to pack deckmud into the shape you need than most other products.

the thickness needed to be able to maintain a monolitic shape will depend on the substrate - a slab requires less, a wooden subfloor more.

The standards are set to ensure a 300-pound point load will not damage the surface.

If you can point to a nationally recognized, published standard, then fine. But to say outright the whole concept is wrong, is misguided. Please keep your personal gripes to yourself.

[times5]

I have read all the posts, and I am getting a little confused. I also am trying to put in a shower on a slab floor. I bought the liner and what I am unsure of is the order of the process. The area where I am building the shower pan is where there was a old tub. The slope will go forward to the old drain of the tub. So do I use thin set to build a slope? Then is the liner put in place? then do I put more thin set or cement board on the rubber liner? Then tile? Thanks Jesse

[jadnashua]

All those questions will be answered if you check out the 'Liberry' at www.johnbridge.com. You may need to do some addtional work first, though. You tub drain is very likely a 1.5" one, and a shower requires 2" all the way back to where it is at least 2" pipe (can't throttle it down by going from a 2" drain to a 1.5" pipe).

Basically, a traditional shower pan is composed of 5-layers (well, six if you consider the first):
1 - a bonding agent to make sure the next layer sticks to the slab
2 - deck mud (mix of sand and portland cement) shaped with the proper pitch to the drain at 1/4" per foot from the longest distance. This can get messy if the drain isn't centered.
3 - the liner
4- the setting bed - another layer of deck mud (actually parallel to the sloped layer - i.e., equal thickness)
5 - thinset to hold the tile down
6 - finished tile.

There are also special considerations to ensure the curb remains waterproof and you can tile it. Over concrete it's good to use bricks or pavers to make the curb rather than wood, which is often used over a wooden subfloor.