Preslope under cultured marble base?

**kfp** · 03-22-2012, 08:04 PM

I am having a shower installed in my basement. The shower is approx. 2.5' by 4'. I am having an cultured marble type of material installed in the shower. It is 3/4" thick on the base and 3/8" thick on the walls. The installer indicated that he wants to wait until I have the water-resistent drywall or cement board installed before he proceeds. He would then come in and install a vinyl liner directly on the cement floor (no pre-slope) and the vinyl would not be behind the wall board. He then puts down a bed of mortar and install the preformed presloped cultured marble base and glues the walls to the wallboard. Is this going to last or am I just asking for trouble?

**jadnashua** · 03-22-2012, 09:31 PM

Doesn't sound right....

The preformed base shouldn't have a liner and shouldn't need one - it is fully waterproof on its own. If the floor isn't flat and level, then setting the pan in mortar is an easy way to make it nice and level and fully supported.

What brand and model pan is it? Do you have it? Did you read the installation instructions to see what the manufacturer says? If not, can you find and read it online?

A preslope and liner is used when you are building a traditional shower...a preformed pan isn't a traditional shower. The reason the liner is needed is that the tile is not considered fully waterproof, and the preslope with the liner over it directs any moisture that does get in down to the weep holes in the drain. The drain used on a preformed pan has no weep holes, so if any moisture did get in the pan, it would just sit there and fester since it has nowhere to go.

**kfp** · 03-22-2012, 09:55 PM

I may have misled you a little. The base is a custom cast piece. Before it it fully cured they weigh down the center where the drain goes to create a slope. The base is essentially flat except for the slight slope that has been created. The walls are butt jointed to the base and sealed with silicone. I haven't committed to this installer yet. Here are a couple of pictures of his work.

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**Hackney plumbing** · 03-23-2012, 03:45 AM

Cultured marble bases do not get a liner. They are waterproof.

**johnfrwhipple** · 03-23-2012, 05:46 AM

See - a little info is a dangerous thing.

Your quest for information can lead you and hundreds more down the wrong path.

Some stone company's make slabs cut to fit a shower pan. Some are just a stone that is set over a shower drain pan set up so yes you might need a clamping drain and liner.

Other products are primary shower pans and will bear a cUPC symbol or CSA symbol and you can simple find out first hand by visiting the IAMPO website and running a search by name.

If you are unsure ask for the product to be delivered first and investigate further.

Now skipping a pre-slope in any job will make your installers job easier. It might be that the stone is cut with a flat bottom. If this is the case I would set the liner over a pre-slope and then adjust the collar on the clamping drain and mud out a flat bed. You will need a good 1 1/2" of deck mud for the top layer.

Do you have a model number we can look up?

JW

hj · 03-23-2012, 06:01 AM

The cultured marble base usually DOES need a liner, because in most cases the drain just sits in a hole in the base which means it is NOT a waterproof seal. The liner is under the preslope because it clamps into the drain fitting.

**johnfrwhipple** · 03-23-2012, 06:49 AM

Originally Posted by hj

The cultured marble base usually DOES need a liner, because in most cases the drain just sits in a hole in the base which means it is NOT a waterproof seal. The liner is under the preslope because it clamps into the drain fitting.

Thanks HJ

Building a shower is not rocket science but you need to know there are thousands of ways to pull them off.

Hire a pro plumber. Number one rule.

Work with approved fixtures. They have stamps and approvals right on them.

Specify that the TCNA, ANSI or TTMAC specifications are followed by all trades involved. Let your crew figure out what that is or hire a new crew if they think it is not necessary.

If you are in this business and do not know what the TCNA, ANSI and TTMAC are - you are part of the problem!

JW

**johnfrwhipple** · 03-23-2012, 06:52 AM

Originally Posted by kfp

I may have misled you a little. The base is a custom cast piece. ...

A Custom base will not bear a cUPC mark. It will need to be installed over an approved drain and liner. Flood test. Inspection.

Then installation of the topping material. if it is allowed to be installed over a liner. I bet a mud bed will be needed first.

JW

**kfp** · 03-23-2012, 07:34 AM

That's the part that concerns me. Without a waterproof seal between the base and the drain i would expect at some point in time that water will work it's way down into the mortar between the base and the liner.

**johnfrwhipple** · 03-23-2012, 08:50 AM

With a properly prepared clamping drain and liner you will have multiple weep hole locations. These can be improved with a Noble Weep Hole Protector, Candle Wick, Pea Gravel or what ever your tile setter prefers to prevent them from being plugged while setting a mud bed over the liner.

This mud bed can be fine tuned to fit your base perfectly. Often the base supplier will have one or two drains that work with it. Make sure this drain makes it's way to the plumber for approval before the install boys arrive. Set the drain (allow for preslope material), install liner (40 mil most likely required in your town) and flood test.

Once this is passed you can prepare the mud bed over the liner and then install the base. Any water making its way between the seal of the base and drain will weep through the weep holes.

A proven system that has been working for decades when built correctly.

Good Luck.

JW

hj · 03-23-2012, 08:54 AM

quote; Without a waterproof seal between the base and the drain i would expect at some point in time that water will work it's way down into the mortar between the base and the liner.

It WILL, and that is why you install the liner properly.

**jadnashua** · 03-23-2012, 11:02 AM

If, after reading the instructions, the pan needs a preslope and liner, then the liner should sit on top of the preslope so any water that gets there can flow into the weepholes. Can you point to the website that may have this on? Are the instructions available online? Have you read them?

Basicially, if a shower requires a liner, then that is considered the primary waterproof surface. The primary waterproof surface needs to be sloped to the drain so it can do just that - drain; it should not be flat so it acts like a pond and holds water.

**Hackney plumbing** · 03-23-2012, 11:55 AM

Please post a link to the cultured marble bases that require a pan liner. I'd love to see one.

**Hackney plumbing** · 03-23-2012, 11:59 AM

Originally Posted by hj

The cultured marble base usually DOES need a liner, because in most cases the drain just sits in a hole in the base which means it is NOT a waterproof seal. The liner is under the preslope because it clamps into the drain fitting.