[lizardrider]

I am renovating a bathroom and looking for help 'mating' my tile to my new fibreglass shower pan. Here is where I am at currently. I have framed, roughed in the plumbing and hung the concrete backerboard and drywall. I am about to start mudding the drywall and putting thinset on the concreteboard seams and corners. I am looking ahead to how I join the tile/grout/thinset at the bottom of the wall, where it meets the fibreglass shower pan.

The concrete backerboard is hung and measures 5/8" from the finished horizontal flange of the shower pan. The vertical flange of the shower pan extends up behind the backerboard. I sealed between the showerpan and framing and also between the concreteboard and the vertical flange on the shower pan with a bead of silicone.

Now I want to fill and seal that 5/8" gap from the bottom of the backerboard and the shower pan. Do I use thinset when I seal the seams and corners? Fill the space with thinset (1/2" backerboard thickness) and and finish it with a layer of grout over top? Do I just leave it as is until after and fill the space entirely with grout?

My instinct is to partially fill with thinset (say 1/4" thickness) and then after tiling I can finish it with grout over the thinset, to match thickness of the grout in the groutlines.

I then assume that I seal the grout and all is waterproof. What about a bead of silicone where the grout meets the showerpan? I dont' think this will look great and not sure if would be necessary.

Any help is appreciated!
thx in advance.

 

[Just Bill]

The tile should not touch the base. There will be a gap, 1/4-3/8 is good, and that gets caulk, urethane or silicone. Grout will not stay in that joint, dissimilar materials and different planes of movement.

 

[Ron6519]

If the cementboard drops down over the showerbase flange, there's no reason to do anything. The tile will come down to within 1/8"-3/16" of the shower base and that will be caulked.
Ron

 

[lizardrider]

Great guys thanks for the info. That's kinda what I figured but it seems strange to me to have a small hollow space between the tile bottom and the vertical flange of the shower pan. But as long as it is waterproofed with silicone between the tile bottom and the shower pan....who cares...right?!

 

[Bud Cline]

Did you put a moisture barrier behind the cement board on the studs?

Cement board IS NOT waterproof and all of the caulking of joints and seams means nothing if the water can still get into the cement board everywhere else.

 

[lizardrider]

Yep, moisture barrier behind and going to put Redi guard on the outside prior to applying the tile.

 

[Bud Cline]

Yep, moisture barrier behind and going to put Redi guard on the outside prior to applying the tile.

Not a good idea now. The industry recommends against using both at the same time, one or the other but not both. Doing both will create a trap for moisture in the board via condensation.